diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/configfs/configfs.txt | 10 | ||||
| -rw-r--r-- | Documentation/filesystems/configfs/configfs_example.c | 14 | ||||
| -rw-r--r-- | Documentation/filesystems/ubifs.txt | 164 |
3 files changed, 178 insertions, 10 deletions
diff --git a/Documentation/filesystems/configfs/configfs.txt b/Documentation/filesystems/configfs/configfs.txt index 44c97e6accb..15838d706ea 100644 --- a/Documentation/filesystems/configfs/configfs.txt +++ b/Documentation/filesystems/configfs/configfs.txt @@ -233,10 +233,12 @@ accomplished via the group operations specified on the group's config_item_type. struct configfs_group_operations { - struct config_item *(*make_item)(struct config_group *group, - const char *name); - struct config_group *(*make_group)(struct config_group *group, - const char *name); + int (*make_item)(struct config_group *group, + const char *name, + struct config_item **new_item); + int (*make_group)(struct config_group *group, + const char *name, + struct config_group **new_group); int (*commit_item)(struct config_item *item); void (*disconnect_notify)(struct config_group *group, struct config_item *item); diff --git a/Documentation/filesystems/configfs/configfs_example.c b/Documentation/filesystems/configfs/configfs_example.c index 25151fd5c2c..0b422acd470 100644 --- a/Documentation/filesystems/configfs/configfs_example.c +++ b/Documentation/filesystems/configfs/configfs_example.c @@ -273,13 +273,13 @@ static inline struct simple_children *to_simple_children(struct config_item *ite return item ? container_of(to_config_group(item), struct simple_children, group) : NULL; } -static struct config_item *simple_children_make_item(struct config_group *group, const char *name) +static int simple_children_make_item(struct config_group *group, const char *name, struct config_item **new_item) { struct simple_child *simple_child; simple_child = kzalloc(sizeof(struct simple_child), GFP_KERNEL); if (!simple_child) - return NULL; + return -ENOMEM; config_item_init_type_name(&simple_child->item, name, @@ -287,7 +287,8 @@ static struct config_item *simple_children_make_item(struct config_group *group, simple_child->storeme = 0; - return &simple_child->item; + *new_item = &simple_child->item; + return 0; } static struct configfs_attribute simple_children_attr_description = { @@ -359,20 +360,21 @@ static struct configfs_subsystem simple_children_subsys = { * children of its own. */ -static struct config_group *group_children_make_group(struct config_group *group, const char *name) +static int group_children_make_group(struct config_group *group, const char *name, struct config_group **new_group) { struct simple_children *simple_children; simple_children = kzalloc(sizeof(struct simple_children), GFP_KERNEL); if (!simple_children) - return NULL; + return -ENOMEM; config_group_init_type_name(&simple_children->group, name, &simple_children_type); - return &simple_children->group; + *new_group = &simple_children->group; + return 0; } static struct configfs_attribute group_children_attr_description = { diff --git a/Documentation/filesystems/ubifs.txt b/Documentation/filesystems/ubifs.txt new file mode 100644 index 00000000000..540e9e7f59c --- /dev/null +++ b/Documentation/filesystems/ubifs.txt @@ -0,0 +1,164 @@ +Introduction +============= + +UBIFS file-system stands for UBI File System. UBI stands for "Unsorted +Block Images". UBIFS is a flash file system, which means it is designed +to work with flash devices. It is important to understand, that UBIFS +is completely different to any traditional file-system in Linux, like +Ext2, XFS, JFS, etc. UBIFS represents a separate class of file-systems +which work with MTD devices, not block devices. The other Linux +file-system of this class is JFFS2. + +To make it more clear, here is a small comparison of MTD devices and +block devices. + +1 MTD devices represent flash devices and they consist of eraseblocks of + rather large size, typically about 128KiB. Block devices consist of + small blocks, typically 512 bytes. +2 MTD devices support 3 main operations - read from some offset within an + eraseblock, write to some offset within an eraseblock, and erase a whole + eraseblock. Block devices support 2 main operations - read a whole + block and write a whole block. +3 The whole eraseblock has to be erased before it becomes possible to + re-write its contents. Blocks may be just re-written. +4 Eraseblocks become worn out after some number of erase cycles - + typically 100K-1G for SLC NAND and NOR flashes, and 1K-10K for MLC + NAND flashes. Blocks do not have the wear-out property. +5 Eraseblocks may become bad (only on NAND flashes) and software should + deal with this. Blocks on hard drives typically do not become bad, + because