From 525d27b23555419e0e7b73fb6e78d4d678cb4f32 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 11 Feb 2015 13:40:17 +0000 Subject: [PATCH] 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 Signed-off-by: Al Viro --- include/linux/dcache.h | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) 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) 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) -- GitLab