diff options
Diffstat (limited to 'Documentation/virtual')
| -rw-r--r-- | Documentation/virtual/00-INDEX | 3 | ||||
| -rw-r--r-- | Documentation/virtual/kvm/api.txt | 71 | ||||
| -rw-r--r-- | Documentation/virtual/lguest/lguest.c | 5 | ||||
| -rw-r--r-- | Documentation/virtual/uml/UserModeLinux-HOWTO.txt | 532 | ||||
| -rw-r--r-- | Documentation/virtual/virtio-spec.txt | 2200 |
5 files changed, 2542 insertions, 269 deletions
diff --git a/Documentation/virtual/00-INDEX b/Documentation/virtual/00-INDEX index fe0251c4cfb..8e601991d91 100644 --- a/Documentation/virtual/00-INDEX +++ b/Documentation/virtual/00-INDEX @@ -8,3 +8,6 @@ lguest/ - Extremely simple hypervisor for experimental/educational use. uml/ - User Mode Linux, builds/runs Linux kernel as a userspace program. +virtio.txt + - Text version of draft virtio spec. + See http://ozlabs.org/~rusty/virtio-spec diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index b0e4b9cd6a6..7945b0bd35e 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -175,10 +175,30 @@ Parameters: vcpu id (apic id on x86) Returns: vcpu fd on success, -1 on error This API adds a vcpu to a virtual machine. The vcpu id is a small integer -in the range [0, max_vcpus). You can use KVM_CAP_NR_VCPUS of the -KVM_CHECK_EXTENSION ioctl() to determine the value for max_vcpus at run-time. +in the range [0, max_vcpus). + +The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of +the KVM_CHECK_EXTENSION ioctl() at run-time. +The maximum possible value for max_vcpus can be retrieved using the +KVM_CAP_MAX_VCPUS of the KVM_CHECK_EXTENSION ioctl() at run-time. + If the KVM_CAP_NR_VCPUS does not exist, you should assume that max_vcpus is 4 cpus max. +If the KVM_CAP_MAX_VCPUS does not exist, you should assume that max_vcpus is +same as the value returned from KVM_CAP_NR_VCPUS. + +On powerpc using book3s_hv mode, the vcpus are mapped onto virtual +threads in one or more virtual CPU cores. (This is because the +hardware requires all the hardware threads in a CPU core to be in the +same partition.) The KVM_CAP_PPC_SMT capability indicates the number +of vcpus per virtual core (vcore). The vcore id is obtained by +dividing the vcpu id by the number of vcpus per vcore. The vcpus in a +given vcore will always be in the same physical core as each other +(though that might be a different physical core from time to time). +Userspace can control the threading (SMT) mode of the guest by its +allocation of vcpu ids. For example, if userspace wants +single-threaded guest vcpus, it should make all vcpu ids be a multiple +of the number of vcpus per vcore. On powerpc using book3s_hv mode, the vcpus are mapped onto virtual threads in one or more virtual CPU cores. (This is because the @@ -1633,3 +1653,50 @@ developer registration required to access it). char padding[256]; }; }; + +6. Capabilities that can be enabled + +There are certain capabilities that change the behavior of the virtual CPU when +enabled. To enable them, please see section 4.37. Below you can find a list of +capabilities and what their effect on the vCPU is when enabling them. + +The following information is provided along with the description: + + Architectures: which instruction set architectures provide this ioctl. + x86 includes both i386 and x86_64. + + Parameters: what parameters are accepted by the capability. + + Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL) + are not detailed, but errors with specific meanings are. + +6.1 KVM_CAP_PPC_OSI + +Architectures: ppc +Parameters: none +Returns: 0 on success; -1 on error + +This capability enables interception of OSI hypercalls that otherwise would +be treated as normal system calls to be injected into the guest. OSI hypercalls +were invented by Mac-on-Linux to have a standardized communication mechanism +between the guest and the host. + +When this capability is enabled, KVM_EXIT_OSI can occur. + +6.2 KVM_CAP_PPC_PAPR + +Architectures: ppc +Parameters: none +Returns: 0 on success; -1 on error + +This capability enables interception of PAPR hypercalls. PAPR hypercalls are +done using the hypercall instruction "sc 1". + +It also sets the guest privilege level to "supervisor" mode. Usually the guest +runs in "hypervisor" privilege mode with a few missing features. + +In addition to the above, it changes the semantics of SDR1. In this mode, the +HTAB address part of SDR1 contains an HVA instead of a GPA, as PAPR keeps the +HTAB invisible to the guest. + +When this capability is enabled, KVM_EXIT_PAPR_HCALL can occur. diff --git a/Documentation/virtual/lguest/lguest.c b/Documentation/virtual/lguest/lguest.c index 043bd7df313..c095d79cae7 100644 --- a/Documentation/virtual/lguest/lguest.c +++ b/Documentation/virtual/lguest/lguest.c @@ -436,7 +436,7 @@ static unsigned long load_bzimage(int fd) /* * Go back to the start of the file and read the header. It should be - * a Linux boot header (see Documentation/x86/i386/boot.txt) + * a Linux boot header (see Documentation/x86/boot.txt) */ lseek(fd, 0, SEEK_SET); read(fd, &boot, sizeof(boot)); @@ -1996,6 +1996,9 @@ int main(int argc, char *argv[]) /* We use a simple helper to copy the arguments separated by spaces. */ concat((char *)(boot + 1), argv+optind+2); + /* Set kernel alignment to 16M (CONFIG_PHYSICAL_ALIGN) */ + boot->hdr.kernel_alignment = 0x1000000; + /* Boot protocol version: 2.07 supports the fields for lguest. */ boot->hdr.version = 0x207; diff --git a/Documentation/virtual/uml/UserModeLinux-HOWTO.txt b/Documentation/virtual/uml/UserModeLinux-HOWTO.txt index 5d0fc8bfcdb..77dfecf4e2d 100644 --- a/Documentation/virtual/uml/UserModeLinux-HOWTO.txt +++ b/Documentation/virtual/uml/UserModeLinux-HOWTO.txt @@ -134,13 +134,13 @@ ______________________________________________________________________ - 11.. IInnttrroodduuccttiioonn + 1. Introduction Welcome to User Mode Linux. It's going to be fun. - 11..11.. HHooww iiss UUsseerr MMooddee LLiinnuuxx DDiiffffeerreenntt?? + 1.1. How is User Mode Linux Different? Normally, the Linux Kernel talks straight to your hardware (video card, keyboard, hard drives, etc), and any programs which run ask the @@ -181,7 +181,7 @@ - 11..22.. WWhhyy WWoouulldd II WWaanntt UUsseerr MMooddee LLiinnuuxx?? + 1.2. Why Would I Want User Mode Linux? 1. If User Mode Linux crashes, your host kernel is still fine. @@ -206,12 +206,12 @@ - 22.. CCoommppiilliinngg tthhee kkeerrnneell aanndd mmoodduulleess + 2. Compiling the kernel and modules - 22..11.. CCoommppiilliinngg tthhee kkeerrnneell + 2.1. Compiling the kernel Compiling the user mode kernel is just like compiling any other @@ -322,7 +322,7 @@ bug fixes and enhancements that have gone into subsequent releases. - 22..22.. CCoommppiilliinngg aanndd iinnssttaalllliinngg kkeerrnneell mmoodduulleess + 2.2. Compiling and installing kernel modules UML modules are built in the same way as the native kernel (with the exception of the 'ARCH=um' that you always need for UML): @@ -386,19 +386,19 @@ - 22..33.. CCoommppiilliinngg aanndd iinnssttaalllliinngg uummll__uuttiilliittiieess + 2.3. Compiling and installing uml_utilities Many features of the UML kernel require a user-space helper program, so a uml_utilities package is distributed separately from the kernel patch which provides these helpers. Included within this is: - +o port-helper - Used by consoles which connect to xterms or ports + o port-helper - Used by consoles which connect to xterms or ports - +o tunctl - Configuration tool to create and delete tap devices + o tunctl - Configuration tool to create and delete tap devices - +o uml_net - Setuid binary for automatic tap device configuration + o uml_net - Setuid binary for automatic tap device configuration - +o uml_switch - User-space virtual switch required for daemon + o uml_switch - User-space virtual switch required for daemon transport The uml_utilities tree is compiled with: @@ -423,11 +423,11 @@ - 33.. RRuunnnniinngg UUMMLL aanndd llooggggiinngg iinn + 3. Running UML and logging in - 33..11.. RRuunnnniinngg UUMMLL + 3.1. Running UML It runs on 2.2.15 or later, and all 2.4 kernels. @@ -454,7 +454,7 @@ - 33..22.. LLooggggiinngg iinn + 3.2. Logging in @@ -468,7 +468,7 @@ There are a couple of other ways to log in: - +o On a virtual console + o On a virtual console @@ -480,7 +480,7 @@ - +o Over the serial line + o Over the serial line In the boot output, find a line that looks like: @@ -503,7 +503,7 @@ - +o Over the net + o Over the net If the network is running, then you can telnet to the virtual @@ -514,13 +514,13 @@ down and the process will exit. - 33..33.. EExxaammpplleess + 3.3. Examples Here are some examples of UML in action: - +o A login session <http://user-mode-linux.sourceforge.net/login.html> + o A login session <http://user-mode-linux.sourceforge.net/login.html> - +o A virtual network <http://user-mode-linux.sourceforge.net/net.html> + o A virtual network <http://user-mode-linux.sourceforge.net/net.html> @@ -528,12 +528,12 @@ - 44.. UUMMLL oonn 22GG//22GG hhoossttss + 4. UML on 2G/2G hosts - 44..11.. IInnttrroodduuccttiioonn + 4.1. Introduction Most Linux machines are configured so that the kernel occupies the @@ -546,7 +546,7 @@ - 44..22.. TThhee pprroobblleemm + 4.2. The problem The prebuilt UML binaries on this site will not run on 2G/2G hosts @@ -558,7 +558,7 @@ - 44..33.. TThhee ssoolluuttiioonn + 4.3. The solution The fix for this is to rebuild UML from source after enabling @@ -576,7 +576,7 @@ - 55.. SSeettttiinngg uupp sseerriiaall lliinneess aanndd ccoonnssoolleess + 5. Setting up serial lines and consoles It is possible to attach UML serial lines and consoles to many types @@ -586,12 +586,12 @@ You can attach them to host ptys, ttys, file descriptors, and ports. This allows you to do things like - +o have a UML console appear on an unused host console, + o have a UML console appear on an unused host console, - +o hook two virtual machines together by having one attach to a pty + o hook two virtual machines together by having one attach to a pty and having the other attach to the corresponding tty - +o make a virtual machine accessible from the net by attaching a + o make a virtual machine accessible from the net by attaching a console to a port on the host. @@ -599,7 +599,7 @@ - 55..11.. SSppeecciiffyyiinngg tthhee ddeevviiccee + 5.1. Specifying the device Devices are specified with "con" or "ssl" (console or serial line, respectively), optionally with a device number if you are talking @@ -626,13 +626,13 @@ - 55..22.. SSppeecciiffyyiinngg tthhee cchhaannnneell + 5.2. Specifying the channel There are a number of different types of channels to attach a UML device to, each with a different way of specifying exactly what to attach to. - +o pseudo-terminals - device=pty pts terminals - device=pts + o pseudo-terminals - device=pty pts terminals - device=pts This will cause UML to allocate a free host pseudo-terminal for the @@ -640,20 +640,20 @@ log. You access it by attaching a terminal program to the corresponding tty: - +o screen /dev/pts/n + o screen /dev/pts/n - +o screen /dev/ttyxx + o screen /dev/ttyxx - +o minicom -o -p /dev/ttyxx - minicom seems not able to handle pts + o minicom -o -p /dev/ttyxx - minicom seems not able to handle pts devices - +o kermit - start it up, 'open' the device, then 'connect' + o kermit - start it up, 'open' the device, then 'connect' - +o terminals - device=tty:tty device file + o terminals - device=tty:tty device file This will make UML attach the device to the specified tty (i.e @@ -672,7 +672,7 @@ - +o xterms - device=xterm + o xterms - device=xterm UML will run an xterm and the device will be attached to it. @@ -681,7 +681,7 @@ - +o Port - device=port:port number + o Port - device=port:port number This will attach the UML devices to the specified host port. @@ -725,7 +725,7 @@ - +o already-existing file descriptors - device=file descriptor + o already-existing file descriptors - device=file descriptor If you set up a file descriptor on the UML command line, you can @@ -743,7 +743,7 @@ - +o Nothing - device=null + o Nothing - device=null This allows the device to be opened, in contrast to 'none', but @@ -754,7 +754,7 @@ - +o None - device=none + o None - device=none This causes the device to disappear. @@ -770,7 +770,7 @@ - will cause serial line 3 to accept input on the host's /dev/tty3 and + will cause serial line 3 to accept input on the host's /dev/tty2 and display output on an xterm. That's a silly example - the most common use of this syntax is to reattach the main console to stdin and stdout as shown above. @@ -785,7 +785,7 @@ - 55..33.. EExxaammpplleess + 5.3. Examples There are a number of interesting things you can do with this capability. @@ -838,7 +838,7 @@ prompt of the other virtual machine. - 66.. SSeettttiinngg uupp tthhee nneettwwoorrkk + 6. Setting up the network @@ -858,19 +858,19 @@ There are currently five transport types available for a UML virtual machine to exchange packets with other hosts: - +o ethertap + o ethertap - +o TUN/TAP + o TUN/TAP - +o Multicast + o Multicast - +o a switch daemon + o a switch daemon - +o slip + o slip - +o slirp + o slirp - +o pcap + o pcap The TUN/TAP, ethertap, slip, and slirp transports allow a UML instance to exchange packets with the host. They may be directed @@ -893,28 +893,28 @@ With so many host transports, which one should you use? Here's when you should use each one: - +o ethertap - if you want access to the host networking and it is + o ethertap - if you want access to the host networking and it is running 2.2 - +o TUN/TAP - if you want access to the host networking and it is + o TUN/TAP - if you want access to the host networking and it is running 2.4. Also, the TUN/TAP transport is able to use a preconfigured device, allowing it to avoid using the setuid uml_net helper, which is a security advantage. - +o Multicast - if you want a purely virtual network and you don't want + o Multicast - if you want a purely virtual network and you don't want to set up anything but the UML - +o a switch daemon - if you want a purely virtual network and you + o a switch daemon - if you want a purely virtual network and you don't mind running the daemon in order to get somewhat