libxl: Change default for b_info->{cpu, node}map to "not allocated"

by avoiding allocating them in libxl__domain_build_info_setdefault.
In fact, back in 7e449837 ("libxl: provide _init and _setdefault for
libxl_domain_build_info") and a5d30c23 ("libxl: allow for explicitly
specifying node-affinity"), it was decided that the default for these
fields was for them to be allocated and filled.

That is now causing problem, whenever we have to figure out whether
the caller is using or not one of those fields. In fact, when we see
a full bitmap, is it just the default value, or is the user that
wants it that way?

Since that kind of knowledge has become important, change the default
to be "bitmap not allocated". It then becomes easy to know whether a
libxl caller is using one of the fields, just by checking whether the
bitmap is actually there with a non-zero size.

This is very important for the following patches introducing new ways
of specifying hard and soft affinity. It also allows us to improve
the checks around NUMA automatic placement, during domain creation
(and that bit is done in this very patch).

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl_create.c

@@ -187,20 +187,8 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
     } else if (b_info->avail_vcpus.size > HVM_MAX_VCPUS)
         return ERROR_FAIL;
 
-    if (!b_info->cpumap.size) {
-        if (libxl_cpu_bitmap_alloc(CTX, &b_info->cpumap, 0))
-            return ERROR_FAIL;
-        libxl_bitmap_set_any(&b_info->cpumap);
-    }
-
     libxl_defbool_setdefault(&b_info->numa_placement, true);
 
-    if (!b_info->nodemap.size) {
-        if (libxl_node_bitmap_alloc(CTX, &b_info->nodemap, 0))
-            return ERROR_FAIL;
-        libxl_bitmap_set_any(&b_info->nodemap);
-    }
-
     if (b_info->max_memkb == LIBXL_MEMKB_DEFAULT)
         b_info->max_memkb = 32 * 1024;
     if (b_info->target_memkb == LIBXL_MEMKB_DEFAULT)

tools/libxl/libxl_dom.c

@@ -241,28 +241,39 @@ int libxl__build_pre(libxl__gc *gc, uint32_t domid,
     }
 
     /*
-     * Check if the domain has any CPU affinity. If not, try to build
-     * up one. In case numa_place_domain() find at least a suitable
-     * candidate, it will affect info->nodemap accordingly; if it
-     * does not, it just leaves it as it is. This means (unless
-     * some weird error manifests) the subsequent call to
-     * libxl_domain_set_nodeaffinity() will do the actual placement,
-     * whatever that turns out to be.
+     * Check if the domain has any CPU or node affinity already. If not, try
+     * to build up the latter via automatic NUMA placement. In fact, in case
+     * numa_place_domain() manage to find a placement, in info->nodemap is
+     * updated accordingly; if it does not manage, info->nodemap is just left
+     * alone. It is then the the subsequent call to
+     * libxl_domain_set_nodeaffinity() that enacts the actual placement.
      */
     if (libxl_defbool_val(info->numa_placement)) {
-        if (!libxl_bitmap_is_full(&info->cpumap)) {
+        if (info->cpumap.size) {
             LOG(ERROR, "Can run NUMA placement only if no vcpu "
-                       "affinity is specified");
+                       "affinity is specified explicitly");
             return ERROR_INVAL;
         }
+        if (info->nodemap.size) {
+            LOG(ERROR, "Can run NUMA placement only if the domain does not "
+                       "have any NUMA node affinity set already");
+            return ERROR_INVAL;
+        }
+
+        rc = libxl_node_bitmap_alloc(ctx, &info->nodemap, 0);
+        if (rc)
+            return rc;
+        libxl_bitmap_set_any(&info->nodemap);
 
         rc = numa_place_domain(gc, domid, info);
         if (rc)
             return rc;
     }
-    libxl_domain_set_nodeaffinity(ctx, domid, &info->nodemap);
-    libxl_set_vcpuaffinity_all(ctx, domid, info->max_vcpus,
-                               &info->cpumap, NULL);
+    if (info->nodemap.size)
+        libxl_domain_set_nodeaffinity(ctx, domid, &info->nodemap);
+    if (info->cpumap.size)
+        libxl_set_vcpuaffinity_all(ctx, domid, info->max_vcpus,
+                                   &info->cpumap, NULL);
 
     if (xc_domain_setmaxmem(ctx->xch, domid, info->target_memkb +
         LIBXL_MAXMEM_CONSTANT) < 0) {