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>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 hw/scsi/scsi-generic.c | 18 ++++++++++++++++--
 hw/scsi/trace-events   |  1 +
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 0306ccc7b1..c9b08a9926 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -256,6 +256,18 @@ static int scsi_generic_emulate_block_limits(SCSIGenericReq *r, SCSIDevice *s)
     return r->buflen;
 }
 
+static void refresh_max_lba(SCSIDevice *s)
+{
+    BlockBackend *blk = s->conf.blk;
+    BlockDriverState *bs = blk_bs(blk);
+    uint64_t max_lba = bs->total_sectors - 1;
+
+    if (max_lba != s->max_lba) {
+        trace_scsi_generic_max_lba_refreshed(s->max_lba, max_lba);
+        s->max_lba = max_lba;
+    }
+}
+
 static void scsi_read_complete(void * opaque, int ret)
 {
     SCSIGenericReq *r = (SCSIGenericReq *)opaque;
@@ -315,11 +327,13 @@ 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;
+        refresh_max_lba(s);
+        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]);
+        refresh_max_lba(s);
+        stq_be_p(&r->buf[0], s->max_lba);
     }
     blk_set_guest_block_size(s->conf.blk, s->blocksize);
 
diff --git a/hw/scsi/trace-events b/hw/scsi/trace-events
index ae8551f279..44d064a656 100644
--- a/hw/scsi/trace-events
+++ b/hw/scsi/trace-events
@@ -352,3 +352,4 @@ scsi_generic_realize_blocksize(int blocksize) "block size %d"
 scsi_generic_aio_sgio_command(uint32_t tag, uint8_t cmd, uint32_t timeout) "generic aio sgio: tag=0x%x cmd=0x%x timeout=%u"
 scsi_generic_ioctl_sgio_command(uint8_t cmd, uint32_t timeout) "generic ioctl sgio: cmd=0x%x timeout=%u"
 scsi_generic_ioctl_sgio_done(uint8_t cmd, int ret, uint8_t status, uint8_t host_status) "generic ioctl sgio: cmd=0x%x ret=%d status=0x%x host_status=0x%x"
+scsi_generic_max_lba_refreshed(uint64_t old_max_lba, uint64_t new_max_lba) "old max_lba %" PRIu64 ",new max_lba %" PRIu64
-- 
2.26.2