better performance - +o slip - there is no particular reason to run the slip backend unless + o slip - there is no particular reason to run the slip backend unless ethertap and TUN/TAP are just not available for some reason - +o slirp - if you don't have root access on the host to setup + o slirp - if you don't have root access on the host to setup networking, or if you don't want to allocate an IP to your UML - +o pcap - not much use for actual network connectivity, but great for + o pcap - not much use for actual network connectivity, but great for monitoring traffic on the host Ethertap is available on 2.4 and works fine. TUN/TAP is preferred @@ -926,7 +926,7 @@ exploit the helper's root privileges. - 66..11.. GGeenneerraall sseettuupp + 6.1. General setup First, you must have the virtual network enabled in your UML. If are running a prebuilt kernel from this site, everything is already @@ -995,7 +995,7 @@ - 66..22.. UUsseerrssppaaccee ddaaeemmoonnss + 6.2. Userspace daemons You will likely need the setuid helper, or the switch daemon, or both. They are both installed with the RPM and deb, so if you've installed @@ -1011,7 +1011,7 @@ - 66..33.. SSppeecciiffyyiinngg eetthheerrnneett aaddddrreesssseess + 6.3. Specifying ethernet addresses Below, you will see that the TUN/TAP, ethertap, and daemon interfaces allow you to specify hardware addresses for the virtual ethernet @@ -1023,11 +1023,11 @@ sufficient to guarantee a unique hardware address for the device. A couple of exceptions are: - +o Another set of virtual ethernet devices are on the same network and + o Another set of virtual ethernet devices are on the same network and they are assigned hardware addresses using a different scheme which may conflict with the UML IP address-based scheme - +o You aren't going to use the device for IP networking, so you don't + o You aren't going to use the device for IP networking, so you don't assign the device an IP address If you let the driver provide the hardware address, you should make @@ -1049,7 +1049,7 @@ - 66..44.. UUMMLL iinntteerrffaaccee sseettuupp + 6.4. UML interface setup Once the network devices have been described on the command line, you should boot UML and log in. @@ -1131,7 +1131,7 @@ - 66..55.. MMuullttiiccaasstt + 6.5. Multicast The simplest way to set up a virtual network between multiple UMLs is to use the mcast transport. This was written by Harald Welte and is @@ -1194,7 +1194,7 @@ - 66..66.. TTUUNN//TTAAPP wwiitthh tthhee uummll__nneett hheellppeerr + 6.6. TUN/TAP with the uml_net helper TUN/TAP is the preferred mechanism on 2.4 to exchange packets with the host. The TUN/TAP backend has been in UML since 2.4.9-3um. @@ -1247,10 +1247,10 @@ There are a couple potential problems with running the TUN/TAP transport on a 2.4 host kernel - +o TUN/TAP seems not to work on 2.4.3 and earlier. Upgrade the host + o TUN/TAP seems not to work on 2.4.3 and earlier. Upgrade the host kernel or use the ethertap transport. - +o With an upgraded kernel, TUN/TAP may fail with + o With an upgraded kernel, TUN/TAP may fail with File descriptor in bad state @@ -1269,7 +1269,7 @@ - 66..77.. TTUUNN//TTAAPP wwiitthh aa pprreeccoonnffiigguurreedd ttaapp ddeevviiccee + 6.7. TUN/TAP with a preconfigured tap device If you prefer not to have UML use uml_net (which is somewhat insecure), with UML 2.4.17-11, you can set up a TUN/TAP device @@ -1277,7 +1277,7 @@ there is no need for root assistance. Setting up the device is done as follows: - +o Create the device with tunctl (available from the UML utilities + o Create the device with tunctl (available from the UML utilities tarball) @@ -1291,7 +1291,7 @@ where uid is the user id or username that UML will be run as. This will tell you what device was created. - +o Configure the device IP (change IP addresses and device name to + o Configure the device IP (change IP addresses and device name to suit) @@ -1303,7 +1303,7 @@ - +o Set up routing and arping if desired - this is my recipe, there are + o Set up routing and arping if desired - this is my recipe, there are other ways of doing the same thing @@ -1338,7 +1338,7 @@ utility which reads the information from a config file and sets up devices at boot time. - +o Rather than using up two IPs and ARPing for one of them, you can + o Rather than using up two IPs and ARPing for one of them, you can also provide direct access to your LAN by the UML by using a bridge. @@ -1417,7 +1417,7 @@ Note that 'br0' should be setup using ifconfig with the existing IP address of eth0, as eth0 no longer has its own IP. - +o + o Also, the /dev/net/tun device must be writable by the user running @@ -1438,11 +1438,11 @@ devices and chgrp /dev/net/tun to that group with mode 664 or 660. - +o Once the device is set up, run UML with 'eth0=tuntap,device name' + o Once the device is set up, run UML with 'eth0=tuntap,device name' (i.e. 'eth0=tuntap,tap0') on the command line (or do it with the mconsole config command). - +o Bring the eth device up in UML and you're in business. + o Bring the eth device up in UML and you're in business. If you don't want that tap device any more, you can make it non- persistent with @@ -1465,7 +1465,7 @@ - 66..88.. EEtthheerrttaapp + 6.8. Ethertap Ethertap is the general mechanism on 2.2 for userspace processes to exchange packets with the kernel. @@ -1561,9 +1561,9 @@ - 66..99.. TThhee sswwiittcchh ddaaeemmoonn + 6.9. The switch daemon - NNoottee: This is the daemon formerly known as uml_router, but which was + Note: This is the daemon formerly known as uml_router, but which was renamed so the network weenies of the world would stop growling at me. @@ -1649,7 +1649,7 @@ - 66..1100.. SSlliipp + 6.10. Slip Slip is another, less general, mechanism for a process to communicate with the host networking. In contrast to the ethertap interface, @@ -1681,7 +1681,7 @@ - 66..1111.. SSlliirrpp + 6.11. Slirp slirp uses an external program, usually /usr/bin/slirp, to provide IP only networking connectivity through the host. This is similar to IP @@ -1737,7 +1737,7 @@ - 66..1122.. ppccaapp + 6.12. pcap The pcap transport is attached to a UML ethernet device on the command line or with uml_mconsole with the following syntax: @@ -1777,7 +1777,7 @@ - 66..1133.. SSeettttiinngg uupp tthhee hhoosstt yyoouurrsseellff + 6.13. Setting up the host yourself If you don't specify an address for the host side of the ethertap or slip device, UML won't do any setup on the host. So this is what is @@ -1785,7 +1785,7 @@ 192.168.0.251 and a UML-side IP of 192.168.0.250 - adjust to suit your own network): - +o The device needs to be configured with its IP address. Tap devices + o The device needs to be configured with its IP address. Tap devices are also configured with an mtu of 1484. Slip devices are configured with a point-to-point address pointing at the UML ip address. @@ -1805,7 +1805,7 @@ - +o If a tap device is being set up, a route is set to the UML IP. + o If a tap device is being set up, a route is set to the UML IP. UML# route add -host 192.168.0.250 gw 192.168.0.251 @@ -1814,7 +1814,7 @@ - +o To allow other hosts on your network to see the virtual machine, + o To allow other hosts on your network to see the virtual machine, proxy arp is set up for it. @@ -1824,7 +1824,7 @@ - +o Finally, the host is set up to route packets. + o Finally, the host is set up to route packets. host# echo 1 > /proc/sys/net/ipv4/ip_forward @@ -1838,12 +1838,12 @@ - 77.. SShhaarriinngg FFiilleessyysstteemmss bbeettwweeeenn VViirrttuuaall MMaacchhiinneess + 7. Sharing Filesystems between Virtual Machines - 77..11.. AA wwaarrnniinngg + 7.1. A warning Don't attempt to share filesystems simply by booting two UMLs from the same file. That's the same thing as booting two physical machines @@ -1851,7 +1851,7 @@ - 77..22.. UUssiinngg llaayyeerreedd bblloocckk ddeevviicceess + 7.2. Using layered block devices The way to share a filesystem between two virtual machines is to use the copy-on-write (COW) layering capability of the ubd block driver. @@ -1896,7 +1896,7 @@ - 77..33.. NNoottee!! + 7.3. Note! When checking the size of the COW file in order to see the gobs of space that you're saving, make sure you use 'ls -ls' to see the actual @@ -1926,7 +1926,7 @@ - 77..44.. AAnnootthheerr wwaarrnniinngg + 7.4. Another warning Once a filesystem is being used as a readonly backing file for a COW file, do not boot directly from it or modify it in any way. Doing so @@ -1952,7 +1952,7 @@ - 77..55.. uummll__mmoooo :: MMeerrggiinngg aa CCOOWW ffiillee wwiitthh iittss bbaacckkiinngg ffiillee + 7.5. uml_moo : Merging a COW file with its backing file Depending on how you use UML and COW devices, it may be advisable to merge the changes in the COW file into the backing file every once in @@ -2001,7 +2001,7 @@ - 88.. CCrreeaattiinngg ffiilleessyysstteemmss + 8. Creating filesystems You may want to create and mount new UML filesystems, either because @@ -2015,7 +2015,7 @@ should be easy to translate to the filesystem of your choice. - 88..11.. CCrreeaattee tthhee ffiilleessyysstteemm ffiillee + 8.1. Create the filesystem file dd is your friend. All you need to do is tell dd to create an empty file of the appropriate size. I usually make it sparse to save time @@ -2032,7 +2032,7 @@ - 88..22.. AAssssiiggnn tthhee ffiillee ttoo aa UUMMLL ddeevviiccee + 8.2. Assign the file to a UML device Add an argument like the following to the UML command line: @@ -2045,7 +2045,7 @@ - 88..33.. CCrreeaattiinngg aanndd mmoouunnttiinngg tthhee ffiilleessyysstteemm + 8.3. Creating and mounting the filesystem Make sure that the filesystem is available, either by being built into the kernel, or available as a module, then boot up UML and log in. If @@ -2096,7 +2096,7 @@ - 99.. HHoosstt ffiillee aacccceessss + 9. Host file access If you want to access files on the host machine from inside UML, you @@ -2112,7 +2112,7 @@ files contained in it just as you would on the host. - 99..11.. UUssiinngg hhoossttffss + 9.1. Using hostfs To begin with, make sure that hostfs is available inside the virtual machine with @@ -2151,7 +2151,7 @@ - 99..22.. hhoossttffss aass tthhee rroooott ffiilleessyysstteemm + 9.2. hostfs as the root filesystem It's possible to boot from a directory hierarchy on the host using hostfs rather than using the standard filesystem in a file. @@ -2194,20 +2194,20 @@ UML should then boot as it does normally. - 99..33.. BBuuiillddiinngg hhoossttffss + 9.3. Building hostfs If you need to build hostfs because it's not in your kernel, you have two choices: - +o Compiling hostfs into the kernel: + o Compiling hostfs into the kernel: Reconfigure the kernel and set the 'Host filesystem' option under - +o Compiling hostfs as a module: + o Compiling hostfs as a module: Reconfigure the kernel and set the 'Host filesystem' option under @@ -2228,7 +2228,7 @@ - 1100.. TThhee MMaannaaggeemmeenntt CCoonnssoollee + 10. The Management Console @@ -2240,15 +2240,15 @@ There are a number of things you can do with the mconsole interface: - +o get the kernel version + o get the kernel version - +o add and remove devices + o add and remove devices - +o halt or reboot the machine + o halt or reboot the machine - +o Send SysRq commands + o Send SysRq commands - +o Pause and resume the UML + o Pause and resume the UML You need the mconsole client (uml_mconsole) which is present in CVS @@ -2300,28 +2300,28 @@ You'll get a prompt, at which you can run one of these commands: - +o version + o version - +o halt + o halt - +o reboot + o reboot - +o config + o config - +o remove + o remove - +o sysrq + o sysrq - +o help + o help - +o cad + o cad - +o stop + o stop - +o go + o go - 1100..11.. vveerrssiioonn + 10.1. version This takes no arguments. It prints the UML version. @@ -2342,7 +2342,7 @@ - 1100..22.. hhaalltt aanndd rreebboooott + 10.2. halt and reboot These take no arguments. They shut the machine down immediately, with no syncing of disks and no clean shutdown of userspace. So, they are @@ -2357,7 +2357,7 @@ - 1100..33.. ccoonnffiigg + 10.3. config "config" adds a new device to the virtual machine. Currently the ubd and network drivers support this. It takes one argument, which is the @@ -2378,7 +2378,7 @@ - 1100..44.. rreemmoovvee + 10.4. remove "remove" deletes a device from the system. Its argument is just the name of the device to be removed. The device must be idle in whatever @@ -2397,7 +2397,7 @@ - 1100..55.. ssyyssrrqq + 10.5. sysrq This takes one argument, which is a single letter. It calls the generic kernel's SysRq driver, which does whatever is called for by @@ -2407,14 +2407,14 @@ - 1100..66.. hheellpp + 10.6. help "help" returns a string listing the valid commands and what each one does. - 1100..77.. ccaadd + 10.7. cad This invokes the Ctl-Alt-Del action on init. What exactly this ends up doing is up to /etc/inittab. Normally, it reboots the machine. @@ -2432,7 +2432,7 @@ - 1100..88.. ssttoopp + 10.8. stop This puts the UML in a loop reading mconsole requests until a 'go' mconsole command is received. This is very useful for making backups @@ -2448,7 +2448,7 @@ - 1100..99.. ggoo + 10.9. go This resumes a UML after being paused by a 'stop' command. Note that when the UML has resumed, TCP connections may have timed out and if @@ -2462,10 +2462,10 @@ - 1111.. KKeerrnneell ddeebbuuggggiinngg + 11. Kernel debugging - NNoottee:: The interface that makes debugging, as described here, possible + Note: The interface that makes debugging, as described here, possible is present in 2.4.0-test6 kernels and later. @@ -2485,7 +2485,7 @@ - 1111..11.. SSttaarrttiinngg tthhee kkeerrnneell uunnddeerr ggddbb + 11.1. Starting the kernel under gdb You can have the kernel running under the control of gdb from the beginning by putting 'debug' on the command line. You will get an @@ -2498,7 +2498,7 @@ There is a transcript of a debugging session here <debug- session.html> , with breakpoints being set in the scheduler and in an interrupt handler. - 1111..22.. EExxaammiinniinngg sslleeeeppiinngg pprroocceesssseess + 11.2. Examining sleeping processes Not every bug is evident in the currently running process. Sometimes, processes hang in the kernel when they shouldn't