637 lines
24 KiB
Plaintext
637 lines
24 KiB
Plaintext
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. BKL should have been shifted into
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individual fs sb_op 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 SB_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 gone. 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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setattr_prepare (which used to be inode_change_ok) now includes the size checks
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for ATTR_SIZE and must be called 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; the method has to use truncate_inode_pages_final() to get rid
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of those. Caller makes sure async writeback cannot be running for the inode while
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(or after) ->evict_inode() is called.
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->drop_inode() returns int now; it's called on final iput() with
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inode->i_lock held and it returns true if filesystems wants the inode to be
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dropped. As before, generic_drop_inode() is still the default and it's been
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updated appropriately. generic_delete_inode() is also alive and it consists
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simply of return 1. Note that all actual eviction work is done by caller after
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->drop_inode() returns.
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As before, clear_inode() must be called exactly once on each call of
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->evict_inode() (as it used to be for each call of ->delete_inode()). Unlike
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before, if you are using inode-associated metadata buffers (i.e.
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mark_buffer_dirty_inode()), it's your responsibility to call
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invalidate_inode_buffers() before clear_inode().
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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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Even though i_dentry and i_rcu share storage in a union, we will
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initialize the former in inode_init_always(), so just leave it alone in
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the callback. It used to be necessary to clean it there, but not anymore
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(starting at 3.2).
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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 is an inode permission check that is called on many or all
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directory inodes on the way down a path walk (to check for exec permission). It
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must now be rcu-walk aware (mask & MAY_NOT_BLOCK). See
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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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--
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[mandatory]
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->get_sb() is gone. Switch to use of ->mount(). Typically it's just
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a matter of switching from calling get_sb_... to mount_... and changing the
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function type. If you were doing it manually, just switch from setting ->mnt_root
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to some pointer to returning that pointer. On errors return ERR_PTR(...).
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--
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[mandatory]
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->permission() and generic_permission()have lost flags
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argument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask.
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generic_permission() has also lost the check_acl argument; ACL checking
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has been taken to VFS and filesystems need to provide a non-NULL ->i_op->get_acl
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to read an ACL from disk.
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--
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[mandatory]
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If you implement your own ->llseek() you must handle SEEK_HOLE and
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SEEK_DATA. You can hanle this by returning -EINVAL, but it would be nicer to
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support it in some way. The generic handler assumes that the entire file is
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data and there is a virtual hole at the end of the file. So if the provided
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offset is less than i_size and SEEK_DATA is specified, return the same offset.
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If the above is true for the offset and you are given SEEK_HOLE, return the end
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of the file. If the offset is i_size or greater return -ENXIO in either case.
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[mandatory]
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If you have your own ->fsync() you must make sure to call
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filemap_write_and_wait_range() so that all dirty pages are synced out properly.
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You must also keep in mind that ->fsync() is not called with i_mutex held
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anymore, so if you require i_mutex locking you must make sure to take it and
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release it yourself.
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--
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[mandatory]
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d_alloc_root() is gone, along with a lot of bugs caused by code
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misusing it. Replacement: d_make_root(inode). The difference is,
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d_make_root() drops the reference to inode if dentry allocation fails.
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--
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[mandatory]
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The witch is dead! Well, 2/3 of it, anyway. ->d_revalidate() and
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->lookup() do *not* take struct nameidata anymore; just the flags.
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--
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[mandatory]
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->create() doesn't take struct nameidata *; unlike the previous
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two, it gets "is it an O_EXCL or equivalent?" boolean argument. Note that
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local filesystems can ignore tha argument - they are guaranteed that the
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object doesn't exist. It's remote/distributed ones that might care...
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--
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[mandatory]
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FS_REVAL_DOT is gone; if you used to have it, add ->d_weak_revalidate()
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in your dentry operations instead.
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--
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[mandatory]
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vfs_readdir() is gone; switch to iterate_dir() instead
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--
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[mandatory]
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->readdir() is gone now; switch to ->iterate()
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[mandatory]
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vfs_follow_link has been removed. Filesystems must use nd_set_link
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from ->follow_link for normal symlinks, or nd_jump_link for magic
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/proc/<pid> style links.
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--
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[mandatory]
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iget5_locked()/ilookup5()/ilookup5_nowait() test() callback used to be
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called with both ->i_lock and inode_hash_lock held; the former is *not*
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taken anymore, so verify that your callbacks do not rely on it (none
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of the in-tree instances did). inode_hash_lock is still held,
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of course, so they are still serialized wrt removal from inode hash,
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as well as wrt set() callback of iget5_locked().
