[PATCH v2 12/14] fs: 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 | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index a0d77f5f512e..6316448083d2 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -546,6 +546,37 @@ 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)
+{
+	xfs_extlen_t		extsz = xfs_get_extsz(ip);
+	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
+	struct block_device	*bdev = target->bt_bdev;
+	struct request_queue	*q = bdev->bd_queue;
+	struct xfs_mount	*mp = ip->i_mount;
+	struct xfs_sb		*sbp = &mp->m_sb;
+	unsigned int		awu_min, awu_max;
+	unsigned int		extsz_bytes = XFS_FSB_TO_B(mp, extsz);
+
+	awu_min = queue_atomic_write_unit_min_bytes(q);
+	awu_max = queue_atomic_write_unit_max_bytes(q);
+
+	if (sbp->sb_blocksize > awu_max || awu_min > sbp->sb_blocksize ||
+	    !xfs_inode_atomicwrites(ip)) {
+		*unit_min = 0;
+		*unit_max = 0;
+		return;
+	}
+
+	/* Floor at FS block size */
+	*unit_min = max(sbp->sb_blocksize, awu_min);
+
+	*unit_max = min(extsz_bytes, awu_max);
+}
+
 STATIC int
 xfs_vn_getattr(
 	struct mnt_idmap	*idmap,
@@ -619,6 +650,13 @@ 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