because they've @@ -2516,7 +2516,7 @@ Now what you do is this: - +o detach from the current thread + o detach from the current thread (UML gdb) det @@ -2525,7 +2525,7 @@ - +o attach to the thread you are interested in + o attach to the thread you are interested in (UML gdb) att <host pid> @@ -2534,7 +2534,7 @@ - +o look at its stack and anything else of interest + o look at its stack and anything else of interest (UML gdb) bt @@ -2545,7 +2545,7 @@ Note that you can't do anything at this point that requires that a process execute, e.g. calling a function - +o when you're done looking at that process, reattach to the current + o when you're done looking at that process, reattach to the current thread and continue it @@ -2569,12 +2569,12 @@ - 1111..33.. RRuunnnniinngg dddddd oonn UUMMLL + 11.3. Running ddd on UML ddd works on UML, but requires a special kludge. The process goes like this: - +o Start ddd + o Start ddd host% ddd linux @@ -2583,14 +2583,14 @@ - +o With ps, get the pid of the gdb that ddd started. You can ask the + o With ps, get the pid of the gdb that ddd started. You can ask the gdb to tell you, but for some reason that confuses things and causes a hang. - +o run UML with 'debug=parent gdb-pid=<pid>' added to the command line + o run UML with 'debug=parent gdb-pid=<pid>' added to the command line - it will just sit there after you hit return - +o type 'att 1' to the ddd gdb and you will see something like + o type 'att 1' to the ddd gdb and you will see something like 0xa013dc51 in __kill () @@ -2602,12 +2602,12 @@ - +o At this point, type 'c', UML will boot up, and you can use ddd just + o At this point, type 'c', UML will boot up, and you can use ddd just as you do on any other process. - 1111..44.. DDeebbuuggggiinngg mmoodduulleess + 11.4. Debugging modules gdb has support for debugging code which is dynamically loaded into the process. This support is what is needed to debug kernel modules @@ -2823,7 +2823,7 @@ - 1111..55.. AAttttaacchhiinngg ggddbb ttoo tthhee kkeerrnneell + 11.5. Attaching gdb to the kernel If you don't have the kernel running under gdb, you can attach gdb to it later by sending the tracing thread a SIGUSR1. The first line of @@ -2857,7 +2857,7 @@ - 1111..66.. UUssiinngg aalltteerrnnaattee ddeebbuuggggeerrss + 11.6. Using alternate debuggers UML has support for attaching to an already running debugger rather than starting gdb itself. This is present in CVS as of 17 Apr 2001. @@ -2886,7 +2886,7 @@ An example of an alternate debugger is strace. You can strace the actual kernel as follows: - +o Run the following in a shell + o Run the following in a shell host% @@ -2894,10 +2894,10 @@ - +o Run UML with 'debug' and 'gdb-pid=<pid>' with the pid printed out + o Run UML with 'debug' and 'gdb-pid=<pid>' with the pid printed out by the previous command - +o Hit return in the shell, and UML will start running, and strace + o Hit return in the shell, and UML will start running, and strace output will start accumulating in the output file. Note that this is different from running @@ -2917,9 +2917,9 @@ - 1122.. KKeerrnneell ddeebbuuggggiinngg eexxaammpplleess + 12. Kernel debugging examples - 1122..11.. TThhee ccaassee ooff tthhee hhuunngg ffsscckk + 12.1. The case of the hung fsck When booting up the kernel, fsck failed, and dropped me into a shell to fix things up. I ran fsck -y, which hung: @@ -3154,9 +3154,9 @@ The interesting things here are : - +o There are two segfaults on this stack (frames 9 and 14) + o There are two segfaults on this stack (frames 9 and 14) - +o The first faulting address (frame 11) is 0x50000800 + o The first faulting address (frame 11) is 0x50000800 (gdb) p (void *)1342179328 $16 = (void *) 0x50000800 @@ -3399,7 +3399,7 @@ on will be somewhat clearer. - 1122..22.. EEppiissooddee 22:: TThhee ccaassee ooff tthhee hhuunngg ffsscckk + 12.2. Episode 2: The case of the hung fsck After setting a trap in the SEGV handler for accesses to the signal thread's stack, I reran the kernel. @@ -3788,12 +3788,12 @@ - 1133.. WWhhaatt ttoo ddoo wwhheenn UUMMLL ddooeessnn''tt wwoorrkk + 13. What to do when UML doesn't work - 1133..11.. SSttrraannggee ccoommppiillaattiioonn eerrrroorrss wwhheenn yyoouu bbuuiilldd ffrroomm ssoouurrccee + 13.1. Strange compilation errors when you build from source As of test11, it is necessary to have "ARCH=um" in the environment or on the make command line for all steps in building UML, including @@ -3824,8 +3824,8 @@ - 1133..33.. AA vvaarriieettyy ooff ppaanniiccss aanndd hhaannggss wwiitthh //ttmmpp oonn aa rreeiisseerrffss ffiilleessyyss-- - tteemm + 13.3. A variety of panics and hangs with /tmp on a reiserfs filesys- + tem I saw this on reiserfs 3.5.21 and it seems to be fixed in 3.5.27. Panics preceded by @@ -3842,8 +3842,8 @@ - 1133..44.. TThhee ccoommppiillee ffaaiillss wwiitthh eerrrroorrss aabboouutt ccoonnfflliiccttiinngg ttyyppeess ffoorr - ''ooppeenn'',, ''dduupp'',, aanndd ''wwaaiittppiidd'' + 13.4. The compile fails with errors about conflicting types for + 'open', 'dup', and 'waitpid' This happens when you build in /usr/src/linux. The UML build makes the include/asm link point to include/asm-um. /usr/include/asm points @@ -3854,14 +3854,14 @@ - 1133..55.. UUMMLL ddooeessnn''tt wwoorrkk wwhheenn //ttmmpp iiss aann NNFFSS ffiilleessyysstteemm + 13.5. UML doesn't work when /tmp is an NFS filesystem This seems to be a similar situation with the ReiserFS problem above. Some versions of NFS seems not to handle mmap correctly, which UML depends on. The workaround is have /tmp be a non-NFS directory. - 1133..66.. UUMMLL hhaannggss oonn bboooott wwhheenn ccoommppiilleedd wwiitthh ggpprrooff ssuuppppoorrtt + 13.6. UML hangs on boot when compiled with gprof support If you build UML with gprof support and, early in the boot, it does this @@ -3878,7 +3878,7 @@ - 1133..77.. ssyyssllooggdd ddiieess wwiitthh aa SSIIGGTTEERRMM oonn ssttaarrttuupp + 13.7. syslogd dies with a SIGTERM on startup The exact boot error depends on the distribution that you're booting, but Debian produces this: @@ -3897,17 +3897,17 @@ - 1133..88.. TTUUNN//TTAAPP nneettwwoorrkkiinngg ddooeessnn''tt wwoorrkk oonn aa 22..44 hhoosstt + 13.8. TUN/TAP networking doesn't work on a 2.4 host There are a couple of problems which were <http://www.geocrawler.com/lists/3/SourceForge/597/0/> name="pointed out"> by Tim Robinson <timro at trkr dot net> - +o It doesn't work on hosts running 2.4.7 (or thereabouts) or earlier. + o It doesn't work on hosts running 2.4.7 (or thereabouts) or earlier. The fix is to upgrade to something more recent and then read the next item. - +o If you see + o If you see File descriptor in bad state @@ -3921,8 +3921,8 @@ - 1133..99.. YYoouu ccaann nneettwwoorrkk ttoo tthhee hhoosstt bbuutt nnoott ttoo ootthheerr mmaacchhiinneess oonn tthhee - nneett + 13.9. You can network to the host but not to other machines on the + net If you can connect to the host, and the host can connect to UML, but you cannot connect to any other machines, then you may need to enable @@ -3972,7 +3972,7 @@ - 1133..1100.. II hhaavvee nnoo rroooott aanndd II wwaanntt ttoo ssccrreeaamm + 13.10. I have no root and I want to scream Thanks to Birgit Wahlich for telling me about this strange one. It turns out that there's a limit of six environment variables on the @@ -3987,7 +3987,7 @@ - 1133..1111.. UUMMLL bbuuiilldd ccoonnfflliicctt bbeettwweeeenn ppttrraaccee..hh aanndd uuccoonntteexxtt..hh + 13.11. UML build conflict between ptrace.h and ucontext.h On some older systems, /usr/include/asm/ptrace.h and /usr/include/sys/ucontext.h define the same names. So, when they're @@ -4007,7 +4007,7 @@ - 1133..1122.. TThhee UUMMLL BBooggooMMiippss iiss eexxaaccttllyy hhaallff tthhee hhoosstt''ss BBooggooMMiippss + 13.12. The UML BogoMips is exactly half the host's BogoMips On i386 kernels, there are two ways of running the loop that is used to calculate the BogoMips rating, using the TSC if it's there or using @@ -4019,7 +4019,7 @@ - 1133..1133.. WWhheenn yyoouu rruunn UUMMLL,, iitt iimmmmeeddiiaatteellyy sseeggffaauullttss + 13.13. When you run UML, it immediately segfaults If the host is configured with the 2G/2G address space split, that's why. See ``UML on 2G/2G hosts'' for the details on getting UML to @@ -4027,7 +4027,7 @@ - 1133..1144.. xxtteerrmmss aappppeeaarr,, tthheenn iimmmmeeddiiaatteellyy ddiissaappppeeaarr + 13.14. xterms appear, then immediately disappear If you're running an up to date kernel with an old release of uml_utilities, the port-helper program will not work properly, so @@ -4039,7 +4039,7 @@ - 1133..1155.. AAnnyy ootthheerr ppaanniicc,, hhaanngg,, oorr ssttrraannggee bbeehhaavviioorr + 13.15. Any other panic, hang, or strange behavior If you're seeing truly strange behavior, such as hangs or panics that happen in random places, or you try running the debugger to see what's @@ -4059,7 +4059,7 @@ If you want to be super-helpful, read ``Diagnosing Problems'' and follow the instructions contained therein. - 1144.. DDiiaaggnnoossiinngg PPrroobblleemmss + 14. Diagnosing Problems If you get UML to crash, hang, or otherwise misbehave, you should @@ -4078,7 +4078,7 @@ ``Kernel debugging'' UML first. - 1144..11.. CCaassee 11 :: NNoorrmmaall kkeerrnneell ppaanniiccss + 14.1. Case 1 : Normal kernel panics The most common case is for a normal thread to panic. To debug this, you will need to run it under the debugger (add 'debug' to the command @@ -4128,7 +4128,7 @@ to get that information from the faulting ip. - 1144..22.. CCaassee 22 :: TTrraacciinngg tthhrreeaadd ppaanniiccss + 14.2. Case 2 : Tracing thread panics The less common and more painful case is when the tracing thread panics. In this case, the kernel debugger will be useless because it @@ -4161,7 +4161,7 @@ backtrace in and wait for our crack debugging team to fix the problem. - 1144..33.. CCaassee 33 :: TTrraacciinngg tthhrreeaadd ppaanniiccss ccaauusseedd bbyy ootthheerr tthhrreeaaddss + 14.3. Case 3 : Tracing thread panics caused by other threads However, there are cases where the misbehavior of another thread caused the problem. The most common panic of this type is: @@ -4227,7 +4227,7 @@ - 1144..44.. CCaassee 44 :: HHaannggss + 14.4. Case 4 : Hangs Hangs seem to be fairly rare, but they sometimes happen. When a hang happens, we need a backtrace from the offending process. Run the @@ -4257,7 +4257,7 @@ - 1155.. TThhaannkkss + 15. Thanks A number of people have helped this project in various ways, and this @@ -4274,20 +4274,20 @@ bookkeeping lapses and I forget about contributions. - 1155..11.. CCooddee aanndd DDooccuummeennttaattiioonn + 15.1. Code and Documentation Rusty Russell <rusty at linuxcare.com.au> - - +o wrote the HOWTO <http://user-mode- + o wrote the HOWTO <http://user-mode- linux.sourceforge.net/UserModeLinux-HOWTO.html> - +o prodded me into making this project official and putting it on + o prodded me into making this project official and putting it on SourceForge - +o came up with the way cool UML logo <http://user-mode- + o came up with the way cool UML logo <http://user-mode- linux.sourceforge.net/uml-small.png> - +o redid the config process + o redid the config process Peter Moulder <reiter at netspace.net.au> - Fixed my config and build @@ -4296,18 +4296,18 @@ Bill Stearns <wstearns at pobox.com> - - +o HOWTO updates + o HOWTO updates - +o lots of bug reports + o lots of bug reports - +o lots of testing + o lots of testing - +o dedicated a box (uml.ists.dartmouth.edu) to support UML development + o dedicated a box (uml.ists.dartmouth.edu) to support UML development - +o wrote the mkrootfs script, which allows bootable filesystems of + o wrote the mkrootfs script, which allows bootable filesystems of RPM-based distributions to be cranked out - +o cranked out a large number of filesystems with said script + o cranked out a large number of filesystems with said script Jim Leu <jleu at mindspring.com> - Wrote the virtual ethernet driver @@ -4375,176 +4375,176 @@ David Coulson <http://davidcoulson.net> - - +o Set up the usermodelinux.org <http://usermodelinux.org> site, + o Set up the usermodelinux.org <http://usermodelinux.org> site, which is a great way of keeping the UML user community on top of UML goings-on. - +o Site documentation and updates + o Site documentation and updates - +o Nifty little UML management daemon UMLd + o Nifty little UML management daemon UMLd <http://uml.openconsultancy.com/umld/> - +o Lots of testing and bug reports + o Lots of testing and bug reports - 1155..22.. FFlluusshhiinngg oouutt bbuuggss + 15.2. Flushing out bugs - +o Yuri Pudgorodsky + o Yuri Pudgorodsky - +o Gerald Britton + o Gerald Britton - +o Ian Wehrman + o Ian Wehrman - +o Gord Lamb + o Gord Lamb - +o Eugene Koontz + o Eugene Koontz - +o John H. Hartman + o John H. Hartman - +o Anders Karlsson + o Anders Karlsson - +o Daniel Phillips + o Daniel Phillips - +o John Fremlin + o John Fremlin - +o Rainer Burgstaller + o Rainer Burgstaller - +o James Stevenson + o James Stevenson - +o Matt Clay + o Matt Clay - +o Cliff Jefferies + o Cliff Jefferies - +o Geoff Hoff + o Geoff Hoff - +o Lennert Buytenhek + o Lennert Buytenhek - +o Al Viro + o Al Viro - +o Frank Klingenhoefer + o Frank Klingenhoefer - +o Livio Baldini Soares + o Livio Baldini Soares - +o Jon Burgess + o Jon Burgess - +o Petru Paler + o Petru Paler - +o Paul + o Paul - +o Chris Reahard + o Chris Reahard - +o Sverker Nilsson + o Sverker Nilsson - +o Gong Su + o Gong Su - +o johan verrept + o johan verrept - +o Bjorn Eriksson + o Bjorn Eriksson - +o Lorenzo Allegrucci + o Lorenzo Allegrucci - +o Muli Ben-Yehuda + o Muli Ben-Yehuda - +o David Mansfield + o David Mansfield - +o Howard Goff + o Howard Goff - +o Mike Anderson + o Mike Anderson - +o John Byrne + o John Byrne - +o Sapan J. Batia + o Sapan J. Batia - +o Iris Huang + o Iris Huang - +o Jan Hudec + o Jan Hudec - +o Voluspa + o Voluspa - 1155..33.. BBuugglleettss aanndd cclleeaann--uuppss + 15.3. Buglets and clean-ups - +o Dave Zarzycki + o Dave Zarzycki - +o Adam Lazur + o Adam Lazur - +o Boria Feigin + o Boria Feigin - +o Brian J. Murrell + o Brian J. Murrell - +o JS + o JS - +o Roman Zippel + o Roman Zippel - +o Wil Cooley + o Wil Cooley - +o Ayelet Shemesh + o Ayelet Shemesh - +o Will Dyson + o Will Dyson - +o Sverker Nilsson + o Sverker Nilsson - +o dvorak + o dvorak - +o v.naga srinivas + o v.naga srinivas - +o Shlomi Fish + o Shlomi Fish - +o Roger Binns + o Roger Binns - +o johan verrept + o johan verrept - +o MrChuoi + o MrChuoi - +o Peter Cleve + o Peter Cleve - +o Vincent Guffens + o Vincent Guffens - +o Nathan Scott + o Nathan Scott - +o Patrick Caulfield + o Patrick Caulfield - +o jbearce + o jbearce - +o Catalin Marinas + o Catalin Marinas - +o Shane Spencer + o Shane Spencer - +o Zou Min + o Zou Min - +o Ryan Boder + o Ryan Boder - +o Lorenzo Colitti + o Lorenzo Colitti - +o Gwendal Grignou + o Gwendal Grignou - +o Andre' Breiler + o Andre' Breiler - +o Tsutomu Yasuda + o Tsutomu Yasuda - 1155..44.. CCaassee SSttuuddiieess + 15.4. Case Studies - +o Jon Wright + o Jon Wright - +o William McEwan + o William McEwan - +o Michael Richardson + o Michael Richardson - 1155..55.. OOtthheerr ccoonnttrriibbuuttiioonnss + 15.5. Other contributions Bill Carr <Bill.Carr at compaq.com> made the Red Hat mkrootfs script diff --git a/Documentation/virtual/virtio-spec.txt b/Documentation/virtual/virtio-spec.txt new file mode 100644 index 00000000000..a350ae135b8 --- /dev/null +++ b/Documentation/virtual/virtio-spec.txt @@ -0,0 +1,2200 @@ +[Generated file: see http://ozlabs.org/~rusty/virtio-spec/] +Virtio PCI Card Specification +v0.9.1 DRAFT +- + +Rusty Russell <rusty@rustcorp.com.au>IBM Corporation (Editor) + +2011 August 1. + +Purpose and Description + +This document describes the specifications of the “virtio” family +of PCI[LaTeX Command: nomenclature] devices. These are devices +are found in virtual environments[LaTeX Command: nomenclature], +yet by design they are not all that different from physical PCI +devices, and this document treats them as such. This allows the +guest to use standard PCI drivers and discovery mechanisms. + +The purpose of virtio and this specification is that virtual +environments and guests should have a straightforward, efficient, +standard and extensible mechanism for virtual devices, rather +than boutique per-environment or per-OS mechanisms. + + Straightforward: Virtio PCI devices use normal PCI mechanisms + of interrupts and DMA which should be familiar to any device + driver author. There is no exotic page-flipping or COW + mechanism: it's just a PCI device.[footnote: +This lack of page-sharing implies that the implementation of the +device (e.g. the hypervisor or host) needs full access to the +guest memory. Communication with untrusted parties (i.e. +inter-guest communication) requires copying. +] + + Efficient: Virtio PCI devices consist of rings of descriptors + for input and output, which are neatly separated to avoid cache + effects from both guest and device writing to the same cache + lines. + + Standard: Virtio PCI makes no assumptions about the environment + in which it operates, beyond supporting PCI. In fact the virtio + devices specified in the appendices do not require PCI at all: + they have been implemented on non-PCI buses.[footnote: +The Linux implementation further separates the PCI virtio code +from the specific virtio drivers: these drivers are shared with +the non-PCI implementations (currently lguest and S/390). +] + + Extensible: Virtio PCI devices contain feature bits which are + acknowledged by the guest operating system during device setup. + This allows forwards and backwards compatibility: the device + offers all the features it knows about, and the driver + acknowledges those it understands and wishes to use. + + Virtqueues + +The mechanism for bulk data transport on virtio PCI devices is +pretentiously called a virtqueue. Each device can have zero or +more virtqueues: for example, the network device has one for +transmit and one for receive. + +Each virtqueue occupies two or more physically-contiguous pages +(defined, for the purposes of this specification, as 4096 bytes), +and consists of three parts: + + ++-------------------+-----------------------------------+-----------+ +| Descriptor Table | Available Ring (padding) | Used Ring | ++-------------------+-----------------------------------+-----------+ + + +When the driver wants to send buffers to the device, it puts them +in one or more slots in the descriptor table, and writes the +descriptor indices into the available ring. It then notifies the +device. When the device has finished with the buffers, it writes +the descriptors into the used ring, and sends an interrupt. + +Specification + + PCI Discovery + +Any PCI device with Vendor ID 0x1AF4, and Device ID 0x1000 +through 0x103F inclusive is a virtio device[footnote: +The actual value within this range is ignored +]. The device must also have a Revision ID of 0 to match this +specification. + +The Subsystem Device ID indicates which virtio device is +supported by the device. The Subsystem Vendor ID should reflect +the PCI Vendor ID of the environment (it's currently only used +for informational purposes by the guest). + + ++----------------------+--------------------+---------------+ +| Subsystem Device ID | Virtio Device | Specification | ++----------------------+--------------------+---------------+ ++----------------------+--------------------+---------------+ +| 1 | network card | Appendix C | ++----------------------+--------------------+---------------+ +| 2 | block device | Appendix D | ++----------------------+--------------------+---------------+ +| 3 | console | Appendix E | ++----------------------+--------------------+---------------+ +| 4 | entropy source | Appendix F | ++----------------------+--------------------+---------------+ +| 5 | memory ballooning | Appendix G | ++----------------------+--------------------+---------------+ +| 6 | ioMemory | - | ++----------------------+--------------------+---------------+ +| 9 | 9P transport | - | ++----------------------+--------------------+---------------+ + + + Device Configuration + +To configure the device, we use the first I/O region of the PCI +device. This contains a virtio header followed by a +device-specific region. + +There may be different widths of accesses to the I/O region; the “ +natural” access method for each field in the virtio header must +be used (i.e. 32-bit accesses for 32-bit fields, etc), but the +device-specific region can be accessed using any width accesses, +and should obtain the same results. + +Note that this is possible because while the virtio header is PCI +(i.e. little) endian, the device-specific region is encoded in +the native endian of the guest (where such distinction is +applicable). + + Device Initialization Sequence + +We start with an overview of device initialization, then expand +on the details of the device and how each step is preformed. + + Reset the device. This is not required on initial start up. + + The ACKNOWLEDGE status bit is set: we have noticed the device. + + The DRIVER status bit is set: we know how to drive the device. + + Device-specific setup, including reading the Device Feature + Bits, discovery of virtqueues for the device, optional MSI-X + setup, and reading and possibly writing the virtio + configuration space. + + The subset of Device Feature Bits understood by the driver is + written to the device. + + The DRIVER_OK status bit is set. + + The device can now be used (ie. buffers added to the + virtqueues)[footnote: +Historically, drivers have used the device before steps 5 and 6. +This is only allowed if the driver does not use any features +which would alter this early use of the device. +] + +If any of these steps go irrecoverably wrong, the guest should +set the FAILED status bit to indicate that it has given up on the +device (it can reset the device later to restart if desired). + +We now cover the fields required for general setup in detail. + + Virtio Header + +The virtio header looks as follows: + + ++------------++---------------------+---------------------+----------+--------+---------+---------+---------+--------+ +| Bits || 32 | 32 | 32 | 16 | 16 | 16 | 8 | 8 | ++------------++---------------------+---------------------+----------+--------+---------+---------+---------+--------+ +| Read/Write || R | R+W | R+W | R | R+W | R+W | R+W | R | ++------------++---------------------+---------------------+----------+--------+---------+---------+---------+--------+ +| Purpose || Device | Guest | Queue | Queue | Queue | Queue | Device | ISR | +| || Features bits 0:31 | Features bits 0:31 | Address | Size | Select | Notify | Status | Status | ++------------++---------------------+---------------------+----------+--------+---------+---------+---------+--------+ + + +If MSI-X is enabled for the device, two additional fields +immediately follow this header: + + ++------------++----------------+--------+ +| Bits || 16 | 16 | + +----------------+--------+ ++------------++----------------+--------+ +| Read/Write || R+W | R+W | ++------------++----------------+--------+ +| Purpose || Configuration | Queue | +| (MSI-X) || Vector | Vector | ++------------++----------------+--------+ + + +Finally, if feature bits (VIRTIO_F_FEATURES_HI) this is +immediately followed by two additional fields: + + ++------------++----------------------+---------------------- +| Bits || 32 | 32 ++------------++----------------------+---------------------- +| Read/Write || R | R+W ++------------++----------------------+---------------------- +| Purpose || Device | Guest +| || Features bits 32:63 | Features bits 32:63 ++------------++----------------------+---------------------- + + +Immediately following these general headers, there may be +device-specific headers: + + ++------------++--------------------+ +| Bits || Device Specific | + +--------------------+ ++------------++--------------------+ +| Read/Write || Device Specific | ++------------++--------------------+ +| Purpose || Device Specific... | +| || | ++------------++--------------------+ + + + Device Status + +The Device Status field is updated by the guest to indicate its +progress. This provides a simple low-level diagnostic: it's most +useful to imagine them hooked up to traffic lights on the console +indicating the status of each device. + +The device can be reset by writing a 0 to this field, otherwise +at least one bit should be set: + + ACKNOWLEDGE (1) Indicates that the guest OS has found the + device and recognized it as a valid virtio device. + + DRIVER (2) Indicates that the guest OS knows how to drive the + device. Under Linux, drivers can be loadable modules so there + may be a significant (or infinite) delay before setting this + bit. + + DRIVER_OK (3) Indicates that the driver is set up and ready to + drive the device. + + FAILED (8) Indicates that something went wrong in the guest, + and it has given up on the device. This could be an internal + error, or the driver didn't like the device for some reason, or + even a fatal error during device operation. The device must be + reset before attempting to re-initialize. + + Feature Bits + +The least significant 31 bits of the first configuration field +indicates the features that the device supports (the high bit is +reserved, and will be used to indicate the presence of future +feature bits elsewhere). If more than 31 feature bits are +supported, the device indicates so by setting feature bit 31 (see +[cha:Reserved-Feature-Bits]). The bits are allocated as follows: + + 0 to 23 Feature bits for the specific device type + + 24 to 40 Feature bits reserved for extensions to the queue and + feature negotiation mechanisms + + 41 to 63 Feature bits reserved for future extensions + +For example, feature bit 0 for a network device (i.e. Subsystem +Device ID 1) indicates that the device supports checksumming of +packets. + +The feature bits are negotiated: the device lists all the +features it understands in the Device Features field, and the +guest writes the subset that it understands into the Guest +Features field. The only way to renegotiate is to reset the +device. + +In particular, new fields in the device configuration header are +indicated by offering a feature bit, so the guest can check +before accessing that part of the configuration space. + +This allows for forwards and backwards compatibility: if the +device is enhanced with a new feature bit, older guests will not +write that feature bit back to the Guest Features field and it +can go into backwards compatibility mode. Similarly, if a guest +is enhanced with a feature that the device doesn't support, it +will not see that feature bit in the Device Features field and +can go into backwards compatibility mode (or, for poor +implementations, set the FAILED Device Status bit). + +Access to feature bits 32 to 63 is enabled by Guest by setting +feature bit 31. If this bit is unset, Device must assume that all +feature bits > 31 are unset. + + Configuration/Queue Vectors + +When MSI-X capability is present and enabled in the device +(through standard PCI configuration space) 4 bytes at byte offset +20 are used to map configuration change and queue interrupts to +MSI-X vectors. In this case, the ISR Status field is unused, and +device specific configuration starts at byte offset 24 in virtio +header structure. When MSI-X capability is not enabled, device +specific configuration starts at byte offset 20 in virtio header. + +Writing a valid MSI-X Table entry number, 0 to 0x7FF, to one of +Configuration/Queue Vector registers, maps interrupts triggered +by the configuration change/selected queue events respectively to +the corresponding MSI-X vector. To disable interrupts for a +specific event type, unmap it by writing a special NO_VECTOR +value: + +/* Vector value used to disable MSI for queue */ + +#define VIRTIO_MSI_NO_VECTOR 0xffff + +Reading these registers returns vector mapped to a given event, +or NO_VECTOR if unmapped. All queue and configuration change +events are unmapped by default. + +Note that mapping an event to vector might require allocating +internal device resources, and might fail. Devices report such +failures by returning the NO_VECTOR value when the relevant +Vector field is read. After mapping an event to vector, the +driver must verify success by reading the Vector field value: on +success, the previously written value is returned, and on +failure, NO_VECTOR is returned. If a mapping failure is detected, +the driver can retry mapping with fewervectors, or disable MSI-X. + + Virtqueue Configuration + +As a device can have zero or more virtqueues for bulk data +transport (for example, the network driver has two), the driver +needs to configure them as part of the device-specific +configuration. + +This is done as follows, for each virtqueue a device has: + + Write the virtqueue index (first queue is 0) to the Queue + Select field. + + Read the virtqueue size from the Queue Size field, which is + always a power of 2. This controls how big the virtqueue is + (see below). If this field is 0, the virtqueue does not exist. + + Allocate and zero virtqueue in contiguous physical memory, on a + 4096 byte alignment. Write the physical address, divided by + 4096 to the Queue Address field.