Re: [Xen-devel] [PATCH MINI-OS v3 2/2] xenbus: workaround oxenstored short-write

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>]

Wei Liu, le Tue 27 Oct 2015 15:43:29 +0000, a écrit :
> Oxenstored has a behaviour that it only writes a contiguous piece of
> data. When it writes across ring boundary it will return a short-write
> while there is still room. That leads to mini-os stalling when it sees
> there is not enough data in the ring.
> 
> Given that oxenstored is the default xenstored implementation we think
> it would be useful to workaround this for the benefit of running mini-os
> (and unikernel based on it) on any Xen installation.
> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>

As discussed in the previous thread, this is rather a workaround. Better
be safe than sorry.

Acked-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>

And could too be backported to stable branches.

> ---
>  xenbus/xenbus.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/xenbus/xenbus.c b/xenbus/xenbus.c
> index 0ab387a..abf8b1b 100644
> --- a/xenbus/xenbus.c
> +++ b/xenbus/xenbus.c
> @@ -205,8 +205,11 @@ static void xenbus_thread_func(void *ign)
>              prod = xenstore_buf->rsp_prod;
>              DEBUG("Rsp_cons %d, rsp_prod %d.\n", xenstore_buf->rsp_cons,
>                      xenstore_buf->rsp_prod);
> -            if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons < 
> sizeof(msg))
> +            if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons < 
> sizeof(msg)) {
> +                /* Work around oxenstored bug */
> +                notify_remote_via_evtchn(start_info.store_evtchn);
>                  break;
> +            }
>              rmb();
>              memcpy_from_ring(xenstore_buf->rsp,
>                      &msg,
> @@ -217,8 +220,11 @@ static void xenbus_thread_func(void *ign)
>                      xenstore_buf->rsp_prod - xenstore_buf->rsp_cons,
>                      msg.req_id);
>              if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons <
> -                    sizeof(msg) + msg.len)
> +                    sizeof(msg) + msg.len) {
> +                /* Work around oxenstored bug */
> +                notify_remote_via_evtchn(start_info.store_evtchn);
>                  break;
> +            }
>  
>              DEBUG("Message is good.\n");
>  
> -- 
> 2.1.4
> 

-- 
Samuel
"c'est pas nous qui sommes à la rue, c'est la rue qui est à nous"

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