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Diffstat (limited to 'Documentation/filesystems/porting')
| -rw-r--r-- | Documentation/filesystems/porting | 453 |
1 files changed, 0 insertions, 453 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting deleted file mode 100644 index 206a1bdc7321..000000000000 --- a/Documentation/filesystems/porting +++ /dev/null @@ -1,453 +0,0 @@ -Changes since 2.5.0: - ---- -[recommended] - -New helpers: sb_bread(), sb_getblk(), sb_find_get_block(), set_bh(), - sb_set_blocksize() and sb_min_blocksize(). - -Use them. - -(sb_find_get_block() replaces 2.4's get_hash_table()) - ---- -[recommended] - -New methods: ->alloc_inode() and ->destroy_inode(). - -Remove inode->u.foo_inode_i -Declare - struct foo_inode_info { - /* fs-private stuff */ - struct inode vfs_inode; - }; - static inline struct foo_inode_info *FOO_I(struct inode *inode) - { - return list_entry(inode, struct foo_inode_info, vfs_inode); - } - -Use FOO_I(inode) instead of &inode->u.foo_inode_i; - -Add foo_alloc_inode() and foo_destroy_inode() - the former should allocate -foo_inode_info and return the address of ->vfs_inode, the latter should free -FOO_I(inode) (see in-tree filesystems for examples). - -Make them ->alloc_inode and ->destroy_inode in your super_operations. - -Keep in mind that now you need explicit initialization of private data -typically between calling iget_locked() and unlocking the inode. - -At some point that will become mandatory. - ---- -[mandatory] - -Change of file_system_type method (->read_super to ->get_sb) - -->read_super() is no more. Ditto for DECLARE_FSTYPE and DECLARE_FSTYPE_DEV. - -Turn your foo_read_super() into a function that would return 0 in case of -success and negative number in case of error (-EINVAL unless you have more -informative error value to report). Call it foo_fill_super(). Now declare - -int foo_get_sb(struct file_system_type *fs_type, - int flags, const char *dev_name, void *data, struct vfsmount *mnt) -{ - return get_sb_bdev(fs_type, flags, dev_name, data, foo_fill_super, - mnt); -} - -(or similar with s/bdev/nodev/ or s/bdev/single/, depending on the kind of -filesystem). - -Replace DECLARE_FSTYPE... with explicit initializer and have ->get_sb set as -foo_get_sb. - ---- -[mandatory] - -Locking change: ->s_vfs_rename_sem is taken only by cross-directory renames. -Most likely there is no need to change anything, but if you relied on -global exclusion between renames for some internal purpose - you need to -change your internal locking. Otherwise exclusion warranties remain the -same (i.e. parents and victim are locked, etc.). - ---- -[informational] - -Now we have the exclusion between ->lookup() and directory removal (by -->rmdir() and ->rename()). If you used to need that exclusion and do -it by internal locking (most of filesystems couldn't care less) - you -can relax your locking. - ---- -[mandatory] - -->lookup(), ->truncate(), ->create(), ->unlink(), ->mknod(), ->mkdir(), -->rmdir(), ->link(), ->lseek(), ->symlink(), ->rename() -and ->readdir() are called without BKL now. Grab it on entry, drop upon return -- that will guarantee the same locking you used to have. If your method or its -parts do not need BKL - better yet, now you can shift lock_kernel() and -unlock_kernel() so that they would protect exactly what needs to be -protected. - ---- -[mandatory] - -BKL is also moved from around sb operations. BKL should have been shifted into -individual fs sb_op functions. If you don't need it, remove it. - ---- -[informational] - -check for ->link() target not being a directory is done by callers. Feel -free to drop it... - ---- -[informational] - -->link() callers hold ->i_mutex on the object we are linking to. Some of your -problems might be over... - ---- -[mandatory] - -new file_system_type method - kill_sb(superblock). If you are converting -an existing filesystem, set it according to ->fs_flags: - FS_REQUIRES_DEV - kill_block_super - FS_LITTER - kill_litter_super - neither - kill_anon_super -FS_LITTER is gone - just remove it from fs_flags. - ---- -[mandatory] - - FS_SINGLE is gone (actually, that had happened back when ->get_sb() -went in - and hadn't been documented ;-/). Just remove it from fs_flags -(and see ->get_sb() entry for other