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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>
This commit is contained in:
Paolo Bonzini 2011-11-04 15:51:22 +01:00 committed by Kevin Wolf
parent a517e88baa
commit c1f8fdc362
1 changed files with 59 additions and 9 deletions
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68
qemu-nbd.c
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@ -226,8 +226,13 @@ static void *nbd_client_thread(void *arg)
/* 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 @@ int main(int argc, char **argv)
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 @@ int main(int argc, char **argv)
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));