From: Darrick J. Wong <djwong@xxxxxxxxxx>
Source kernel commit: fb102fe7fe02e70f8a49cc7f74bc0769cdab2912
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@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
libxfs/libxfs_priv.h | 18 ++++++++++++++++++
libxfs/xfs_attr.c | 3 +++
libxfs/xfs_parent.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
libxfs/xfs_parent.h | 5 +++++
4 files changed, 73 insertions(+)
diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index 4136b277f..023444082 100644
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -618,4 +618,22 @@ int xfs_bmap_last_extent(struct xfs_trans *tp, struct xfs_inode *ip,
/* xfs_inode.h */
#define xfs_iflags_set(ip, flags) do { } while (0)
+/* linux/wordpart.h */
+
+/**
+ * upper_32_bits - return bits 32-63 of a number
+ * @n: the number we're accessing
+ *
+ * A basic shift-right of a 64- or 32-bit quantity. Use this to suppress
+ * the "right shift count >= width of type" warning when that quantity is
+ * 32-bits.
+ */
+#define upper_32_bits(n) ((uint32_t)(((n) >> 16) >> 16))
+
+/**
+ * lower_32_bits - return bits 0-31 of a number
+ * @n: the number we're accessing
+ */
+#define lower_32_bits(n) ((uint32_t)((n) & 0xffffffff))
+
#endif /* __LIBXFS_INTERNAL_XFS_H__ */
diff --git a/libxfs/xfs_attr.c b/libxfs/xfs_attr.c
index 345132921..344b34aa4 100644
--- a/libxfs/xfs_attr.c
+++ b/libxfs/xfs_attr.c
@@ -436,6 +436,9 @@ 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/libxfs/xfs_parent.c b/libxfs/xfs_parent.c
index 50da527b6..7447acc2c 100644
--- a/libxfs/xfs_parent.c
+++ b/libxfs/xfs_parent.c
@@ -87,3 +87,50 @@ 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/libxfs/xfs_parent.h b/libxfs/xfs_parent.h
index ef8aff860..6a4028871 100644
--- a/libxfs/xfs_parent.h
+++ b/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__ */
