VFS: Add owner-filesystem positive/negative dentry checks (525d27b2) · Commits · 戴 / test

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>

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)

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