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Commit 525d27b2 authored by David Howells's avatar David Howells Committed by Al Viro
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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: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 65a4a1ca

include/linux/dcache.h

+38 −0
Original line number Diff line number Diff line
@@ -482,6 +482,44 @@ static inline bool d_is_positive(const struct dentry *dentry) 
	return !d_is_negative(dentry);

}



/**

 * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)

 * @dentry: The dentry in question

 *

 * Returns true if the dentry represents either an absent name or a name that

 * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent

 * a true miss, a whiteout that isn't represented by a 0,0 chardev or a

 * fallthrough marker in an opaque directory.

 *

 * Note!  (1) This should be used *only* by a filesystem to examine its own

 * dentries.  It should not be used to look at some other filesystem's

 * dentries.  (2) It should also be used in combination with d_inode() to get

 * the inode.  (3) The dentry may have something attached to ->d_lower and the

 * type field of the flags may be set to something other than miss or whiteout.

 */

static inline bool d_really_is_negative(const struct dentry *dentry)

{

	return dentry->d_inode == NULL;

}



/**

 * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)

 * @dentry: The dentry in question

 *

 * Returns true if the dentry represents a name that maps to an inode

 * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if

 * that is represented on medium as a 0,0 chardev.

 *

 * Note!  (1) This should be used *only* by a filesystem to examine its own

 * dentries.  It should not be used to look at some other filesystem's

 * dentries.  (2) It should also be used in combination with d_inode() to get

 * the inode.

 */

static inline bool d_really_is_positive(const struct dentry *dentry)

{

	return dentry->d_inode != NULL;

}



extern void d_set_fallthru(struct dentry *dentry);



static inline bool d_is_fallthru(const struct dentry *dentry)