path: root/fs/exofs/super.c
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authorBoaz Harrosh <bharrosh@panasas.com>2010-01-28 11:58:08 +0200
committerBoaz Harrosh <bharrosh@panasas.com>2010-02-28 03:35:28 -0800
commitd9c740d2253e75db8cef8f87a3125c450f3ebd82 (patch)
tree7217cf62b8d102e00257be6e0675d25852045bc6 /fs/exofs/super.c
parent46f4d973f6874c06b7a41a3bf8f4c1717d90f97a (diff)
exofs: Define on-disk per-inode optional layout attribute
* Layouts describe the way a file is spread on multiple devices. The layout information is stored in the objects attribute introduced in this patch. * There can be multiple generating function for the layout. Currently defined: - No attribute present - use below moving-window on global device table, all devices. (This is the only one currently used in exofs) - an obj_id generated moving window - the obj_id is a randomizing factor in the otherwise global map layout. - An explicit layout stored, including a data_map and a device index list. - More might be defined in future ... * There are two attributes defined of the same structure: A-data-files-layout - This layout is used by data-files. If present at a directory, all files of that directory will be created with this layout. A-meta-data-layout - This layout is used by a directory and other meta-data information. Also inherited at creation of subdirectories. * At creation time inodes are created with the layout specified above. A usermode utility may change the creation layout on a give directory or file. Which in the case of directories, will also apply to newly created files/subdirectories, children of that directory. In the simple unaltered case of a newly created exofs, no layout attributes are present, and all layouts adhere to the layout specified at the device-table. * In case of a future file system loaded in an old exofs-driver. At iget(), the generating_function is inspected and if not supported will return an IO error to the application and the inode will not be loaded. So not to damage any data. Note: After this patch we do not yet support any type of layout only the RAID0 patch that enables striping at the super-block level will add support for RAID0 layouts above. This way we are past and future compatible and fully bisectable. * Access to the device table is done by an accessor since it will change according to above information. Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
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