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. It's not recommended however, because block_resize will report the change to the guest directly with a CAPACITY HAS CHANGED unit attention condition. Thanks, Paolo
