: xl: catch invalid numeric domain ID

Hi,

if you run any domain specific xl command with an invalid (aka non-existing) numeric domain ID, the command does not abort, but proceeds with some bogus number:

# xl destroy 42
libxl: error: libxl.c:692:libxl_domain_destroy xc_domain_pause failed for 42
libxl: error: libxl_dm.c:705:libxl__destroy_device_model Couldn't find device model's pid: No such file or directory
libxl: error: libxl.c:696:libxl_domain_destroy libxl__destroy_device_model failed for 42
libxl: error: libxl_device.c:325:libxl__devices_destroy /local/domain/42/device is empty
libxl: error: libxl_dom.c:536:userdata_path unable to find domain info for domain 42: Success
libxl: error: libxl.c:713:libxl_domain_destroy xc_domain_destroy failed for 42

The attached patch catches a non-existing domain and returns early (as an invalid domain _name_ would do). Please apply to Xen 4.1.0-rc.

Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany

diff -r 003acf02d416 tools/libxl/xl_cmdimpl.c
@@ -170,6 +170,10 @@
         exit(2);
     }
     common_domname = was_name ? p : libxl_domid_to_name(&ctx, domid);
+    if (common_domname == NULL) {
+    	fprintf(stderr, "%d is not a valid domain\n", domid);
+    	exit(2);
+    }
 }
 
 static int acquire_lock(void)

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Andre Przywara writes ("[PATCH]: xl: catch invalid numeric domain ID"):

Thanks, but I'm not 100% convinced that it is impossible to ever get into a situation where a domain exists but has no name. In that case, this patch of yours would leave an undestroyable domain.

I think the right answer is to use libxl_domain_info to check whether the domain exists. It returns ERROR_INVAL, without logging anything, if the domain does not exist. On other failures xl destroy should probably carry on and attempt to destroy the domain.

Ian.

OK, I looked around the bit, libxl_domain_info really seems to be the easiest solution. So please consider the attached patch. I am not 100% happy with it, actually I think find_domain should return an error value. In this case we could abort the commands gracefully (like xl list does) and avoid the rather impolite exit(2). On the other hand I am not sure if fixing the 30 or so callers of find_domain() is appropriate in this state of development.
Please tell me if you prefer this more elaborated version and I will send a patch.

Regards,
Andre.

Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany

index 359970b..deae3f7 100644
@@ -163,12 +163,18 @@ static int cpupool_qualifier_to_cpupoolid(const char *p, uint32_t *poolid_r,
 static void find_domain(const char *p)
 {
     int rc, was_name;
+    libxl_dominfo info_buf;
 
     rc = domain_qualifier_to_domid(p, &domid, &was_name);
     if (rc) {
         fprintf(stderr, "%s is an invalid domain identifier (rc=%d)\n", p, rc);
         exit(2);
     }
+    rc = libxl_domain_info(&ctx, &info_buf, domid);
+    if (rc == ERROR_INVAL) {
+        fprintf(stderr, "Error: Domain \'%d\' does not exist.\n", domid);
+        exit(2);
+    }
     common_domname = was_name ? p : libxl_domid_to_name(&ctx, domid);
 }
 

@@ -3149,11 +3155,6 @@ int main_list(int argc, char **argv)
     } else if (optind == argc-1) {
         find_domain(argv[optind]);
         rc = libxl_domain_info(&ctx, &info_buf, domid);
-        if (rc == ERROR_INVAL) {
-            fprintf(stderr, "Error: Domain \'%s\' does not exist.\n",
-                argv[optind]);
-            return -rc;
-        }
         if (rc) {
             fprintf(stderr, "libxl_domain_info failed (code %d).\n", rc);
             return -rc;

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