[footnote: +The 4096 is based on the x86 page size, but it's also large +enough to ensure that the separate parts of the virtqueue are on +separate cache lines. +] + + Optionally, if MSI-X capability is present and enabled on the + device, select a vector to use to request interrupts triggered + by virtqueue events. Write the MSI-X Table entry number + corresponding to this vector in Queue Vector field. Read the + Queue Vector field: on success, previously written value is + returned; on failure, NO_VECTOR value is returned. + +The Queue Size field controls the total number of bytes required +for the virtqueue according to the following formula: + +#define ALIGN(x) (((x) + 4095) & ~4095) + +static inline unsigned vring_size(unsigned int qsz) + +{ + + return ALIGN(sizeof(struct vring_desc)*qsz + sizeof(u16)*(2 ++ qsz)) + + + ALIGN(sizeof(struct vring_used_elem)*qsz); + +} + +This currently wastes some space with padding, but also allows +future extensions. The virtqueue layout structure looks like this +(qsz is the Queue Size field, which is a variable, so this code +won't compile): + +struct vring { + + /* The actual descriptors (16 bytes each) */ + + struct vring_desc desc[qsz]; + + + + /* A ring of available descriptor heads with free-running +index. */ + + struct vring_avail avail; + + + + // Padding to the next 4096 boundary. + + char pad[]; + + + + // A ring of used descriptor heads with free-running index. + + struct vring_used used; + +}; + + A Note on Virtqueue Endianness + +Note that the endian of these fields and everything else in the +virtqueue is the native endian of the guest, not little-endian as +PCI normally is. This makes for simpler guest code, and it is +assumed that the host already has to be deeply aware of the guest +endian so such an “endian-aware” device is not a significant +issue. + + Descriptor Table + +The descriptor table refers to the buffers the guest is using for +the device. The addresses are physical addresses, and the buffers +can be chained via the next field. Each descriptor describes a +buffer which is read-only or write-only, but a chain of +descriptors can contain both read-only and write-only buffers. + +No descriptor chain may be more than 2^32 bytes long in total.struct vring_desc { + + /* Address (guest-physical). */ + + u64 addr; + + /* Length. */ + + u32 len; + +/* This marks a buffer as continuing via the next field. */ + +#define VRING_DESC_F_NEXT 1 + +/* This marks a buffer as write-only (otherwise read-only). */ + +#define VRING_DESC_F_WRITE 2 + +/* This means the buffer contains a list of buffer descriptors. +*/ + +#define VRING_DESC_F_INDIRECT 4 + + /* The flags as indicated above. */ + + u16 flags; + + /* Next field if flags & NEXT */ + + u16 next; + +}; + +The number of descriptors in the table is specified by the Queue +Size field for this virtqueue. + + <sub:Indirect-Descriptors>Indirect Descriptors + +Some devices benefit by concurrently dispatching a large number +of large requests. The VIRTIO_RING_F_INDIRECT_DESC feature can be +used to allow this (see [cha:Reserved-Feature-Bits]). To increase +ring capacity it is possible to store a table of indirect +descriptors anywhere in memory, and insert a descriptor in main +virtqueue (with flags&INDIRECT on) that refers to memory buffer +containing this indirect descriptor table; fields addr and len +refer to the indirect table address and length in bytes, +respectively. The indirect table layout structure looks like this +(len is the length of the descriptor that refers to this table, +which is a variable, so this code won't compile): + +struct indirect_descriptor_table { + + /* The actual descriptors (16 bytes each) */ + + struct vring_desc desc[len / 16]; + +}; + +The first indirect descriptor is located at start of the indirect +descriptor table (index 0), additional indirect descriptors are +chained by next field. An indirect descriptor without next field +(with flags&NEXT off) signals the end of the indirect descriptor +table, and transfers control back to the main virtqueue. An +indirect descriptor can not refer to another indirect descriptor +table (flags&INDIRECT must be off). A single indirect descriptor +table can include both read-only and write-only descriptors; +write-only flag (flags&WRITE) in the descriptor that refers to it +is ignored. + + Available Ring + +The available ring refers to what descriptors we are offering the +device: it refers to the head of a descriptor chain. The “flags” +field is currently 0 or 1: 1 indicating that we do not need an +interrupt when the device consumes a descriptor from the +available ring. Alternatively, the guest can ask the device to +delay interrupts until an entry with an index specified by the “ +used_event” field is written in the used ring (equivalently, +until the idx field in the used ring will reach the value +used_event + 1). The method employed by the device is controlled +by the VIRTIO_RING_F_EVENT_IDX feature bit (see [cha:Reserved-Feature-Bits] +). This interrupt suppression is merely an optimization; it may +not suppress interrupts entirely. + +The “idx” field indicates where we would put the next descriptor +entry (modulo the ring size). This starts at 0, and increases. + +struct vring_avail { + +#define VRING_AVAIL_F_NO_INTERRUPT 1 + + u16 flags; + + u16 idx; + + u16 ring[qsz]; /* qsz is the Queue Size field read from device +*/ + + u16 used_event; + +}; + + Used Ring + +The used ring is where the device returns buffers once it is done +with them. The flags field can be used by the device to hint that +no notification is necessary when the guest adds to the available +ring. Alternatively, the “avail_event” field can be used by the +device to hint that no notification is necessary until an entry +with an index specified by the “avail_event” is written in the +available ring (equivalently, until the idx field in the +available ring will reach the value avail_event + 1). The method +employed by the device is controlled by the guest through the +VIRTIO_RING_F_EVENT_IDX feature bit (see [cha:Reserved-Feature-Bits] +). [footnote: +These fields are kept here because this is the only part of the +virtqueue written by the device +]. + +Each entry in the ring is a pair: the head entry of the +descriptor chain describing the buffer (this matches an entry +placed in the available ring by the guest earlier), and the total +of bytes written into the buffer. The latter is extremely useful +for guests using untrusted buffers: if you do not know exactly +how much has been written by the device, you usually have to zero +the buffer to ensure no data leakage occurs. + +/* u32 is used here for ids for padding reasons. */ + +struct vring_used_elem { + + /* Index of start of used descriptor chain. */ + + u32 id; + + /* Total length of the descriptor chain which was used +(written to) */ + + u32 len; + +}; + + + +struct vring_used { + +#define VRING_USED_F_NO_NOTIFY 1 + + u16 flags; + + u16 idx; + + struct vring_used_elem ring[qsz]; + + u16 avail_event; + +}; + + Helpers for Managing Virtqueues + +The Linux Kernel Source code contains the definitions above and +helper routines in a more usable form, in +include/linux/virtio_ring.h. This was explicitly licensed by IBM +and Red Hat under the (3-clause) BSD license so that it can be +freely used by all other projects, and is reproduced (with slight +variation to remove Linux assumptions) in Appendix A. + + Device Operation + +There are two parts to device operation: supplying new buffers to +the device, and processing used buffers from the device. As an +example, the virtio network device has two virtqueues: the +transmit virtqueue and the receive virtqueue. The driver adds +outgoing (read-only) packets to the transmit virtqueue, and then +frees them after they are used. Similarly, incoming (write-only) +buffers are added to the receive virtqueue, and processed after +they are used. + + Supplying Buffers to The Device + +Actual transfer of buffers from the guest OS to the device +operates as follows: + + Place the buffer(s) into free descriptor(s). + + If there are no free descriptors, the guest may choose to + notify the device even if notifications are suppressed (to + reduce latency).[footnote: +The Linux drivers do this only for read-only buffers: for +write-only buffers, it is assumed that the driver is merely +trying to keep the receive buffer ring full, and no notification +of this expected condition is necessary. +] + + Place the id of the buffer in the next ring entry of the + available ring. + + The steps (1) and (2) may be performed repeatedly if batching + is possible. + + A memory barrier should be executed to ensure the device sees + the updated descriptor table and available ring before the next + step. + + The available “idx” field should be increased by the number of + entries added to the available ring. + + A memory barrier should be executed to ensure that we update + the idx field before checking for notification suppression. + + If notifications are not suppressed, the device should be + notified of the new buffers. + +Note that the above code does not take precautions against the +available ring buffer wrapping around: this is not possible since +the ring buffer is the same size as the descriptor table, so step +(1) will prevent such a condition. + +In addition, the maximum queue size is 32768 (it must be a power +of 2 which fits in 16 bits), so the 16-bit “idx” value can always +distinguish between a full and empty buffer. + +Here is a description of each stage in more detail. + + Placing Buffers Into The Descriptor Table + +A buffer consists of zero or more read-only physically-contiguous +elements followed by zero or more physically-contiguous +write-only elements (it must have at least one element). This +algorithm maps it into the descriptor table: + + for each buffer element, b: + + Get the next free descriptor table entry, d + + Set d.addr to the physical address of the start of b + + Set d.len to the length of b. + + If b is write-only, set d.flags to VRING_DESC_F_WRITE, + otherwise 0. + + If there is a buffer element after this: + + Set d.next to the index of the next free descriptor element. + + Set the VRING_DESC_F_NEXT bit in d.flags. + +In practice, the d.next fields are usually used to chain free +descriptors, and a separate count kept to check there are enough +free descriptors before beginning the mappings. + + Updating The Available Ring + +The head of the buffer we mapped is the first d in the algorithm +above. A naive implementation would do the following: + +avail->ring[avail->idx % qsz] = head; + +However, in general we can add many descriptors before we update +the “idx” field (at which point they become visible to the +device), so we keep a counter of how many we've added: + +avail->ring[(avail->idx + added++) % qsz] = head; + + Updating The Index Field + +Once the idx field of the virtqueue is updated, the device will +be able to access the descriptor entries we've created and the +memory they refer to. This is why a memory barrier is generally +used before the idx update, to ensure it sees the most up-to-date +copy. + +The idx field always increments, and we let it wrap naturally at +65536: + +avail->idx += added; + + <sub:Notifying-The-Device>Notifying The Device + +Device notification occurs by writing the 16-bit virtqueue index +of this virtqueue to the Queue Notify field of the virtio header +in the first I/O region of the PCI device. This can be expensive, +however, so the device can suppress such notifications if it +doesn't need them. We have to be careful to expose the new idx +value before checking the suppression flag: it's OK to notify +gratuitously, but not to omit a required notification. So again, +we use a memory barrier here before reading the flags or the +avail_event field. + +If the VIRTIO_F_RING_EVENT_IDX feature is not negotiated, and if +the VRING_USED_F_NOTIFY flag is not set, we go ahead and write to +the PCI configuration space. + +If the VIRTIO_F_RING_EVENT_IDX feature is negotiated, we read the +avail_event field in the available ring structure. If the +available index crossed_the avail_event field value since the +last notification, we go ahead and write to the PCI configuration +space. The avail_event field wraps naturally at 65536 as well: + +(u16)(new_idx - avail_event - 1) < (u16)(new_idx - old_idx) + + <sub:Receiving-Used-Buffers>Receiving Used Buffers From The + Device + +Once the device has used a buffer (read from or written to it, or +parts of both, depending on the nature of the virtqueue and the +device), it sends an interrupt, following an algorithm very +similar to the algorithm used for the driver to send the device a +buffer: + + Write the head descriptor number to the next field in the used + ring. + + Update the used ring idx. + + Determine whether an interrupt is necessary: + + If the VIRTIO_F_RING_EVENT_IDX feature is not negotiated: check + if f the VRING_AVAIL_F_NO_INTERRUPT flag is not set in avail- + >flags + + If the VIRTIO_F_RING_EVENT_IDX feature is negotiated: check + whether the used index crossed the used_event field value + since the last update. The