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Based on kernel version 3.16. Page generated on 2014-08-06 21:39 EST.

1	Changes since 2.5.0:
2	
3	---
4	[recommended]
5	
6	New helpers: sb_bread(), sb_getblk(), sb_find_get_block(), set_bh(),
7		sb_set_blocksize() and sb_min_blocksize().
8	
9	Use them.
10	
11	(sb_find_get_block() replaces 2.4's get_hash_table())
12	
13	---
14	[recommended]
15	
16	New methods: ->alloc_inode() and ->destroy_inode().
17	
18	Remove inode->u.foo_inode_i
19	Declare
20		struct foo_inode_info {
21			/* fs-private stuff */
22			struct inode vfs_inode;
23		};
24		static inline struct foo_inode_info *FOO_I(struct inode *inode)
25		{
26			return list_entry(inode, struct foo_inode_info, vfs_inode);
27		}
28	
29	Use FOO_I(inode) instead of &inode->u.foo_inode_i;
30	
31	Add foo_alloc_inode() and foo_destroy_inode() - the former should allocate
32	foo_inode_info and return the address of ->vfs_inode, the latter should free
33	FOO_I(inode) (see in-tree filesystems for examples).
34	
35	Make them ->alloc_inode and ->destroy_inode in your super_operations.
36	
37	Keep in mind that now you need explicit initialization of private data
38	typically between calling iget_locked() and unlocking the inode.
39	
40	At some point that will become mandatory.
41	
42	---
43	[mandatory]
44	
45	Change of file_system_type method (->read_super to ->get_sb)
46	
47	->read_super() is no more.  Ditto for DECLARE_FSTYPE and DECLARE_FSTYPE_DEV.
48	
49	Turn your foo_read_super() into a function that would return 0 in case of
50	success and negative number in case of error (-EINVAL unless you have more
51	informative error value to report).  Call it foo_fill_super().  Now declare
52	
53	int foo_get_sb(struct file_system_type *fs_type,
54		int flags, const char *dev_name, void *data, struct vfsmount *mnt)
55	{
56		return get_sb_bdev(fs_type, flags, dev_name, data, foo_fill_super,
57				   mnt);
58	}
59	
60	(or similar with s/bdev/nodev/ or s/bdev/single/, depending on the kind of
61	filesystem).
62	
63	Replace DECLARE_FSTYPE... with explicit initializer and have ->get_sb set as
64	foo_get_sb.
65	
66	---
67	[mandatory]
68	
69	Locking change: ->s_vfs_rename_sem is taken only by cross-directory renames.
70	Most likely there is no need to change anything, but if you relied on
71	global exclusion between renames for some internal purpose - you need to
72	change your internal locking.  Otherwise exclusion warranties remain the
73	same (i.e. parents and victim are locked, etc.).
74	
75	---
76	[informational]
77	
78	Now we have the exclusion between ->lookup() and directory removal (by
79	->rmdir() and ->rename()).  If you used to need that exclusion and do
80	it by internal locking (most of filesystems couldn't care less) - you
81	can relax your locking.
82	
83	---
84	[mandatory]
85	
86	->lookup(), ->truncate(), ->create(), ->unlink(), ->mknod(), ->mkdir(),
87	->rmdir(), ->link(), ->lseek(), ->symlink(), ->rename()
88	and ->readdir() are called without BKL now.  Grab it on entry, drop upon return
89	- that will guarantee the same locking you used to have.  If your method or its
90	parts do not need BKL - better yet, now you can shift lock_kernel() and
91	unlock_kernel() so that they would protect exactly what needs to be
92	protected.
93	
94	---
95	[mandatory]
96	
97	BKL is also moved from around sb operations. BKL should have been shifted into
98	individual fs sb_op functions.  If you don't need it, remove it.
99	
100	---
101	[informational]
102	
103	check for ->link() target not being a directory is done by callers.  Feel
104	free to drop it...
105	
106	---
107	[informational]
108	
109	->link() callers hold ->i_mutex on the object we are linking to.  Some of your
110	problems might be over...
111	
112	---
113	[mandatory]
114	
115	new file_system_type method - kill_sb(superblock).  If you are converting
116	an existing filesystem, set it according to ->fs_flags:
117		FS_REQUIRES_DEV		-	kill_block_super
118		FS_LITTER		-	kill_litter_super
119		neither			-	kill_anon_super
120	FS_LITTER is gone - just remove it from fs_flags.
121	
122	---
123	[mandatory]
124	
125		FS_SINGLE is gone (actually, that had happened back when ->get_sb()
126	went in - and hadn't been documented ;-/).  Just remove it from fs_flags
127	(and see ->get_sb() entry for other actions).
