Hi all, thanks for the notification.I want to note that the official "in kernel qcow2 (ro)" project was renamed to "xloop" and is now maintained on Github [1]. So far we are successfully using xloop toimplement our use case explained in [2]. Seems like we have a technical alternative to get file-format specific functionality out of the kernel. When I presented the "in kernel qcow2 (ro)" project idea on the mailing list [3], there was a discussion about whether file formats like qcow2 should be implemented in the kernel or not? Now, this question should be obsolete. [1] https://github.com/bwLehrpool/xloop [2] https://www.spinics.net/lists/linux-block/msg44858.html [3] https://www.spinics.net/lists/linux-block/msg39538.html Regards, Manuel On 9/30/22 11:24, Ming Lei wrote: > Hello, > > ublk-qcow2 is available now. > > So far it provides basic read/write function, and compression and snapshot > aren't supported yet. The target/backend implementation is completely > based on io_uring, and share the same io_uring with ublk IO command > handler, just like what ublk-loop does. > > Follows the main motivations of ublk-qcow2: > > - building one complicated target from scratch helps libublksrv APIs/functions > become mature/stable more quickly, since qcow2 is complicated and needs more > requirement from libublksrv compared with other simple ones(loop, null) > > - there are several attempts of implementing qcow2 driver in kernel, such as > ``qloop`` [2], ``dm-qcow2`` [3] and ``in kernel qcow2(ro)`` [4], so ublk-qcow2 > might useful be for covering requirement in this field > > - performance comparison with qemu-nbd, and it was my 1st thought to evaluate > performance of ublk/io_uring backend by writing one ublk-qcow2 since ublksrv > is started > > - help to abstract common building block or design pattern for writing new ublk > target/backend > > So far it basically passes xfstest(XFS) test by using ublk-qcow2 block > device as TEST_DEV, and kernel building workload is verified too. Also > soft update approach is applied in meta flushing, and meta data > integrity is guaranteed, 'make test T=qcow2/040' covers this kind of > test, and only cluster leak is reported during this test. > > The performance data looks much better compared with qemu-nbd, see > details in commit log[1], README[5] and STATUS[6]. And the test covers both > empty image and pre-allocated image, for example of pre-allocated qcow2 > image(8GB): > > - qemu-nbd (make test T=qcow2/002) > randwrite(4k): jobs 1, iops 24605 > randread(4k): jobs 1, iops 30938 > randrw(4k): jobs 1, iops read 13981 write 14001 > rw(512k): jobs 1, iops read 724 write 728 > > - ublk-qcow2 (make test T=qcow2/022) > randwrite(4k): jobs 1, iops 104481 > randread(4k): jobs 1, iops 114937 > randrw(4k): jobs 1, iops read 53630 write 53577 > rw(512k): jobs 1, iops read 1412 write 1423 > > Also ublk-qcow2 aligns queue's chunk_sectors limit with qcow2's cluster size, > which is 64KB at default, this way simplifies backend io handling, but > it could be increased to 512K or more proper size for improving sequential > IO perf, just need one coroutine to handle more than one IOs. > > > [1] https://github.com/ming1/ubdsrv/commit/9faabbec3a92ca83ddae92335c66eabbeff654e7 > [2] https://upcommons.upc.edu/bitstream/handle/2099.1/9619/65757.pdf?sequence=1&isAllowed=y > [3] https://lwn.net/Articles/889429/ > [4] https://lab.ks.uni-freiburg.de/projects/kernel-qcow2/repository > [5] https://github.com/ming1/ubdsrv/blob/master/qcow2/README.rst > [6] https://github.com/ming1/ubdsrv/blob/master/qcow2/STATUS.rst > > Thanks, > Ming