actions). - ---- -[mandatory] - -->setattr() is called without BKL now. Caller _always_ holds ->i_mutex, so -watch for ->i_mutex-grabbing code that might be used by your ->setattr(). -Callers of notify_change() need ->i_mutex now. - ---- -[recommended] - -New super_block field "struct export_operations *s_export_op" for -explicit support for exporting, e.g. via NFS. The structure is fully -documented at its declaration in include/linux/fs.h, and in -Documentation/filesystems/nfs/Exporting. - -Briefly it allows for the definition of decode_fh and encode_fh operations -to encode and decode filehandles, and allows the filesystem to use -a standard helper function for decode_fh, and provide file-system specific -support for this helper, particularly get_parent. - -It is planned that this will be required for exporting once the code -settles down a bit. - -[mandatory] - -s_export_op is now required for exporting a filesystem. -isofs, ext2, ext3, resierfs, fat -can be used as examples of very different filesystems. - ---- -[mandatory] - -iget4() and the read_inode2 callback have been superseded by iget5_locked() -which has the following prototype, - - struct inode *iget5_locked(struct super_block *sb, unsigned long ino, - int (*test)(struct inode *, void *), - int (*set)(struct inode *, void *), - void *data); - -'test' is an additional function that can be used when the inode -number is not sufficient to identify the actual file object. 'set' -should be a non-blocking function that initializes those parts of a -newly created inode to allow the test function to succeed. 'data' is -passed as an opaque value to both test and set functions. - -When the inode has been created by iget5_locked(), it will be returned with the -I_NEW flag set and will still be locked. The filesystem then needs to finalize -the initialization. Once the inode is initialized it must be unlocked by -calling unlock_new_inode(). - -The filesystem is responsible for setting (and possibly testing) i_ino -when appropriate. There is also a simpler iget_locked function that -just takes the superblock and inode number as arguments and does the -test and set for you. - -e.g. - inode = iget_locked(sb, ino); - if (inode->i_state & I_NEW) { - err = read_inode_from_disk(inode); - if (err < 0) { - iget_failed(inode); - return err; - } - unlock_new_inode(inode); - } - -Note that if the process of setting up a new inode fails, then iget_failed() -should be called on the inode to render it dead, and an appropriate error -should be passed back to the caller. - ---- -[recommended] - -->getattr() finally getting used. See instances in nfs, minix, etc. - ---- -[mandatory] - -->revalidate() is gone. If your filesystem had it - provide ->getattr() -and let it call whatever you had as ->revlidate() + (for symlinks that -had ->revalidate()) add calls in ->follow_link()/->readlink(). - ---- -[mandatory] - -->d_parent changes are not protected by BKL anymore. Read access is safe -if at least one of the following is true: - * filesystem has no cross-directory rename() - * we know that parent had been locked (e.g. we are looking at -->d_parent of ->lookup() argument). - * we are called from ->rename(). - * the child's ->d_lock is held -Audit your code and add locking if needed. Notice that any place that is -not protected by the conditions above is risky even in the old tree - you -had been relying on BKL and that's prone to screwups. Old tree had quite -a few holes of that kind - unprotected access to ->d_parent leading to -anything from oops to silent memory corruption. - ---- -[mandatory] - - FS_NOMOUNT is gone. If you use it - just set MS_NOUSER in flags -(see rootfs for one kind of solution and bdev/socket/pipe for another). - ---- -[recommended] - - Use bdev_read_only(bdev) instead of is_read_only(kdev). The latter -is still alive, but only because of the mess in drivers/s390/block/dasd.c. -As soon as it gets fixed is_read_only() will die. - ---- -[mandatory] - -->permission() is called without BKL now. Grab it on entry, drop upon -return - that will guarantee the same locking you used to have. If -your method or its parts do not need BKL - better yet, now you can -shift lock_kernel() and unlock_kernel() so that they would protect -exactly what needs to be protected. - ---- -[mandatory] - -->statfs() is