On Wed, Jul 26, 2023 at 09:26:45AM +0200, Stefano Garzarella wrote: > On Tue, Jul 25, 2023 at 04:00:38PM -0400, Stefan Hajnoczi wrote: > > On Mon, Jul 24, 2023 at 05:46:10PM +0200, Stefano Garzarella wrote: > > > libblkio 1.3.0 added support of "fd" property for virtio-blk-vhost-vdpa > > > driver. In QEMU, starting from commit cad2ccc395 ("block/blkio: use > > > qemu_open() to support fd passing for virtio-blk") we are using > > > `blkio_get_int(..., "fd")` to check if the "fd" property is supported > > > for all the virtio-blk-* driver. > > > > > > Unfortunately that property is also available for those driver that do > > > not support it, such as virtio-blk-vhost-user. Indeed now QEMU is > > > failing if used with virtio-blk-vhost-user in this way: > > > > > > -blockdev > > > node-name=drive0,driver=virtio-blk-vhost-user,path=vhost-user-blk.sock,cache.direct=on: > > > Could not open 'vhost-user-blk.sock': No such device or address > > > > > > So, `blkio_get_int()` is not enough to check whether the driver supports > > > the `fd` property or not. This is because the virito-blk common libblkio > > > driver only checks whether or not `fd` is set during `blkio_connect()` > > > and fails for those transports that do not support it (all except > > > vhost-vdpa for now). > > > > > > So for now let's also check that the driver is virtio-blk-vhost-vdpa, > > > since that's the only one that supports it. > > > > What happens when more virtio-blk-* libblkio drivers gain support for > > `fd`? I think we'll be back to the same problem because QEMU will be > > unable to distinguish between old and new libraries. > > If we release a v1.3.1 version of libblkio with > https://gitlab.com/libblkio/libblkio/-/merge_requests/208 > we can set a minimum requirement in QEMU and use blkio_set_fd() here. > > > > > How about retrying with `path` if opening with `fd` fails? > > IIUC the only way is to check if blkio_connect() will fail with -EINVAL, > that can also be generated by other issues, then retry forcing `path`. > > Do you see other ways?
No. Checking for -EINVAL and then retrying with `path` is what I had in mind. > The code wouldn't be great, but we could do it for now and then when > we release a new version of libblkio, do the revert and use > blkio_set_int(fd) to see if it's supported or not. > > I don't know if it is worth it, or if it is better to merge this, > release libblkio v1.3.1 and force the minimum requirement. > > WDYT? I prefer retrying on -EINVAL because even if libblkio 1.3.1 is released today, we don't have control over when it becomes available in distros. Stefan
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