Re: How to extend QEMU's vhost-user tests after implementing vhost-user-blk device backend

[Stefan Hajnoczi]

On Wed, Dec 11, 2019 at 11:25:32PM +0800, Coiby Xu wrote:
> I'm now writing the tests for vhost-user-blk device based on
> tests/virtio-blk-test.c. But block_resize command doesn't apply to
> vhost-user-blk device.
> 
> After launching vhost-user backend server, I type the following
> command to connect to it
> 
> (qemu) chardev-add socket,id=char1,path=/tmp/vhost-user-blk_vhost.socket
> (qemu) object_add memory-backend-memfd,id=mem,size=256M,share=on
> (qemu) device_add vhost-user-blk-pci,id=blk0,chardev=char1
> (qemu) block_resize blk0 512
> Error: Cannot find device=blk0 nor node_name=
> 
> QEMU can't find the device although in the guest OS I can already
> mount /dev/vda. And `info block` doesn't list the newly added
> vhost-user-blk device,
> (qemu) info block
> disk (#block154): dpdk.img (raw)
>     Attached to:      /machine/peripheral-anon/device[0]
>     Cache mode:       writeback
> 
> floppy0: [not inserted]
>     Attached to:      /machine/unattached/device[17]
>     Removable device: not locked, tray closed
> 
> sd0: [not inserted]
>     Removable device: not locked, tray close
> 
> It seems `info block` and `block_resize` only work with `drive_add`
> which is not necessary for vhost-user-blk device.

Yes, -device vhost-user-blk doesn't have a BlockDriverState (-drive or
-blockdev) because it communicates with the vhost-user device backend
over a character device instead.

> Should I let QEMU
> support adding vhost-user backend device in the way similar to adding
> NBD device(`drive_add -n buddy
> file.driver=nbd,file.host=localhost,file.port=49153,file.export=disk,node-name=nbd_client1`),
> i.e., a drive can be added via `drive_add -n buddy
> file.driver=vhost-user,file.sock=/tmp/vhost-user-blk_vhost.socket,node-name=vhost_user_client1`?

That is probably too much work.  It's fine to skip test cases that
resize the disk.

Stefan

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