commit f6f4620cbbe03fbdbddddd9c325ab3ea0dad33c6
author Denis V. Lunev <den@openvz.org> Wed Sep 06 11:32:08 2023 +0200
committer Eric Blake <eblake@redhat.com> Fri Sep 08 07:20:58 2023 -0500
tree fdf2f4752f9874eb5e70dcf88f02d18eae768939
parent 2eb7c2abe0b85a945549e91cb794d214c0905403

qemu-nbd: Restore "qemu-nbd -v --fork" output

Closing stderr earlier is good for daemonized qemu-nbd under ssh
earlier, but breaks the case where -v is being used to track what is
happening in the server, as in iotest 233.

When we know we are verbose, we should preserve original stderr and
restore it once the setup stage is done. This commit restores the
original behavior with -v option. In this case original output
inside the test is kept intact.

Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Eric Blake <eblake@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
CC: Hanna Reitz <hreitz@redhat.com>
CC: Mike Maslenkin <mike.maslenkin@gmail.com>
Fixes: 5c56dd27a2 ("qemu-nbd: fix regression with qemu-nbd --fork run over ssh")
Message-ID: <20230906093210.339585-7-den@openvz.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Tested-by: Eric Blake <eblake@redhat.com>
[eblake: fix build by avoiding stderr as struct member name]
Signed-off-by: Eric Blake <eblake@redhat.com>

qemu-nbd.c

diff --git a/qemu-nbd.c b/qemu-nbd.c
index 7c4e22d..30eeb6f 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -255,18 +255,23 @@
     char *device;
     char *srcpath;
     SocketAddress *saddr;
+    int old_stderr;
     bool fork_process;
     bool verbose;
 };
 
-static void nbd_client_release_pipe(void)
+static void nbd_client_release_pipe(int old_stderr)
 {
     /* Close stderr so that the qemu-nbd process exits.  */
-    if (dup2(STDOUT_FILENO, STDERR_FILENO) < 0) {
+    if (dup2(old_stderr, STDERR_FILENO) < 0) {
         error_report("Could not release pipe to parent: %s",
                      strerror(errno));
         exit(EXIT_FAILURE);
     }
+    if (old_stderr != STDOUT_FILENO && close(old_stderr) < 0) {
+        error_report("Could not release qemu-nbd: %s", strerror(errno));
+        exit(EXIT_FAILURE);
+    }
 }
 
 #if HAVE_NBD_DEVICE
@@ -332,7 +337,7 @@
         fprintf(stderr, "NBD device %s is now connected to %s\n",
                 opts->device, opts->srcpath);
     } else {
-        nbd_client_release_pipe();
+        nbd_client_release_pipe(opts->old_stderr);
     }
 
     if (nbd_client(fd) < 0) {
@@ -597,6 +602,7 @@
         .device = NULL,
         .srcpath = NULL,
         .saddr = NULL,
+        .old_stderr = STDOUT_FILENO,
     };
 
 #ifdef CONFIG_POSIX
@@ -951,6 +957,16 @@
 
             close(stderr_fd[0]);
 
+            /* Remember parent's stderr if we will be restoring it. */
+            if (opts.verbose /* fork_process is set */) {
+                opts.old_stderr = dup(STDERR_FILENO);
+                if (opts.old_stderr < 0) {
+                    error_report("Could not dup original stderr: %s",
+                                 strerror(errno));
+                    exit(EXIT_FAILURE);
+                }
+            }
+
             ret = qemu_daemon(1, 0);
             saved_errno = errno;    /* dup2 will overwrite error below */
 
@@ -1181,7 +1197,7 @@
     }
 
     if (opts.fork_process) {
-        nbd_client_release_pipe();
+        nbd_client_release_pipe(opts.old_stderr);
     }
 
     state = RUNNING;