Re: [Xen-devel] [PATCH 07/14] libxl: disks: Make LIBXL_DISK_BACKEND_UNKNOWN work

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-05-12 at 15:36 +0100, Ian Jackson wrote:
> libxl callers should not be required to specify the backend if they
> don't want to.  So LIBXL_DISK_BACKEND_UNKNOWN should instruct libxl to
> choose the backend for itself.

I guess the selection of LIBXL_DISK_BACKEND_TAP was chosen to give the
greatest coverage as a stop gap measure until more smarts arrive? (It'll
fall back to QDISK as necessary too, which is nice). 

> 
> More thorough fixes for the disk handling will follow.
> 
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

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

> ---
>  tools/libxl/libxl.c |   15 +++++++++++++++
>  1 files changed, 15 insertions(+), 0 deletions(-)
> 
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index fe012cb..73fc3e9 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -989,6 +989,21 @@ int libxl_device_disk_add(libxl_ctx *ctx, uint32_t 
> domid, libxl_device_disk *dis
>      device.domid = domid;
>      device.kind = DEVICE_VBD;
>  
> +
> +    /*
> +     * Fixing the incoming backend type to try to decide on which
> +     * backend to use.  Unfortunately at the moment this code is
> +     * utterly broken, but it more or less works.
> +     */
> +
> +    /*
> +     * Backend type UNKNOWN should mean "caller does not want to specify",
> +     * not "break pointlessely".  (Callers should not be required to
> +     * specify the backend if they don't want to.)
> +     */
> +    if (disk->backend == LIBXL_DISK_BACKEND_UNKNOWN)
> +        disk->backend = LIBXL_DISK_BACKEND_TAP;
> +
>      /* If blktap is not available then fallback to qdisk */
>      if (disk->backend == LIBXL_DISK_BACKEND_TAP && 
> !libxl__blktap_enabled(&gc))
>          disk->backend = LIBXL_DISK_BACKEND_QDISK;



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