hardware has mechanisms to substitute bad blocks, at least in + modern LBA disks. + +It should be quite obvious why UBIFS is very different to traditional +file-systems. + +UBIFS works on top of UBI. UBI is a separate software layer which may be +found in drivers/mtd/ubi. UBI is basically a volume management and +wear-leveling layer. It provides so called UBI volumes which is a higher +level abstraction than a MTD device. The programming model of UBI devices +is very similar to MTD devices - they still consist of large eraseblocks, +they have read/write/erase operations, but UBI devices are devoid of +limitations like wear and bad blocks (items 4 and 5 in the above list). + +In a sense, UBIFS is a next generation of JFFS2 file-system, but it is +very different and incompatible to JFFS2. The following are the main +differences. + +* JFFS2 works on top of MTD devices, UBIFS depends on UBI and works on + top of UBI volumes. +* JFFS2 does not have on-media index and has to build it while mounting, + which requires full media scan. UBIFS maintains the FS indexing + information on the flash media and does not require full media scan, + so it mounts many times faster than JFFS2. +* JFFS2 is a write-through file-system, while UBIFS supports write-back, + which makes UBIFS much faster on writes. + +Similarly to JFFS2, UBIFS supports on-the-flight compression which makes +it possible to fit quite a lot of data to the flash. + +Similarly to JFFS2, UBIFS is tolerant of unclean reboots and power-cuts. +It does not need stuff like ckfs.ext2. UBIFS automatically replays its +journal and recovers from crashes, ensuring that the on-flash data +structures are consistent. + +UBIFS scales logarithmically (most of the data structures it uses are +trees), so the mount time and memory consumption do not linearly depend +on the flash size, like in case of JFFS2. This is because UBIFS +maintains the FS index on the flash media. However, UBIFS depends on +UBI, which scales linearly. So overall UBI/UBIFS stack scales linearly. +Nevertheless, UBI/UBIFS scales considerably better than JFFS2. + +The authors of UBIFS believe, that it is possible to develop UBI2 which +would scale logarithmically as well. UBI2 would support the same API as UBI, +but it would be binary incompatible to UBI. So UBIFS would not need to be +changed to use UBI2 + + +Mount options +============= + +(*) == default. + +norm_unmount (*) commit on unmount; the journal is committed + when the file-system is unmounted so that the + next mount does not have to replay the journal + and it becomes very fast; +fast_unmount do not commit on unmount; this option makes + unmount faster, but the next mount slower + because of the need to replay the journal. + + +Quick usage instructions +======================== + +The UBI volume to mount is specified using "ubiX_Y" or "ubiX:NAME" syntax, +where "X" is UBI device number, "Y" is UBI volume number, and "NAME" is +UBI volume name. + +Mount volume 0 on UBI device 0 to /mnt/ubifs: +$ mount -t ubifs ubi0_0 /mnt/ubifs + +Mount "rootfs" volume of UBI device 0 to /mnt/ubifs ("rootfs" is volume +name): +$ mount -t ubifs ubi0:rootfs /mnt/ubifs + +The following is an example of the kernel boot arguments to attach mtd0 +to UBI and mount volume "rootfs": +ubi.mtd=0 root=ubi0:rootfs rootfstype=ubifs + + +Module Parameters for Debugging +=============================== + +When UBIFS has been compiled with debugging enabled, there are 3 module +parameters that are available to control aspects of testing and debugging. +The parameters are unsigned integers where each bit controls an option. +The parameters are: + +debug_msgs Selects which debug messages to display, as follows: + + Message Type Flag value + + General messages 1 + Journal messages 2 + Mount messages 4 + Commit messages 8 + LEB search messages 16 + Budgeting messages 32 + Garbage collection messages 64 + Tree Node Cache (TNC) messages 128 + LEB properties (lprops) messages 256 + Input/output messages 512 + Log messages 1024 + Scan messages 2048 + Recovery messages 4096 + +debug_chks Selects extra checks that UBIFS can do while running: + + Check Flag value + + General checks 1 + Check Tree Node Cache (TNC) 2 + Check indexing tree size 4 + Check orphan area 8 + Check old indexing tree 16 + Check LEB properties (lprops) 32 + Check leaf nodes and inodes 64 + +debug_tsts Selects a mode of testing, as follows: + + Test mode Flag value + + Force in-the-gaps method 2 + Failure mode for recovery testing 4 + +For example, set debug_msgs to 5 to display General messages and Mount +messages. + + +References +========== + +UBIFS documentation and FAQ/HOWTO at the MTD web site: +http://www.linux-mtd.infradead.org/doc/ubifs.html +http://www.linux-mtd.infradead.org/faq/ubifs.html |