[PATCH] scsi-generic: replace logical block count of response of READ CAPACITY

[Lin Ma]

While using SCSI passthrough, Following scenario makes qemu doesn't
realized the capacity change of remote scsi target:
1. online resize the scsi target.
2. issue 'rescan-scsi-bus.sh -s ...' in host.
3. issue 'rescan-scsi-bus.sh -s ...' in vm.

In above scenario I used to experienced errors while accessing the
additional disk space in vm. I think the reasonable operations should
be:
1. online resize the scsi target.
2. issue 'rescan-scsi-bus.sh -s ...' in host.
3. issue 'block_resize' via qmp to notify qemu.
4. issue 'rescan-scsi-bus.sh -s ...' in vm.

The errors disappear once I notify qemu by block_resize via qmp.

So this patch replaces the number of logical blocks of READ CAPACITY
response from scsi target by qemu's bs->total_sectors. If the user in
vm wants to access the additional disk space, The administrator of
host must notify qemu once resizeing the scsi target.

Bonus is that domblkinfo of libvirt can reflect the consistent capacity
information between host and vm in case of missing block_resize in qemu.
E.g:
...
    <disk type='block' device='lun'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/sdc' index='1'/>
      <backingStore/>
      <target dev='sda' bus='scsi'/>
      <alias name='scsi0-0-0-0'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
...

Before:
1. online resize the scsi target.
2. host:~  # rescan-scsi-bus.sh -s /dev/sdc
3. guest:~ # rescan-scsi-bus.sh -s /dev/sda
4  host:~  # virsh domblkinfo --domain $DOMAIN --human --device sda
Capacity:       4.000 GiB
Allocation:     0.000 B
Physical:       8.000 GiB

5. guest:~ # lsblk /dev/sda
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda      8:0    0   8G  0 disk
└─sda1   8:1    0   2G  0 part

After:
1. online resize the scsi target.
2. host:~  # rescan-scsi-bus.sh -s /dev/sdc
3. guest:~ # rescan-scsi-bus.sh -s /dev/sda
4  host:~  # virsh domblkinfo --domain $DOMAIN --human --device sda
Capacity:       4.000 GiB
Allocation:     0.000 B
Physical:       8.000 GiB

5. guest:~ # lsblk /dev/sda
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda      8:0    0   4G  0 disk
└─sda1   8:1    0   2G  0 part

Signed-off-by: Lin Ma <lma@suse.com>
---
 hw/scsi/scsi-generic.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 0306ccc7b1..343b51c2c0 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -315,11 +315,17 @@ static void scsi_read_complete(void * opaque, int ret)
     if (r->req.cmd.buf[0] == READ_CAPACITY_10 &&
         (ldl_be_p(&r->buf[0]) != 0xffffffffU || s->max_lba == 0)) {
         s->blocksize = ldl_be_p(&r->buf[4]);
-        s->max_lba = ldl_be_p(&r->buf[0]) & 0xffffffffULL;
+        BlockBackend *blk = s->conf.blk;
+        BlockDriverState *bs = blk_bs(blk);
+        s->max_lba = bs->total_sectors - 1;
+        stl_be_p(&r->buf[0], s->max_lba);
     } else if (r->req.cmd.buf[0] == SERVICE_ACTION_IN_16 &&
                (r->req.cmd.buf[1] & 31) == SAI_READ_CAPACITY_16) {
         s->blocksize = ldl_be_p(&r->buf[8]);
-        s->max_lba = ldq_be_p(&r->buf[0]);
+        BlockBackend *blk = s->conf.blk;
+        BlockDriverState *bs = blk_bs(blk);
+        s->max_lba = bs->total_sectors - 1;
+        stq_be_p(&r->buf[0], s->max_lba);
     }
     blk_set_guest_block_size(s->conf.blk, s->blocksize);
 
-- 
2.26.2