qemu-nbd: print error messages from the daemon through a pipe
In order to get nice error messages, keep the qemu-nbd process running
until before issuing NBD_DO_IT and connected to the daemon with a pipe.
This lets the qemu-nbd process relay error messages from the daemon and
exit with a nonzero status if appropriate.
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/qemu-nbd.c b/qemu-nbd.c
index ffc2a8a..b330d8d 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -226,8 +226,13 @@
/* update partition table */
pthread_create(&show_parts_thread, NULL, show_parts, NULL);
- fprintf(stderr, "NBD device %s is now connected to %s\n",
- device, srcpath);
+ if (verbose) {
+ fprintf(stderr, "NBD device %s is now connected to %s\n",
+ device, srcpath);
+ } else {
+ /* Close stderr so that the qemu-nbd process exits. */
+ dup2(STDOUT_FILENO, STDERR_FILENO);
+ }
ret = nbd_client(fd);
if (ret) {
@@ -406,6 +411,58 @@
return 0;
}
+ if (device && !verbose) {
+ int stderr_fd[2];
+ pid_t pid;
+ int ret;
+
+ if (qemu_pipe(stderr_fd) == -1) {
+ err(EXIT_FAILURE, "Error setting up communication pipe");
+ }
+
+ /* Now daemonize, but keep a communication channel open to
+ * print errors and exit with the proper status code.
+ */
+ pid = fork();
+ if (pid == 0) {
+ close(stderr_fd[0]);
+ ret = qemu_daemon(0, 0);
+
+ /* Temporarily redirect stderr to the parent's pipe... */
+ dup2(stderr_fd[1], STDERR_FILENO);
+ if (ret == -1) {
+ err(EXIT_FAILURE, "Failed to daemonize");
+ }
+
+ /* ... close the descriptor we inherited and go on. */
+ close(stderr_fd[1]);
+ } else {
+ bool errors = false;
+ char *buf;
+
+ /* In the parent. Print error messages from the child until
+ * it closes the pipe.
+ */
+ close(stderr_fd[1]);
+ buf = g_malloc(1024);
+ while ((ret = read(stderr_fd[0], buf, 1024)) > 0) {
+ errors = true;
+ ret = qemu_write_full(STDERR_FILENO, buf, ret);
+ if (ret == -1) {
+ exit(EXIT_FAILURE);
+ }
+ }
+ if (ret == -1) {
+ err(EXIT_FAILURE, "Cannot read from daemon");
+ }
+
+ /* Usually the daemon should not print any message.
+ * Exit with zero status in that case.
+ */
+ exit(errors);
+ }
+ }
+
bdrv_init();
bs = bdrv_new("hda");
@@ -433,13 +490,6 @@
err(EXIT_FAILURE, "Failed to open %s", device);
}
- if (!verbose) {
- /* detach client and server */
- if (qemu_daemon(0, 0) == -1) {
- err(EXIT_FAILURE, "Failed to daemonize");
- }
- }
-
if (sockpath == NULL) {
sockpath = g_malloc(128);
snprintf(sockpath, 128, SOCKET_PATH, basename(device));
