cgroup: don't include trailing / in cgns_prefix

We could do the math on the consuming side (and indeed, I tried), but it
seems much cleaner to just not include this in the first place so that all
consumers of it don't need to do the same thing.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/cgroup.c

@@ -1604,12 +1604,12 @@ static int rewrite_cgsets(CgroupEntry *cge, char **controllers, int n_controller
 				 */
 				if (!set_from) {
 					set_from = true;
-					/* -2 because cgns_prefix includes leading and trailing /'s */
-					*from = xsprintf("%s%s", to, (*from) + cg->cgns_prefix - 2);
+					/* -1 because cgns_prefix includes leading / */
+					*from = xsprintf("%s%s", to, (*from) + cg->cgns_prefix - 1);
 				}
 
 				cg->path = xsprintf("%s%s", to, cg->path +
-							cg->cgns_prefix - 1);
+							cg->cgns_prefix);
 				cg->cgns_prefix = strlen(to);
 			} else {
 				/* otherwise, use the old rewriting strategy */

criu/proc_parse.c

@@ -2283,6 +2283,8 @@ int parse_task_cgroup(int pid, struct parasite_dump_cgroup_args *args, struct li
 			}
 
 			ext->cgns_prefix = pos - ext->path;
+			if (ext->path[ext->cgns_prefix-1] == '/')
+				ext->cgns_prefix--;
 		}
 	}