used_event field wraps naturally + at 65536 as well:(u16)(new_idx - used_event - 1) < (u16)(new_idx - old_idx) + + If an interrupt is necessary: + + If MSI-X capability is disabled: + + Set the lower bit of the ISR Status field for the device. + + Send the appropriate PCI interrupt for the device. + + If MSI-X capability is enabled: + + Request the appropriate MSI-X interrupt message for the + device, Queue Vector field sets the MSI-X Table entry + number. + + If Queue Vector field value is NO_VECTOR, no interrupt + message is requested for this event. + +The guest interrupt handler should: + + If MSI-X capability is disabled: read the ISR Status field, + which will reset it to zero. If the lower bit is zero, the + interrupt was not for this device. Otherwise, the guest driver + should look through the used rings of each virtqueue for the + device, to see if any progress has been made by the device + which requires servicing. + + If MSI-X capability is enabled: look through the used rings of + each virtqueue mapped to the specific MSI-X vector for the + device, to see if any progress has been made by the device + which requires servicing. + +For each ring, guest should then disable interrupts by writing +VRING_AVAIL_F_NO_INTERRUPT flag in avail structure, if required. +It can then process used ring entries finally enabling interrupts +by clearing the VRING_AVAIL_F_NO_INTERRUPT flag or updating the +EVENT_IDX field in the available structure, Guest should then +execute a memory barrier, and then recheck the ring empty +condition. This is necessary to handle the case where, after the +last check and before enabling interrupts, an interrupt has been +suppressed by the device: + +vring_disable_interrupts(vq); + +for (;;) { + + if (vq->last_seen_used != vring->used.idx) { + + vring_enable_interrupts(vq); + + mb(); + + if (vq->last_seen_used != vring->used.idx) + + break; + + } + + struct vring_used_elem *e = +vring.used->ring[vq->last_seen_used%vsz]; + + process_buffer(e); + + vq->last_seen_used++; + +} + + Dealing With Configuration Changes + +Some virtio PCI devices can change the device configuration +state, as reflected in the virtio header in the PCI configuration +space. In this case: + + If MSI-X capability is disabled: an interrupt is delivered and + the second highest bit is set in the ISR Status field to + indicate that the driver should re-examine the configuration + space.Note that a single interrupt can indicate both that one + or more virtqueue has been used and that the configuration + space has changed: even if the config bit is set, virtqueues + must be scanned. + + If MSI-X capability is enabled: an interrupt message is + requested. The Configuration Vector field sets the MSI-X Table + entry number to use. If Configuration Vector field value is + NO_VECTOR, no interrupt message is requested for this event. + +Creating New Device Types + +Various considerations are necessary when creating a new device +type: + + How Many Virtqueues? + +It is possible that a very simple device will operate entirely +through its configuration space, but most will need at least one +virtqueue in which it will place requests. A device with both +input and output (eg. console and network devices described here) +need two queues: one which the driver fills with buffers to +receive input, and one which the driver places buffers to +transmit output. + + What Configuration Space Layout? + +Configuration space is generally used for rarely-changing or +initialization-time parameters. But it is a limited resource, so +it might be better to use a virtqueue to update configuration +information (the network device does this for filtering, +otherwise the table in the config space could potentially be very +large). + +Note that this space is generally the guest's native endian, +rather than PCI's little-endian. + + What Device Number? + +Currently device numbers are assigned quite freely: a simple +request mail to the author of this document or the Linux +virtualization mailing list[footnote: + +https://lists.linux-foundation.org/mailman/listinfo/virtualization +] will be sufficient to secure a unique one. + +Meanwhile for experimental drivers, use 65535 and work backwards. + + How many MSI-X vectors? + +Using the optional MSI-X capability devices can speed up +interrupt processing by removing the need to read ISR Status +register by guest driver (which might be an expensive operation), +reducing interrupt sharing between devices and queues within the +device, and handling interrupts from multiple CPUs. However, some +systems impose a limit (which might be as low as 256) on the +total number of MSI-X vectors that can be allocated to all +devices. Devices and/or device drivers should take this into +account, limiting the number of vectors used unless the device is +expected to cause a high volume of interrupts. Devices can +control the number of vectors used by limiting the MSI-X Table +Size or not presenting MSI-X capability in PCI configuration +space. Drivers can control this by mapping events to as small +number of vectors as possible, or disabling MSI-X capability +altogether. + + Message Framing + +The descriptors used for a buffer should not effect the semantics +of the message, except for the total length of the buffer. For +example, a network buffer consists of a 10 byte header followed +by the network packet. Whether this is presented in the ring +descriptor chain as (say) a 10 byte buffer and a 1514 byte +buffer, or a single 1524 byte buffer, or even three buffers, +should have no effect. + +In particular, no implementation should use the descriptor +boundaries to determine the size of any header in a request.[footnote: +The current qemu device implementations mistakenly insist that +the first descriptor cover the header in these cases exactly, so +a cautious driver should arrange it so. +] + + Device Improvements + +Any change to configuration space, or new virtqueues, or +behavioural changes, should be indicated by negotiation of a new +feature bit. This establishes clarity[footnote: +Even if it does mean documenting design or implementation +mistakes! +] and avoids future expansion problems. + +Clusters of functionality which are always implemented together +can use a single bit, but if one feature makes sense without the +others they should not be gratuitously grouped together to +conserve feature bits. We can always extend the spec when the +first person needs more than 24 feature bits for their device. + +[LaTeX Command: printnomenclature] + +Appendix A: virtio_ring.h + +#ifndef VIRTIO_RING_H + +#define VIRTIO_RING_H + +/* An interface for efficient virtio implementation. + + * + + * This header is BSD licensed so anyone can use the definitions + + * to implement compatible drivers/servers. + + * + + * Copyright 2007, 2009, IBM Corporation + + * Copyright 2011, Red Hat, Inc + + * All rights reserved. + + * + + * Redistribution and use in source and binary forms, with or +without + + * modification, are permitted provided that the following +conditions + + * are met: + + * 1. Redistributions of source code must retain the above +copyright + + * notice, this list of conditions and the following +disclaimer. + + * 2. Redistributions in binary form must reproduce the above +copyright + + * notice, this list of conditions and the following +disclaimer in the + + * documentation and/or other materials provided with the +distribution. + + * 3. Neither the name of IBM nor the names of its contributors + + * may be used to endorse or promote products derived from +this software + + * without specific prior written permission. + + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND +CONTRIBUTORS ``AS IS'' AND + + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED +TO, THE + + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +PARTICULAR PURPOSE + + * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE +LIABLE + + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR +CONSEQUENTIAL + + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF +SUBSTITUTE GOODS + + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS +INTERRUPTION) + + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN +CONTRACT, STRICT + + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING +IN ANY WAY + + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +POSSIBILITY OF + + * SUCH DAMAGE. + + */ + + + +/* This marks a buffer as continuing via the next field. */ + +#define VRING_DESC_F_NEXT 1 + +/* This marks a buffer as write-only (otherwise read-only). */ + +#define VRING_DESC_F_WRITE 2 + + + +/* The Host uses this in used->flags to advise the Guest: don't +kick me + + * when you add a buffer. It's unreliable, so it's simply an + + * optimization. Guest will still kick if it's out of buffers. +*/ + +#define VRING_USED_F_NO_NOTIFY 1 + +/* The Guest uses this in avail->flags to advise the Host: don't + + * interrupt me when you consume a buffer. It's unreliable, so +it's + + * simply an optimization. */ + +#define VRING_AVAIL_F_NO_INTERRUPT 1 + + + +/* Virtio ring descriptors: 16 bytes. + + * These can chain together via "next". */ + +struct vring_desc { + + /* Address (guest-physical). */ + + uint64_t addr; + + /* Length. */ + + uint32_t len; + + /* The flags as indicated above. */ + + uint16_t flags; + + /* We chain unused descriptors via this, too */ + + uint16_t next; + +}; + + + +struct vring_avail { + + uint16_t flags; + + uint16_t idx; + + uint16_t ring[]; + + uint16_t used_event; + +}; + + + +/* u32 is used here for ids for padding reasons. */ + +struct vring_used_elem { + + /* Index of start of used descriptor chain. */ + + uint32_t id; + + /* Total length of the descriptor chain which was written +to. */ + + uint32_t len; + +}; + + + +struct vring_used { + + uint16_t flags; + + uint16_t idx; + + struct vring_used_elem ring[]; + + uint16_t avail_event; + +}; + + + +struct vring { + + unsigned int num; + + + + struct vring_desc *desc; + + struct vring_avail *avail; + + struct vring_used *used; + +}; + + + +/* The standard layout for the ring is a continuous chunk of +memory which + + * looks like this. We assume num is a power of 2. + + * + + * struct vring { + + * // The actual descriptors (16 bytes each) + + * struct vring_desc desc[num]; + + * + + * // A ring of available descriptor heads with free-running +index. + + * __u16 avail_flags; + + * __u16 avail_idx; + + * __u16 available[num]; + + * + + * // Padding to the next align boundary. + + * char pad[]; + + * + + * // A ring of used descriptor heads with free-running +index. + + * __u16 used_flags; + + * __u16 EVENT_IDX; + + * struct vring_used_elem used[num]; + + * }; + + * Note: for virtio PCI, align is 4096. + + */ + +static inline void vring_init(struct vring *vr, unsigned int num, +void *p, + + unsigned long align) + +{ + + vr->num = num; + + vr->desc = p; + + vr->avail = p + num*sizeof(struct vring_desc); + + vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + + + align-1) + + & ~(align - 1)); + +} + + + +static inline unsigned vring_size(unsigned int num, unsigned long +align) + +{ + + return ((sizeof(struct vring_desc)*num + +sizeof(uint16_t)*(2+num) + + + align - 1) & ~(align - 1)) + + + sizeof(uint16_t)*3 + sizeof(struct +vring_used_elem)*num; + +} + + + +static inline int vring_need_event(uint16_t event_idx, uint16_t +new_idx, uint16_t old_idx) + +{ + + return (uint16_t)(new_idx - event_idx - 1) < +(uint16_t)(new_idx - old_idx); + +} + +#endif /* VIRTIO_RING_H */ + +<cha:Reserved-Feature-Bits>Appendix B: Reserved Feature Bits + +Currently there are five device-independent feature bits defined: + + VIRTIO_F_NOTIFY_ON_EMPTY (24) Negotiating this feature + indicates that the driver wants an interrupt if the device runs + out of available descriptors on a virtqueue, even though + interrupts are suppressed using the VRING_AVAIL_F_NO_INTERRUPT + flag or the used_event field. An example of this is the + networking driver: it doesn't need to know every time a packet + is transmitted, but it does need to free the transmitted + packets a finite time after they are transmitted. It can avoid + using a timer if the device interrupts it when all the packets + are transmitted. + + VIRTIO_F_RING_INDIRECT_DESC (28) Negotiating this feature + indicates that the driver can use descriptors with the + VRING_DESC_F_INDIRECT flag set, as described in [sub:Indirect-Descriptors] + . + + VIRTIO_F_RING_EVENT_IDX(29) This feature enables the used_event + and the avail_event fields. If set, it indicates that the + device should ignore the flags field in the available ring + structure. Instead, the used_event field in this structure is + used by guest to suppress device interrupts. Further, the + driver should ignore the flags field in the used ring + structure. Instead, the avail_event field in this structure is + used by the device to suppress notifications. If unset, the + driver should ignore the used_event field; the device should + ignore the avail_event field; the flags field is used + + VIRTIO_F_BAD_FEATURE(30) This feature should never be + negotiated by the guest; doing so is an indication that the + guest is faulty[footnote: +An experimental virtio PCI driver contained in Linux version +2.6.25 had this problem, and this feature bit can be used to +detect it. +] + + VIRTIO_F_FEATURES_HIGH(31) This feature indicates that the + device supports feature bits 32:63. If unset, feature bits + 32:63 are unset. + +Appendix C: Network Device + +The virtio network device is a virtual ethernet card, and is the +most complex of the devices supported so far by virtio. It has +enhanced rapidly and demonstrates clearly how support for new +features should be added to an existing device. Empty buffers are +placed in one virtqueue for receiving packets, and outgoing +packets are enqueued into another for transmission in that order. +A third command queue is used to control advanced filtering +features. + + Configuration + + Subsystem Device ID 1 + + Virtqueues 0:receiveq. 1:transmitq. 