xfs: allocate xattr buffer on demand

From: Dave Chinner <[email protected]>

Shortform, leaf and remote value attr value retrieval return different values for success. This makes it more complex to handle actual errors xfs_attr_get() as some errors mean success and some mean failure. Make the return values consistent for success and failure consistent for all attribute formats.

Signed-off-by Dave Chinner <[email protected]>

---
 fs/xfs/libxfs/xfs_attr.c        | 57 +++++++++++++++++++++------------
 fs/xfs/libxfs/xfs_attr_leaf.c   | 15 ++++++---
 fs/xfs/libxfs/xfs_attr_remote.c |  2 ++
 fs/xfs/scrub/attr.c             |  2 --
 4 files changed, 49 insertions(+), 27 deletions(-)

fs/xfs/libxfs/xfs_attr.c +16 -6

index d48fcf11cc35..776343c4f22b 100644
@@ -97,7 +97,10 @@ xfs_inode_hasattr(
  * Overall external interface routines.
  *========================================================================*/
 
-/* Retrieve an extended attribute and its value.  Must have ilock. */
+/*
+ * Retrieve an extended attribute and its value.  Must have ilock.
+ * Returns 0 on successful retrieval, otherwise an error.
+ */
 int
 xfs_attr_get_ilocked(
 	struct xfs_inode	*ip,

@@ -147,7 +150,7 @@ xfs_attr_get(
 	xfs_iunlock(ip, lock_mode);
 
 	*valuelenp = args.valuelen;
-	return error == -EEXIST ? 0 : error;
+	return error;
 }
 
 /*

@@ -768,6 +771,8 @@ xfs_attr_leaf_removename(
  *
  * This leaf block cannot have a "remote" value, we only call this routine
  * if bmap_one_block() says there is only one block (ie: no remote blks).
+ *
+ * Returns 0 on successful retrieval, otherwise an error.
  */
 STATIC int
 xfs_attr_leaf_get(xfs_da_args_t *args)

@@ -789,10 +794,15 @@ xfs_attr_leaf_get(xfs_da_args_t *args)
 	}
 	error = xfs_attr3_leaf_getvalue(bp, args);
 	xfs_trans_brelse(args->trans, bp);
-	if (!error && (args->rmtblkno > 0) && !(args->flags & ATTR_KERNOVAL)) {
-		error = xfs_attr_rmtval_get(args);
-	}
-	return error;
+	if (error)
+		return error;
+
+	/* check if we have to retrieve a remote attribute to get the value */
+	if (args->flags & ATTR_KERNOVAL)
+		return 0;
+	if (!args->rmtblkno)
+		return 0;
+	return xfs_attr_rmtval_get(args);
 }
 
 /*========================================================================

fs/xfs/libxfs/xfs_attr.c +2 -0

  *
  * This routine gets called for any attribute fork that has more than one
  * block, ie: both true Btree attr lists and for single-leaf-blocks with
  * "remote" values taking up more blocks.
+ *
+ * Returns 0 on successful retrieval, otherwise an error.
  */
 STATIC int
 xfs_attr_node_get(xfs_da_args_t *args)

fs/xfs/libxfs/xfs_attr.c +16 -13

 	 */
 	error = xfs_da3_node_lookup_int(state, &retval);
 	if (error) {
 		retval = error;
-	} else if (retval == -EEXIST) {
-		blk = &state->path.blk[ state->path.active-1 ];
-		ASSERT(blk->bp != NULL);
-		ASSERT(blk->magic == XFS_ATTR_LEAF_MAGIC);
-
-		/*
-		 * Get the value, local or "remote"
-		 */
-		retval = xfs_attr3_leaf_getvalue(blk->bp, args);
-		if (!retval && (args->rmtblkno > 0)
-		    && !(args->flags & ATTR_KERNOVAL)) {
-			retval = xfs_attr_rmtval_get(args);
-		}
+		goto out_release;
 	}
+	if (retval != -EEXIST)
+		goto out_release;
+
+	/*
+	 * Get the value, local or "remote"
+	 */
+	blk = &state->path.blk[state->path.active - 1];
+	retval = xfs_attr3_leaf_getvalue(blk->bp, args);
+	if (retval)
+		goto out_release;
+	if (args->flags & ATTR_KERNOVAL)
+		goto out_release;
+	if (args->rmtblkno > 0)
+		retval = xfs_attr_rmtval_get(args);
 
 	/*
 	 * If not in a transaction, we have to release all the buffers.
 	 */
+out_release:
 	for (i = 0; i < state->path.active; i++) {
 		xfs_trans_brelse(args->trans, state->path.blk[i].bp);
 		state->path.blk[i].bp = NULL;

fs/xfs/libxfs/xfs_attr_leaf.c +11 -4

index 70eb941d02e4..d056767b5c53 100644
@@ -720,9 +720,12 @@ xfs_attr_shortform_lookup(xfs_da_args_t *args)
 }
 
