Documentation/filesystems/porting - linux/kernel/git/davem/net - Git at Google

 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_destory_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 in ->read_inode() and after getting an inode from new_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.  ->write_super() Is now called
 without BKL held.  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_sem 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_sem, so
 watch for ->i_sem-grabbing code that might be used by your ->setattr().
 Callers of notify_change() need ->i_sem 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/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. read_inode has not been
 called so the file system still has 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) {
                read_inode_from_disk(inode);
                unlock_new_inode(inode);
        }

 ---
 [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()
 	* dcache_lock is held
 	* 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.
	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_destory_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 in ->read_inode() and after getting an inode from new_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. ->write_super() Is now called
	without BKL held. 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_sem 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_sem, so
	watch for ->i_sem-grabbing code that might be used by your ->setattr().
	Callers of notify_change() need ->i_sem 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/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. read_inode has not been
	called so the file system still has 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) {
	read_inode_from_disk(inode);
	unlock_new_inode(inode);
	}

	---
	[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()
	* dcache_lock is held
	* 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.