[PATCH v4 16/25] xfs: add XBF_DOUBLE_ALLOC to increase size of the buffer

[Andrey Albershteyn <aalbersh@redhat.com>]

For fs-verity integration, XFS needs to supply kaddr'es of Merkle
tree blocks to fs-verity core and track which blocks are already
verified. One way to track verified status is to set xfs_buf flag
(previously added XBF_VERITY_SEEN). When xfs_buf is evicted from
memory we loose verified status. Otherwise, fs-verity hits the
xfs_buf which is still in cache and contains already verified blocks.

However, the leaf blocks which are read to the xfs_buf contains leaf
headers. xfs_attr_get() allocates new pages and copies out the data
without header. Those newly allocated pages with extended attribute
data are not attached to the buffer anymore.

Add new XBF_DOUBLE_ALLOC which makes xfs_buf allocates x2 memory for
the buffer. Additional memory will be used for a copy of the
attribute data but without any headers. Also, make
xfs_attr_rmtval_get() to copy data to the buffer itself if XFS asked
for fs-verity block.

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
---
 fs/xfs/libxfs/xfs_attr_remote.c | 26 ++++++++++++++++++++++++--
 fs/xfs/xfs_buf.c                |  6 +++++-
 fs/xfs/xfs_buf.h                |  2 ++
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
index 5762135dc2a6..1d32041412cc 100644
--- a/fs/xfs/libxfs/xfs_attr_remote.c
+++ b/fs/xfs/libxfs/xfs_attr_remote.c
@@ -392,12 +392,22 @@ xfs_attr_rmtval_get(
 	int			blkcnt = args->rmtblkcnt;
 	int			i;
 	int			offset = 0;
+	int			flags = 0;
+	void			*addr;
 
 	trace_xfs_attr_rmtval_get(args);
 
 	ASSERT(args->valuelen != 0);
 	ASSERT(args->rmtvaluelen == args->valuelen);
 
+	/*
+	 * We also check for _OP_BUFFER as we want to trigger on
+	 * verity blocks only, not on verity_descriptor
+	 */
+	if (args->attr_filter & XFS_ATTR_VERITY &&
+			args->op_flags & XFS_DA_OP_BUFFER)
+		flags = XBF_DOUBLE_ALLOC;
+
 	valuelen = args->rmtvaluelen;
 	while (valuelen > 0) {
 		nmap = ATTR_RMTVALUE_MAPSIZE;
@@ -417,10 +427,21 @@ xfs_attr_rmtval_get(
 			dblkno = XFS_FSB_TO_DADDR(mp, map[i].br_startblock);
 			dblkcnt = XFS_FSB_TO_BB(mp, map[i].br_blockcount);
 			error = xfs_buf_read(mp->m_ddev_targp, dblkno, dblkcnt,
-					0, &bp, &xfs_attr3_rmt_buf_ops);
+					flags, &bp, &xfs_attr3_rmt_buf_ops);
 			if (error)
 				return error;
 
+			/*
+			 * For fs-verity we allocated more space. That space is
+			 * filled with the same xattr data but without leaf
+			 * headers. Point args->value to that data
+			 */
+			if (flags & XBF_DOUBLE_ALLOC) {
+				addr = xfs_buf_offset(bp, BBTOB(bp->b_length));
+				args->value = addr;
+				dst = addr;
+			}
+
 			error = xfs_attr_rmtval_copyout(mp, bp, args->dp->i_ino,
 							&offset, &valuelen,
 							&dst);
@@ -521,7 +542,8 @@ xfs_attr_rmtval_set_value(
 		dblkno = XFS_FSB_TO_DADDR(mp, map.br_startblock),
 		dblkcnt = XFS_FSB_TO_BB(mp, map.br_blockcount);
 
-		error = xfs_buf_get(mp->m_ddev_targp, dblkno, dblkcnt, 0, &bp);
+		error = xfs_buf_get(mp->m_ddev_targp, dblkno, dblkcnt,
+				XBF_DOUBLE_ALLOC, &bp);
 		if (error)
 			return error;
 		bp->b_ops = &xfs_attr3_rmt_buf_ops;
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 8e5bd50d29fe..2645e64f2439 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -328,6 +328,9 @@ xfs_buf_alloc_kmem(
 	xfs_km_flags_t	kmflag_mask = KM_NOFS;
 	size_t		size = BBTOB(bp->b_length);
 
+	if (flags & XBF_DOUBLE_ALLOC)
+		size *= 2;
+
 	/* Assure zeroed buffer for non-read cases. */
 	if (!(flags & XBF_READ))
 		kmflag_mask |= KM_ZERO;
@@ -358,6 +361,7 @@ xfs_buf_alloc_pages(
 {
 	gfp_t		gfp_mask = __GFP_NOWARN;
 	long		filled = 0;
+	int		mul = (bp->b_flags & XBF_DOUBLE_ALLOC) ? 2 : 1;
 
 	if (flags & XBF_READ_AHEAD)
 		gfp_mask |= __GFP_NORETRY;
@@ -365,7 +369,7 @@ xfs_buf_alloc_pages(
 		gfp_mask |= GFP_NOFS;
 
 	/* Make sure that we have a page list */
-	bp->b_page_count = DIV_ROUND_UP(BBTOB(bp->b_length), PAGE_SIZE);
+	bp->b_page_count = DIV_ROUND_UP(BBTOB(bp->b_length*mul), PAGE_SIZE);
 	if (bp->b_page_count <= XB_PAGES) {
 		bp->b_pages = bp->b_page_array;
 	} else {
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 80566ee444f8..8ca8760c401e 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -33,6 +33,7 @@ struct xfs_buf;
 #define XBF_STALE		(1u << 6) /* buffer has been staled, do not find it */
 #define XBF_WRITE_FAIL		(1u << 7) /* async writes have failed on this buffer */
 #define XBF_VERITY_SEEN		(1u << 8) /* buffer was processed by fs-verity */
+#define XBF_DOUBLE_ALLOC	(1u << 9) /* double allocated space */
 
 /* buffer type flags for write callbacks */
 #define _XBF_INODES	 (1u << 16)/* inode buffer */
@@ -67,6 +68,7 @@ typedef unsigned int xfs_buf_flags_t;
 	{ XBF_STALE,		"STALE" }, \
 	{ XBF_WRITE_FAIL,	"WRITE_FAIL" }, \
 	{ XBF_VERITY_SEEN,	"VERITY_SEEN" }, \
+	{ XBF_DOUBLE_ALLOC,	"DOUBLE_ALLOC" }, \
 	{ _XBF_INODES,		"INODES" }, \
 	{ _XBF_DQUOTS,		"DQUOTS" }, \
 	{ _XBF_LOGRECOVERY,	"LOG_RECOVERY" }, \
-- 
2.42.0