 /*
- * Look up a name in a shortform attribute list structure.
+ * Retreive the attribute value and length.
+ *
+ * If ATTR_KERNOVAL is specified, only the length needs to be returned.
+ * Unlike a lookup, we only return an error if the attribute does not
+ * exist or we can't retrieve the value.
  */
-/*ARGSUSED*/
 int
 xfs_attr_shortform_getvalue(xfs_da_args_t *args)
 {

@@ -743,7 +746,7 @@ xfs_attr_shortform_getvalue(xfs_da_args_t *args)
 			continue;
 		if (args->flags & ATTR_KERNOVAL) {
 			args->valuelen = sfe->valuelen;
-			return -EEXIST;
+			return 0;
 		}
 		if (args->valuelen < sfe->valuelen) {
 			args->valuelen = sfe->valuelen;

@@ -752,7 +755,7 @@ xfs_attr_shortform_getvalue(xfs_da_args_t *args)
 		args->valuelen = sfe->valuelen;
 		memcpy(args->value, &sfe->nameval[args->namelen],
 						    args->valuelen);
-		return -EEXIST;
+		return 0;
 	}
 	return -ENOATTR;
 }

@@ -2350,6 +2353,10 @@ xfs_attr3_leaf_lookup_int(
 /*
  * Get the value associated with an attribute name from a leaf attribute
  * list structure.
+ *
+ * If ATTR_KERNOVAL is specified, only the length needs to be returned.
+ * Unlike a lookup, we only return an error if the attribute does not
+ * exist or we can't retrieve the value.
  */
 int
 xfs_attr3_leaf_getvalue(

fs/xfs/libxfs/xfs_attr_remote.c +2 -0

index 4eb30d357045..3e39b7d40f25 100644
@@ -358,6 +358,8 @@ xfs_attr_rmtval_copyin(
 /*
  * Read the value associated with an attribute from the out-of-line buffer
  * that we stored it in.
+ *
+ * Returns 0 on successful retrieval, otherwise an error.
  */
 int
 xfs_attr_rmtval_get(

fs/xfs/scrub/attr.c +0 -2

index 1afc58bf71dd..e9248ad4f842 100644
@@ -163,8 +163,6 @@ xchk_xattr_listent(
 	args.valuelen = valuelen;
 
 	error = xfs_attr_get_ilocked(context->dp, &args);
-	if (error == -EEXIST)
-		error = 0;
 	if (!xchk_fblock_process_error(sx->sc, XFS_ATTR_FORK, args.blkno,
 			&error))
 		goto fail_xref;

Signature · 1 line

2.23.0.rc1

From: Dave Chinner <[email protected]>

Shortform, leaf and remote value attr value retrieval return different values for success. This makes it more complex to handle actual errors xfs_attr_get() as some errors mean success and some mean failure. Make the return values consistent for success and failure consistent for all attribute formats.

Signed-off-by Dave Chinner <[email protected]>

---
 fs/xfs/libxfs/xfs_attr.c        | 57 +++++++++++++++++++++------------
 fs/xfs/libxfs/xfs_attr_leaf.c   | 15 ++++++---
 fs/xfs/libxfs/xfs_attr_remote.c |  2 ++
 fs/xfs/scrub/attr.c             |  2 --
 4 files changed, 49 insertions(+), 27 deletions(-)

fs/xfs/libxfs/xfs_attr.c +19 -7

index d48fcf11cc35..776343c4f22b 100644
@@ -97,7 +97,10 @@ xfs_inode_hasattr(
  * Overall external interface routines.
  *========================================================================*/
 
-/* Retrieve an extended attribute and its value.  Must have ilock. */
+/*
+ * Retrieve an extended attribute and its value.  Must have ilock.
+ * Returns 0 on successful retrieval, otherwise an error.
+ */
 int
 xfs_attr_get_ilocked(
 	struct xfs_inode	*ip,

@@ -147,7 +150,7 @@ xfs_attr_get(
 	xfs_iunlock(ip, lock_mode);
 
 	*valuelenp = args.valuelen;
-	return error == -EEXIST ? 0 : error;
+	return error;
 }
 
 /*

@@ -768,6 +771,8 @@ xfs_attr_leaf_removename(
  *
  * This leaf block cannot have a "remote" value, we only call this routine
  * if bmap_one_block() says there is only one block (ie: no remote blks).
+ *
+ * Returns 0 on successful retrieval, otherwise an error.
  */
 STATIC int
 xfs_attr_leaf_get(xfs_da_args_t *args)

