1 files changed, 79 insertions, 1 deletions

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 86089e27b8e7..29276fe60df9 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -742,6 +742,82 @@ xfs_calc_atomic_write_unit_max(
 			max_agsize, max_rgsize);
 }
 
+/*
+ * Try to set the atomic write maximum to a new value that we got from
+ * userspace via mount option.
+ */
+int
+xfs_set_max_atomic_write_opt(
+	struct xfs_mount	*mp,
+	unsigned long long	new_max_bytes)
+{
+	const xfs_filblks_t	new_max_fsbs = XFS_B_TO_FSBT(mp, new_max_bytes);
+	const xfs_extlen_t	max_write = xfs_calc_atomic_write_max(mp);
+	const xfs_extlen_t	max_group =
+		max(mp->m_groups[XG_TYPE_AG].blocks,
+		    mp->m_groups[XG_TYPE_RTG].blocks);
+	const xfs_extlen_t	max_group_write =
+		max(xfs_calc_perag_awu_max(mp), xfs_calc_rtgroup_awu_max(mp));
+	int			error;
+
+	if (new_max_bytes == 0)
+		goto set_limit;
+
+	ASSERT(max_write <= U32_MAX);
+
+	/* generic_atomic_write_valid enforces power of two length */
+	if (!is_power_of_2(new_max_bytes)) {
+		xfs_warn(mp,
+ "max atomic write size of %llu bytes is not a power of 2",
+				new_max_bytes);
+		return -EINVAL;
+	}
+
+	if (new_max_bytes & mp->m_blockmask) {
+		xfs_warn(mp,
+ "max atomic write size of %llu bytes not aligned with fsblock",
+				new_max_bytes);
+		return -EINVAL;
+	}
+
+	if (new_max_fsbs > max_write) {
+		xfs_warn(mp,
+ "max atomic write size of %lluk cannot be larger than max write size %lluk",
+				new_max_bytes >> 10,
+				XFS_FSB_TO_B(mp, max_write) >> 10);
+		return -EINVAL;
+	}
+
+	if (new_max_fsbs > max_group) {
+		xfs_warn(mp,
+ "max atomic write size of %lluk cannot be larger than allocation group size %lluk",
+				new_max_bytes >> 10,
+				XFS_FSB_TO_B(mp, max_group) >> 10);
+		return -EINVAL;
+	}
+
+	if (new_max_fsbs > max_group_write) {
+		xfs_warn(mp,
+ "max atomic write size of %lluk cannot be larger than max allocation group write size %lluk",
+				new_max_bytes >> 10,
+				XFS_FSB_TO_B(mp, max_group_write) >> 10);
+		return -EINVAL;
+	}
+
+set_limit:
+	error = xfs_calc_atomic_write_reservation(mp, new_max_fsbs);
+	if (error) {
+		xfs_warn(mp,
+ "cannot support completing atomic writes of %lluk",
+				new_max_bytes >> 10);
+		return error;
+	}
+
+	xfs_calc_atomic_write_unit_max(mp);
+	mp->m_awu_max_bytes = new_max_bytes;
+	return 0;
+}
+
 /* Compute maximum possible height for realtime btree types for this fs. */
 static inline void
 xfs_rtbtree_compute_maxlevels(
@@ -1163,7 +1239,9 @@ xfs_mountfs(
 	 * derived from transaction reservations, so we must do this after the
 	 * log is fully initialized.
 	 */
-	xfs_calc_atomic_write_unit_max(mp);
+	error = xfs_set_max_atomic_write_opt(mp, mp->m_awu_max_bytes);
+	if (error)
+		goto out_agresv;
 
 	return 0;