pc-bios/s390-ccw: Break up virtio-scsi read into multiples

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 on the virtio-scsi controller device,
and break up all requests (both sd and sg) to avoid this problem.
Signed-off-by: NEric Farman <farman@linux.vnet.ibm.com>
Message-Id: <20170510155359.32727-4-farman@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

pc-bios/s390-ccw/s390-ccw.h

@@ -42,6 +42,13 @@ typedef unsigned long long __u64;
 #ifndef NULL
 #define NULL    0
 #endif
+#ifndef MIN
+#define MIN(a, b) (((a) < (b)) ? (a) : (b))
+#endif
+#ifndef MIN_NON_ZERO
+#define MIN_NON_ZERO(a, b) ((a) == 0 ? (b) : \
+                            ((b) == 0 ? (a) : (MIN(a, b))))
+#endif
 
 #include "cio.h"
 #include "iplb.h"

pc-bios/s390-ccw/virtio-scsi.c

@@ -202,6 +202,7 @@ static void virtio_scsi_locate_device(VDev *vdev)
     debug_print_int("config.scsi.max_channel", vdev->config.scsi.max_channel);
     debug_print_int("config.scsi.max_target ", vdev->config.scsi.max_target);
     debug_print_int("config.scsi.max_lun    ", vdev->config.scsi.max_lun);
+    debug_print_int("config.scsi.max_sectors", vdev->config.scsi.max_sectors);
 
     if (vdev->scsi_device_selected) {
         sdev->channel = vdev->selected_scsi_device.channel;
@@ -254,12 +255,21 @@ 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_NON_ZERO(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;
 }