On 09/03/2016 09:00, Fam Zheng wrote: >> > On 09/03/2016 04:35, Fam Zheng wrote: >>>>> > >> > enum BdrvTrackedRequestType { >>>>> > >> > BDRV_TRACKED_READ, >>>>> > >> > BDRV_TRACKED_WRITE, >>>>> > >> > - BDRV_TRACKED_FLUSH, >>>>> > >> > - BDRV_TRACKED_IOCTL, >>>>> > >> > BDRV_TRACKED_DISCARD, >>> > > Okay, so flush and ioctl are not needed, but why is discard different? >> > >> > Discard can modify the contents of the device, so I think it's safer to >> > serialize it against RMW and copy-on-read operations. > Okay, that makes sense, but ioctl like SG_IO can also modify content, no?
If you use SG_IO you shouldn't use RMW (because scsi_read_complete traps READ CAPACITY and sets the host block size as the guest block size) or copy-on-read (because raw has no backing file). Besides, BDRV_TRACKED_IOCTL didn't include sector_num/nr_sectors operations so it didn't provide serialization. Paolo