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Message-ID: <4947CB0C.3000406@panasas.com> Date: Tue, 16 Dec 2008 17:36:44 +0200 From: Boaz Harrosh <bharrosh@...asas.com> To: Avishay Traeger <avishay@...il.com>, Jeff Garzik <jeff@...zik.org>, Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...IV.linux.org.uk>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, open-osd <osd-dev@...n-osd.org> CC: linux-kernel <linux-kernel@...r.kernel.org> Subject: [PATCH 8/9] exofs: Documentation Added some documentation in exofs.txt, as well as a BUGS file. For further reading, operation instructions, example scripts and up to date infomation and code please see: http://open-osd.org Signed-off-by: Boaz Harrosh <bharrosh@...asas.com> --- Documentation/filesystems/exofs.txt | 173 +++++++++++++++++++++++++++++++++++ fs/exofs/BUGS | 6 + 2 files changed, 179 insertions(+), 0 deletions(-) create mode 100644 Documentation/filesystems/exofs.txt create mode 100644 fs/exofs/BUGS diff --git a/Documentation/filesystems/exofs.txt b/Documentation/filesystems/exofs.txt new file mode 100644 index 0000000..ec5040c --- /dev/null +++ b/Documentation/filesystems/exofs.txt @@ -0,0 +1,173 @@ +=============================================================================== +WHAT IS EXOFS? +=============================================================================== + +exofs is a file system that uses an OSD and exports the API of a normal Linux +file system. Users access exofs like any other local file system, and exofs +will in turn issue commands to the local initiator. + +=============================================================================== +ENVIRONMENT +=============================================================================== + +To use this file system, you need to have an object store to run it on. You +may download a target from: +http://open-osd.org + +See drivers/scsi/osd/README for how to setup a working osd environment. + +=============================================================================== +USAGE +=============================================================================== + +1. Download and compile exofs and open-osd initiator: + You need an external Kernel source tree or kernel headers from your + distribution. (anything based on 2.6.26 or later). + + a. download open-osd including exofs source using: + [parent-directory]$ git clone git://git.open-osd.org/open-osd.git + + b. Build the library module like this: + [parent-directory]$ make -C KSRC=$(KER_DIR) open-osd + + This will build both the open-osd initiator as well as the exofs kernel + module. Use whatever parameters you compiled your Kernel with and + $(KER_DIR) above pointing to the Kernel you compile against. See the file + open-osd/top-level-Makefile for an example. + +2. Get the OSD initiator and target set up properly, and login to the target. + See drivers/scsi/osd/README for farther instructions. Also see ./do-osd-test + for example script that does all these steps. + +3. Insmod the exofs.ko module: + [exofs]$ insmod exofs.ko + +4. Make sure the directory where you want to mount exists. If not, create it. + (For example, /mnt/exofs) + +5. At first run you will need to invoke the mkexofs.c routine + + As an example, this will create the file system on: + /dev/osd0 partition ID 65540, max capacity 1024 Mg bytes + + mount -t exofs -o pid=65540,mkfs=1,format=1024 /dev/osd0 /mnt/exofs/ + + The format=1024 is optional if not specified no OSD_FORMAT will be preformed + and a clean file system will be created in the specified pid, in the + available space of the target. + If pid already exist it will be deleted and a new one will be created in it's + place. Be careful. + +6. Mount the file system. The above command left the filesystem mounted, + but on subsequent runs the mkfs=1 should not be invoked. + + For example, to mount /dev/osd0, partition ID 65540 on /mnt/exofs: + + mount -t exofs -o pid=65540 /dev/osd0 /mnt/exofs/ + +7. For reference (under fs/exofs/): + do-exofs start - an example of how to perform the above steps. + do-exofs stop - an example of how to unmount the file system. + +8. Extra compilation flags (uncomment in fs/exofs/Kbuild): + EXOFS_DEBUG - for debug messages and extra checks. + +=============================================================================== +exofs mount options +=============================================================================== +Similar to any mount command: + mount -t exofs -o exofs_options /dev/osdX mount_exofs_directory + +Where: + -t exofs: specifies the exofs file system + + /dev/osdX: X is a decimal number. /dev/osdX was created after a successful + login into an OSD target. + + mount_exofs_directory: The directory to mount the file system on + + exofs_options: Options are separated by commas (,) + pid=<integer> - The partition number