Re: [Xen-devel] [PATCH RESEND v3 1/2] libxl: postpone backend name resolution

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-03-14 at 14:23 +0000, Daniel De Graaf wrote:
> This adds a backend_domname field in libxl devices that contain a
> backend_domid field, allowing either a domid or a domain name to be
> specified in the configuration structures.  The domain name is resolved
> into a domain ID in the _setdefault function when adding the device.
> This change allows the backend of the block devices to be specified
> (which previously required passing the libxl_ctx down into the block
> device parser), and will simplify specification of backend domains in
> other users of libxl.

please can we get a #define LIBXL_HAVE_DEVICE_BACKEND_NAME (or something
similar) in libxl.h so applications can tell that it is safe to use
this.

> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> ---
> 
> This patch does not include the changes to tools/libxl/libxlu_disk_l.c
> and tools/libxl/libxlu_disk_l.h because the diffs contain unrelated
> changes due to different generator versions.
> 
>  docs/misc/xl-disk-configuration.txt | 12 +++++++++
>  tools/libxl/libxl.c                 | 49 
> ++++++++++++++++++++++++++++++++++++-
>  tools/libxl/libxl_types.idl         |  5 ++++
>  tools/libxl/libxlu_disk_l.l         |  1 +
>  tools/libxl/xl_cmdimpl.c            | 36 ++++++---------------------
>  5 files changed, 73 insertions(+), 30 deletions(-)
> 
> diff --git a/docs/misc/xl-disk-configuration.txt 
> b/docs/misc/xl-disk-configuration.txt
> index 86c16be..5bd456d 100644
> --- a/docs/misc/xl-disk-configuration.txt
> +++ b/docs/misc/xl-disk-configuration.txt
> @@ -139,6 +139,18 @@ cdrom
>  Convenience alias for "devtype=cdrom".
>  
> 
> +backend=<domain-name>
> +---------------------
> +
> +Description:           Designates a backend domain for the device
> +Supported values:      Valid domain names
> +Mandatory:             No
> +
> +Specifies the backend domain which this device should attach to. This
> +defaults to domain 0. Specifying another domain requires setting up a
> +driver domain which is outside the scope of this document.
> +
> +
>  backendtype=<backend-type>
>  --------------------------
>  
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index 73e0dc3..e442afc 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -1730,12 +1730,35 @@ static int libxl__device_nextid(libxl__gc *gc, 
> uint32_t domid, char *device)
>      return nextid;
>  }
>  
> +/* backend domain name-to-domid conversion utility */
> +static int libxl__resolve_domain(libxl__gc *gc, const char *name)
> +{
> +    int i, rv;
> +    uint32_t domid;
> +    for (i=0; name[i]; i++) {
> +        if (!isdigit(name[i])) {
> +            rv = libxl_name_to_domid(libxl__gc_owner(gc), name, &domid);
> +            if (rv)
> +                return rv;
> +            return domid;
> +        }
> +    }

What are the constraints on the names of domains? I suppose it is
toolstack specific but the xl docs jsut say it has to be unique.

I'd suggest a simple rule like they cannot start with a digit, that
would make the loop in the above unnecessary. In any case the loop is a
bit odd since AFAICT it will treat "123boo" as "boo", I think it should
either treat the entire string as a name or a number.

I think you should just move domain_qualifier_to_domid  from xl to libxl
and use that...

> +    return atoi(name);
> +}
> +
>  
> /******************************************************************************/
>  int libxl__device_vtpm_setdefault(libxl__gc *gc, libxl_device_vtpm *vtpm)
>  {
> +   int rc;
>     if(libxl_uuid_is_nil(&vtpm->uuid)) {
>        libxl_uuid_generate(&vtpm->uuid);
>     }
> +   if (vtpm->backend_domname) {
> +       rc = libxl__resolve_domain(gc, vtpm->backend_domname);
> +       if (rc < 0)
> +           return rc;
> +       vtpm->backend_domid = rc;
> +   }

How about
        rc = libxl__resole_domain(gc, vtpm->backend_domname, 
&vtpm->backend_domid);
        if (rc < 0)
                return rc;
?

Then the if (...) which is repeated could be in the function and it'd be
easier to keep the logic the same for all of them.

Ian.


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