[Libguestfs] [PATCH nbdkit] New plugin: blkio [incomplete]

[Alberto Faria]

> This is upstream in nbdkit now:
> https://gitlab.com/nbdkit/nbdkit/-/tree/master/plugins/blkio
>
> Another question:
>
> (6) vhost-user + "read-only" property acts a bit strangely.  After
> opening virtio-blk-vhost-user it throws an EROFS error if you try to
> "blkio_start" it.  However if you set the "read-only" property to true
> then it's OK to start it, and subsequent read operations work too.
>
> I would expect that any device can be started without needing to set
> this property, and in general I don't understand why vhost-user is r/o
> since everything I read about it seems to indicate it's a general
> purpose writable protocol.

read-only has POSIX file open-like semantics: if the device is itself
read only but the read-only property is false, blkio_start() fails.

With qemu-storage-daemon, you must set writable=on on the
vhost-user-blk export for the device to be writable.

Alberto