@@ -789,10 +794,15 @@ xfs_attr_leaf_get(xfs_da_args_t *args)
 	}
 	error = xfs_attr3_leaf_getvalue(bp, args);
 	xfs_trans_brelse(args->trans, bp);
-	if (!error && (args->rmtblkno > 0) && !(args->flags & ATTR_KERNOVAL)) {
-		error = xfs_attr_rmtval_get(args);
-	}
-	return error;
+	if (error)
+		return error;
+
+	/* check if we have to retrieve a remote attribute to get the value */
+	if (args->flags & ATTR_KERNOVAL)
+		return 0;
+	if (!args->rmtblkno)
+		return 0;
+	return xfs_attr_rmtval_get(args);
 }
 
 /*========================================================================

@@ -1268,11 +1278,13 @@ xfs_attr_refillstate(xfs_da_state_t *state)
 }
 
 /*
- * Look up a filename in a node attribute list.
+ * Retreive the attribute data from a node attribute list.
  *
  * This routine gets called for any attribute fork that has more than one
  * block, ie: both true Btree attr lists and for single-leaf-blocks with
  * "remote" values taking up more blocks.
+ *
+ * Returns 0 on successful retrieval, otherwise an error.
  */
 STATIC int
 xfs_attr_node_get(xfs_da_args_t *args)

Quoted 3 lines · Dave Chinner

fs/xfs/libxfs/xfs_attr.c +0 -0

@@ -1289,29 +1301,32 @@ xfs_attr_node_get(xfs_da_args_t *args)
 	state->mp = args->dp->i_mount;
 

fs/xfs/libxfs/xfs_attr.c xfs_attr_node_get(xfs_da_args_t *args) · line 1308

Quoted 7 lines

fs/xfs/libxfs/xfs_attr.c +1 -1

 	/*
-	 * Search to see if name exists, and get back a pointer to it.
+	  Search to see if name exists, and get back a pointer to it.
 	 */
 	error = xfs_da3_node_lookup_int(state, &retval);
 	if (error) {
 		retval = error;

Given that you are cleaning up this mess, can you check if there is any point in the weird xfs_da3_node_lookup_int calling conventions?

It looks like it can return errnos in both the return value and *revtval, and from a quick check it seems like all callers treat them more or less the same.

From: Dave Chinner <[email protected]>

Because we repeat exactly the same code to get the remote attribute value after both calls to xfs_attr3_leaf_getvalue() if it's a remote attr. Just do it in xfs_attr3_leaf_getvalue() so the callers don't have to care about it.

Signed-off-by Dave Chinner <[email protected]>

---
 fs/xfs/libxfs/xfs_attr.c      | 16 +---------------
 fs/xfs/libxfs/xfs_attr_leaf.c | 35 ++++++++++++++++++-----------------
 2 files changed, 19 insertions(+), 32 deletions(-)

fs/xfs/libxfs/xfs_attr.c +1 -15

index 776343c4f22b..5e6b6846e607 100644
@@ -794,15 +794,7 @@ xfs_attr_leaf_get(xfs_da_args_t *args)
 	}
 	error = xfs_attr3_leaf_getvalue(bp, args);
 	xfs_trans_brelse(args->trans, bp);
-	if (error)
-		return error;
-
-	/* check if we have to retrieve a remote attribute to get the value */
-	if (args->flags & ATTR_KERNOVAL)
-		return 0;
-	if (!args->rmtblkno)
-		return 0;
-	return xfs_attr_rmtval_get(args);
+	return error;
 }
 
 /*========================================================================

@@ -1316,12 +1308,6 @@ xfs_attr_node_get(xfs_da_args_t *args)
 	 */
 	blk = &state->path.blk[state->path.active - 1];
 	retval = xfs_attr3_leaf_getvalue(blk->bp, args);
-	if (retval)
-		goto out_release;
-	if (args->flags & ATTR_KERNOVAL)
-		goto out_release;
-	if (args->rmtblkno > 0)
-		retval = xfs_attr_rmtval_get(args);
 
 	/*
 	 * If not in a transaction, we have to release all the buffers.

