xfs: allow xattr matching on name and value for parent pointers

If a file is hardlinked with the same name but from multiple parents,
the parent pointers will all have the same dirent name (== attr name)
but with different parent_ino/parent_gen values.  To disambiguate, we
need to be able to match on both the attr name and the attr value.  This
is in contrast to regular xattrs, which are matchtg edit
d only on name.

Therefore, plumb in the ability to match shortform and local attrs on
name and value in the XFS_ATTR_PARENT namespace.  Parent pointer attr
values are never large enough to be stored in a remote attr, so we need
can reject these cases as corruption.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_attr_leaf.c

@@ -514,12 +514,37 @@ static inline unsigned int xfs_attr_match_mask(const struct xfs_da_args *args)
 	return XFS_ATTR_NSP_ONDISK_MASK | XFS_ATTR_INCOMPLETE;
 }
 
+static inline bool
+xfs_attr_parent_match(
+	const struct xfs_da_args	*args,
+	const void			*value,
+	unsigned int			valuelen)
+{
+	ASSERT(args->value != NULL);
+
+	/* Parent pointers do not use remote values */
+	if (!value)
+		return false;
+
+	/*
+	 * The only value we support is a parent rec.  However, we'll accept
+	 * any valuelen so that offline repair can delete ATTR_PARENT values
+	 * that are not parent pointers.
+	 */
+	if (valuelen != args->valuelen)
+		return false;
+
+	return memcmp(args->value, value, valuelen) == 0;
+}
+
 static bool
 xfs_attr_match(
 	struct xfs_da_args	*args,
 	unsigned int		attr_flags,
 	const unsigned char	*name,
-	unsigned int		namelen)
+	unsigned int		namelen,
+	const void		*value,
+	unsigned int		valuelen)
 {
 	unsigned int		mask = xfs_attr_match_mask(args);
 
@@ -530,6 +555,9 @@ xfs_attr_match(
 	if (memcmp(args->name, name, namelen) != 0)
 		return false;
 
+	if (attr_flags & XFS_ATTR_PARENT)
+		return xfs_attr_parent_match(args, value, valuelen);
+
 	return true;
 }
 
@@ -539,6 +567,13 @@ xfs_attr_copy_value(
 	unsigned char		*value,
 	int			valuelen)
 {
+	/*
+	 * Parent pointer lookups require the caller to specify the name and
+	 * value, so don't copy anything.
+	 */
+	if (args->attr_filter & XFS_ATTR_PARENT)
+		return 0;
+
 	/*
 	 * No copy if all we have to do is get the length
 	 */
@@ -748,7 +783,8 @@ xfs_attr_sf_findname(
 	     sfe < xfs_attr_sf_endptr(sf);
 	     sfe = xfs_attr_sf_nextentry(sfe)) {
 		if (xfs_attr_match(args, sfe->flags, sfe->nameval,
-					sfe->namelen))
+				sfe->namelen, &sfe->nameval[sfe->namelen],
+				sfe->valuelen))
 			return sfe;
 	}
 
@@ -2444,18 +2480,22 @@ xfs_attr3_leaf_lookup_int(
 		if (entry->flags & XFS_ATTR_LOCAL) {
 			name_loc = xfs_attr3_leaf_name_local(leaf, probe);
 			if (!xfs_attr_match(args, entry->flags,
-						name_loc->nameval,
-						name_loc->namelen))
+					name_loc->nameval, name_loc->namelen,
+					&name_loc->nameval[name_loc->namelen],
+					be16_to_cpu(name_loc->valuelen)))
 				continue;
 			args->index = probe;
 			return -EEXIST;
 		} else {
+			unsigned int	valuelen;
+
 			name_rmt = xfs_attr3_leaf_name_remote(leaf, probe);
+			valuelen = be32_to_cpu(name_rmt->valuelen);
 			if (!xfs_attr_match(args, entry->flags, name_rmt->name,
-						name_rmt->namelen))
+					name_rmt->namelen, NULL, valuelen))
 				continue;
 			args->index = probe;
-			args->rmtvaluelen = be32_to_cpu(name_rmt->valuelen);
+			args->rmtvaluelen = valuelen;
 			args->rmtblkno = be32_to_cpu(name_rmt->valueblk);
 			args->rmtblkcnt = xfs_attr3_rmt_blocks(
 							args->dp->i_mount,