2:controlq[footnote: +Only if VIRTIO_NET_F_CTRL_VQ set +] + + Feature bits + + VIRTIO_NET_F_CSUM (0) Device handles packets with partial + checksum + + VIRTIO_NET_F_GUEST_CSUM (1) Guest handles packets with partial + checksum + + VIRTIO_NET_F_MAC (5) Device has given MAC address. + + VIRTIO_NET_F_GSO (6) (Deprecated) device handles packets with + any GSO type.[footnote: +It was supposed to indicate segmentation offload support, but +upon further investigation it became clear that multiple bits +were required. +] + + VIRTIO_NET_F_GUEST_TSO4 (7) Guest can receive TSOv4. + + VIRTIO_NET_F_GUEST_TSO6 (8) Guest can receive TSOv6. + + VIRTIO_NET_F_GUEST_ECN (9) Guest can receive TSO with ECN. + + VIRTIO_NET_F_GUEST_UFO (10) Guest can receive UFO. + + VIRTIO_NET_F_HOST_TSO4 (11) Device can receive TSOv4. + + VIRTIO_NET_F_HOST_TSO6 (12) Device can receive TSOv6. + + VIRTIO_NET_F_HOST_ECN (13) Device can receive TSO with ECN. + + VIRTIO_NET_F_HOST_UFO (14) Device can receive UFO. + + VIRTIO_NET_F_MRG_RXBUF (15) Guest can merge receive buffers. + + VIRTIO_NET_F_STATUS (16) Configuration status field is + available. + + VIRTIO_NET_F_CTRL_VQ (17) Control channel is available. + + VIRTIO_NET_F_CTRL_RX (18) Control channel RX mode support. + + VIRTIO_NET_F_CTRL_VLAN (19) Control channel VLAN filtering. + + Device configuration layout Two configuration fields are + currently defined. The mac address field always exists (though + is only valid if VIRTIO_NET_F_MAC is set), and the status field + only exists if VIRTIO_NET_F_STATUS is set. Only one bit is + currently defined for the status field: VIRTIO_NET_S_LINK_UP. #define VIRTIO_NET_S_LINK_UP 1 + + + +struct virtio_net_config { + + u8 mac[6]; + + u16 status; + +}; + + Device Initialization + + The initialization routine should identify the receive and + transmission virtqueues. + + If the VIRTIO_NET_F_MAC feature bit is set, the configuration + space “mac” entry indicates the “physical” address of the the + network card, otherwise a private MAC address should be + assigned. All guests are expected to negotiate this feature if + it is set. + + If the VIRTIO_NET_F_CTRL_VQ feature bit is negotiated, identify + the control virtqueue. + + If the VIRTIO_NET_F_STATUS feature bit is negotiated, the link + status can be read from the bottom bit of the “status” config + field. Otherwise, the link should be assumed active. + + The receive virtqueue should be filled with receive buffers. + This is described in detail below in “Setting Up Receive + Buffers”. + + A driver can indicate that it will generate checksumless + packets by negotating the VIRTIO_NET_F_CSUM feature. This “ + checksum offload” is a common feature on modern network cards. + + If that feature is negotiated, a driver can use TCP or UDP + segmentation offload by negotiating the VIRTIO_NET_F_HOST_TSO4 + (IPv4 TCP), VIRTIO_NET_F_HOST_TSO6 (IPv6 TCP) and + VIRTIO_NET_F_HOST_UFO (UDP fragmentation) features. It should + not send TCP packets requiring segmentation offload which have + the Explicit Congestion Notification bit set, unless the + VIRTIO_NET_F_HOST_ECN feature is negotiated.[footnote: +This is a common restriction in real, older network cards. +] + + The converse features are also available: a driver can save the + virtual device some work by negotiating these features.[footnote: +For example, a network packet transported between two guests on +the same system may not require checksumming at all, nor +segmentation, if both guests are amenable. +] The VIRTIO_NET_F_GUEST_CSUM feature indicates that partially + checksummed packets can be received, and if it can do that then + the VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6, + VIRTIO_NET_F_GUEST_UFO and VIRTIO_NET_F_GUEST_ECN are the input + equivalents of the features described above. See “Receiving + Packets” below. + + Device Operation + +Packets are transmitted by placing them in the transmitq, and +buffers for incoming packets are placed in the receiveq. In each +case, the packet itself is preceeded by a header: + +struct virtio_net_hdr { + +#define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 + + u8 flags; + +#define VIRTIO_NET_HDR_GSO_NONE 0 + +#define VIRTIO_NET_HDR_GSO_TCPV4 1 + +#define VIRTIO_NET_HDR_GSO_UDP 3 + +#define VIRTIO_NET_HDR_GSO_TCPV6 4 + +#define VIRTIO_NET_HDR_GSO_ECN 0x80 + + u8 gso_type; + + u16 hdr_len; + + u16 gso_size; + + u16 csum_start; + + u16 csum_offset; + +/* Only if VIRTIO_NET_F_MRG_RXBUF: */ + + u16 num_buffers + +}; + +The controlq is used to control device features such as +filtering. + + Packet Transmission + +Transmitting a single packet is simple, but varies depending on +the different features the driver negotiated. + + If the driver negotiated VIRTIO_NET_F_CSUM, and the packet has + not been fully checksummed, then the virtio_net_hdr's fields + are set as follows. Otherwise, the packet must be fully + checksummed, and flags is zero. + + flags has the VIRTIO_NET_HDR_F_NEEDS_CSUM set, + + <ite:csum_start-is-set>csum_start is set to the offset within + the packet to begin checksumming, and + + csum_offset indicates how many bytes after the csum_start the + new (16 bit ones' complement) checksum should be placed.[footnote: +For example, consider a partially checksummed TCP (IPv4) packet. +It will have a 14 byte ethernet header and 20 byte IP header +followed by the TCP header (with the TCP checksum field 16 bytes +into that header). csum_start will be 14+20 = 34 (the TCP +checksum includes the header), and csum_offset will be 16. The +value in the TCP checksum field will be the sum of the TCP pseudo +header, so that replacing it by the ones' complement checksum of +the TCP header and body will give the correct result. +] + + <enu:If-the-driver>If the driver negotiated + VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO, and the packet requires + TCP segmentation or UDP fragmentation, then the “gso_type” + field is set to VIRTIO_NET_HDR_GSO_TCPV4, TCPV6 or UDP. + (Otherwise, it is set to VIRTIO_NET_HDR_GSO_NONE). In this + case, packets larger than 1514 bytes can be transmitted: the + metadata indicates how to replicate the packet header to cut it + into smaller packets. The other gso fields are set: + + hdr_len is a hint to the device as to how much of the header + needs to be kept to copy into each packet, usually set to the + length of the headers, including the transport header.[footnote: +Due to various bugs in implementations, this field is not useful +as a guarantee of the transport header size. +] + + gso_size is the size of the packet beyond that header (ie. + MSS). + + If the driver negotiated the VIRTIO_NET_F_HOST_ECN feature, the + VIRTIO_NET_HDR_GSO_ECN bit may be set in “gso_type” as well, + indicating that the TCP packet has the ECN bit set.[footnote: +This case is not handled by some older hardware, so is called out +specifically in the protocol. +] + + If the driver negotiated the VIRTIO_NET_F_MRG_RXBUF feature, + the num_buffers field is set to zero. + + The header and packet are added as one output buffer to the + transmitq, and the device is notified of the new entry (see [sub:Notifying-The-Device] + ).[footnote: +Note that the header will be two bytes longer for the +VIRTIO_NET_F_MRG_RXBUF case. +] + + Packet Transmission Interrupt + +Often a driver will suppress transmission interrupts using the +VRING_AVAIL_F_NO_INTERRUPT flag (see [sub:Receiving-Used-Buffers] +) and check for used packets in the transmit path of following +packets. However, it will still receive interrupts if the +VIRTIO_F_NOTIFY_ON_EMPTY feature is negotiated, indicating that +the transmission queue is completely emptied. + +The normal behavior in this interrupt handler is to retrieve and +new descriptors from the used ring and free the corresponding +headers and packets. + + Setting Up Receive Buffers + +It is generally a good idea to keep the receive virtqueue as +fully populated as possible: if it runs out, network performance +will suffer. + +If the VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6 or +VIRTIO_NET_F_GUEST_UFO features are used, the Guest will need to +accept packets of up to 65550 bytes long (the maximum size of a +TCP or UDP packet, plus the 14 byte ethernet header), otherwise +1514 bytes. So unless VIRTIO_NET_F_MRG_RXBUF is negotiated, every +buffer in the receive queue needs to be at least this length [footnote: +Obviously each one can be split across multiple descriptor +elements. +]. + +If VIRTIO_NET_F_MRG_RXBUF is negotiated, each buffer must be at +least the size of the struct virtio_net_hdr. + + Packet Receive Interrupt + +When a packet is copied into a buffer in the receiveq, the +optimal path is to disable further interrupts for the receiveq +(see [sub:Receiving-Used-Buffers]) and process packets until no +more are found, then re-enable them. + +Processing packet involves: + + If the driver negotiated the VIRTIO_NET_F_MRG_RXBUF feature, + then the “num_buffers” field indicates how many descriptors + this packet is spread over (including this one). This allows + receipt of large packets without having to allocate large + buffers. In this case, there will be at least “num_buffers” in + the used ring, and they should be chained together to form a + single packet. The other buffers will not begin with a struct + virtio_net_hdr. + + If the VIRTIO_NET_F_MRG_RXBUF feature was not negotiated, or + the “num_buffers” field is one, then the entire packet will be + contained within this buffer, immediately following the struct + virtio_net_hdr. + + If the VIRTIO_NET_F_GUEST_CSUM feature was negotiated, the + VIRTIO_NET_HDR_F_NEEDS_CSUM bit in the “flags” field may be + set: if so, the checksum on the packet is incomplete and the “ + csum_start” and “csum_offset” fields indicate how to calculate + it (see [ite:csum_start-is-set]). + + If the VIRTIO_NET_F_GUEST_TSO4, TSO6 or UFO options were + negotiated, then the “gso_type” may be something other than + VIRTIO_NET_HDR_GSO_NONE, and the “gso_size” field indicates the + desired MSS (see [enu:If-the-driver]).Control Virtqueue + +The driver uses the control virtqueue (if VIRTIO_NET_F_VTRL_VQ is +negotiated) to send commands to manipulate various features of +the device which would not easily map into the configuration +space. + +All commands are of the following form: + +struct virtio_net_ctrl { + + u8 class; + + u8 command; + + u8 command-specific-data[]; + + u8 ack; + +}; + + + +/* ack values */ + +#define VIRTIO_NET_OK 0 + +#define VIRTIO_NET_ERR 1 + +The class, command and command-specific-data are set by the +driver, and the device sets the ack byte. There is little it can +do except issue a diagnostic if the ack byte is not +VIRTIO_NET_OK. + + Packet Receive Filtering + +If the VIRTIO_NET_F_CTRL_RX feature is negotiated, the driver can +send control commands for promiscuous mode, multicast receiving, +and filtering of MAC addresses. + +Note that in general, these commands are best-effort: unwanted +packets may still arrive. + + Setting Promiscuous Mode + +#define VIRTIO_NET_CTRL_RX 0 + + #define VIRTIO_NET_CTRL_RX_PROMISC 0 + + #define VIRTIO_NET_CTRL_RX_ALLMULTI 1 + +The class VIRTIO_NET_CTRL_RX has two commands: +VIRTIO_NET_CTRL_RX_PROMISC turns promiscuous mode on and off, and +VIRTIO_NET_CTRL_RX_ALLMULTI turns all-multicast receive on and +off. The command-specific-data is one byte containing 0 (off) or +1 (on). + + Setting MAC Address Filtering + +struct virtio_net_ctrl_mac { + + u32 entries; + + u8 macs[entries][ETH_ALEN]; + +}; + + + +#define VIRTIO_NET_CTRL_MAC 1 + + #define VIRTIO_NET_CTRL_MAC_TABLE_SET 0 + +The device can filter incoming packets by any number of +destination MAC addresses.[footnote: +Since there are no guarentees, it can use a hash filter +orsilently switch to allmulti or promiscuous mode if it is given +too many addresses. +] This table is set using the class VIRTIO_NET_CTRL_MAC and the +command VIRTIO_NET_CTRL_MAC_TABLE_SET. The command-specific-data +is two variable length tables of 6-byte MAC addresses. The first +table contains unicast addresses, and the second contains +multicast addresses. + + VLAN Filtering + +If the driver negotiates the VIRTION_NET_F_CTRL_VLAN feature, it +can control a VLAN filter table in the device. + +#define VIRTIO_NET_CTRL_VLAN 2 + + #define VIRTIO_NET_CTRL_VLAN_ADD 0 + + #define VIRTIO_NET_CTRL_VLAN_DEL 1 + +Both the VIRTIO_NET_CTRL_VLAN_ADD and VIRTIO_NET_CTRL_VLAN_DEL +command take a 16-bit VLAN id as the command-specific-data. + +Appendix D: Block Device + +The virtio block device is a simple virtual block device (ie. +disk). Read and write requests (and other exotic requests) are +placed in the queue, and serviced (probably out of order) by the +device except where noted. + + Configuration + + Subsystem Device ID 2 + + Virtqueues 0:requestq. + + Feature bits + + VIRTIO_BLK_F_BARRIER (0) Host supports request barriers. + + VIRTIO_BLK_F_SIZE_MAX (1) Maximum size of any single segment is + in “size_max”. + + VIRTIO_BLK_F_SEG_MAX (2) Maximum number of segments in a + request is in “seg_max”. + + VIRTIO_BLK_F_GEOMETRY (4) Disk-style geometry specified in “ + geometry”. + + VIRTIO_BLK_F_RO (5) Device is read-only. + + VIRTIO_BLK_F_BLK_SIZE (6) Block size of disk is in “blk_size”. + + VIRTIO_BLK_F_SCSI (7) Device supports scsi packet commands. + + VIRTIO_BLK_F_FLUSH (9) Cache flush command support. + + + + Device configuration layout The capacity of the device + (expressed in 512-byte sectors) is always present. The + availability of the others all depend on various feature bits + as indicated above. struct virtio_blk_config { + + u64 capacity; + + u32 size_max; + + u32 seg_max; + + struct virtio_blk_geometry { + + u16 cylinders; + + u8 heads; + + u8 sectors; + + } geometry; + + u32 blk_size; + + + +}; + + Device Initialization + + The device size should be read from the “capacity” + configuration field. No requests should be submitted which goes + beyond this limit. + + If the VIRTIO_BLK_F_BLK_SIZE feature is negotiated, the + blk_size field can be read to determine the optimal sector size + for the driver to use. This does not effect the units used in + the protocol (always 512 bytes), but awareness of the correct + value can effect performance. + + If the VIRTIO_BLK_F_RO feature is set by the device, any write + requests will