[PATCH 14/31] xfs: create a hashname function for parent pointers

Darrick J. Wong
2024-04-16T01:29:42Z

Although directory entry and parent pointer recordsets look very similar
(name -> ino), there's one major difference between them: a file can be
hardlinked from multiple parent directories with the same filename.
This is common in shared container environments where a base directory
tree might be hardlink-copied multiple times. IOWs the same 'ls'
program might be hardlinked to multiple /srv/*/bin/ls paths.

We don't want parent pointer operations to bog down on hash collisions
between the same dirent name, so create a special hash function that
mixes in the parent directory inode number.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/libxfs/xfs_attr.c | 3 +++
fs/xfs/libxfs/xfs_parent.c | 47 ++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/libxfs/xfs_parent.h | 5 +++++
fs/xfs/scrub/attr.c | 4 ++++
4 files changed, 59 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index 93524efa6e56c..8c283e5c24702 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -437,6 +437,9 @@ xfs_attr_hashval(
{
ASSERT(xfs_attr_check_namespace(attr_flags));

+ if (attr_flags & XFS_ATTR_PARENT)
+ return xfs_parent_hashattr(mp, name, namelen, value, valuelen);
+
return xfs_attr_hashname(name, namelen);
}

diff --git a/fs/xfs/libxfs/xfs_parent.c b/fs/xfs/libxfs/xfs_parent.c
index 5961fa8c85615..d564baf2549c5 100644
--- a/fs/xfs/libxfs/xfs_parent.c
+++ b/fs/xfs/libxfs/xfs_parent.c
@@ -90,3 +90,50 @@ xfs_parent_valuecheck(

return true;
}
+
+/* Compute the attribute name hash for a parent pointer. */
+xfs_dahash_t
+xfs_parent_hashval(
+ struct xfs_mount *mp,
+ const uint8_t *name,
+ int namelen,
+ xfs_ino_t parent_ino)
+{
+ struct xfs_name xname = {
+ .name = name,
+ .len = namelen,
+ };
+
+ /*
+ * Use the same dirent name hash as would be used on the directory, but
+ * mix in the parent inode number to avoid collisions on hardlinked
+ * files with identical names but different parents.
+ */
+ return xfs_dir2_hashname(mp, &xname) ^
+ upper_32_bits(parent_ino) ^ lower_32_bits(parent_ino);
+}
+
+/* Compute the attribute name hash from the xattr components. */
+xfs_dahash_t
+xfs_parent_hashattr(
+ struct xfs_mount *mp,
+ const uint8_t *name,
+ int namelen,
+ const void *value,
+ int valuelen)
+{
+ const struct xfs_parent_rec *rec = value;
+
+ /* Requires a local attr value in xfs_parent_rec format */
+ if (valuelen != sizeof(struct xfs_parent_rec)) {
+ ASSERT(valuelen == sizeof(struct xfs_parent_rec));
+ return 0;
+ }
+
+ if (!value) {
+ ASSERT(value != NULL);
+ return 0;
+ }
+
+ return xfs_parent_hashval(mp, name, namelen, be64_to_cpu(rec->p_ino));
+}
diff --git a/fs/xfs/libxfs/xfs_parent.h b/fs/xfs/libxfs/xfs_parent.h
index ef8aff8607801..6a4028871b72a 100644
--- a/fs/xfs/libxfs/xfs_parent.h
+++ b/fs/xfs/libxfs/xfs_parent.h
@@ -12,4 +12,9 @@ bool xfs_parent_namecheck(unsigned int attr_flags, const void *name,
bool xfs_parent_valuecheck(struct xfs_mount *mp, const void *value,
size_t valuelen);

+xfs_dahash_t xfs_parent_hashval(struct xfs_mount *mp, const uint8_t *name,
+ int namelen, xfs_ino_t parent_ino);
+xfs_dahash_t xfs_parent_hashattr(struct xfs_mount *mp, const uint8_t *name,
+ int namelen, const void *value, int valuelen);
+
#endif /* __XFS_PARENT_H__ */
diff --git a/fs/xfs/scrub/attr.c b/fs/xfs/scrub/attr.c
index 22d7ef4df1699..c07d050b39b2e 100644
--- a/fs/xfs/scrub/attr.c
+++ b/fs/xfs/scrub/attr.c
@@ -536,6 +536,10 @@ xchk_xattr_rec(
xchk_da_set_corrupt(ds, level);
goto out;
}
+ if (ent->flags & XFS_ATTR_PARENT) {
+ xchk_da_set_corrupt(ds, level);
+ goto out;
+ }
calc_hash = xfs_attr_hashval(mp, ent->flags, rentry->name,
rentry->namelen, NULL,
be32_to_cpu(rentry->valuelen));