128	
129	---
130	[mandatory]
131	
132	->setattr() is called without BKL now.  Caller _always_ holds ->i_mutex, so
133	watch for ->i_mutex-grabbing code that might be used by your ->setattr().
134	Callers of notify_change() need ->i_mutex now.
135	
136	---
137	[recommended]
138	
139	New super_block field "struct export_operations *s_export_op" for
140	explicit support for exporting, e.g. via NFS.  The structure is fully
141	documented at its declaration in include/linux/fs.h, and in
142	Documentation/filesystems/nfs/Exporting.
143	
144	Briefly it allows for the definition of decode_fh and encode_fh operations
145	to encode and decode filehandles, and allows the filesystem to use
146	a standard helper function for decode_fh, and provide file-system specific
147	support for this helper, particularly get_parent.
148	
149	It is planned that this will be required for exporting once the code
150	settles down a bit.
151	
152	[mandatory]
153	
154	s_export_op is now required for exporting a filesystem.
155	isofs, ext2, ext3, resierfs, fat
156	can be used as examples of very different filesystems.
157	
158	---
159	[mandatory]
160	
161	iget4() and the read_inode2 callback have been superseded by iget5_locked()
162	which has the following prototype,
163	
164	    struct inode *iget5_locked(struct super_block *sb, unsigned long ino,
165					int (*test)(struct inode *, void *),
166					int (*set)(struct inode *, void *),
167					void *data);
168	
169	'test' is an additional function that can be used when the inode
170	number is not sufficient to identify the actual file object. 'set'
171	should be a non-blocking function that initializes those parts of a
172	newly created inode to allow the test function to succeed. 'data' is
173	passed as an opaque value to both test and set functions.
174	
175	When the inode has been created by iget5_locked(), it will be returned with the
176	I_NEW flag set and will still be locked.  The filesystem then needs to finalize
177	the initialization. Once the inode is initialized it must be unlocked by
178	calling unlock_new_inode().
179	
180	The filesystem is responsible for setting (and possibly testing) i_ino
181	when appropriate. There is also a simpler iget_locked function that
182	just takes the superblock and inode number as arguments and does the
183	test and set for you.
184	
185	e.g.
186		inode = iget_locked(sb, ino);
187		if (inode->i_state & I_NEW) {
188			err = read_inode_from_disk(inode);
189			if (err < 0) {
190				iget_failed(inode);
191				return err;
192			}
193			unlock_new_inode(inode);
194		}
195	
196	Note that if the process of setting up a new inode fails, then iget_failed()
197	should be called on the inode to render it dead, and an appropriate error
198	should be passed back to the caller.
199	
200	---
201	[recommended]
202	
203	->getattr() finally getting used.  See instances in nfs, minix, etc.
204	
205	---
206	[mandatory]
207	
208	->revalidate() is gone.  If your filesystem had it - provide ->getattr()
209	and let it call whatever you had as ->revlidate() + (for symlinks that
210	had ->revalidate()) add calls in ->follow_link()/->readlink().
211	
212	---
213	[mandatory]
214	
215	->d_parent changes are not protected by BKL anymore.  Read access is safe
216	if at least one of the following is true:
217		* filesystem has no cross-directory rename()
218		* we know that parent had been locked (e.g. we are looking at
219	->d_parent of ->lookup() argument).
220		* we are called from ->rename().
221		* the child's ->d_lock is held
222	Audit your code and add locking if needed.  Notice that any place that is
223	not protected by the conditions above is risky even in the old tree - you
224	had been relying on BKL and that's prone to screwups.  Old tree had quite
225	a few holes of that kind - unprotected access to ->d_parent leading to
226	anything from oops to silent memory corruption.
227	
228	---
229	[mandatory]
230	
231		FS_NOMOUNT is gone.  If you use it - just set MS_NOUSER in flags
232	(see rootfs for one kind of solution and bdev/socket/pipe for another).
233	
234	---
235	[recommended]
236	
237		Use bdev_read_only(bdev) instead of is_read_only(kdev).  The latter
238	is still alive, but only because of the mess in drivers/s390/block/dasd.c.
239	As soon as it gets fixed is_read_only() will die.
240	
241	---
242	[mandatory]
243	
244	->permission() is called without BKL now. Grab it on entry, drop upon
245	return - that will guarantee the same locking you used to have.  If
246	your method or its parts do not need BKL - better yet, now you can
247	shift lock_kernel() and unlock_kernel() so that they would protect
248	exactly what needs to be protected.
249	
250	---
251	[mandatory]
252	
253	->statfs() is now called without BKL held.  BKL should have been
254	shifted into individual fs sb_op functions where it's not clear that
255	it's safe to remove it.  If you don't need it, remove it.
