From e0892ced0534b1009d009e32c3e338456018ab15 Mon Sep 17 00:00:00 2001 From: "Denis V. Lunev" Date: Mon, 17 Jul 2023 16:55:42 +0200 Subject: [PATCH] qemu-nbd: properly report error on error in dup2() after qemu_daemon() We are trying to temporarily 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 CC: Eric Blake CC: Vladimir Sementsov-Ogievskiy Message-ID: <20230717145544.194786-4-den@openvz.org> Reviewed-by: Eric Blake [eblake: rearrange patch series, fix typo] Signed-off-by: Eric Blake --- qemu-nbd.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/qemu-nbd.c b/qemu-nbd.c index 5a8ae1f747..f27613cb57 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -940,7 +940,20 @@ int main(int argc, char **argv) saved_errno = errno; /* dup2 will overwrite error below */ /* 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(saved_errno)); exit(EXIT_FAILURE);