Re: [Xen-devel] [PATCH 6 of 6] libxl: use hotplug-status to synchronize the destruction of block devices

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-09-22 at 13:01 +0100, Roger Pau Monne wrote:
> # HG changeset patch
> # User Roger Pau Monne <roger.pau@xxxxxxxxxxxxx>
> # Date 1316692512 -7200
> # Node ID 9e9c68768676b0e1c9c76599e00d0922c6184602
> # Parent  a5c9a6083bef9d4789a0194389db234740cd6005
> libxl: use hotplug-status to synchronize the destruction of block devices
> 
> Use hotplug-status to synchronize the destruction of vbd devices instead of 
> state, which did not reflect when the hotplug script had been executed.
> 
> Signed-off-by: Roger Pau Monne <roger.pau@xxxxxxxxxxxxx>

I wonder if we can remove the hard coding of the VBD special case
somehow? For example an ops struct in an array mapping DEVICE_* to
        int (*watch_for_disconnect)(relevant arguments)
        int (*has_disconnected)(relevant arguments)
which would have two implementations, one checking state and the other
hotplug-status.

That leaves the change in wait_for_dev_destroy which unfortunately
doesn't have the context to do much else than what you've done. Perhaps
that's ok as is until I can finish of the patch series I have which
fixes that aspect. I suppose a function pointer could be encoded in the
XS_WATCH_TOKEN and sscanf'd back out again...

> 
> diff -r a5c9a6083bef -r 9e9c68768676 tools/libxl/libxl_device.c
> --- a/tools/libxl/libxl_device.c      Thu Sep 22 13:55:03 2011 +0200
> +++ b/tools/libxl/libxl_device.c      Thu Sep 22 13:55:12 2011 +0200
> @@ -371,14 +371,26 @@ int libxl__device_destroy(libxl__gc *gc,
>      libxl_ctx *ctx = libxl__gc_owner(gc);
>      xs_transaction_t t;
>      char *state_path = libxl__sprintf(gc, "%s/state", be_path);
> +    char *hotplug_path = libxl__sprintf(gc, "%s/hotplug-status", be_path);
>      char *state = libxl__xs_read(gc, XBT_NULL, state_path);
> +    char *hotplug = libxl__xs_read(gc, XBT_NULL, hotplug_path);
>      int rc = 0;
>  
>      if (!state)
>          goto out;
> -    if (atoi(state) != 4) {
> -        xs_rm(ctx->xsh, XBT_NULL, be_path);
> -        goto out;
> +
> +    if (!strstr(be_path, string_of_kinds[DEVICE_VBD])) {
> +        if (atoi(state) != 4) {
> +            xs_rm(ctx->xsh, XBT_NULL, be_path);
> +            goto out;
> +        }
> +    } else {
> +        if (!hotplug)
> +            goto out;
> +        if (!strcmp(hotplug, "disconnected")) {
> +            xs_rm(ctx->xsh, XBT_NULL, be_path);
> +            goto out;
> +        }
>      }
>  
>  retry_transaction:
> @@ -394,8 +406,13 @@ retry_transaction:
>          }
>      }
>      if (!force) {
> -        xs_watch(ctx->xsh, state_path, be_path);
> -        rc = 1;
> +        if (strstr(be_path, string_of_kinds[DEVICE_VBD])) {
> +            xs_watch(ctx->xsh, hotplug_path, be_path);
> +            rc = 1;
> +        } else {
> +            xs_watch(ctx->xsh, state_path, be_path);
> +            rc = 1;
> +        }
>      } else {
>          xs_rm(ctx->xsh, XBT_NULL, be_path);
>      }
> @@ -410,6 +427,7 @@ static int wait_for_dev_destroy(libxl__g
>      unsigned int n;
>      fd_set rfds;
>      char **l1 = NULL;
> +    char *state, *hotplug;
>  
>      rc = 1;
>      nfds = xs_fileno(ctx->xsh) + 1;
> @@ -418,12 +436,26 @@ static int wait_for_dev_destroy(libxl__g
>      if (select(nfds, &rfds, NULL, NULL, tv) > 0) {
>          l1 = xs_read_watch(ctx->xsh, &n);
>          if (l1 != NULL) {
> -            char *state = libxl__xs_read(gc, XBT_NULL, l1[XS_WATCH_PATH]);
> -            if (!state || atoi(state) == 6) {
> -                xs_unwatch(ctx->xsh, l1[0], l1[1]);
> -                xs_rm(ctx->xsh, XBT_NULL, l1[XS_WATCH_TOKEN]);
> -                LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "Destroyed device backend 
> at %s", l1[XS_WATCH_TOKEN]);
> -                rc = 0;
> +            if (strstr(l1[XS_WATCH_PATH], "hotplug-status")) {
> +                hotplug = libxl__xs_read(gc, XBT_NULL, l1[XS_WATCH_PATH]);
> +                if (!hotplug || !strcmp(hotplug, "disconnected")) {
> +                    xs_unwatch(ctx->xsh, l1[0], l1[1]);
> +                    xs_rm(ctx->xsh, XBT_NULL, l1[XS_WATCH_TOKEN]);
> +                    LIBXL__LOG(ctx, LIBXL__LOG_DEBUG,
> +                        "Destroyed device backend at %s hotplug-status: %s",
> +                        l1[XS_WATCH_TOKEN], hotplug);
> +                    rc = 0;
> +                }
> +            } else {
> +                state = libxl__xs_read(gc, XBT_NULL, l1[XS_WATCH_PATH]);
> +                if (!state || atoi(state) == 6) {
> +                    xs_unwatch(ctx->xsh, l1[0], l1[1]);
> +                    xs_rm(ctx->xsh, XBT_NULL, l1[XS_WATCH_TOKEN]);
> +                    LIBXL__LOG(ctx, LIBXL__LOG_DEBUG,
> +                        "Destroyed device backend at %s",
> +                        l1[XS_WATCH_TOKEN]);
> +                    rc = 0;
> +                }
>              }
>              free(l1);
>          }
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel