[PATCH v4 20/22] xfs: Support atomic write for statx

[John Garry <john.g.garry@oracle.com>]

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, but a
lower limit could be supported in future. This is required by iomap
DIO.

The atomic write unit min and max is limited by the guaranteed extent
alignment for the inode.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 fs/xfs/xfs_iops.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index ff222827e550..d4c957793e07 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -563,6 +563,27 @@ xfs_stat_blksize(
 	return PAGE_SIZE;
 }
 
+static void
+xfs_get_atomic_write_attr(
+	struct xfs_inode	*ip,
+	unsigned int		*unit_min,
+	unsigned int		*unit_max)
+{
+	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
+	struct xfs_mount	*mp = ip->i_mount;
+	struct xfs_sb		*sbp = &mp->m_sb;
+	unsigned int		extsz_bytes = XFS_FSB_TO_B(mp, ip->i_extsize);
+
+	if (!xfs_inode_has_atomicwrites(ip)) {
+		*unit_min = 0;
+		*unit_max = 0;
+		return;
+	}
+
+	*unit_min = sbp->sb_blocksize;
+	*unit_max = min(target->bt_bdev_awu_max, extsz_bytes);
+}
+
 STATIC int
 xfs_vn_getattr(
 	struct mnt_idmap	*idmap,
@@ -636,6 +657,13 @@ 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