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authorRusty Russell <rusty@rustcorp.com.au>2007-07-26 10:41:03 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-26 11:35:17 -0700
commite2c9784325490c878b7f69aeec1bed98b288bd97 (patch)
treed474007607c713a30db818107ca0581269f059a2 /include/linux/lguest_launcher.h
parentb2b47c214f4e85ce3968120d42e8b18eccb4f4e3 (diff)
lguest: documentation III: Drivers
Documentation: The Drivers Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/lguest_launcher.h')
-rw-r--r--include/linux/lguest_launcher.h60
1 files changed, 57 insertions, 3 deletions
diff --git a/include/linux/lguest_launcher.h b/include/linux/lguest_launcher.h
index 0ba414a40c8..64167057944 100644
--- a/include/linux/lguest_launcher.h
+++ b/include/linux/lguest_launcher.h
@@ -9,14 +9,45 @@
/* How many devices? Assume each one wants up to two dma arrays per device. */
#define LGUEST_MAX_DEVICES (LGUEST_MAX_DMA/2)
+/*D:200
+ * Lguest I/O
+ *
+ * The lguest I/O mechanism is the only way Guests can talk to devices. There
+ * are two hypercalls involved: SEND_DMA for output and BIND_DMA for input. In
+ * each case, "struct lguest_dma" describes the buffer: this contains 16
+ * addr/len pairs, and if there are fewer buffer elements the len array is
+ * terminated with a 0.
+ *
+ * I/O is organized by keys: BIND_DMA attaches buffers to a particular key, and
+ * SEND_DMA transfers to buffers bound to particular key. By convention, keys
+ * correspond to a physical address within the device's page. This means that
+ * devices will never accidentally end up with the same keys, and allows the
+ * Host use The Futex Trick (as we'll see later in our journey).
+ *
+ * SEND_DMA simply indicates a key to send to, and the physical address of the
+ * "struct lguest_dma" to send. The Host will write the number of bytes
+ * transferred into the "struct lguest_dma"'s used_len member.
+ *
+ * BIND_DMA indicates a key to bind to, a pointer to an array of "struct
+ * lguest_dma"s ready for receiving, the size of that array, and an interrupt
+ * to trigger when data is received. The Host will only allow transfers into
+ * buffers with a used_len of zero: it then sets used_len to the number of
+ * bytes transferred and triggers the interrupt for the Guest to process the
+ * new input. */
struct lguest_dma
{
- /* 0 if free to be used, filled by hypervisor. */
+ /* 0 if free to be used, filled by the Host. */
u32 used_len;
unsigned long addr[LGUEST_MAX_DMA_SECTIONS];
u16 len[LGUEST_MAX_DMA_SECTIONS];
};
+/*:*/
+/*D:460 This is the layout of a block device memory page. The Launcher sets up
+ * the num_sectors initially to tell the Guest the size of the disk. The Guest
+ * puts the type, sector and length of the request in the first three fields,
+ * then DMAs to the Host. The Host processes the request, sets up the result,
+ * then DMAs back to the Guest. */
struct lguest_block_page
{
/* 0 is a read, 1 is a write. */
@@ -28,27 +59,47 @@ struct lguest_block_page
u32 num_sectors; /* Disk length = num_sectors * 512 */
};
-/* There is a shared page of these. */
+/*D:520 The network device is basically a memory page where all the Guests on
+ * the network publish their MAC (ethernet) addresses: it's an array of "struct
+ * lguest_net": */
struct lguest_net
{
/* Simply the mac address (with multicast bit meaning promisc). */
unsigned char mac[6];
};
+/*:*/
/* Where the Host expects the Guest to SEND_DMA console output to. */
#define LGUEST_CONSOLE_DMA_KEY 0
-/* We have a page of these descriptors in the lguest_device page. */
+/*D:010
+ * Drivers
+ *
+ * The Guest needs devices to do anything useful. Since we don't let it touch
+ * real devices (think of the damage it could do!) we provide virtual devices.
+ * We could emulate a PCI bus with various devices on it, but that is a fairly
+ * complex burden for the Host and suboptimal for the Guest, so we have our own
+ * "lguest" bus and simple drivers.
+ *
+ * Devices are described by an array of LGUEST_MAX_DEVICES of these structs,
+ * placed by the Launcher just above the top of physical memory:
+ */
struct lguest_device_desc {
+ /* The device type: console, network, disk etc. */
u16 type;
#define LGUEST_DEVICE_T_CONSOLE 1
#define LGUEST_DEVICE_T_NET 2
#define LGUEST_DEVICE_T_BLOCK 3
+ /* The specific features of this device: these depends on device type
+ * except for LGUEST_DEVICE_F_RANDOMNESS. */
u16 features;
#define LGUEST_NET_F_NOCSUM 0x4000 /* Don't bother checksumming */
#define LGUEST_DEVICE_F_RANDOMNESS 0x8000 /* IRQ is fairly random */
+ /* This is how the Guest reports status of the device: the Host can set
+ * LGUEST_DEVICE_S_REMOVED to indicate removal, but the rest are only
+ * ever manipulated by the Guest, and only ever set. */
u16 status;
/* 256 and above are device specific. */
#define LGUEST_DEVICE_S_ACKNOWLEDGE 1 /* We have seen device. */
@@ -58,9 +109,12 @@ struct lguest_device_desc {
#define LGUEST_DEVICE_S_REMOVED_ACK 16 /* Driver has been told. */
#define LGUEST_DEVICE_S_FAILED 128 /* Something actually failed */
+ /* Each device exists somewhere in Guest physical memory, over some
+ * number of pages. */
u16 num_pages;
u32 pfn;
};
+/*:*/
/* Write command first word is a request. */
enum lguest_req