| Message ID | 20230717145544.194786-4-den@openvz.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | qemu-nbd: fix regression with qemu-nbd --fork run over ssh | expand |
On Mon, Jul 17, 2023 at 04:55:42PM +0200, Denis V. Lunev wrote: > We are trying to temporary redirect stderr of daemonized process to temporarily > a pipe to report a error and get failed. In that case we could not > use error_report() helper, but should write the message directly into > the problematic pipe. > > Signed-off-by: Denis V. Lunev <den@openvz.org> > CC: Eric Blake <eblake@redhat.com> > CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> > --- > qemu-nbd.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/qemu-nbd.c b/qemu-nbd.c > index 186ce9474c..4450cc826b 100644 > --- a/qemu-nbd.c > +++ b/qemu-nbd.c > @@ -937,7 +937,20 @@ int main(int argc, char **argv) > ret = qemu_daemon(1, 0); > errno from qemu_daemon... > /* Temporarily redirect stderr to the parent's pipe... */ > - dup2(stderr_fd[1], STDERR_FILENO); > + if (dup2(stderr_fd[1], STDERR_FILENO) < 0) { ...is still potentially lost here... > + char str[256]; > + snprintf(str, sizeof(str), > + "%s: Failed to link stderr to the pipe: %s\n", > + g_get_prgname(), strerror(errno)); > + /* > + * We are unable to use error_report() here as we need to get > + * stderr pointed to the parent's pipe. Write to that pipe > + * manually. > + */ > + ret = write(stderr_fd[1], str, strlen(str)); > + exit(EXIT_FAILURE); > + } > + > if (ret < 0) { > error_report("Failed to daemonize: %s", strerror(errno)); ...before use here. Patch 4/5 addresses that, but I'm inclined to just swap the order of the two patches when applying the series in my NBD tree. Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/qemu-nbd.c b/qemu-nbd.c index 186ce9474c..4450cc826b 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -937,7 +937,20 @@ int main(int argc, char **argv) ret = qemu_daemon(1, 0); /* Temporarily redirect stderr to the parent's pipe... */ - dup2(stderr_fd[1], STDERR_FILENO); + if (dup2(stderr_fd[1], STDERR_FILENO) < 0) { + char str[256]; + snprintf(str, sizeof(str), + "%s: Failed to link stderr to the pipe: %s\n", + g_get_prgname(), strerror(errno)); + /* + * We are unable to use error_report() here as we need to get + * stderr pointed to the parent's pipe. Write to that pipe + * manually. + */ + ret = write(stderr_fd[1], str, strlen(str)); + exit(EXIT_FAILURE); + } + if (ret < 0) { error_report("Failed to daemonize: %s", strerror(errno)); exit(EXIT_FAILURE);
We are trying to temporary redirect stderr of daemonized process to a pipe to report a error and get failed. In that case we could not use error_report() helper, but should write the message directly into the problematic pipe. Signed-off-by: Denis V. Lunev <den@openvz.org> CC: Eric Blake <eblake@redhat.com> CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> --- qemu-nbd.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)