now called without BKL held. BKL should have been -shifted into individual fs sb_op functions where it's not clear that -it's safe to remove it. If you don't need it, remove it. - ---- -[mandatory] - - is_read_only() is gone; use bdev_read_only() instead. - ---- -[mandatory] - - destroy_buffers() is gone; use invalidate_bdev(). - ---- -[mandatory] - - fsync_dev() is gone; use fsync_bdev(). NOTE: lvm breakage is -deliberate; as soon as struct block_device * is propagated in a reasonable -way by that code fixing will become trivial; until then nothing can be -done. - -[mandatory] - - block truncatation on error exit from ->write_begin, and ->direct_IO -moved from generic methods (block_write_begin, cont_write_begin, -nobh_write_begin, blockdev_direct_IO*) to callers. Take a look at -ext2_write_failed and callers for an example. - -[mandatory] - - ->truncate is gone. The whole truncate sequence needs to be -implemented in ->setattr, which is now mandatory for filesystems -implementing on-disk size changes. Start with a copy of the old inode_setattr -and vmtruncate, and the reorder the vmtruncate + foofs_vmtruncate sequence to -be in order of zeroing blocks using block_truncate_page or similar helpers, -size update and on finally on-disk truncation which should not fail. -inode_change_ok now includes the size checks for ATTR_SIZE and must be called -in the beginning of ->setattr unconditionally. - -[mandatory] - - ->clear_inode() and ->delete_inode() are gone; ->evict_inode() should -be used instead. It gets called whenever the inode is evicted, whether it has -remaining links or not. Caller does *not* evict the pagecache or inode-associated -metadata buffers; getting rid of those is responsibility of method, as it had -been for ->delete_inode(). Caller makes sure async writeback cannot be running -for the inode while (or after) ->evict_inode() is called. - - ->drop_inode() returns int now; it's called on final iput() with -inode->i_lock held and it returns true if filesystems wants the inode to be -dropped. As before, generic_drop_inode() is still the default and it's been -updated appropriately. generic_delete_inode() is also alive and it consists -simply of return 1. Note that all actual eviction work is done by caller after -->drop_inode() returns. - - As before, clear_inode() must be called exactly once on each call of -->evict_inode() (as it used to be for each call of ->delete_inode()). Unlike -before, if you are using inode-associated metadata buffers (i.e. -mark_buffer_dirty_inode()), it's your responsibility to call -invalidate_inode_buffers() before clear_inode(). - - NOTE: checking i_nlink in the beginning of ->write_inode() and bailing out -if it's zero is not *and* *never* *had* *been* enough. Final unlink() and iput() -may happen while the inode is in the middle of ->write_inode(); e.g. if you blindly -free the on-disk inode, you may end up doing that while ->write_inode() is writing -to it. - ---- -[mandatory] - - .d_delete() now only advises the dcache as to whether or not to cache -unreferenced dentries, and is now only called when the dentry refcount goes to -0. Even on 0 refcount transition, it must be able to tolerate being called 0, -1, or more times (eg. constant, idempotent). - ---- -[mandatory] - - .d_compare() calling convention and locking rules are significantly -changed. Read updated documentation in Documentation/filesystems/vfs.txt (and -look at examples of other filesystems) for guidance. - ---- -[mandatory] - - .d_hash() calling convention and locking rules are significantly -changed. Read updated documentation in Documentation/filesystems/vfs.txt (and -look at examples of other filesystems) for guidance. - ---- -[mandatory] - dcache_lock is gone, replaced by fine grained locks. See fs/dcache.c -for details of what locks to replace dcache_lock with in order to protect -particular things. Most of the time, a filesystem only needs ->d_lock, which -protects *all* the dcache state of a given dentry. - --- -[mandatory] - - Filesystems must RCU-free their inodes, if they can have been accessed -via rcu-walk path walk (basically, if the file can have had a path name in the -vfs namespace). - - Even though i_dentry and i_rcu share storage in a union, we will -initialize the former in