init: record exit code of the entrypoint

Use the newly added exit code recording feature in virtio-fs to record
the exit code from workload's entrypoint.

We need to stop ignoring SIGCHLD, as otherwise waitpid doesn't record
the exit code of our child, which also means we need to do a waitpid
on every children to ensure we aren't leaving zombie processes.

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

Author: slp

init/init.c

@@ -28,6 +28,8 @@
 #include "tee/snp_attest.h"
 #endif
 
+#define KRUN_EXIT_CODE_IOCTL 0x7602
+
 #define KRUN_MAGIC "KRUN"
 #define KRUN_FOOTER_LEN 12
 #define CMDLINE_SECRET_PATH "/sfs/secrets/coco/cmdline"
@@ -954,10 +956,30 @@ int setup_redirects()
     return 0;
 }
 
+void set_exit_code(int code)
+{
+    int fd;
+    int ret;
+
+    fd = open("/", O_RDONLY);
+    if (fd < 0) {
+        perror("Couldn't open root filesystem to report exit code");
+        return;
+    }
+
+    ret = ioctl(fd, KRUN_EXIT_CODE_IOCTL, code);
+    if (ret < 0) {
+        perror("Error using the ioctl to set the exit code");
+    }
+
+    close(fd);
+}
+
 int main(int argc, char **argv)
 {
     struct ifreq ifr;
     int sockfd;
+    int status;
     char localhost[] = "localhost\0";
     char *hostname;
     char *krun_home;
@@ -1042,12 +1064,12 @@ int main(int argc, char **argv)
 
     // We need to fork ourselves, because pid 1 cannot doesn't receive SIGINT
     // signal
-    int pid = fork();
-    if (pid < 0) {
+    int child = fork();
+    if (child < 0) {
         perror("fork");
         exit(-3);
     }
-    if (pid == 0) { // child
+    if (child == 0) { // child
         if (setup_redirects() < 0) {
             exit(-4);
         }
@@ -1057,11 +1079,19 @@ int main(int argc, char **argv)
             exit(-3);
         }
     } else { // parent
-        // tell the kernel we don't want to be notified on SIGCHLD so it'll reap
-        // our children for us
-        signal(SIGCHLD, SIG_IGN);
-        // wait for children since we can't exit init
-        waitpid(pid, NULL, 0);
+        // Wait until the workload's entrypoint has exited, ignoring any other
+        // children.
+        while (waitpid(-1, &status, 0) != child) {
+            // Not the first child, ignore it.
+        };
+
+        // The workload's entrypoint has exited, record its exit code and exit
+        // ourselves.
+        if (WIFEXITED(status)) {
+            set_exit_code(WEXITSTATUS(status));
+        } else if (WIFSIGNALED(status)) {
+            set_exit_code(WTERMSIG(status) + 128);
+        }
     }
 
     return 0;