Re: [PATCH] libxl: trigger attach events for devices attached before xl devd startup

["Roger Pau Monné" <roger.pau@citrix.com>]

On Sun, Jul 10, 2016 at 07:35:47PM +0200, Marek Marczykowski-Górecki wrote:
> When this daemon is started after creating backend device, that device
> will not be configured.
> 
> Racy situation:
> 1. driver domain is started
> 2. frontend domain is started (just after kicking driver domain off)
> 3. device in frontend domain is connected to the backend (as specified
>    in frontend domain configuration)
> 4. xl devd is started in driver domain
> 
> End result is that backend device in driver domain is not configured
> (like network interface is not enabled), so the device doesn't work.
> 
> Fix this by artifically triggering events for devices already present in
> xenstore before xl devd is started. Do this only after xenstore watch is
> already registered, and only for devices not already initialized (in
> XenbusStateInitWait state).

Thanks!

> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> Cc: Wei Liu <wei.liu2@citrix.com>
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
> ---
>  tools/libxl/libxl.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index 1c81239..99815a7 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -4743,8 +4743,16 @@ int libxl_device_events_handler(libxl_ctx *ctx,
>      uint32_t domid;
>      libxl__ddomain ddomain;
>      char *be_path;
> +    char **kinds = NULL, **domains = NULL, **devs = NULL;
> +    const char *sstate;
> +    char *state_path;
> +    int state;
> +    unsigned int nkinds, ndomains, ndevs;
> +    int i, j, k;
> +    xs_transaction_t t;
>  
>      ddomain.ao = ao;
> +    FILLZERO(ddomain.watch);

Is this a different bugfix or stray change?

>      LIBXL_SLIST_INIT(&ddomain.guests);
>  
>      rc = libxl__get_domid(gc, &domid);
> @@ -4762,9 +4770,41 @@ int libxl_device_events_handler(libxl_ctx *ctx,
>                                      be_path);
>      if (rc) goto out;
>  
> +    rc = libxl__xs_transaction_start(gc, &t);
> +    if (rc) goto out;

Why do you need to start a transaction here if you end up aborting it when 
finished?

> +    kinds = libxl__xs_directory(gc, t, be_path, &nkinds);
> +    if (kinds) {
> +        for (i = 0; i < nkinds; i++) {
> +            domains = libxl__xs_directory(gc, t,
> +                    GCSPRINTF("%s/%s", be_path, kinds[i]), &ndomains);
> +            if (!domains)
> +                continue;
> +            for (j = 0; j < ndomains; j++) {
> +                devs = libxl__xs_directory(gc, t,
> +                        GCSPRINTF("%s/%s/%s", be_path, kinds[i], domains[j]), &ndevs);
> +                if (!devs)
> +                    continue;
> +                for (k = 0; k < ndevs; k++) {
> +                    state_path = GCSPRINTF("%s/%s/%s/%s/state",
> +                            be_path, kinds[i], domains[j], devs[k]);
> +                    rc = libxl__xs_read_checked(gc, t, state_path, &sstate);
> +                    if (rc)
> +                        continue;
> +                    state = atoi(sstate);
> +                    if (state == XenbusStateInitWait)
> +                        backend_watch_callback(egc, &ddomain.watch,
> +                                be_path, state_path);
> +                }
> +            }
> +        }
> +    }
> +
> +    libxl__xs_transaction_abort(gc, &t);
> +
>      return AO_INPROGRESS;
>  
>  out:
> +    libxl__ev_xswatch_deregister(gc, &ddomain.watch);

This seems to be part of a different bugfix also.

Roger.

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