Re: [libvirt] [PATCH v3 1/4] block: Pass bdrv_* methods to bs->file by default

Am 04.07.2017 um 10:40 hat Manos Pitsidianakis geschrieben: > The following functions fail if bs->drv does not implement them: > > bdrv_probe_blocksizes > bdrv_probe_geometry > bdrv_truncate > bdrv_has_zero_init > bdrv_get_info > bdrv_media_changed > bdrv_eject > bdrv_lock_medium > bdrv_co_ioctl > > Instead, the call should be passed to bs->file if it exists, to allow > filter drivers to support those methods without implementing them. >

> + return bdrv_probe_blocksizes(bs->file->bs, bsz); > } > > return -ENOTSUP; This change actually changes existing behaviour. Basically, all of your additions also apply for qcow2 images or other image formats, and we need to check whether they make sense there. bdrv_probe_blocksizes() is used for the default values for the physical and logical block sizes for block devices if no value is explicitly specified in -device. This makes sense as it will allow the guest to optimise its requests so that they align with the block size that is optimal for the storage that contains the image. (I also think that we probably should implement .bdrv_probe_blocksizes() not only for host_device, but also for regular files to get optimal performance by default.) Changing the defaults can be a problem for cross-version live migration if the default values are used. Management tools that want to do live migration are supposed to explicitly provide all options they can, so this should be okay. Eric, does libvirt set the physical/logical block size explicitly? If not, it would be good if it started to do so.