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