fail. + + + + Device Operation + +The driver queues requests to the virtqueue, and they are used by +the device (not necessarily in order). Each request is of form: + +struct virtio_blk_req { + + + + u32 type; + + u32 ioprio; + + u64 sector; + + char data[][512]; + + u8 status; + +}; + +If the device has VIRTIO_BLK_F_SCSI feature, it can also support +scsi packet command requests, each of these requests is of form:struct virtio_scsi_pc_req { + + u32 type; + + u32 ioprio; + + u64 sector; + + char cmd[]; + + char data[][512]; + +#define SCSI_SENSE_BUFFERSIZE 96 + + u8 sense[SCSI_SENSE_BUFFERSIZE]; + + u32 errors; + + u32 data_len; + + u32 sense_len; + + u32 residual; + + u8 status; + +}; + +The type of the request is either a read (VIRTIO_BLK_T_IN), a +write (VIRTIO_BLK_T_OUT), a scsi packet command +(VIRTIO_BLK_T_SCSI_CMD or VIRTIO_BLK_T_SCSI_CMD_OUT[footnote: +the SCSI_CMD and SCSI_CMD_OUT types are equivalent, the device +does not distinguish between them +]) or a flush (VIRTIO_BLK_T_FLUSH or VIRTIO_BLK_T_FLUSH_OUT[footnote: +the FLUSH and FLUSH_OUT types are equivalent, the device does not +distinguish between them +]). If the device has VIRTIO_BLK_F_BARRIER feature the high bit +(VIRTIO_BLK_T_BARRIER) indicates that this request acts as a +barrier and that all preceeding requests must be complete before +this one, and all following requests must not be started until +this is complete. Note that a barrier does not flush caches in +the underlying backend device in host, and thus does not serve as +data consistency guarantee. Driver must use FLUSH request to +flush the host cache. + +#define VIRTIO_BLK_T_IN 0 + +#define VIRTIO_BLK_T_OUT 1 + +#define VIRTIO_BLK_T_SCSI_CMD 2 + +#define VIRTIO_BLK_T_SCSI_CMD_OUT 3 + +#define VIRTIO_BLK_T_FLUSH 4 + +#define VIRTIO_BLK_T_FLUSH_OUT 5 + +#define VIRTIO_BLK_T_BARRIER 0x80000000 + +The ioprio field is a hint about the relative priorities of +requests to the device: higher numbers indicate more important +requests. + +The sector number indicates the offset (multiplied by 512) where +the read or write is to occur. This field is unused and set to 0 +for scsi packet commands and for flush commands. + +The cmd field is only present for scsi packet command requests, +and indicates the command to perform. This field must reside in a +single, separate read-only buffer; command length can be derived +from the length of this buffer. + +Note that these first three (four for scsi packet commands) +fields are always read-only: the data field is either read-only +or write-only, depending on the request. The size of the read or +write can be derived from the total size of the request buffers. + +The sense field is only present for scsi packet command requests, +and indicates the buffer for scsi sense data. + +The data_len field is only present for scsi packet command +requests, this field is deprecated, and should be ignored by the +driver. Historically, devices copied data length there. + +The sense_len field is only present for scsi packet command +requests and indicates the number of bytes actually written to +the sense buffer. + +The residual field is only present for scsi packet command +requests and indicates the residual size, calculated as data +length - number of bytes actually transferred. + +The final status byte is written by the device: either +VIRTIO_BLK_S_OK for success, VIRTIO_BLK_S_IOERR for host or guest +error or VIRTIO_BLK_S_UNSUPP for a request unsupported by host:#define VIRTIO_BLK_S_OK 0 + +#define VIRTIO_BLK_S_IOERR 1 + +#define VIRTIO_BLK_S_UNSUPP 2 + +Historically, devices assumed that the fields type, ioprio and +sector reside in a single, separate read-only buffer; the fields +errors, data_len, sense_len and residual reside in a single, +separate write-only buffer; the sense field in a separate +write-only buffer of size 96 bytes, by itself; the fields errors, +data_len, sense_len and residual in a single write-only buffer; +and the status field is a separate read-only buffer of size 1 +byte, by itself. + +Appendix E: Console Device + +The virtio console device is a simple device for data input and +output. A device may have one or more ports. Each port has a pair +of input and output virtqueues. Moreover, a device has a pair of +control IO virtqueues. The control virtqueues are used to +communicate information between the device and the driver about +ports being opened and closed on either side of the connection, +indication from the host about whether a particular port is a +console port, adding new ports, port hot-plug/unplug, etc., and +indication from the guest about whether a port or a device was +successfully added, port open/close, etc.. For data IO, one or +more empty buffers are placed in the receive queue for incoming +data and outgoing characters are placed in the transmit queue. + + Configuration + + Subsystem Device ID 3 + + Virtqueues 0:receiveq(port0). 1:transmitq(port0), 2:control + receiveq[footnote: +Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set +], 3:control transmitq, 4:receiveq(port1), 5:transmitq(port1), + ... + + Feature bits + + VIRTIO_CONSOLE_F_SIZE (0) Configuration cols and rows fields + are valid. + + VIRTIO_CONSOLE_F_MULTIPORT(1) Device has support for multiple + ports; configuration fields nr_ports and max_nr_ports are + valid and control virtqueues will be used. + + Device configuration layout The size of the console is supplied + in the configuration space if the VIRTIO_CONSOLE_F_SIZE feature + is set. Furthermore, if the VIRTIO_CONSOLE_F_MULTIPORT feature + is set, the maximum number of ports supported by the device can + be fetched.struct virtio_console_config { + + u16 cols; + + u16 rows; + + + + u32 max_nr_ports; + +}; + + Device Initialization + + If the VIRTIO_CONSOLE_F_SIZE feature is negotiated, the driver + can read the console dimensions from the configuration fields. + + If the VIRTIO_CONSOLE_F_MULTIPORT feature is negotiated, the + driver can spawn multiple ports, not all of which may be + attached to a console. Some could be generic ports. In this + case, the control virtqueues are enabled and according to the + max_nr_ports configuration-space value, the appropriate number + of virtqueues are created. A control message indicating the + driver is ready is sent to the host. The host can then send + control messages for adding new ports to the device. After + creating and initializing each port, a + VIRTIO_CONSOLE_PORT_READY control message is sent to the host + for that port so the host can let us know of any additional + configuration options set for that port. + + The receiveq for each port is populated with one or more + receive buffers. + + Device Operation + + For output, a buffer containing the characters is placed in the + port's transmitq.[footnote: +Because this is high importance and low bandwidth, the current +Linux implementation polls for the buffer to be used, rather than +waiting for an interrupt, simplifying the implementation +significantly. However, for generic serial ports with the +O_NONBLOCK flag set, the polling limitation is relaxed and the +consumed buffers are freed upon the next write or poll call or +when a port is closed or hot-unplugged. +] + + When a buffer is used in the receiveq (signalled by an + interrupt), the contents is the input to the port associated + with the virtqueue for which the notification was received. + + If the driver negotiated the VIRTIO_CONSOLE_F_SIZE feature, a + configuration change interrupt may occur. The updated size can + be read from the configuration fields. + + If the driver negotiated the VIRTIO_CONSOLE_F_MULTIPORT + feature, active ports are announced by the host using the + VIRTIO_CONSOLE_PORT_ADD control message. The same message is + used for port hot-plug as well. + + If the host specified a port `name', a sysfs attribute is + created with the name filled in, so that udev rules can be + written that can create a symlink from the port's name to the + char device for port discovery by applications in the guest. + + Changes to ports' state are effected by control messages. + Appropriate action is taken on the port indicated in the + control message. The layout of the structure of the control + buffer and the events associated are:struct virtio_console_control { + + uint32_t id; /* Port number */ + + uint16_t event; /* The kind of control event */ + + uint16_t value; /* Extra information for the event */ + +}; + + + +/* Some events for the internal messages (control packets) */ + + + +#define VIRTIO_CONSOLE_DEVICE_READY 0 + +#define VIRTIO_CONSOLE_PORT_ADD 1 + +#define VIRTIO_CONSOLE_PORT_REMOVE 2 + +#define VIRTIO_CONSOLE_PORT_READY 3 + +#define VIRTIO_CONSOLE_CONSOLE_PORT 4 + +#define VIRTIO_CONSOLE_RESIZE 5 + +#define VIRTIO_CONSOLE_PORT_OPEN 6 + +#define VIRTIO_CONSOLE_PORT_NAME 7 + +Appendix F: Entropy Device + +The virtio entropy device supplies high-quality randomness for +guest use. + + Configuration + + Subsystem Device ID 4 + + Virtqueues 0:requestq. + + Feature bits None currently defined + + Device configuration layout None currently defined. + + Device Initialization + + The virtqueue is initialized + + Device Operation + +When the driver requires random bytes, it places the descriptor +of one or more buffers in the queue. It will be completely filled +by random data by the device. + +Appendix G: Memory Balloon Device + +The virtio memory balloon device is a primitive device for +managing guest memory: the device asks for a certain amount of +memory, and the guest supplies it (or withdraws it, if the device +has more than it asks for). This allows the guest to adapt to +changes in allowance of underlying physical memory. If the +feature is negotiated, the device can also be used to communicate +guest memory statistics to the host. + + Configuration + + Subsystem Device ID 5 + + Virtqueues 0:inflateq. 1:deflateq. 2:statsq.[footnote: +Only if VIRTIO_BALLON_F_STATS_VQ set +] + + Feature bits + + VIRTIO_BALLOON_F_MUST_TELL_HOST (0) Host must be told before + pages from the balloon are used. + + VIRTIO_BALLOON_F_STATS_VQ (1) A virtqueue for reporting guest + memory statistics is present. + + Device configuration layout Both fields of this configuration + are always available. Note that they are little endian, despite + convention that device fields are guest endian:struct virtio_balloon_config { + + u32 num_pages; + + u32 actual; + +}; + + Device Initialization + + The inflate and deflate virtqueues are identified. + + If the VIRTIO_BALLOON_F_STATS_VQ feature bit is negotiated: + + Identify the stats virtqueue. + + Add one empty buffer to the stats virtqueue and notify the + host. + +Device operation begins immediately. + + Device Operation + + Memory Ballooning The device is driven by the receipt of a + configuration change interrupt. + + The “num_pages” configuration field is examined. If this is + greater than the “actual” number of pages, memory must be given + to the balloon. If it is less than the “actual” number of + pages, memory may be taken back from the balloon for general + use. + + To supply memory to the balloon (aka. inflate): + + The driver constructs an array of addresses of unused memory + pages. These addresses are divided by 4096[footnote: +This is historical, and independent of the guest page size +] and the descriptor describing the resulting 32-bit array is + added to the inflateq. + + To remove memory from the balloon (aka. deflate): + + The driver constructs an array of addresses of memory pages it + has previously given to the balloon, as described above. This + descriptor is added to the deflateq. + + If the VIRTIO_BALLOON_F_MUST_TELL_HOST feature is set, the + guest may not use these requested pages until that descriptor + in the deflateq has been used by the device. + + Otherwise, the guest may begin to re-use pages previously given + to the balloon before the device has acknowledged their + withdrawl. [footnote: +In this case, deflation advice is merely a courtesy +] + + In either case, once the device has completed the inflation or + deflation, the “actual” field of the configuration should be + updated to reflect the new number of pages in the balloon.[footnote: +As updates to configuration space are not atomic, this field +isn't particularly reliable, but can be used to diagnose buggy +guests. +] + + Memory Statistics + +The stats virtqueue is atypical because communication is driven +by the device (not the driver). The channel becomes active at +driver initialization time when the driver adds an empty buffer +and notifies the device. A request for memory statistics proceeds +as follows: + + The device pushes the buffer onto the used ring and sends an + interrupt. + + The driver pops the used buffer and discards it. + + The driver collects memory statistics and writes them into a + new buffer. + + The driver adds the buffer to the virtqueue and notifies the + device. + + The device pops the buffer (retaining it to initiate a + subsequent request) and consumes the statistics. + + Memory Statistics Format Each statistic consists of a 16 bit + tag and a 64 bit value. Both quantities are represented in the + native endian of the guest. All statistics are optional and the + driver may choose which ones to supply. To guarantee backwards + compatibility, unsupported statistics should be omitted. + + struct virtio_balloon_stat { + +#define VIRTIO_BALLOON_S_SWAP_IN 0 + +#define VIRTIO_BALLOON_S_SWAP_OUT 1 + +#define VIRTIO_BALLOON_S_MAJFLT 2 + +#define VIRTIO_BALLOON_S_MINFLT 3 + +#define VIRTIO_BALLOON_S_MEMFREE 4 + +#define VIRTIO_BALLOON_S_MEMTOT 5 + + u16 tag; + + u64 val; + +} __attribute__((packed)); + + Tags + + VIRTIO_BALLOON_S_SWAP_IN The amount of memory that has been + swapped in (in bytes). + + VIRTIO_BALLOON_S_SWAP_OUT The amount of memory that has been + swapped out to disk (in bytes). + + VIRTIO_BALLOON_S_MAJFLT The number of major page faults that + have occurred. + + VIRTIO_BALLOON_S_MINFLT The number of minor page faults that + have occurred. + + VIRTIO_BALLOON_S_MEMFREE The amount of memory not being used + for any purpose (in bytes). + + VIRTIO_BALLOON_S_MEMTOT The total amount of memory available + (in bytes). + |