[Qemu-devel] [PATCH] scsi-disk: Don't enlarge min_io_size to max_io_size

[Fam Zheng <famz@redhat.com>]

Some backends report big max_io_sectors. Making min_io_size the same
value in this case will make it impossible for guest to align memory,
therefore the disk may not be usable at all.

Change the default behavior (when min_io_size and opt_io_size are not
specified in the command line), do not assume max_io_sectors is a good
value for opt_io_size and min_io_size, use 512 instead.

Reported-by: David Gibson <dgibson@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 hw/scsi/scsi-disk.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 5b7a48f5a5..76e3c9eaa4 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -714,10 +714,8 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, uint8_t *outbuf)
 
                 /* min_io_size and opt_io_size can't be greater than
                  * max_io_sectors */
-                min_io_size =
-                    MIN_NON_ZERO(min_io_size, max_io_sectors);
-                opt_io_size =
-                    MIN_NON_ZERO(opt_io_size, max_io_sectors);
+                min_io_size = MIN(min_io_size ? : 512, max_io_sectors);
+                opt_io_size = MIN(opt_io_size ? : 512, max_io_sectors);
             }
             /* required VPD size with unmap support */
             buflen = 0x40;
-- 
2.14.3