[PATCH] mkfs: use a default sector size that is also suitable for the rtdev

[Christoph Hellwig <hch@lst.de>]

When creating a filesytem where the data device has a sector size
smalle than that of the RT device without further options, mkfs
currently fails with:

mkfs.xfs: error - cannot set blocksize 512 on block device $RTDEV: Invalid argument

This is because XFS sets the sector size based on logical block size
of the data device, but not that of the RT device.  Change the code
so that is uses the larger of the two values.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mkfs/xfs_mkfs.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index 6cc7e6439ca1..0627af81da37 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2368,7 +2368,9 @@ validate_sectorsize(
 		 * advertised sector size of the device.  We use the physical
 		 * sector size unless the requested block size is smaller
 		 * than that, then we can use logical, but warn about the
-		 * inefficiency.
+		 * inefficiency.  If the file system has a RT device, the
+		 * sectorsize needs to be the maximum of the data and RT
+		 * device.
 		 *
 		 * Some architectures have a page size > XFS_MAX_SECTORSIZE.
 		 * In that case, a ramdisk or persistent memory device may
@@ -2378,8 +2380,18 @@ validate_sectorsize(
 			ft->data.physical_sector_size =
 				ft->data.logical_sector_size;
 		}
-
 		cfg->sectorsize = ft->data.physical_sector_size;
+
+		if (cli->xi->rt.name) {
+			if (ft->rt.physical_sector_size > XFS_MAX_SECTORSIZE) {
+				ft->rt.physical_sector_size =
+					ft->rt.logical_sector_size;
+			}
+
+			if (cfg->sectorsize < ft->rt.physical_sector_size)
+				cfg->sectorsize = ft->rt.physical_sector_size;
+		}
+
 		if (cfg->blocksize < cfg->sectorsize &&
 		    cfg->blocksize >= ft->data.logical_sector_size) {
 			fprintf(stderr,
-- 
2.45.2