Re: Virtio-disk updates for latest Xen ?

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

On 07.12.22 05:59, Viresh Kumar wrote:

Hello Viresh

First of all, sorry for the late response.
The second, thank you for the investigation.


> On 07-12-22, 05:51, Viresh Kumar wrote:
> > I am not sure how to get this working, as there is no finalizing event
> > for the directory. Maybe our design is broken from the start and we
> > need to do it properly in some recommended way ?
> For now this is what I have done to make it work:
>
> diff --git a/xs_dev.c b/xs_dev.c
> index a6c8403cfe84..4643394a52a2 100755
> --- a/xs_dev.c
> +++ b/xs_dev.c
> @@ -413,20 +413,7 @@ static int xenstore_get_fe_domid(struct xs_dev *dev)
>   
>   static int xenstore_poll_be_watch(struct xs_dev *dev)
>   {
> -    unsigned int num;
> -    char **vec;
> -    int rc = 0;
> -
> -    vec = xs_read_watch(dev->xsh, &num);
> -    if (!vec)
> -        return -1;
> -
> -    if (!strcmp(vec[XS_WATCH_PATH], dev->path))
> -        rc = xenstore_get_fe_domid(dev);
> -
> -    free(vec);
> -
> -    return rc;
> +    return xenstore_get_fe_domid(dev);
>   }
>
> This rns xenstore_get_fe_domid() for each event in the path
> "backend/virtio", and in my case it passes with the second event
> itself, which came for "backend/virtio/1/0" and this code doesn't run
> after that.
>
> Note that I have tested this with my rust counterpart which received a
> similar change, I didn't test virtio-disk directly.

Today I had a chance to check virtio-disk on my H/W using new Xen branch 
which does include Juergen's series with commit 3a96013a3e17 
("tools/xenstore: reduce number of watch events").
Very interesting, but I didn't manage to reproduce an issue the similar 
to what you had already faced with the rust counterparts before (caused 
by the lack of Xenstore watches?). Note that I didn't debug what exactly 
events I had got during guest creation/destruction, I just made sure 
that backend worked as before. I checked that by running the backend in 
Dom0 and DomD and performed a couple of guest power cycles (reboot, 
destroy/create).
If you could provide the debug patch which you seem to use to print 
incoming events which you described in previous email, I think I would 
be able to re-check the situation at my side more deeper.