fs/xfs/libxfs/xfs_attr_leaf.c +18 -17

index d056767b5c53..e325cdbc9818 100644
@@ -2391,25 +2391,26 @@ xfs_attr3_leaf_getvalue(
 		}
 		args->valuelen = valuelen;
 		memcpy(args->value, &name_loc->nameval[args->namelen], valuelen);
-	} else {
-		name_rmt = xfs_attr3_leaf_name_remote(leaf, args->index);
-		ASSERT(name_rmt->namelen == args->namelen);
-		ASSERT(memcmp(args->name, name_rmt->name, args->namelen) == 0);
-		args->rmtvaluelen = be32_to_cpu(name_rmt->valuelen);
-		args->rmtblkno = be32_to_cpu(name_rmt->valueblk);
-		args->rmtblkcnt = xfs_attr3_rmt_blocks(args->dp->i_mount,
-						       args->rmtvaluelen);
-		if (args->flags & ATTR_KERNOVAL) {
-			args->valuelen = args->rmtvaluelen;
-			return 0;
-		}
-		if (args->valuelen < args->rmtvaluelen) {
-			args->valuelen = args->rmtvaluelen;
-			return -ERANGE;
-		}
+		return 0;
+	}
+
+	name_rmt = xfs_attr3_leaf_name_remote(leaf, args->index);
+	ASSERT(name_rmt->namelen == args->namelen);
+	ASSERT(memcmp(args->name, name_rmt->name, args->namelen) == 0);
+	args->rmtvaluelen = be32_to_cpu(name_rmt->valuelen);
+	args->rmtblkno = be32_to_cpu(name_rmt->valueblk);
+	args->rmtblkcnt = xfs_attr3_rmt_blocks(args->dp->i_mount,
+					       args->rmtvaluelen);
+	if (args->flags & ATTR_KERNOVAL) {
 		args->valuelen = args->rmtvaluelen;
+		return 0;
 	}
-	return 0;
+	if (args->valuelen < args->rmtvaluelen) {
+		args->valuelen = args->rmtvaluelen;
+		return -ERANGE;
+	}
+	args->valuelen = args->rmtvaluelen;
+	return xfs_attr_rmtval_get(args);
 }
 
 /*========================================================================

Signature · 1 line

2.23.0.rc1

From: Dave Chinner <[email protected]>

Because we repeat exactly the same code to get the remote attribute value after both calls to xfs_attr3_leaf_getvalue() if it's a remote attr. Just do it in xfs_attr3_leaf_getvalue() so the callers don't have to care about it.

From: Dave Chinner <[email protected]>

When doing file lookups and checking for permissions, we end up in xfs_get_acl() to see if there are any ACLs on the inode. This requires and xattr lookup, and to do that we have to supply a buffer large enough to hold an maximum sized xattr.

On workloads were we are accessing a wide range of cache cold files under memory pressure (e.g. NFS fileservers) we end up spending a lot of time allocating the buffer. The buffer is 64k in length, so is a contiguous multi-page allocation, and if that then fails we fall back to vmalloc(). Hence the allocation here is /expensive/ when we are looking up hundreds of thousands of files a second.

Initial numbers from a bpf trace show average time in xfs_get_acl() is ~32us, with ~19us of that in the memory allocation. Note these are average times, so there are going to be affected by the worst case allocations more than the common fast case...

To avoid this, we could just do a "null" lookup to see if the ACL xattr exists and then only do the allocation if it exists. This, however, optimises the path for the "no ACL present" case at the expense of the "acl present" case. i.e. we can halve the time in xfs_get_acl() for the no acl case (i.e down to ~10-15us), but that then increases the ACL case by 30% (i.e. up to 40-45us).

To solve this and speed up both cases, drive the xattr buffer allocation into the attribute code once we know what the actual xattr length is. For the no-xattr case, we avoid the allocation completely, speeding up that case. For the common ACL case, we'll end up with a fast heap allocation (because it'll be smaller than a page), and only for the rarer "we have a remote xattr" will we have a multi-page allocation occur. Hence the common ACL case will be much faster, too.

Signed-off-by Dave Chinner <[email protected]>

---
 fs/xfs/libxfs/xfs_attr.c      | 42 +++++++++++++---
 fs/xfs/libxfs/xfs_attr.h      |  6 ++-
 fs/xfs/libxfs/xfs_attr_leaf.c | 95 +++++++++++++++++++++--------------
 fs/xfs/libxfs/xfs_da_btree.h  |  4 +-
 fs/xfs/xfs_acl.c              | 16 ++----
 fs/xfs/xfs_ioctl.c            |  2 +-
 fs/xfs/xfs_xattr.c            |  2 +-
 7 files changed, 105 insertions(+), 62 deletions(-)

fs/xfs/libxfs/xfs_attr.c +36 -6

index 5e6b6846e607..99f9e0cf05a6 100644
@@ -118,12 +118,28 @@ xfs_attr_get_ilocked(
 		return xfs_attr_node_get(args);
 }
 
