diff options
author | David Howells <dhowells@redhat.com> | 2015-02-11 08:40:17 -0500 |
---|---|---|
committer | Al Viro <viro@zeniv.linux.org.uk> | 2015-04-15 15:04:42 -0400 |
commit | 525d27b23555419e0e7b73fb6e78d4d678cb4f32 (patch) | |
tree | cf89cdba77a6d468503131bdd6bf3e4742d0c8c7 | |
parent | 65a4a1cad7c56e7056fb4b35ac2d93695612612c (diff) |
VFS: Add owner-filesystem positive/negative dentry checks
Supply two functions to test whether a filesystem's own dentries are positive
or negative (d_really_is_positive() and d_really_is_negative()).
The problem is that the DCACHE_ENTRY_TYPE field of dentry->d_flags may be
overridden by the union part of a layered filesystem and isn't thus
necessarily indicative of the type of dentry.
Normally, this would involve a negative dentry (ie. ->d_inode == NULL) having
->d_layer.lower pointed to a lower layer dentry, DCACHE_PINNING_LOWER set and
the DCACHE_ENTRY_TYPE field set to something other than DCACHE_MISS_TYPE - but
it could also involve, say, a DCACHE_SPECIAL_TYPE being overridden to
DCACHE_WHITEOUT_TYPE if a 0,0 chardev is detected in the top layer.
However, inside a filesystem, when that fs is looking at its own dentries, it
probably wants to know if they are really negative or not - and doesn't care
about the fallthrough bits used by the union.
To this end, a filesystem should normally use d_really_is_positive/negative()
when looking at its own dentries rather than d_is_positive/negative() and
should use d_inode() to get at the inode.
Anyone looking at someone else's dentries (this includes pathwalk) should use
d_is_xxx() and d_backing_inode().
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r-- | include/linux/dcache.h | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/include/linux/dcache.h b/include/linux/dcache.h index d8358799c594..e83768ee38fc 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h | |||
@@ -482,6 +482,44 @@ static inline bool d_is_positive(const struct dentry *dentry) | |||
482 | return !d_is_negative(dentry); | 482 | return !d_is_negative(dentry); |
483 | } | 483 | } |
484 | 484 | ||
485 | /** | ||
486 | * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs) | ||
487 | * @dentry: The dentry in question | ||
488 | * | ||
489 | * Returns true if the dentry represents either an absent name or a name that | ||
490 | * doesn't map to an inode (ie. ->d_inode is NULL). The dentry could represent | ||
491 | * a true miss, a whiteout that isn't represented by a 0,0 chardev or a | ||
492 | * fallthrough marker in an opaque directory. | ||
493 | * | ||
494 | * Note! (1) This should be used *only* by a filesystem to examine its own | ||
495 | * dentries. It should not be used to look at some other filesystem's | ||
496 | * dentries. (2) It should also be used in combination with d_inode() to get | ||
497 | * the inode. (3) The dentry may have something attached to ->d_lower and the | ||
498 | * type field of the flags may be set to something other than miss or whiteout. | ||
499 | */ | ||
500 | static inline bool d_really_is_negative(const struct dentry *dentry) | ||
501 | { | ||
502 | return dentry->d_inode == NULL; | ||
503 | } | ||
504 | |||
505 | /** | ||
506 | * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs) | ||
507 | * @dentry: The dentry in question | ||
508 | * | ||
509 | * Returns true if the dentry represents a name that maps to an inode | ||
510 | * (ie. ->d_inode is not NULL). The dentry might still represent a whiteout if | ||
511 | * that is represented on medium as a 0,0 chardev. | ||
512 | * | ||
513 | * Note! (1) This should be used *only* by a filesystem to examine its own | ||
514 | * dentries. It should not be used to look at some other filesystem's | ||
515 | * dentries. (2) It should also be used in combination with d_inode() to get | ||
516 | * the inode. | ||
517 | */ | ||
518 | static inline bool d_really_is_positive(const struct dentry *dentry) | ||
519 | { | ||
520 | return dentry->d_inode != NULL; | ||
521 | } | ||
522 | |||
485 | extern void d_set_fallthru(struct dentry *dentry); | 523 | extern void d_set_fallthru(struct dentry *dentry); |
486 | 524 | ||
487 | static inline bool d_is_fallthru(const struct dentry *dentry) | 525 | static inline bool d_is_fallthru(const struct dentry *dentry) |