Re: [Xen-devel] [PATCH v5 7/8] xl/libxl: implement QDISK libxl_device_disk_local_attach

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-05-04 at 12:13 +0100, Stefano Stabellini wrote:
> - Spawn a QEMU instance at boot time to handle disk local attach
> requests.
> 
> - Implement libxl_device_disk_local_attach for QDISKs in terms of a
> regular disk attach with the frontend and backend running in the same
> domain.
> 
> Chanegs in v5:
> - replace LIBXL__LOG with LOG.
> 
> Changes on v4:
> - improve error handling and exit paths in libxl__device_disk_local_attach.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>  tools/hotplug/Linux/init.d/sysconfig.xencommons |    3 +
>  tools/hotplug/Linux/init.d/xencommons           |    3 +
>  tools/libxl/libxl_internal.c                    |   58 ++++++++++++++++++----
>  3 files changed, 53 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/hotplug/Linux/init.d/sysconfig.xencommons 
> b/tools/hotplug/Linux/init.d/sysconfig.xencommons
> index 6543204..0f3b9ad 100644
> --- a/tools/hotplug/Linux/init.d/sysconfig.xencommons
> +++ b/tools/hotplug/Linux/init.d/sysconfig.xencommons
> @@ -12,3 +12,6 @@
>  
>  # Running xenbackendd in debug mode
>  #XENBACKENDD_DEBUG=[yes|on|1]
> +
> +# qemu path and log file

What does "and log file" mean?

Apart from that:
Acked-by:Ian Campbell <ian.campbell@xxxxxxxxxx>

> +#QEMU_XEN=/usr/lib/xen/bin/qemu-system-i386
> diff --git a/tools/hotplug/Linux/init.d/xencommons 
> b/tools/hotplug/Linux/init.d/xencommons
> index 2f81ea2..9dda6e2 100644
> --- a/tools/hotplug/Linux/init.d/xencommons
> +++ b/tools/hotplug/Linux/init.d/xencommons
> @@ -104,6 +104,9 @@ do_start () {
>       xenconsoled --pid-file=$XENCONSOLED_PIDFILE $XENCONSOLED_ARGS
>       test -z "$XENBACKENDD_DEBUG" || XENBACKENDD_ARGS="-d"
>       test "`uname`" != "NetBSD" || xenbackendd $XENBACKENDD_ARGS
> +     echo Starting QEMU as disk backend for dom0
> +     test -z "$QEMU_XEN" && QEMU_XEN=/usr/lib/xen/bin/qemu-system-i386
> +     $QEMU_XEN -xen-domid 0 -xen-attach -name dom0 -nographic -M xenpv 
> -daemonize -monitor /dev/null
>  }
>  do_stop () {
>          echo Stopping xenconsoled
> diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
> index 7a1e017..e180498 100644
> --- a/tools/libxl/libxl_internal.c
> +++ b/tools/libxl/libxl_internal.c
> @@ -519,6 +519,7 @@ char * libxl__device_disk_local_attach(libxl__gc *gc,
>      libxl_ctx *ctx = gc->owner;
>      char *dev = NULL;
>      int rc;
> +    xs_transaction_t t = XBT_NULL;
>      libxl_device_disk *disk = libxl__zalloc(gc, sizeof(libxl_device_disk));
>  
>      memcpy(disk, in_disk, sizeof(libxl_device_disk));
> @@ -561,13 +562,35 @@ char * libxl__device_disk_local_attach(libxl__gc *gc,
>              break;
>          case LIBXL_DISK_BACKEND_QDISK:
>              if (disk->format != LIBXL_DISK_FORMAT_RAW) {
> -                LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "cannot locally"
> -                           " attach a qdisk image if the format is not raw");
> -                break;
> +                do {
> +                    t = xs_transaction_start(ctx->xsh);
> +                    if (t == XBT_NULL) {
> +                        LOG(ERROR, "failed to start a xenstore transaction");
> +                        goto out;
> +                    }
> +                    disk->vdev = libxl__alloc_vdev(gc, blkdev_start, t);
> +                    if (disk->vdev == NULL) {
> +                        LOG(ERROR, "libxl__alloc_vdev failed");
> +                        goto out;
> +                    }
> +                    if (libxl__device_disk_add(gc, LIBXL_TOOLSTACK_DOMID,
> +                                t, disk)) {
> +                        LOG(ERROR, "libxl_device_disk_add failed");
> +                        goto out;
> +                    }
> +                    rc = xs_transaction_end(ctx->xsh, t, 0);
> +                } while (rc == 0 && errno == EAGAIN);
> +                t = XBT_NULL;
> +                if (rc == 0) {
> +                    LOGE(ERROR, "xenstore transaction failed");
> +                    goto out;
> +                }
> +                dev = GCSPRINTF("/dev/%s", disk->vdev);
> +            } else {
> +                dev = disk->pdev_path;
>              }
>              LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "locally attaching qdisk %s\n",
> -                       in_disk->pdev_path);
> -            dev = disk->pdev_path;
> +                       dev);
>              break;
>          default:
>              LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "unrecognized disk backend "
> @@ -576,18 +599,31 @@ char * libxl__device_disk_local_attach(libxl__gc *gc,
>      }
>  
>   out:
> +    if (t != XBT_NULL)
> +        xs_transaction_end(ctx->xsh, t, 1);
>      *new_disk = disk;
>      return dev;
>  }
>  
>  int libxl__device_disk_local_detach(libxl__gc *gc, libxl_device_disk *disk)
>  {
> -    /* Nothing to do for PHYSTYPE_PHY. */
> -
> -    /*
> -     * For other device types assume that the blktap2 process is
> -     * needed by the soon to be started domain and do nothing.
> -     */
> +    switch (disk->backend) {
> +        case LIBXL_DISK_BACKEND_QDISK:
> +            if (disk->vdev != NULL) {
> +                libxl_device_disk_remove(gc->owner, LIBXL_TOOLSTACK_DOMID,
> +                        disk, 0);
> +                return libxl_device_disk_destroy(gc->owner,
> +                        LIBXL_TOOLSTACK_DOMID, disk);
> +            }
> +            break;
> +        default:
> +            /*
> +             * Nothing to do for PHYSTYPE_PHY.
> +             * For other device types assume that the blktap2 process is
> +             * needed by the soon to be started domain and do nothing.
> +             */
> +            break;
> +    }
>  
>      return 0;
>  }



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