porting 9.3 KB
Newer Older
L
Linus Torvalds 已提交
1 2
Changes since 2.5.0:

3
---
L
Linus Torvalds 已提交
4 5 6 7 8 9 10 11 12
[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())

13
---
L
Linus Torvalds 已提交
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
[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;

31
Add foo_alloc_inode() and foo_destroy_inode() - the former should allocate
L
Linus Torvalds 已提交
32 33 34 35 36
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.

37 38
Keep in mind that now you need explicit initialization of private data
typically between calling iget_locked() and unlocking the inode.
L
Linus Torvalds 已提交
39 40 41 42 43 44 45 46 47 48 49 50 51 52

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

53 54
int foo_get_sb(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
L
Linus Torvalds 已提交
55
{
56 57
	return get_sb_bdev(fs_type, flags, dev_name, data, foo_fill_super,
			   mnt);
L
Linus Torvalds 已提交
58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109
}

(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]

110
->link() callers hold ->i_mutex on the object we are linking to.  Some of your
L
Linus Torvalds 已提交
111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
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]

133 134 135
->setattr() is called without BKL now.  Caller _always_ holds ->i_mutex, so
watch for ->i_mutex-grabbing code that might be used by your ->setattr().
Callers of notify_change() need ->i_mutex now.
L
Linus Torvalds 已提交
136 137 138 139 140 141 142

---
[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
143
Documentation/filesystems/nfs/Exporting.
L
Linus Torvalds 已提交
144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175

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.

176 177 178 179
When the inode has been created by iget5_locked(), it will be returned with the
I_NEW flag set and will still be locked.  The filesystem then needs to finalize
the initialization. Once the inode is initialized it must be unlocked by
calling unlock_new_inode().
L
Linus Torvalds 已提交
180 181 182 183 184 185 186

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.
187 188 189 190 191 192 193 194 195 196 197 198 199
	inode = iget_locked(sb, ino);
	if (inode->i_state & I_NEW) {
		err = read_inode_from_disk(inode);
		if (err < 0) {
			iget_failed(inode);
			return err;
		}
		unlock_new_inode(inode);
	}

Note that if the process of setting up a new inode fails, then iget_failed()
should be called on the inode to render it dead, and an appropriate error
should be passed back to the caller.
L
Linus Torvalds 已提交
200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275

---
[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.
276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293

[mandatory]

	block truncatation on error exit from ->write_begin, and ->direct_IO
moved from generic methods (block_write_begin, cont_write_begin,
nobh_write_begin, blockdev_direct_IO*) to callers.  Take a look at
ext2_write_failed and callers for an example.

[mandatory]

	->truncate is going away.  The whole truncate sequence needs to be
implemented in ->setattr, which is now mandatory for filesystems
implementing on-disk size changes.  Start with a copy of the old inode_setattr
and vmtruncate, and the reorder the vmtruncate + foofs_vmtruncate sequence to
be in order of zeroing blocks using block_truncate_page or similar helpers,
size update and on finally on-disk truncation which should not fail.
inode_change_ok now includes the size checks for ATTR_SIZE and must be called
in the beginning of ->setattr unconditionally.