[Qemu-devel] [RFC PATCH v1 4/5] pc-bios/s390-ccw: Break up virtio-scsi read into multiples

[Eric Farman <farman@linux.vnet.ibm.com>]

A virtio-scsi request that goes through the host sd driver and
exceeds the maximum transfer size is automatically broken up
for us. But the equivalent request going to the sg driver
presumes that any length requirements have already been honored.
Let's use the max_sectors field from the device and break up
all virtio-scsi requests (both sd and sg) to avoid problem from
the host drivers.

Signed-off-by: Eric Farman <farman@linux.vnet.ibm.com>
---
 pc-bios/s390-ccw/s390-ccw.h    |  4 ++++
 pc-bios/s390-ccw/virtio-scsi.c | 19 ++++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
index ded67bc..e1f3751 100644
--- a/pc-bios/s390-ccw/s390-ccw.h
+++ b/pc-bios/s390-ccw/s390-ccw.h
@@ -42,6 +42,10 @@ typedef unsigned long long __u64;
 #ifndef NULL
 #define NULL    0
 #endif
+#ifndef MIN
+#define MIN(a, b) (((a) < (b)) ? (a) : (b));
+#endif
+
 
 #include "cio.h"
 #include "iplb.h"
diff --git a/pc-bios/s390-ccw/virtio-scsi.c b/pc-bios/s390-ccw/virtio-scsi.c
index 6d070e2..90a8cc8 100644
--- a/pc-bios/s390-ccw/virtio-scsi.c
+++ b/pc-bios/s390-ccw/virtio-scsi.c
@@ -254,12 +254,21 @@ static void virtio_scsi_locate_device(VDev *vdev)
 int virtio_scsi_read_many(VDev *vdev,
                           ulong sector, void *load_addr, int sec_num)
 {
+    int sector_count;
     int f = vdev->blk_factor;
-    unsigned int data_size = sec_num * virtio_get_block_size() * f;
-
-    if (!scsi_read_10(vdev, sector * f, sec_num * f, load_addr, data_size)) {
-        virtio_scsi_verify_response(&resp, "virtio-scsi:read_many");
-    }
+    unsigned int data_size;
+
+    do {
+        sector_count = MIN(sec_num, vdev->config.scsi.max_sectors);
+        data_size = sector_count * virtio_get_block_size() * f;
+        if (!scsi_read_10(vdev, sector * f, sector_count * f, load_addr,
+                          data_size)) {
+            virtio_scsi_verify_response(&resp, "virtio-scsi:read_many");
+        }
+        load_addr += data_size;
+        sector += sector_count;
+        sec_num -= sector_count;
+    } while (sec_num > 0);
 
     return 0;
 }
-- 
2.10.2