[PATCH v3 14/28] xfs: add XFS_DA_OP_BUFFER to make xfs_attr_get() return buffer

[Andrey Albershteyn <aalbersh@redhat.com>]

With XBF_VERITY_CHECKED flag on xfs_buf XFS can track which buffers
contain verified Merkle tree blocks. However, we also need to expose
the buffer to pass a reference of underlying page to fs-verity.

This patch adds XFS_DA_OP_BUFFER to tell xfs_attr_get() to
xfs_buf_hold() underlying buffer and return it as xfs_da_args->bp.
The caller must then xfs_buf_rele() the buffer. Therefore, XFS will
hold a reference to xfs_buf till fs-verity is verifying xfs_buf's
content.

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
---
 fs/xfs/libxfs/xfs_attr.c        |  5 ++++-
 fs/xfs/libxfs/xfs_attr_leaf.c   |  7 +++++++
 fs/xfs/libxfs/xfs_attr_remote.c | 13 +++++++++++--
 fs/xfs/libxfs/xfs_da_btree.h    |  5 ++++-
 4 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index 711022742e34..298b74245267 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -251,6 +251,8 @@ xfs_attr_get_ilocked(
  * If the attribute is found, but exceeds the size limit set by the caller in
  * args->valuelen, return -ERANGE with the size of the attribute that was found
  * in args->valuelen.
+ *
+ * Using XFS_DA_OP_BUFFER the caller have to release the buffer args->bp.
  */
 int
 xfs_attr_get(
@@ -269,7 +271,8 @@ xfs_attr_get(
 	args->hashval = xfs_da_hashname(args->name, args->namelen);
 
 	/* Entirely possible to look up a name which doesn't exist */
-	args->op_flags = XFS_DA_OP_OKNOENT;
+	args->op_flags = XFS_DA_OP_OKNOENT |
+					(args->op_flags & XFS_DA_OP_BUFFER);
 
 	lock_mode = xfs_ilock_attr_map_shared(args->dp);
 	error = xfs_attr_get_ilocked(args);
diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
index 2580ae47209a..a84795d70de1 100644
--- a/fs/xfs/libxfs/xfs_attr_leaf.c
+++ b/fs/xfs/libxfs/xfs_attr_leaf.c
@@ -2531,6 +2531,13 @@ 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);
+
+		/* must be released by the caller */
+		if (args->op_flags & XFS_DA_OP_BUFFER) {
+			xfs_buf_hold(bp);
+			args->bp = bp;
+		}
+
 		return xfs_attr_copy_value(args,
 					&name_loc->nameval[args->namelen],
 					be16_to_cpu(name_loc->valuelen));
diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
index d440393b40eb..72908e0e1c86 100644
--- a/fs/xfs/libxfs/xfs_attr_remote.c
+++ b/fs/xfs/libxfs/xfs_attr_remote.c
@@ -424,9 +424,18 @@ xfs_attr_rmtval_get(
 			error = xfs_attr_rmtval_copyout(mp, bp, args->dp->i_ino,
 							&offset, &valuelen,
 							&dst);
-			xfs_buf_relse(bp);
-			if (error)
+			xfs_buf_unlock(bp);
+			/* must be released by the caller */
+			if (args->op_flags & XFS_DA_OP_BUFFER)
+				args->bp = bp;
+			else
+				xfs_buf_rele(bp);
+
+			if (error) {
+				if (args->op_flags & XFS_DA_OP_BUFFER)
+					xfs_buf_rele(args->bp);
 				return error;
+			}
 
 			/* roll attribute extent map forwards */
 			lblkno += map[i].br_blockcount;
diff --git a/fs/xfs/libxfs/xfs_da_btree.h b/fs/xfs/libxfs/xfs_da_btree.h
index a4b29827603f..269d26730bca 100644
--- a/fs/xfs/libxfs/xfs_da_btree.h
+++ b/fs/xfs/libxfs/xfs_da_btree.h
@@ -61,6 +61,7 @@ typedef struct xfs_da_args {
 	uint8_t		filetype;	/* filetype of inode for directories */
 	void		*value;		/* set of bytes (maybe contain NULLs) */
 	int		valuelen;	/* length of value */
+	struct xfs_buf	*bp;		/* OUT: xfs_buf which contains the attr */
 	unsigned int	attr_filter;	/* XFS_ATTR_{ROOT,SECURE,INCOMPLETE} */
 	unsigned int	attr_flags;	/* XATTR_{CREATE,REPLACE} */
 	xfs_dahash_t	hashval;	/* hash value of name */
@@ -95,6 +96,7 @@ typedef struct xfs_da_args {
 #define XFS_DA_OP_REMOVE	(1u << 6) /* this is a remove operation */
 #define XFS_DA_OP_RECOVERY	(1u << 7) /* Log recovery operation */
 #define XFS_DA_OP_LOGGED	(1u << 8) /* Use intent items to track op */
+#define XFS_DA_OP_BUFFER	(1u << 9) /* Return underlying buffer */
 
 #define XFS_DA_OP_FLAGS \
 	{ XFS_DA_OP_JUSTCHECK,	"JUSTCHECK" }, \
@@ -105,7 +107,8 @@ typedef struct xfs_da_args {
 	{ XFS_DA_OP_NOTIME,	"NOTIME" }, \
 	{ XFS_DA_OP_REMOVE,	"REMOVE" }, \
 	{ XFS_DA_OP_RECOVERY,	"RECOVERY" }, \
-	{ XFS_DA_OP_LOGGED,	"LOGGED" }
+	{ XFS_DA_OP_LOGGED,	"LOGGED" }, \
+	{ XFS_DA_OP_BUFFER,	"BUFFER" }
 
 /*
  * Storage for holding state during Btree searches and split/join ops.
-- 
2.40.1