[Libguestfs] [PATCH nbdkit 1/2] server: Call .get_ready before redirecting stdin/stdout to /dev/null.

VDDK plugin + --run was broken because of the following sequence of events: (1) After .config_complete, server redirects stdin/stdout to /dev/null. (2) Server then calls vddk_get_ready which reexecs. (3) We restart the server from the top, but with stdin/stdout redirected to /dev/null. So saved_stdin/saved_stdout save /dev/null. (4) run_command is called which "restores" /dev/null as stdin/stdout. (5) The output of the --run option is sent to /dev/null. In addition to fixing this problem with VDDK, it also makes general sense not to redirect stdin/stdout before calling .get_ready since this callback is supposed to be the last chance before the server daemonizes, and redirecting stdin/stdout is part of daemonization. Before this commit: $ ./nbdkit vddk libdir=tests/.libs /dev/null --run 'qemu-img info $nbd' [no output] After this commit: $ ./nbdkit vddk libdir=tests/.libs /dev/null --run 'qemu-img info $nbd' image: nbd://localhost:10809 file format: raw virtual size: 512 KiB (524288 bytes) disk size: unavailable One test (test-stdio.sh) made the assumption that stdin/stdout had already been redirected to /dev/null in .get_ready. I adjusted this test so it checks for redirection in .after_fork instead. --- server/main.c | 10 +++++----- tests/test-stdio-plugin.c | 9 +++++++++ 2 files changed, 14 insertions(+), 5 deletions(-) diff --git a/server/main.c b/server/main.c index 2f0aaf07..11c1614b 100644 --- a/server/main.c +++ b/server/main.c @@ -693,6 +693,11 @@ main (int argc, char *argv[]) /* Select the correct thread model based on config. */ lock_init_thread_model (); + /* Tell the plugin that we are about to start serving. This must be + * called before we change user, fork, or open any sockets. + */ + top->get_ready (top); + /* Sanitize stdin/stdout to /dev/null, after saving the originals * when needed. We are still single-threaded at this point, and * already checked that stdin/out were open, so we don't have to @@ -726,12 +731,7 @@ main (int argc, char *argv[]) perror ("open"); exit (EXIT_FAILURE); } - - /* Tell the plugin that we are about to start serving. This must be - * called before we change user, fork, or open any sockets. - */ configured = true; - top->get_ready (top); start_serving (); diff --git a/tests/test-stdio-plugin.c b/tests/test-stdio-plugin.c index 618eae83..86447278 100644 --- a/tests/test-stdio-plugin.c +++ b/tests/test-stdio-plugin.c @@ -122,6 +122,14 @@ stdio_config_complete (void) static int stdio_get_ready (void) +{ + bool check = stdio_check (); + assert (check == false); + return 0; +} + +static int +stdio_after_fork (void) { bool check = stdio_check (); assert (check == true); @@ -163,6 +171,7 @@ static struct nbdkit_plugin plugin = { .config = stdio_config, .config_complete = stdio_config_complete, .get_ready = stdio_get_ready, + .after_fork = stdio_after_fork, .open = stdio_open, .get_size = stdio_get_size, .pread = stdio_pread, -- 2.27.0