[PATCH RFC 01/10] xfs: Switch atomic write size check in xfs_file_write_iter()

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

Currently the size of atomic write allowed is fixed at the blocksize.

To start to lift this restriction, refactor xfs_get_atomic_write_attr()
to into a helper - xfs_report_atomic_write() - and use that helper to
find the per-inode atomic write limits and check according to that.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 fs/xfs/xfs_file.c | 12 +++++-------
 fs/xfs/xfs_iops.c | 20 +++++++++++++++++---
 fs/xfs/xfs_iops.h |  3 +++
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index f7a7d89c345e..fd05b66aea3f 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -853,14 +853,12 @@ xfs_file_write_iter(
 		return xfs_file_dax_write(iocb, from);
 
 	if (iocb->ki_flags & IOCB_ATOMIC) {
-		/*
-		 * Currently only atomic writing of a single FS block is
-		 * supported. It would be possible to atomic write smaller than
-		 * a FS block, but there is no requirement to support this.
-		 * Note that iomap also does not support this yet.
-		 */
-		if (ocount != ip->i_mount->m_sb.sb_blocksize)
+		unsigned int unit_min, unit_max;
+
+		xfs_get_atomic_write_attr(ip, &unit_min, &unit_max);
+		if (ocount < unit_min || ocount > unit_max)
 			return -EINVAL;
+
 		ret = generic_atomic_write_valid(iocb, from);
 		if (ret)
 			return ret;
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 40289fe6f5b2..ea79fb246e33 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -600,15 +600,29 @@ xfs_report_dioalign(
 		stat->dio_offset_align = stat->dio_read_offset_align;
 }
 
+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 void
 xfs_report_atomic_write(
 	struct xfs_inode	*ip,
 	struct kstat		*stat)
 {
-	unsigned int		unit_min = 0, unit_max = 0;
+	unsigned int		unit_min, unit_max;
+
+	xfs_get_atomic_write_attr(ip, &unit_min, &unit_max);
 
-	if (xfs_inode_can_atomicwrite(ip))
-		unit_min = unit_max = ip->i_mount->m_sb.sb_blocksize;
 	generic_fill_statx_atomic_writes(stat, unit_min, unit_max);
 }
 
diff --git a/fs/xfs/xfs_iops.h b/fs/xfs/xfs_iops.h
index 3c1a2605ffd2..ce7bdeb9a79c 100644
--- a/fs/xfs/xfs_iops.h
+++ b/fs/xfs/xfs_iops.h
@@ -19,5 +19,8 @@ int xfs_inode_init_security(struct inode *inode, struct inode *dir,
 extern void xfs_setup_inode(struct xfs_inode *ip);
 extern void xfs_setup_iops(struct xfs_inode *ip);
 extern void xfs_diflags_to_iflags(struct xfs_inode *ip, bool init);
+void xfs_get_atomic_write_attr(struct xfs_inode *ip,
+		unsigned int *unit_min, unsigned int *unit_max);
+
 
 #endif /* __XFS_IOPS_H__ */
-- 
2.31.1