On Mon, Nov 18, 2019 at 10:27:28PM +0800, Coiby Xu wrote: > Hi all, > > This is an implementation of vhost-user-blk device backend by > following > https://wiki.qemu.org/Google_Summer_of_Code_2019#vhost-user-blk_device_backend. > raw/qcow2 disk images can now be shared via vhost user protocol. In > this way, it could provide better performance than QEMU's existing NBD > support.
Thank you for working on this feature!
> +static size_t vub_iov_to_buf(const struct iovec *iov,
> + const unsigned int iov_cnt, void *buf)
Please take a look at utils/iov.c. iov_to_buf_full() can be used
instead of defining this function.
> +{
> + size_t len;
> + unsigned int i;
> +
> + len = 0;
> + for (i = 0; i < iov_cnt; i++) {
> + memcpy(buf + len, iov[i].iov_base, iov[i].iov_len);
> + len += iov[i].iov_len;
> + }
> + return len;
> +}
> +
> +static VubDev *vub_device;
If you switch to -object (see below) then this global pointer will go
away so I won't comment on it throughout this patch.
> +static void vub_accept(QIONetListener *listener, QIOChannelSocket *sioc,
> + gpointer opaque)
> +{
> + /* only one connection */
> + if (vub_device->sioc) {
> + return;
> + }
> +
> + vub_device->sioc = sioc;
> + vub_device->listener = listener;
> + /*
> + * increase the object reference, so cioc will not freeed by
> + * qio_net_listener_channel_func which will call
> object_unref(OBJECT(sioc))
> + */
> + object_ref(OBJECT(sioc));
> +
> + qio_channel_set_name(QIO_CHANNEL(sioc), "vhost-server");
> + if (!vug_init(&vub_device->parent, VHOST_USER_BLK_MAX_QUEUES, sioc->fd,
> + vub_panic_cb, &vub_iface)) {
> + fprintf(stderr, "Failed to initialized libvhost-user-glib\n");
> + }
vug_init() uses the default GMainContext, which is bad for performance
when there are many devices because it cannot take advantage of
multi-core CPUs. vhost-user-server should support IOThread so that
devices can be run in dedicated threads.
The nbd/server.c:NBDExport->ctx field serves this purpose in the NBD
server. It's a little trickier with libvhost-user-glib because the API
currently doesn't allow passing in a GMainContext and will need to be
extended.
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index cfcc044ce4..d8de179747 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -1614,6 +1614,33 @@ STEXI
> @findex acl_reset
> Remove all matches from the access control list, and set the default
> policy back to @code{deny}.
> +ETEXI
> +
> + {
> + .name = "vhost_user_server_stop",
> + .args_type = "",
> + .params = "vhost_user_server_stop",
> + .help = "stop vhost-user-blk device backend",
> + .cmd = hmp_vhost_user_server_stop,
> + },
> +STEXI
> +@item vhost_user_server_stop
> +@findex vhost_user_server_stop
> +Stop the QEMU embedded vhost-user-blk device backend server.
> +ETEXI
The NBD server supports multiple client connections and exports
(drives). A vhost-user socket only supports one connection and one
device. I think it will be necessary to assign a unique identifier to
every vhost-user server.
By the way, I think the server should be a UserCreatable Object so the
following syntax works:
$ qemu -object vhost-user-server,id=ID,chardev=CHARDEV,writable=on|off
And existing HMP/QMP commands can be used:
(qemu) object_add vhost-user-server,id=ID,chardev=CHARDEV,writable=on|off
(qemu) object_del ID
This way we don't need to define new HMP/QMP/command-line syntax for
vhost-user-server.
If you grep for UserCreatable you'll find examples like "iothread",
"secret", "throttle-group", etc.
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