-/* Retrieve an extended attribute by name, and its value. */
+/*
+ * Retrieve an extended attribute by name, and its value if requested.
+ *
+ * If ATTR_KERNOVAL is set in @flags, then the caller does not want the value,
+ * just an indication whether the attribute exists and the size of the value if
+ * it exists. The size is returned in @valuelenp,
+ *
+ * If the attribute is found, but exceeds the size limit set by the caller in
+ * @valuelenp, return -ERANGE with the size of the attribute that was found in
+ * @valuelenp.
+ *
+ * If ATTR_ALLOC is set in @flags, allocate the buffer for the value after
+ * existence of the attribute has been determined. On success, return that
+ * buffer to the caller and leave them to free it. On failure, free any
+ * allocated buffer and ensure the buffer pointer returned to the caller is
+ * null.
+ */
 int
 xfs_attr_get(
 	struct xfs_inode	*ip,
 	const unsigned char	*name,
-	unsigned char		*value,
+	unsigned char		**value,
 	int			*valuelenp,
 	int			flags)
 {

@@ -131,6 +147,8 @@ xfs_attr_get(
 	uint			lock_mode;
 	int			error;
 
+	ASSERT((flags & (ATTR_ALLOC | ATTR_KERNOVAL)) || *value);
+
 	XFS_STATS_INC(ip->i_mount, xs_attr_get);
 
 	if (XFS_FORCED_SHUTDOWN(ip->i_mount))

@@ -140,17 +158,29 @@ xfs_attr_get(
 	if (error)
 		return error;
 
-	args.value = value;
-	args.valuelen = *valuelenp;
 	/* Entirely possible to look up a name which doesn't exist */
 	args.op_flags = XFS_DA_OP_OKNOENT;
+	if (flags & ATTR_ALLOC)
+		args.op_flags |= XFS_DA_OP_ALLOCVAL;
+	else
+		args.value = *value;
+	args.valuelen = *valuelenp;
 
 	lock_mode = xfs_ilock_attr_map_shared(ip);
 	error = xfs_attr_get_ilocked(ip, &args);
 	xfs_iunlock(ip, lock_mode);
-
 	*valuelenp = args.valuelen;
-	return error;
+
+	/* on error, we have to clean up allocated value buffers */
+	if (error) {
+		if (flags & ATTR_ALLOC) {
+			kmem_free(args.value);
+			*value = NULL;
+		}
+		return error;
+	}
+	*value = args.value;
+	return 0;
 }
 
 /*

fs/xfs/libxfs/xfs_attr.h +4 -2

index ff28ebf3b635..94badfa1743e 100644
@@ -37,6 +37,7 @@ struct xfs_attr_list_context;
 #define ATTR_KERNOVAL	0x2000	/* [kernel] get attr size only, not value */
 
 #define ATTR_INCOMPLETE	0x4000	/* [kernel] return INCOMPLETE attr keys */
+#define ATTR_ALLOC	0x8000	/* allocate xattr buffer on demand */
 
 #define XFS_ATTR_FLAGS \
 	{ ATTR_DONTFOLLOW, 	"DONTFOLLOW" }, \

@@ -47,7 +48,8 @@ struct xfs_attr_list_context;
 	{ ATTR_REPLACE,		"REPLACE" }, \
 	{ ATTR_KERNOTIME,	"KERNOTIME" }, \
 	{ ATTR_KERNOVAL,	"KERNOVAL" }, \
-	{ ATTR_INCOMPLETE,	"INCOMPLETE" }
+	{ ATTR_INCOMPLETE,	"INCOMPLETE" }, \
+	{ ATTR_ALLOC,		"ALLOC" }
 
 /*
  * The maximum size (into the kernel or returned from the kernel) of an

@@ -143,7 +145,7 @@ int xfs_attr_list_int(struct xfs_attr_list_context *);
 int xfs_inode_hasattr(struct xfs_inode *ip);
 int xfs_attr_get_ilocked(struct xfs_inode *ip, struct xfs_da_args *args);
 int xfs_attr_get(struct xfs_inode *ip, const unsigned char *name,
-		 unsigned char *value, int *valuelenp, int flags);
+		 unsigned char **value, int *valuelenp, int flags);
 int xfs_attr_set(struct xfs_inode *dp, const unsigned char *name,
 		 unsigned char *value, int valuelen, int flags);
 int xfs_attr_set_args(struct xfs_da_args *args);

fs/xfs/libxfs/xfs_attr_leaf.c +56 -39

index e325cdbc9818..fe3c164d5cfe 100644
@@ -393,6 +393,51 @@ xfs_attr_namesp_match(int arg_flags, int ondisk_flags)
 	return XFS_ATTR_NSP_ONDISK(ondisk_flags) == XFS_ATTR_NSP_ARGS_TO_ONDISK(arg_flags);
 }
 