256	
257	---
258	[mandatory]
259	
260		is_read_only() is gone; use bdev_read_only() instead.
261	
262	---
263	[mandatory]
264	
265		destroy_buffers() is gone; use invalidate_bdev().
266	
267	---
268	[mandatory]
269	
270		fsync_dev() is gone; use fsync_bdev().  NOTE: lvm breakage is
271	deliberate; as soon as struct block_device * is propagated in a reasonable
272	way by that code fixing will become trivial; until then nothing can be
273	done.
274	
275	[mandatory]
276	
277		block truncatation on error exit from ->write_begin, and ->direct_IO
278	moved from generic methods (block_write_begin, cont_write_begin,
279	nobh_write_begin, blockdev_direct_IO*) to callers.  Take a look at
280	ext2_write_failed and callers for an example.
281	
282	[mandatory]
283	
284		->truncate is gone.  The whole truncate sequence needs to be
285	implemented in ->setattr, which is now mandatory for filesystems
286	implementing on-disk size changes.  Start with a copy of the old inode_setattr
287	and vmtruncate, and the reorder the vmtruncate + foofs_vmtruncate sequence to
288	be in order of zeroing blocks using block_truncate_page or similar helpers,
289	size update and on finally on-disk truncation which should not fail.
290	inode_change_ok now includes the size checks for ATTR_SIZE and must be called
291	in the beginning of ->setattr unconditionally.
292	
293	[mandatory]
294	
295		->clear_inode() and ->delete_inode() are gone; ->evict_inode() should
296	be used instead.  It gets called whenever the inode is evicted, whether it has
297	remaining links or not.  Caller does *not* evict the pagecache or inode-associated
298	metadata buffers; the method has to use truncate_inode_pages_final() to get rid
299	of those. Caller makes sure async writeback cannot be running for the inode while
300	(or after) ->evict_inode() is called.
301	
302		->drop_inode() returns int now; it's called on final iput() with
303	inode->i_lock held and it returns true if filesystems wants the inode to be
304	dropped.  As before, generic_drop_inode() is still the default and it's been
305	updated appropriately.  generic_delete_inode() is also alive and it consists
306	simply of return 1.  Note that all actual eviction work is done by caller after
307	->drop_inode() returns.
308	
309		As before, clear_inode() must be called exactly once on each call of
310	->evict_inode() (as it used to be for each call of ->delete_inode()).  Unlike
311	before, if you are using inode-associated metadata buffers (i.e.
312	mark_buffer_dirty_inode()), it's your responsibility to call
313	invalidate_inode_buffers() before clear_inode().
314	
315		NOTE: checking i_nlink in the beginning of ->write_inode() and bailing out
316	if it's zero is not *and* *never* *had* *been* enough.  Final unlink() and iput()
317	may happen while the inode is in the middle of ->write_inode(); e.g. if you blindly
318	free the on-disk inode, you may end up doing that while ->write_inode() is writing
319	to it.
320	
321	---
322	[mandatory]
323	
324		.d_delete() now only advises the dcache as to whether or not to cache
325	unreferenced dentries, and is now only called when the dentry refcount goes to
326	0. Even on 0 refcount transition, it must be able to tolerate being called 0,
327	1, or more times (eg. constant, idempotent).
328	
329	---
330	[mandatory]
331	
332		.d_compare() calling convention and locking rules are significantly
333	changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
334	look at examples of other filesystems) for guidance.
335	
336	---
337	[mandatory]
338	
339		.d_hash() calling convention and locking rules are significantly
340	changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
341	look at examples of other filesystems) for guidance.
342	
343	---
344	[mandatory]
345		dcache_lock is gone, replaced by fine grained locks. See fs/dcache.c
346	for details of what locks to replace dcache_lock with in order to protect
347	particular things. Most of the time, a filesystem only needs ->d_lock, which
348	protects *all* the dcache state of a given dentry.
349	
350	--
351	[mandatory]
352	
353		Filesystems must RCU-free their inodes, if they can have been accessed
354	via rcu-walk path walk (basically, if the file can have had a path name in the
355	vfs namespace).
356	
357		Even though i_dentry and i_rcu share storage in a union, we will
358	initialize the former in inode_init_always(), so just leave it alone in
359	the callback.  It used to be necessary to clean it there, but not anymore
360	(starting at 3.2).