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--
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[mandatory]
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d_materialise_unique() is gone; d_splice_alias() does everything you
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need now. Remember that they have opposite orders of arguments ;-/
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--
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[mandatory]
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f_dentry is gone; use f_path.dentry, or, better yet, see if you can avoid
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it entirely.
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--
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[mandatory]
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never call ->read() and ->write() directly; use __vfs_{read,write} or
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wrappers; instead of checking for ->write or ->read being NULL, look for
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FMODE_CAN_{WRITE,READ} in file->f_mode.
|
|
--
|
|
[mandatory]
|
|
do _not_ use new_sync_{read,write} for ->read/->write; leave it NULL
|
|
instead.
|
|
--
|
|
[mandatory]
|
|
->aio_read/->aio_write are gone. Use ->read_iter/->write_iter.
|
|
---
|
|
[recommended]
|
|
for embedded ("fast") symlinks just set inode->i_link to wherever the
|
|
symlink body is and use simple_follow_link() as ->follow_link().
|
|
--
|
|
[mandatory]
|
|
calling conventions for ->follow_link() have changed. Instead of returning
|
|
cookie and using nd_set_link() to store the body to traverse, we return
|
|
the body to traverse and store the cookie using explicit void ** argument.
|
|
nameidata isn't passed at all - nd_jump_link() doesn't need it and
|
|
nd_[gs]et_link() is gone.
|
|
--
|
|
[mandatory]
|
|
calling conventions for ->put_link() have changed. It gets inode instead of
|
|
dentry, it does not get nameidata at all and it gets called only when cookie
|
|
is non-NULL. Note that link body isn't available anymore, so if you need it,
|
|
store it as cookie.
|
|
--
|
|
[mandatory]
|
|
any symlink that might use page_follow_link_light/page_put_link() must
|
|
have inode_nohighmem(inode) called before anything might start playing with
|
|
its pagecache. No highmem pages should end up in the pagecache of such
|
|
symlinks. That includes any preseeding that might be done during symlink
|
|
creation. __page_symlink() will honour the mapping gfp flags, so once
|
|
you've done inode_nohighmem() it's safe to use, but if you allocate and
|
|
insert the page manually, make sure to use the right gfp flags.
|
|
--
|
|
[mandatory]
|
|
->follow_link() is replaced with ->get_link(); same API, except that
|
|
* ->get_link() gets inode as a separate argument
|
|
* ->get_link() may be called in RCU mode - in that case NULL
|
|
dentry is passed
|
|
--
|
|
[mandatory]
|
|
->get_link() gets struct delayed_call *done now, and should do
|
|
set_delayed_call() where it used to set *cookie.
|
|
->put_link() is gone - just give the destructor to set_delayed_call()
|
|
in ->get_link().
|
|
--
|
|
[mandatory]
|
|
->getxattr() and xattr_handler.get() get dentry and inode passed separately.
|
|
dentry might be yet to be attached to inode, so do _not_ use its ->d_inode
|
|
in the instances. Rationale: !@#!@# security_d_instantiate() needs to be
|
|
called before we attach dentry to inode.
|
|
--
|
|
[mandatory]
|
|
symlinks are no longer the only inodes that do *not* have i_bdev/i_cdev/
|
|
i_pipe/i_link union zeroed out at inode eviction. As the result, you can't
|
|
assume that non-NULL value in ->i_nlink at ->destroy_inode() implies that
|
|
it's a symlink. Checking ->i_mode is really needed now. In-tree we had
|
|
to fix shmem_destroy_callback() that used to take that kind of shortcut;
|
|
watch out, since that shortcut is no longer valid.
|
|
--
|
|
[mandatory]
|
|
->i_mutex is replaced with ->i_rwsem now. inode_lock() et.al. work as
|
|
they used to - they just take it exclusive. However, ->lookup() may be
|
|
called with parent locked shared. Its instances must not
|
|
* use d_instantiate) and d_rehash() separately - use d_add() or
|
|
d_splice_alias() instead.
|
|
* use d_rehash() alone - call d_add(new_dentry, NULL) instead.
|
|
* in the unlikely case when (read-only) access to filesystem
|
|
data structures needs exclusion for some reason, arrange it
|
|
yourself. None of the in-tree filesystems needed that.
|
|
* rely on ->d_parent and ->d_name not changing after dentry has
|
|
been fed to d_add() or d_splice_alias(). Again, none of the
|
|
in-tree instances relied upon that.
|
|
We are guaranteed that lookups of the same name in the same directory
|
|
will not happen in parallel ("same" in the sense of your ->d_compare()).
|
|
Lookups on different names in the same directory can and do happen in
|
|
parallel now.
|
|
--
|
|
[recommended]
|
|
->iterate_shared() is added; it's a parallel variant of ->iterate().
|
|
Exclusion on struct file level is still provided (as well as that
|
|
between it and lseek on the same struct file), but if your directory
|
|
has been opened several times, you can get these called in parallel.
|
|
Exclusion between that method and all directory-modifying ones is
|
|
still provided, of course.
|
|
|
|
Often enough ->iterate() can serve as ->iterate_shared() without any
|
|
changes - it is a read-only operation, after all. If you have any
|
|
per-inode or per-dentry in-core data structures modified by ->iterate(),
|
|
you might need something to serialize the access to them. If you
|
|
do dcache pre-seeding, you'll need to switch to d_alloc_parallel() for
|
|
that; look for in-tree examples.
|
|
|
|
Old method is only used if the new one is absent; eventually it will
|
|
be removed. Switch while you still can; the old one won't stay.
|
|
--
|
|
[mandatory]
|
|
->atomic_open() calls without O_CREAT may happen in parallel.
|
|
--
|
|
[mandatory]
|
|
->setxattr() and xattr_handler.set() get dentry and inode passed separately.
|
|
dentry might be yet to be attached to inode, so do _not_ use its ->d_inode
|
|
in the instances. Rationale: !@#!@# security_d_instantiate() needs to be
|
|
called before we attach dentry to inode and !@#!@##!@$!$#!@#$!@$!@$ smack
|
|
->d_instantiate() uses not just ->getxattr() but ->setxattr() as well.
|
|
--
|
|
[mandatory]
|
|
->d_compare() doesn't get parent as a separate argument anymore. If you
|
|
used it for finding the struct super_block involved, dentry->d_sb will
|
|
work just as well; if it's something more complicated, use dentry->d_parent.
|
|
Just be careful not to assume that fetching it more than once will yield
|
|
the same value - in RCU mode it could change under you.
|
|
--
|
|
[mandatory]
|
|
->rename() has an added flags argument. Any flags not handled by the
|
|
filesystem should result in EINVAL being returned.
|
|
--
|
|
[recommended]
|
|
->readlink is optional for symlinks. Don't set, unless filesystem needs
|
|
to fake something for readlink(2).
|
|
--
|
|
[mandatory]
|
|
->getattr() is now passed a struct path rather than a vfsmount and
|
|
dentry separately, and it now has request_mask and query_flags arguments
|
|
to specify the fields and sync type requested by statx. Filesystems not
|
|
supporting any statx-specific features may ignore the new arguments.
|
|
--
|
|
[mandatory]
|
|
->atomic_open() calling conventions have changed. Gone is int *opened,
|
|
along with FILE_OPENED/FILE_CREATED. In place of those we have
|
|
FMODE_OPENED/FMODE_CREATED, set in file->f_mode. Additionally, return
|
|
value for 'called finish_no_open(), open it yourself' case has become
|
|
0, not 1. Since finish_no_open() itself is returning 0 now, that part
|
|
does not need any changes in ->atomic_open() instances.
|
|
--
|
|
[mandatory]
|
|
alloc_file() has become static now; two wrappers are to be used instead.
|
|
alloc_file_pseudo(inode, vfsmount, name, flags, ops) is for the cases
|
|
when dentry needs to be created; that's the majority of old alloc_file()
|
|
users. Calling conventions: on success a reference to new struct file
|
|
is returned and callers reference to inode is subsumed by that. On
|
|
failure, ERR_PTR() is returned and no caller's references are affected,
|
|
so the caller needs to drop the inode reference it held.
|
|
alloc_file_clone(file, flags, ops) does not affect any caller's references.
|
|
On success you get a new struct file sharing the mount/dentry with the
|
|
original, on failure - ERR_PTR().
|
|
--
|
|
[mandatory]
|
|
DCACHE_RCUACCESS is gone; having an RCU delay on dentry freeing is the
|
|
default. DCACHE_NORCU opts out, and only d_alloc_pseudo() has any
|
|
business doing so.
|
|
--
|
|
[mandatory]
|
|
|
|
[should've been added in 2016] stale comment in finish_open()
|
|
nonwithstanding, failure exits in ->atomic_open() instances should
|
|
*NOT* fput() the file, no matter what. Everything is handled by the
|
|
caller.
|