+static int
+xfs_attr_copy_value(
+	struct xfs_da_args	*args,
+	unsigned char		*value,
+	int			valuelen)
+{
+	/*
+	 * No copy if all we have to do is get the length
+	 */
+	if (args->flags & ATTR_KERNOVAL) {
+		args->valuelen = valuelen;
+		return 0;
+	}
+
+	/*
+	 * No copy if the length of the existing buffer is too small
+	 */
+	if (args->valuelen < valuelen) {
+		args->valuelen = valuelen;
+		return -ERANGE;
+	}
+
+	if (args->op_flags & XFS_DA_OP_ALLOCVAL) {
+		args->value = kmem_alloc_large(valuelen, KM_SLEEP);
+		if (!args->value)
+			return -ENOMEM;
+	}
+	args->valuelen = valuelen;
+
+	/* remote block xattr requires IO for copy-in */
+	if (args->rmtblkno)
+		return xfs_attr_rmtval_get(args);
+
+	/*
+	 * This is to prevent a GCC warning because the remote xattr case
+	 * doesn't have a value to pass in. In that case, we never reach here,
+	 * but GCC can't work that out and so throws a "passing NULL to
+	 * memcpy" warning.
+	 */
+	if (!value)
+		return -EINVAL;
+	memcpy(args->value, value, valuelen);
+	return 0;
+}
+
 
 /*========================================================================
  * External routines when attribute fork size < XFS_LITINO(mp).

@@ -727,11 +772,12 @@ xfs_attr_shortform_lookup(xfs_da_args_t *args)
  * exist or we can't retrieve the value.
  */
 int
-xfs_attr_shortform_getvalue(xfs_da_args_t *args)
+xfs_attr_shortform_getvalue(
+	struct xfs_da_args	*args)
 {
-	xfs_attr_shortform_t *sf;
-	xfs_attr_sf_entry_t *sfe;
-	int i;
+	struct xfs_attr_shortform *sf;
+	struct xfs_attr_sf_entry *sfe;
+	int			i;
 
 	ASSERT(args->dp->i_afp->if_flags == XFS_IFINLINE);
 	sf = (xfs_attr_shortform_t *)args->dp->i_afp->if_u1.if_data;

@@ -744,18 +790,8 @@ xfs_attr_shortform_getvalue(xfs_da_args_t *args)
 			continue;
 		if (!xfs_attr_namesp_match(args->flags, sfe->flags))
 			continue;
-		if (args->flags & ATTR_KERNOVAL) {
-			args->valuelen = sfe->valuelen;
-			return 0;
-		}
-		if (args->valuelen < sfe->valuelen) {
-			args->valuelen = sfe->valuelen;
-			return -ERANGE;
-		}
-		args->valuelen = sfe->valuelen;
-		memcpy(args->value, &sfe->nameval[args->namelen],
-						    args->valuelen);
-		return 0;
+		return xfs_attr_copy_value(args, &sfe->nameval[args->namelen],
+						sfe->valuelen);
 	}
 	return -ENOATTR;
 }

@@ -2368,7 +2404,6 @@ xfs_attr3_leaf_getvalue(
 	struct xfs_attr_leaf_entry *entry;
 	struct xfs_attr_leaf_name_local *name_loc;
 	struct xfs_attr_leaf_name_remote *name_rmt;
-	int			valuelen;
 
 	leaf = bp->b_addr;
 	xfs_attr3_leaf_hdr_from_disk(args->geo, &ichdr, leaf);

@@ -2380,18 +2415,9 @@ xfs_attr3_leaf_getvalue(
 		name_loc = xfs_attr3_leaf_name_local(leaf, args->index);
 		ASSERT(name_loc->namelen == args->namelen);
 		ASSERT(memcmp(args->name, name_loc->nameval, args->namelen) == 0);
-		valuelen = be16_to_cpu(name_loc->valuelen);
-		if (args->flags & ATTR_KERNOVAL) {
-			args->valuelen = valuelen;
-			return 0;
-		}
-		if (args->valuelen < valuelen) {
-			args->valuelen = valuelen;
-			return -ERANGE;
-		}
-		args->valuelen = valuelen;
-		memcpy(args->value, &name_loc->nameval[args->namelen], valuelen);
-		return 0;
+		return xfs_attr_copy_value(args,
+					&name_loc->nameval[args->namelen],
+					be16_to_cpu(name_loc->valuelen));
 	}
 
 	name_rmt = xfs_attr3_leaf_name_remote(leaf, args->index);

