[PATCH v8 5/7] xfs: Support atomic write for statx

[John Garry]

Support providing info on atomic write unit min and max for an inode.

For simplicity, currently we limit the min at the FS block size. As for
max, we limit also at FS block size, as there is no current method to
guarantee extent alignment or granularity for regular files.

Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 fs/xfs/xfs_buf.c   |  7 +++++++
 fs/xfs/xfs_buf.h   |  3 +++
 fs/xfs/xfs_inode.h | 15 +++++++++++++++
 fs/xfs/xfs_iops.c  | 25 +++++++++++++++++++++++++
 4 files changed, 50 insertions(+)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index aa4dbda7b536..e279e5e139ff 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -2115,6 +2115,13 @@ xfs_alloc_buftarg(
 	btp->bt_daxdev = fs_dax_get_by_bdev(btp->bt_bdev, &btp->bt_dax_part_off,
 					    mp, ops);
 
+	if (bdev_can_atomic_write(btp->bt_bdev)) {
+		struct request_queue *q = bdev_get_queue(btp->bt_bdev);
+
+		btp->bt_bdev_awu_min = queue_atomic_write_unit_min_bytes(q);
+		btp->bt_bdev_awu_max = queue_atomic_write_unit_max_bytes(q);
+	}
+
 	/*
 	 * When allocating the buftargs we have not yet read the super block and
 	 * thus don't know the file system sector size yet.
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 209a389f2abc..2be28bd01087 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -124,6 +124,9 @@ struct xfs_buftarg {
 	struct percpu_counter	bt_io_count;
 	struct ratelimit_state	bt_ioerror_rl;
 
+	/* Atomic write unit values */
+	unsigned int		bt_bdev_awu_min, bt_bdev_awu_max;
+
 	/* built-in cache, if we're not using the perag one */
 	struct xfs_buf_cache	bt_cache[];
 };
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 97ed912306fd..73009a25a119 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -327,6 +327,21 @@ static inline bool xfs_inode_has_bigrtalloc(struct xfs_inode *ip)
 	(XFS_IS_REALTIME_INODE(ip) ? \
 		(ip)->i_mount->m_rtdev_targp : (ip)->i_mount->m_ddev_targp)
 
+static inline bool
+xfs_inode_can_atomicwrite(
+	struct xfs_inode	*ip)
+{
+	struct xfs_mount	*mp = ip->i_mount;
+	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
+
+	if (mp->m_sb.sb_blocksize < target->bt_bdev_awu_min)
+		return false;
+	if (mp->m_sb.sb_blocksize > target->bt_bdev_awu_max)
+		return false;
+
+	return true;
+}
+
 /*
  * In-core inode flags.
  */
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index ee79cf161312..919fbcb4b72a 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -570,6 +570,23 @@ xfs_stat_blksize(
 	return max_t(uint32_t, PAGE_SIZE, mp->m_sb.sb_blocksize);
 }
 
+static void
+xfs_get_atomic_write_attr(
+	struct xfs_inode	*ip,
+	unsigned int		*unit_min,
+	unsigned int		*unit_max)
+{
+	struct xfs_mount	*mp = ip->i_mount;
+	struct xfs_sb		*sbp = &mp->m_sb;
+
+	if (!xfs_inode_can_atomicwrite(ip)) {
+		*unit_min = *unit_max = 0;
+		return;
+	}
+
+	*unit_min = *unit_max = sbp->sb_blocksize;
+}
+
 STATIC int
 xfs_vn_getattr(
 	struct mnt_idmap	*idmap,
@@ -643,6 +660,14 @@ xfs_vn_getattr(
 			stat->dio_mem_align = bdev_dma_alignment(bdev) + 1;
 			stat->dio_offset_align = bdev_logical_block_size(bdev);
 		}
+		if (request_mask & STATX_WRITE_ATOMIC) {
+			unsigned int unit_min, unit_max;
+
+			xfs_get_atomic_write_attr(ip, &unit_min,
+					&unit_max);
+			generic_fill_statx_atomic_writes(stat,
+					unit_min, unit_max);
+		}
 		fallthrough;
 	default:
 		stat->blksize = xfs_stat_blksize(ip);
-- 
2.31.1