Am 07.11.2014 um 09:39 hat lihuiba geschrieben: > Hi, all > > I'm a user of qemu/kvm, and I'm wondering some internals of qemu/kvm, so I'd > better post it in > this developer's mailing list. > > To be specific, I'm wondering how data is flushed to disk. Intuitively, when > the guest issues a > SYNCHRONIZE CACHE command in the SCSI layer, qemu/kvm should call > bdrv_co_flush > (), > which will eventually call the block driver's bdrv_co_flush_to_os() > and bdrv_co_flush_to_disk(). > > But from simple grep-ing, I didn't find any calling to bdrv_co_flush() is > responsible for SYNCHRONIZE > CACHE. So, can you tell me how qemu/kvm ensures guest data be written on > persistent storage?
The relevant code is in hw/scsi/scsi-disk.c, in the function scsi_disk_emulate_command(), for 'case SYNCHRONIZE_CACHE:'. The call chain from there is blk_aio_flush() -> bdrv_aio_flush() -> bdrv_aio_flush_co_entry() -> bdrv_co_flush() Kevin