Re: [Xen-devel] [Patch v3 3/4] tools/libxl: Fix libxl__device_nic_from_xs_be()

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Andrew Cooper writes ("Re: [Xen-devel] [Patch v3 3/4] tools/libxl: Fix 
libxl__device_nic_from_xs_be()"):
> On 26/11/13 15:08, Ian Jackson wrote:
> > From: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > Date: Tue, 26 Nov 2013 12:08:09 +0000
> > Subject: [PATCH] libxl: Fix error handling in libxl__device_nic_from_xs_be
...
> > Introduce here a READ_BACKEND macro to make the code less repetitive.

I was thinking about READ_BACKEND and wondered whether we should have
something like this in libxl_internal.h:

 /*
  * const char *XSREADF_OR_RCOUT(libxl__gc*, const char *format, ...);
  *
  * Reads the xenstore key at sprintf(format, ...).
  * On success returns the string (from the gc tgc), or NULL for ENOENT.
  * On other errors, logs, sets rc, and does "goto out".
  *
  * Expects in its scope:
  *   libxl__gc *gc;  // for the sprintf
  *   int rc;         // trashed
  *   out:            // used on error only; jumped to with rc set
  */
 #define XSREADF_OR_RCOUT(tgc, format, ...) ({                            \
         const char *xsreadf_tmp;                                         \
         rc = libxl__xs_read_checked((tgc), XBT_NULL,                     \
                                     GCSPRINTF((format), __VA_ARGS__),    \
                                     &xsreadf_tmp);                       \
         if (rc) goto out;                                                \
         xsreadf_tmp;                                                     \
     )}

We don't presently have anywhere in libxl_internal.h that assumes the
existence of "out" and "rc" in their scope.

Ian.

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