make domain_create() return a proper error code

While triggered by the XSA-9 fix, this really is of more general use;
that fix just pointed out very sharply that the current situation
with all domain creation failures reported to user (tools) space as
-ENOMEM is very unfortunate (actively misleading users _and_ support
personnel).

Pull over the pointer <-> error code conversion infrastructure from
Linux, and use it in domain_create() and all it callers.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
index c9cc123a40..c036c2c841 100644
--- a/xen/common/cpupool.c
+++ b/xen/common/cpupool.c
@@ -370,14 +370,18 @@ out:
 int cpupool_add_domain(struct domain *d, int poolid)
 {
     struct cpupool *c;
-    int rc = 1;
+    int rc;
     int n_dom = 0;
 
     if ( poolid == CPUPOOLID_NONE )
         return 0;
     spin_lock(&cpupool_lock);
     c = cpupool_find_by_id(poolid);
-    if ( (c != NULL) && cpumask_weight(c->cpu_valid) )
+    if ( c == NULL )
+        rc = -ESRCH;
+    else if ( !cpumask_weight(c->cpu_valid) )
+        rc = -ENODEV;
+    else
     {
         c->n_dom++;
         n_dom = c->n_dom;