inode_init_always(), so just leave it alone in -the callback. It used to be necessary to clean it there, but not anymore -(starting at 3.2). - --- -[recommended] - vfs now tries to do path walking in "rcu-walk mode", which avoids -atomic operations and scalability hazards on dentries and inodes (see -Documentation/filesystems/path-lookup.txt). d_hash and d_compare changes -(above) are examples of the changes required to support this. For more complex -filesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, so -no changes are required to the filesystem. However, this is costly and loses -the benefits of rcu-walk mode. We will begin to add filesystem callbacks that -are rcu-walk aware, shown below. Filesystems should take advantage of this -where possible. - --- -[mandatory] - d_revalidate is a callback that is made on every path element (if -the filesystem provides it), which requires dropping out of rcu-walk mode. This -may now be called in rcu-walk mode (nd->flags & LOOKUP_RCU). -ECHILD should be -returned if the filesystem cannot handle rcu-walk. See -Documentation/filesystems/vfs.txt for more details. - - permission and check_acl are inode permission checks that are called -on many or all directory inodes on the way down a path walk (to check for -exec permission). These must now be rcu-walk aware (flags & IPERM_FLAG_RCU). -See Documentation/filesystems/vfs.txt for more details. - --- -[mandatory] - In ->fallocate() you must check the mode option passed in. If your -filesystem does not support hole punching (deallocating space in the middle of a -file) you must return -EOPNOTSUPP if FALLOC_FL_PUNCH_HOLE is set in mode. -Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set, -so the i_size should not change when hole punching, even when puching the end of -a file off. - --- -[mandatory] - ->get_sb() is gone. Switch to use of ->mount(). Typically it's just -a matter of switching from calling get_sb_... to mount_... and changing the -function type. If you were doing it manually, just switch from setting ->mnt_root -to some pointer to returning that pointer. On errors return ERR_PTR(...). - --- -[mandatory] - ->permission() and generic_permission()have lost flags -argument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask. - generic_permission() has also lost the check_acl argument; ACL checking -has been taken to VFS and filesystems need to provide a non-NULL ->i_op->get_acl -to read an ACL from disk. - --- -[mandatory] - If you implement your own ->llseek() you must handle SEEK_HOLE and -SEEK_DATA. You can hanle this by returning -EINVAL, but it would be nicer to -support it in some way. The generic handler assumes that the entire file is -data and there is a virtual hole at the end of the file. So if the provided -offset is less than i_size and SEEK_DATA is specified, return the same offset. -If the above is true for the offset and you are given SEEK_HOLE, return the end -of the file. If the offset is i_size or greater return -ENXIO in either case. - -[mandatory] - If you have your own ->fsync() you must make sure to call -filemap_write_and_wait_range() so that all dirty pages are synced out properly. -You must also keep in mind that ->fsync() is not called with i_mutex held -anymore, so if you require i_mutex locking you must make sure to take it and -release it yourself. - --- -[mandatory] - d_alloc_root() is gone, along with a lot of bugs caused by code -misusing it. Replacement: d_make_root(inode). The difference is, -d_make_root() drops the reference to inode if dentry allocation fails. - --- -[mandatory] - The witch is dead! Well, 2/3 of it, anyway. ->d_revalidate() and -->lookup() do *not* take struct nameidata anymore; just the flags. --- -[mandatory] - ->create() doesn't take struct nameidata *; unlike the previous -two, it gets "is it an O_EXCL or equivalent?" boolean argument. Note that -local filesystems can ignore tha argument - they are guaranteed that the -object doesn't exist. It's remote/distributed ones that might care... --- -[mandatory] - FS_REVAL_DOT is gone; if you used to have it, add ->d_weak_revalidate() -in your dentry operations instead. --- -[mandatory] - vfs_readdir() is gone; switch to iterate_dir() instead --- -[mandatory] - ->readdir() is gone now; switch to ->iterate() |