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_destory_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 in ->read_inode() and after getting an inode from new_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 struct super_block foo_get_sb(struct file_system_type *fs_type,
54 int flags, const char *dev_name, void *data)
55 {
56 return get_sb_bdev(fs_type, flags, dev_name, data, ext2_fill_super);
57 }
58
59 (or similar with s/bdev/nodev/ or s/bdev/single/, depending on the kind of
60 filesystem).
61
62 Replace DECLARE_FSTYPE... with explicit initializer and have ->get_sb set as
63 foo_get_sb.
64
65 ---
66 [mandatory]
67
68 Locking change: ->s_vfs_rename_sem is taken only by cross-directory renames.
69 Most likely there is no need to change anything, but if you relied on
70 global exclusion between renames for some internal purpose - you need to
71 change your internal locking. Otherwise exclusion warranties remain the
72 same (i.e. parents and victim are locked, etc.).
73
74 ---
75 [informational]
76
77 Now we have the exclusion between ->lookup() and directory removal (by
78 ->rmdir() and ->rename()). If you used to need that exclusion and do
79 it by internal locking (most of filesystems couldn't care less) - you
80 can relax your locking.
81
82 ---
83 [mandatory]
84
85 ->lookup(), ->truncate(), ->create(), ->unlink(), ->mknod(), ->mkdir(),
86 ->rmdir(), ->link(), ->lseek(), ->symlink(), ->rename()
87 and ->readdir() are called without BKL now. Grab it on entry, drop upon return
88 - that will guarantee the same locking you used to have. If your method or its
89 parts do not need BKL - better yet, now you can shift lock_kernel() and
90 unlock_kernel() so that they would protect exactly what needs to be
91 protected.
92
93 ---
94 [mandatory]
95
96 BKL is also moved from around sb operations. ->write_super() Is now called
97 without BKL held. BKL should have been shifted into individual fs sb_op
98 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_sem 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_sem, so
133 watch for ->i_sem-grabbing code that might be used by your ->setattr().
134 Callers of notify_change() need ->i_sem 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/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
176 the I_NEW flag set and will still be locked. read_inode has not been
177 called so the file system still has to finalize the initialization. Once
178 the inode is initialized it must be unlocked by 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 read_inode_from_disk(inode);
189 unlock_new_inode(inode);
190 }
191
192 ---
193 [recommended]
194
195 ->getattr() finally getting used. See instances in nfs, minix, etc.
196
197 ---
198 [mandatory]
199
200 ->revalidate() is gone. If your filesystem had it - provide ->getattr()
201 and let it call whatever you had as ->revlidate() + (for symlinks that
202 had ->revalidate()) add calls in ->follow_link()/->readlink().
203
204 ---
205 [mandatory]
206
207 ->d_parent changes are not protected by BKL anymore. Read access is safe
208 if at least one of the following is true:
209 * filesystem has no cross-directory rename()
210 * dcache_lock is held
211 * we know that parent had been locked (e.g. we are looking at
212 ->d_parent of ->lookup() argument).
213 * we are called from ->rename().
214 * the child's ->d_lock is held
215 Audit your code and add locking if needed. Notice that any place that is
216 not protected by the conditions above is risky even in the old tree - you
217 had been relying on BKL and that's prone to screwups. Old tree had quite
218 a few holes of that kind - unprotected access to ->d_parent leading to
219 anything from oops to silent memory corruption.
220
221 ---
222 [mandatory]
223
224 FS_NOMOUNT is gone. If you use it - just set MS_NOUSER in flags
225 (see rootfs for one kind of solution and bdev/socket/pipe for another).
226
227 ---
228 [recommended]
229
230 Use bdev_read_only(bdev) instead of is_read_only(kdev). The latter
231 is still alive, but only because of the mess in drivers/s390/block/dasd.c.
232 As soon as it gets fixed is_read_only() will die.
233
234 ---
235 [mandatory]
236
237 ->permission() is called without BKL now. Grab it on entry, drop upon
238 return - that will guarantee the same locking you used to have. If
239 your method or its parts do not need BKL - better yet, now you can
240 shift lock_kernel() and unlock_kernel() so that they would protect
241 exactly what needs to be protected.
242
243 ---
244 [mandatory]
245
246 ->statfs() is now called without BKL held. BKL should have been
247 shifted into individual fs sb_op functions where it's not clear that
248 it's safe to remove it. If you don't need it, remove it.
249
250 ---
251 [mandatory]
252
253 is_read_only() is gone; use bdev_read_only() instead.
254
255 ---
256 [mandatory]
257
258 destroy_buffers() is gone; use invalidate_bdev().
259
260 ---
261 [mandatory]
262
263 fsync_dev() is gone; use fsync_bdev(). NOTE: lvm breakage is
264 deliberate; as soon as struct block_device * is propagated in a reasonable
265 way by that code fixing will become trivial; until then nothing can be
266 done.
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