init: use the same exit codes as chroot/podman

For consistency for the container isolation use case, let's use in init
the same exit codes as chroot and podman do:

 125: "init" cannot set up the environment inside the microVM.
 126: "init" can find the executable to be run inside the microVM but cannot not execute it.
 127: "init" cannot find the executable to be run inside the microVM.

Signed-off-by: Sergio Lopez <[email protected]>

Author: slp

include/libkrun.h

@@ -582,10 +582,16 @@ int32_t krun_split_irqchip(uint32_t ctx_id, bool enable);
  * Arguments:
  *  "ctx_id" - the configuration context ID.
  *
- * Returns:
+ * Notes:
  *  This function only returns if an error happens before starting the microVM. Otherwise, the
  *  VMM assumes it has full control of the process, and will call to exit() once the microVM shuts
  *  down.
+ *
+ * Returns:
+ *  -EINVAL - The VMM has detected an error in the microVM configuration.
+ *  125     - "init" cannot set up the environment inside the microVM.
+ *  126     - "init" can find the executable to be run inside the microVM but cannot not execute it.
+ *  127     - "init" cannot find the executable to be run inside the microVM.
  */
 int32_t krun_start_enter(uint32_t ctx_id);
 

init/init.c

@@ -980,6 +980,7 @@ int main(int argc, char **argv)
     struct ifreq ifr;
     int sockfd;
     int status;
+    int saved_errno;
     char localhost[] = "localhost\0";
     char *hostname;
     char *krun_home;
@@ -1067,16 +1068,23 @@ int main(int argc, char **argv)
     int child = fork();
     if (child < 0) {
         perror("fork");
-        exit(-3);
+        set_exit_code(125);
+        exit(125);
     }
     if (child == 0) { // child
         if (setup_redirects() < 0) {
-            exit(-4);
+            exit(125);
         }
         if (execvp(exec_argv[0], exec_argv) < 0) {
+            saved_errno = errno;
             printf("Couldn't execute '%s' inside the vm: %s\n", exec_argv[0],
                    strerror(errno));
-            exit(-3);
+            // Use the same exit code as chroot and podman do.
+            if (saved_errno == ENOENT) {
+                exit(127);
+            } else {
+                exit(126);
+            }
         }
     } else { // parent
         // Wait until the workload's entrypoint has exited, ignoring any other