On 2020-07-08 15:11, Paolo Bonzini wrote:
On 08/07/20 16:44, lma wrote:
Is the 'block_resize' mandatory to notify guest os after online
resizing
a lun passed through disk? I'm curious it because I found there're
couple
of ways can make guest os realize the disk capacity change.
e.g:
* run 'block_resize' via qmp to let virtio-scsi notify the frontend
about
capacity change.
* run 'rescan-scsi-bus.sh -s' inside guest.
* run 'sg_readcap --16 /dev/sda' inside guest.
I knew that the purpose of 'block_resize' is not only to notify guest
os,
but also to update some internal structure's member, say
bs->total_sectors.
What if I forgot to run 'block_resize', but run 'rescan-scsi-bus.sh
-s'
in guest?
Request start and length are checked even for passthrough disks (see
scsi_disk_dma_command in hw/scsi/scsi-disk.c, called by
scsi_block_dma_command), but the maximum LBA is snooped from READ
CAPACITY commands (see scsi_read_complete in hw/scsi/scsi-generic.c).
So as long as rescan-scsi-bus.sh results in a READ CAPACITY command, it
should work.
Yeah, the rescan-scsi-bus.sh does result in a READ CAPACITY command.
It's not recommended however, because block_resize will report the
change to the guest directly with a CAPACITY HAS CHANGED unit attention
condition.
Got it, The 'block_resize' is the recommended or necessary step, Even
for
passthrough disk online resizing.
Thanks for your information,
Lin
