tools/libxc: Prevent erroneous success from xc_domain_restore

The variable 'rc' is set to 1 at the top of xc_domain_restore, and for the
most part is left alone until success, at which point it is set to 0.

There is a separate 'frc' which for the most part is used to check function
calls, keeping errors separate from 'rc'.

For a toolstack which sets callbacks->toolstack_restore(), and the function
returns 0, any subsequent error will end up with code flow going to "out;",
resulting in the migration being declared a success.

For consistency, update the callsites of xc_dom_gnttab{,_hvm}_seed() to use
'frc', even though their use of 'rc' is currently safe.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: George Dunlap <george.dunlap@eu.citrix.com>

tools/libxc/xc_domain_restore.c

@@ -2240,9 +2240,9 @@ int xc_domain_restore(xc_interface *xch, int io_fd, uint32_t dom,
         memcpy(ctx->live_p2m, ctx->p2m, dinfo->p2m_size * sizeof(xen_pfn_t));
     munmap(ctx->live_p2m, P2M_FL_ENTRIES * PAGE_SIZE);
 
-    rc = xc_dom_gnttab_seed(xch, dom, *console_mfn, *store_mfn,
-                            console_domid, store_domid);
-    if (rc != 0)
+    frc = xc_dom_gnttab_seed(xch, dom, *console_mfn, *store_mfn,
+                             console_domid, store_domid);
+    if (frc != 0)
     {
         ERROR("error seeding grant table");
         goto out;
@@ -2257,10 +2257,10 @@ int xc_domain_restore(xc_interface *xch, int io_fd, uint32_t dom,
     {
         if ( callbacks != NULL && callbacks->toolstack_restore != NULL )
         {
-            rc = callbacks->toolstack_restore(dom, tdata.data, tdata.len,
-                        callbacks->data);
+            frc = callbacks->toolstack_restore(dom, tdata.data, tdata.len,
+                                               callbacks->data);
             free(tdata.data);
-            if ( rc < 0 )
+            if ( frc < 0 )
             {
                 PERROR("error calling toolstack_restore");
                 goto out;
@@ -2326,9 +2326,9 @@ int xc_domain_restore(xc_interface *xch, int io_fd, uint32_t dom,
         goto out;
     }
 
-    rc = xc_dom_gnttab_hvm_seed(xch, dom, *console_mfn, *store_mfn,
-                                console_domid, store_domid);
-    if (rc != 0)
+    frc = xc_dom_gnttab_hvm_seed(xch, dom, *console_mfn, *store_mfn,
+                                 console_domid, store_domid);
+    if (frc != 0)
     {
         ERROR("error seeding grant table");
         goto out;