x86/ucode: Distinguish "ucode already up to date"

Right now, Xen returns -ENOENT for both "the provided blob isn't correct for
this CPU", and "the blob isn't newer than what's loaded".

This in turn causes xen-ucode to exit with an error, when "nothing to do" is
more commonly a success condition.

Handle EEXIST specially and exit cleanly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

tools/misc/xen-ucode.c

@@ -125,8 +125,11 @@ int main(int argc, char *argv[])
         exit(1);
     }
 
+    errno = 0;
     ret = xc_microcode_update(xch, buf, len);
-    if ( ret )
+    if ( ret == -1 && errno == EEXIST )
+        printf("Microcode already up to date\n");
+    else if ( ret )
     {
         fprintf(stderr, "Failed to update microcode. (err: %s)\n",
                 strerror(errno));

xen/arch/x86/cpu/microcode/core.c

@@ -640,7 +640,7 @@ static long cf_check microcode_update_helper(void *data)
                    "microcode: couldn't find any newer%s revision in the provided blob!\n",
                    opt_ucode_allow_same ? " (or the same)" : "");
             microcode_free_patch(patch);
-            ret = -ENOENT;
+            ret = -EEXIST;
 
             goto put;
         }