Re: [RFC v3 1/8] blkio: add io_uring block driver using libblkio

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, Jul 27, 2022 at 09:33:40PM +0200, Kevin Wolf wrote:
> Am 08.07.2022 um 06:17 hat Stefan Hajnoczi geschrieben:
> > libblkio (https://gitlab.com/libblkio/libblkio/) is a library for
> > high-performance disk I/O. It currently supports io_uring and
> > virtio-blk-vhost-vdpa with additional drivers under development.
> > 
> > One of the reasons for developing libblkio is that other applications
> > besides QEMU can use it. This will be particularly useful for
> > vhost-user-blk which applications may wish to use for connecting to
> > qemu-storage-daemon.
> > 
> > libblkio also gives us an opportunity to develop in Rust behind a C API
> > that is easy to consume from QEMU.
> > 
> > This commit adds io_uring and virtio-blk-vhost-vdpa BlockDrivers to QEMU
> > using libblkio. It will be easy to add other libblkio drivers since they
> > will share the majority of code.
> > 
> > For now I/O buffers are copied through bounce buffers if the libblkio
> > driver requires it. Later commits add an optimization for
> > pre-registering guest RAM to avoid bounce buffers.
> > 
> > The syntax is:
> > 
> >   --blockdev io_uring,node-name=drive0,filename=test.img,readonly=on|off,cache.direct=on|off
> > 
> > and:
> > 
> >   --blockdev virtio-blk-vhost-vdpa,node-name=drive0,path=/dev/vdpa...,readonly=on|off
> > 
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> The subject line implies only io_uring, but you actually add vhost-vdpa
> support, too. I think the subject line should be changed.
> 
> I think it would also make sense to already implement support for
> vhost-user-blk on the QEMU side even if support isn't compiled in
> libblkio by default and opening vhost-user-blk images would therefore
> always fail with a default build.
> 
> But then you could run QEMU with a custom build of libblkio to make use
> of it without patching QEMU. This is probably useful for getting libvirt
> support for using a storage daemon implemented without having to wait
> for another QEMU release. (Peter, do you have any opinion on this?)

vhost-user-blk is now supported in all builds of libblkio. I'll add it.

Stefan

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