[062/115] xfs: create a hashname function for parent pointers

Commit Message

Darrick J. Wong July 30, 2024, 12:39 a.m. UTC

From: Darrick J. Wong <[e-mail]>

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 <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
---
 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(+)

Patch

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__ */