On Mon, Jul 10, 2023 at 16:39:43 +0300, Андрей Ячменёв wrote: Note that qemu apart from the possibility to explicitly specify the size supports also a 'backend_defaults' option, which is by default in _AUTO mode. Inside of 'blkconf_blocksizes()' the block size defaults are then populated. By default in _AUTO mode 'conf->physical_block_size' and 'conf->logical_block_size' are auto-populated but not 'conf->opt_io_size' or the discard granularity setting. I think we should give the users the possibility to enable the qemu-configured defaults in this case knowing the proper value to configure may be non-trivial, more on that below. Libvirt already handles some of the sibling values for configuring block sizes via: <disk type='block' device='disk'> <driver name='qemu' type='raw'/> <source dev='/dev/sda'/> <geometry cyls='16383' heads='16' secs='63' trans='lba'/> <blockio logical_block_size='512' physical_block_size='4096'/> <target dev='hdj' bus='ide'/> </disk> Thus you should be able to use that placement without the need to reinvent any placement. Placing it under address would even be wrong. In libvirt we generally try to expose config knobs which make sense for the users to set. That requires that the users know how to set the option properly. Based on that I'd suggest that you first and foremost allow the users to enable the backend defaults in qemu, as that seems to set many things optimally without the user needing to know more. Later then you can also add knobs to fine tune the values if necessary. Please don't forget to read our contribution guidelines and follow the coding style we have in place. Note that some of the knobs may not be available in all supported QEMU versions (libvirt currently supports qemu-4.2 and newer) which may require adding a capability check. If you have any questions regarding specifics feel free to ask on-list or on our IRC channel.