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@kernel.org>
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 fs/xfs/xfs_inode.h | 17 +++++++++++++++++
 fs/xfs/xfs_iops.c  | 25 +++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 1c62ee294a5a..1ea73402d592 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -332,6 +332,23 @@ static inline bool xfs_inode_has_atomicwrites(struct xfs_inode *ip)
 	return ip->i_diflags2 & XFS_DIFLAG2_ATOMICWRITES;
 }
 
+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 (!xfs_inode_has_atomicwrites(ip))
+		return false;
+	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