@@ -2401,16 +2427,7 @@ xfs_attr3_leaf_getvalue(
 	args->rmtblkno = be32_to_cpu(name_rmt->valueblk);
 	args->rmtblkcnt = xfs_attr3_rmt_blocks(args->dp->i_mount,
 					       args->rmtvaluelen);
-	if (args->flags & ATTR_KERNOVAL) {
-		args->valuelen = args->rmtvaluelen;
-		return 0;
-	}
-	if (args->valuelen < args->rmtvaluelen) {
-		args->valuelen = args->rmtvaluelen;
-		return -ERANGE;
-	}
-	args->valuelen = args->rmtvaluelen;
-	return xfs_attr_rmtval_get(args);
+	return xfs_attr_copy_value(args, NULL, args->rmtvaluelen);
 }
 
 /*========================================================================

fs/xfs/libxfs/xfs_da_btree.h +3 -1

index 84dd865b6c3d..ae0bbd20d9ca 100644
@@ -81,13 +81,15 @@ typedef struct xfs_da_args {
 #define XFS_DA_OP_ADDNAME	0x0004	/* this is an add operation */
 #define XFS_DA_OP_OKNOENT	0x0008	/* lookup/add op, ENOENT ok, else die */
 #define XFS_DA_OP_CILOOKUP	0x0010	/* lookup to return CI name if found */
+#define XFS_DA_OP_ALLOCVAL	0x0020	/* lookup to alloc buffer if found  */
 
 #define XFS_DA_OP_FLAGS \
 	{ XFS_DA_OP_JUSTCHECK,	"JUSTCHECK" }, \
 	{ XFS_DA_OP_RENAME,	"RENAME" }, \
 	{ XFS_DA_OP_ADDNAME,	"ADDNAME" }, \
 	{ XFS_DA_OP_OKNOENT,	"OKNOENT" }, \
-	{ XFS_DA_OP_CILOOKUP,	"CILOOKUP" }
+	{ XFS_DA_OP_CILOOKUP,	"CILOOKUP" }, \
+	{ XFS_DA_OP_ALLOCVAL,	"ALLOCVAL" }
 
 /*
  * Storage for holding state during Btree searches and split/join ops.

fs/xfs/xfs_acl.c +4 -12

index cbda40d40326..78c5e590b771 100644
@@ -112,7 +112,7 @@ xfs_get_acl(struct inode *inode, int type)
 {
 	struct xfs_inode *ip = XFS_I(inode);
 	struct posix_acl *acl = NULL;
-	struct xfs_acl *xfs_acl;
+	struct xfs_acl *xfs_acl = NULL;
 	unsigned char *ea_name;
 	int error;
 	int len;

@@ -130,17 +130,9 @@ xfs_get_acl(struct inode *inode, int type)
 		BUG();
 	}
 
-	/*
-	 * If we have a cached ACLs value just return it, not need to
-	 * go out to the disk.
-	 */
 	len = XFS_ACL_MAX_SIZE(ip->i_mount);
-	xfs_acl = kmem_zalloc_large(len, KM_SLEEP);
-	if (!xfs_acl)
-		return ERR_PTR(-ENOMEM);
-
-	error = xfs_attr_get(ip, ea_name, (unsigned char *)xfs_acl,
-							&len, ATTR_ROOT);
+	error = xfs_attr_get(ip, ea_name, (unsigned char **)&xfs_acl, &len,
+				ATTR_ALLOC|ATTR_ROOT);
 	if (error) {
 		/*
 		 * If the attribute doesn't exist make sure we have a negative

@@ -151,8 +143,8 @@ xfs_get_acl(struct inode *inode, int type)
 	} else  {
 		acl = xfs_acl_from_disk(xfs_acl, len,
 					XFS_ACL_MAX_ENTRIES(ip->i_mount));
+		kmem_free(xfs_acl);
 	}
-	kmem_free(xfs_acl);
 	return acl;
 }
 

fs/xfs/xfs_ioctl.c +1 -1

index 6f7848cd5527..5f73feb40384 100644
@@ -438,7 +438,7 @@ xfs_attrmulti_attr_get(
 	if (!kbuf)
 		return -ENOMEM;
 
-	error = xfs_attr_get(XFS_I(inode), name, kbuf, (int *)len, flags);
+	error = xfs_attr_get(XFS_I(inode), name, &kbuf, (int *)len, flags);
 	if (error)
 		goto out_kfree;
 

fs/xfs/xfs_xattr.c +1 -1

index 3123b5aaad2a..cb895b1df5e4 100644
@@ -30,7 +30,7 @@ xfs_xattr_get(const struct xattr_handler *handler, struct dentry *unused,
 		value = NULL;
 	}
 
-	error = xfs_attr_get(ip, (unsigned char *)name, value, &asize, xflags);
+	error = xfs_attr_get(ip, name, (unsigned char **)&value, &asize, xflags);
 	if (error)
 		return error;
 	return asize;

