xfs: Support atomic write for statx

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" <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: John Garry <[email protected]>
Signed-off-by: Darrick J. Wong <[email protected]>

Author: johnpgarry

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)) {
+		btp->bt_bdev_awu_min = bdev_atomic_write_unit_min_bytes(
+						btp->bt_bdev);
+		btp->bt_bdev_awu_max = bdev_atomic_write_unit_max_bytes(
+						btp->bt_bdev);
+	}
+
 	/*
 	 * When allocating the buftargs we have not yet read the super block and
 	 * thus don't know the file system sector size yet.

fs/xfs/xfs_buf.h

@@ -124,6 +124,10 @@ 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;
+	unsigned int		bt_bdev_awu_max;
+
 	/* built-in cache, if we're not using the perag one */
 	struct xfs_buf_cache	bt_cache[];
 };

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.
  */

fs/xfs/xfs_iops.c

@@ -570,6 +570,20 @@ 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)
+{
+	if (!xfs_inode_can_atomicwrite(ip)) {
+		*unit_min = *unit_max = 0;
+		return;
+	}
+
+	*unit_min = *unit_max = ip->i_mount->m_sb.sb_blocksize;
+}
+
 STATIC int
 xfs_vn_getattr(
 	struct mnt_idmap	*idmap,
@@ -643,6 +657,14 @@ 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);