Re: [PATCH 5/6] libxl: introduce libxl__alloc_vdev

[Ian Campbell <Ian.Campbell@citrix.com>]

On Tue, 2012-03-27 at 14:59 +0100, Stefano Stabellini wrote:
> Introduce libxl__alloc_vdev: find a spare virtual block device in the
> domain passed as argument.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> ---
>  tools/libxl/libxl.c |   60 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 60 insertions(+), 0 deletions(-)
> 
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index fe63fd5..fa7898a 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -1228,6 +1228,13 @@ int libxl_vncviewer_exec(libxl_ctx *ctx, uint32_t domid, int autopass)
>  
>  /******************************************************************************/
>  
> +static int libxl__append_disk_list_of_type(libxl__gc *gc,
> +                                           uint32_t domid,
> +                                           xs_transaction_t t,
> +                                           const char *type,
> +                                           libxl_device_disk **disks,
> +                                           int *ndisks);
> +
>  int libxl__device_disk_setdefault(libxl__gc *gc, libxl_device_disk *disk)
>  {
>      int rc;
> @@ -1278,6 +1285,59 @@ static int libxl__device_from_disk(libxl__gc *gc, uint32_t domid,
>      return 0;
>  }
>  
> +static int libxl__vdev_to_index(libxl__gc *gc, char *vdev)
> +{
> +    if (vdev == NULL)
> +        return 0;
> +    if (strlen(vdev) > 4 || strlen(vdev) < 4)
> +        return 0;
> +    /* assume xvdz is the last one available */
> +    if (vdev[3] >= 'z')
> +        return -1;
> +    return vdev[3] - 'a';
> +}
> +
> +static char* libxl__index_to_vdev(libxl__gc *gc, int idx)
> +{
> +    if (idx < 0)
> +        return NULL;
> +    return libxl__sprintf(gc, "xvd%c", 'a' + idx);
> +}
> +
> +static char * libxl__alloc_vdev(libxl__gc *gc, uint32_t domid, xs_transaction_t t,
> +        libxl_device_disk *disk)
> +{
> +    int rc = 0;
> +    libxl_device_disk *disks = NULL;
> +    int num = 0, idx = -1, max_idx = -1, i = 0;
> +
> +    rc = libxl__append_disk_list_of_type(gc, domid, t, "vbd", &disks, &num);
> +    if (rc) goto out;
> +
> +    rc = libxl__append_disk_list_of_type(gc, domid, t, "tap", &disks, &num);
> +    if (rc) goto out;
> +
> +    rc = libxl__append_disk_list_of_type(gc, domid, t, "qdisk", &disks, &num);
> +    if (rc) goto out;

This is basically an open-coded version of libxl_disk_list, isn't it?

For this use though wouldn't it be as easy to simply iterate over idx
checking if a frontend dir exists?

> +
> +    for (i = 0; i < num; i++) {
> +        idx = libxl__vdev_to_index(gc, disks[i].vdev);
> +        if (idx < 0) {
> +            max_idx = -1;
> +            goto out;
> +        }
> +        if (idx > max_idx)
> +            max_idx = idx;
> +    }
> +    max_idx++;
> +out:
> +    while (disks && num) {
> +        num--;
> +        libxl_device_disk_dispose(&disks[num]);
> +    }
> +    free(disks);
> +    return libxl__index_to_vdev(gc, max_idx);
> +}
>  
>  static int libxl__device_disk_add_t(libxl__gc *gc, uint32_t domid, xs_transaction_t t,
>          libxl_device_disk *disk)