Signature · 1 line

2.23.0.rc1

+ * If ATTR_ALLOC is set in @flags, allocate the buffer for the value after
+ * existence of the attribute has been determined. On success, return that
+ * buffer to the caller and leave them to free it. On failure, free any
+ * allocated buffer and ensure the buffer pointer returned to the caller is
+ * null.

fs/xfs/libxfs/xfs_attr_leaf.c +18 -0

+static int
+xfs_attr_copy_value(
+	struct xfs_da_args	*args,
+	unsigned char		*value,
+	int			valuelen)
+{
+	/*
+	 * No copy if all we have to do is get the length
+	 */
+	if (args->flags & ATTR_KERNOVAL) {
+		args->valuelen = valuelen;
+		return 0;
+	}
+
+	/*
+	 * No copy if the length of the existing buffer is too small
+	 */
+	if (args->valuelen < valuelen) {

fs/xfs/libxfs/xfs_attr_leaf.c +5 -0

+	/* remote block xattr requires IO for copy-in */
+	if (args->rmtblkno)
+		return xfs_attr_rmtval_get(args);
+
+	/*

Quoted 5 lines · Dave Chinner

+ * If ATTR_ALLOC is set in @flags, allocate the buffer for the value after
+ * existence of the attribute has been determined. On success, return that
+ * buffer to the caller and leave them to free it. On failure, free any
+ * allocated buffer and ensure the buffer pointer returned to the caller is
+ * null.

Given that all three callers pass ATTR_ALLOC, do we even need a flag

and keep the old behavior around, at least at the xfs_attr_get level? For the lower level we still have scrub, but that fills out the args structure directly.

Quoted 24 lines

fs/xfs/libxfs/xfs_attr_leaf.c +24 -0

+static int
+xfs_attr_copy_value(
+	struct xfs_da_args	*args,
+	unsigned char		*value,
+	int			valuelen)
+{
+	/*
+	 * No copy if all we have to do is get the length
+	 */
+	if (args->flags & ATTR_KERNOVAL) {
+		args->valuelen = valuelen;
+		return 0;
+	}
+
+	/*
+	 * No copy if the length of the existing buffer is too small
+	 */
+	if (args->valuelen < valuelen) {
+		args->valuelen = valuelen;
+		return -ERANGE;
+	}
+
+	if (args->op_flags & XFS_DA_OP_ALLOCVAL) {
+		args->value = kmem_alloc_large(valuelen, KM_SLEEP);

fs/xfs/libxfs/xfs_attr_leaf.c xfs_attr_namesp_match(int arg_flags, int ondisk_flags) · line 423

Quoted 4 lines

fs/xfs/libxfs/xfs_attr_leaf.c +4 -0

+		if (!args->value)
+			return -ENOMEM;
+	}
+	args->valuelen = valuelen;

Can't we just move the setting of ->valuelen up to common code shared between all the branches? That means it would also be set on an allocation error, but that should be harmless.

Quoted 11 lines

fs/xfs/libxfs/xfs_attr_leaf.c +11 -0

+	/* remote block xattr requires IO for copy-in */
+	if (args->rmtblkno)
+		return xfs_attr_rmtval_get(args);
+
+	/*
+	 * This is to prevent a GCC warning because the remote xattr case
+	 * doesn't have a value to pass in. In that case, we never reach here,
+	 * but GCC can't work that out and so throws a "passing NULL to
+	 * memcpy" warning.
+	 */
+	if (!value)

fs/xfs/libxfs/xfs_attr_leaf.c xfs_attr_namesp_match(int arg_flags, int ondisk_flags) · line 439

Quoted 4 lines

fs/xfs/libxfs/xfs_attr_leaf.c +4 -0

+		return -EINVAL;
+	memcpy(args->value, value, valuelen);
+	return 0;
+}

Can you split creating this helper into a separate prep patch? While not strictly required it would make reviewing what is consolidation vs what is new code for the on-demand buffer allocation a little easier.

fs/xfs/xfs_acl.c xfs_get_acl(struct inode *inode, int type) · line 135

Quoted 2 lines

fs/xfs/xfs_acl.c +2 -0

+	error = xfs_attr_get(ip, ea_name, (unsigned char **)&xfs_acl, &len,
+				ATTR_ALLOC|ATTR_ROOT);

Please keep space between the symbols and | on each side.

Quoted 1 line

Given that all three callers pass ATTR_ALLOC, do we even need a flag

Only one caller passes ATTR_ALLOC - the ACL code. The other two have their own buffers that are supplied....

Can't overwrite args->valuelen until we've done the ERANGE check. Sure, I could put it in a local variable, but that doesn't reduce the amount of code, or make it obvious that we intentionally return the attribute size when the supplied buffer it too small...