361	
362	--
363	[recommended]
364		vfs now tries to do path walking in "rcu-walk mode", which avoids
365	atomic operations and scalability hazards on dentries and inodes (see
366	Documentation/filesystems/path-lookup.txt). d_hash and d_compare changes
367	(above) are examples of the changes required to support this. For more complex
368	filesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, so
369	no changes are required to the filesystem. However, this is costly and loses
370	the benefits of rcu-walk mode. We will begin to add filesystem callbacks that
371	are rcu-walk aware, shown below. Filesystems should take advantage of this
372	where possible.
373	
374	--
375	[mandatory]
376		d_revalidate is a callback that is made on every path element (if
377	the filesystem provides it), which requires dropping out of rcu-walk mode. This
378	may now be called in rcu-walk mode (nd->flags & LOOKUP_RCU). -ECHILD should be
379	returned if the filesystem cannot handle rcu-walk. See
380	Documentation/filesystems/vfs.txt for more details.
381	
382		permission and check_acl are inode permission checks that are called
383	on many or all directory inodes on the way down a path walk (to check for
384	exec permission). These must now be rcu-walk aware (flags & IPERM_FLAG_RCU).
385	See Documentation/filesystems/vfs.txt for more details.
386	 
387	--
388	[mandatory]
389		In ->fallocate() you must check the mode option passed in.  If your
390	filesystem does not support hole punching (deallocating space in the middle of a
391	file) you must return -EOPNOTSUPP if FALLOC_FL_PUNCH_HOLE is set in mode.
392	Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set,
393	so the i_size should not change when hole punching, even when puching the end of
394	a file off.
395	
396	--
397	[mandatory]
398		->get_sb() is gone.  Switch to use of ->mount().  Typically it's just
399	a matter of switching from calling get_sb_... to mount_... and changing the
400	function type.  If you were doing it manually, just switch from setting ->mnt_root
401	to some pointer to returning that pointer.  On errors return ERR_PTR(...).
402	
403	--
404	[mandatory]
405		->permission() and generic_permission()have lost flags
406	argument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask.
407		generic_permission() has also lost the check_acl argument; ACL checking
408	has been taken to VFS and filesystems need to provide a non-NULL ->i_op->get_acl
409	to read an ACL from disk.
410	
411	--
412	[mandatory]
413		If you implement your own ->llseek() you must handle SEEK_HOLE and
414	SEEK_DATA.  You can hanle this by returning -EINVAL, but it would be nicer to
415	support it in some way.  The generic handler assumes that the entire file is
416	data and there is a virtual hole at the end of the file.  So if the provided
417	offset is less than i_size and SEEK_DATA is specified, return the same offset.
418	If the above is true for the offset and you are given SEEK_HOLE, return the end
419	of the file.  If the offset is i_size or greater return -ENXIO in either case.
420	
421	[mandatory]
422		If you have your own ->fsync() you must make sure to call
423	filemap_write_and_wait_range() so that all dirty pages are synced out properly.
424	You must also keep in mind that ->fsync() is not called with i_mutex held
425	anymore, so if you require i_mutex locking you must make sure to take it and
426	release it yourself.
427	
428	--
429	[mandatory]
430		d_alloc_root() is gone, along with a lot of bugs caused by code
431	misusing it.  Replacement: d_make_root(inode).  The difference is,
432	d_make_root() drops the reference to inode if dentry allocation fails.  
433	
434	--
435	[mandatory]
436		The witch is dead!  Well, 2/3 of it, anyway.  ->d_revalidate() and
437	->lookup() do *not* take struct nameidata anymore; just the flags.
438	--
439	[mandatory]
440		->create() doesn't take struct nameidata *; unlike the previous
441	two, it gets "is it an O_EXCL or equivalent?" boolean argument.  Note that
442	local filesystems can ignore tha argument - they are guaranteed that the
443	object doesn't exist.  It's remote/distributed ones that might care...
444	--
445	[mandatory]
446		FS_REVAL_DOT is gone; if you used to have it, add ->d_weak_revalidate()
447	in your dentry operations instead.
448	--
449	[mandatory]
450		vfs_readdir() is gone; switch to iterate_dir() instead
451	--
452	[mandatory]
453		->readdir() is gone now; switch to ->iterate()
454	[mandatory]
455		vfs_follow_link has been removed.  Filesystems must use nd_set_link
456		from ->follow_link for normal symlinks, or nd_jump_link for magic
457		/proc/<pid> style links.
458	--
459	[mandatory]
460		iget5_locked()/ilookup5()/ilookup5_nowait() test() callback used to be
461		called with both ->i_lock and inode_hash_lock held; the former is *not*
462		taken anymore, so verify that your callbacks do not rely on it (none
463		of the in-tree instances did).  inode_hash_lock is still held,
464		of course, so they are still serialized wrt removal from inode hash,
465		as well as wrt set() callback of iget5_locked().
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