to mount/create as + container of the filesystem. + This option is mandatory + mkfs=<1/0> - If mkfs=1 make a new filesystem before mount. + Default is 0 - don't make. If mkfs=0 pid must + exist and an mkfs=1 was previously preformed + on it. + format=<integer>- If mkfs=1 is specified then the format= + parameter will also invoke an OSD_FORMAT + command prior to creation of the filesystem + partition (mkfs). The integer specified is in + Mega bytes. If not specified or set to 0 then + no format is executed, and a partition is + created in the available space. + If mkfs=0 this option is ignored. + to=<integer> - Timeout in ticks for a single command + default is (60 * HZ) [for debugging only] + +=============================================================================== +DESIGN +=============================================================================== + +* The file system control block (AKA on-disk superblock) resides in an object + with a special ID (defined in common.h). + Information included in the file system control block is used to fill the + in-memory superblock structure at mount time. This object is created before + the file system is used by mkexofs.c It contains information such as: + - The file system's magic number + - The next inode number to be allocated + +* Each file resides in its own object and contains the data (and it will be + possible to extend the file over multiple objects, though this has not been + implemented yet). + +* A directory is treated as a file, and essentially contains a list of <file + name, inode #> pairs for files that are found in that directory. The object + IDs correspond to the files' inode numbers and will be allocated according to + a bitmap (stored in a separate object). Now they are allocated using a + counter. + +* Each file's control block (AKA on-disk inode) is stored in its object's + attributes. This applies to both regular files and other types (directories, + device files, symlinks, etc.). + +* Credentials are generated per object (inode and superblock) when they is + created in memory (read off disk or created). The credential works for all + operations and is used as long as the object remains in memory. + +* Async OSD operations are used whenever possible, but the target may execute + them out of order. The operations that concern us are create, delete, + readpage, writepage, update_inode, and truncate. The following pairs of + operations should execute in the order written, and we need to prevent them + from executing in reverse order: + - The following are handled with the OBJ_CREATED and OBJ_2BCREATED + flags. OBJ_CREATED is set when we know the object exists on the OSD - + in create's callback function, and when we successfully do a read_inode. + OBJ_2BCREATED is set in the beginning of the create function, so we + know that we should wait. + - create/delete: delete should wait until the object is created + on the OSD. + - create/readpage: readpage should be able to return a page + full of zeroes in this case. If there was a write already + en-route (i.e. create, writepage, readpage) then the page + would be locked, and so it would really be the same as + create/writepage. + - create/writepage: if writepage is called for a sync write, it + should wait until the object is created on the OSD. + Otherwise, it should just return. + - create/truncate: truncate should wait until the object is + created on the OSD. + - create/update_inode: update_inode should wait until the + object is created on the OSD. + - Handled by VFS locks: + - readpage/delete: shouldn't happen because of page lock. + - writepage/delete: shouldn't happen because of page lock. + - readpage/writepage: shouldn't happen because of page lock. + +=============================================================================== +LICENSE/COPYRIGHT +=============================================================================== +The exofs file system is based on ext2 v0.5b (distributed with the Linux kernel +version 2.6.10). All files include the original copyrights, and the license +is GPL version 2 (only version 2, as is true for the Linux kernel). The +Linux kernel can be downloaded from www.kernel.org. diff --git a/fs/exofs/BUGS b/fs/exofs/BUGS new file mode 100644 index 0000000..6d6e1f9 --- /dev/null +++ b/fs/exofs/BUGS @@ -0,0 +1,6 @@ +- Some mount time options should have been 64-bit, but are declared as 32-bit + because that's what the kernel's parsing methods support at this time. + +- Out-of-space may cause a severe problem if the object (and directory entry) + were written, but the inode attributes failed. Then if the filesystem was + unmounted and mounted the kernel can get into an endless loop doing a readdir. -- 1.6.0.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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