chardev/parallel: Don't close stdin on inappropriate device

The __linux__ version of qemu_chr_open_pp_fd() tries to claim the
parport device with a PPCLAIM ioctl().  On success, it stores the file
descriptor in the chardev object, and returns success.  On failure, it
closes the file descriptor, and returns failure.

chardev_new() then passes the Chardev to object_unref().  This duly
calls char_parallel_finalize(), which closes the file descriptor
stored in the chardev object.  Since qemu_chr_open_pp_fd() didn't
store it, it's still zero, so this closes standard input.  Ooopsie.

To demonstate, add a unit test.  With the bug above unfixed, running
this test closes standard input.  char_hotswap_test() happens to run
next.  It opens a socket, duly gets file descriptor 0, and since it
tests for success with > 0 instead of >= 0, it fails.

The new unit test needs to be conditional exactly like the chardev it
tests.  Since the condition is rather complicated, steal the solution
from the serial chardev: define HAVE_CHARDEV_PARALLEL in qemu/osdep.h.
This also permits simplifying chardev/meson.build a bit.

The bug fix is easy enough: store the file descriptor, and leave
closing it to char_parallel_finalize().

The next commit will fix char_hotswap_test()'s test for success.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240203080228.2766159-2-armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[Test fixed up for BSDs, indentation fixed up, commit message improved]

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/unit/test-char.c b/tests/unit/test-char.c
index 649fdf64e1..2aea49c3b6 100644
--- a/tests/unit/test-char.c
+++ b/tests/unit/test-char.c
@@ -1203,6 +1203,30 @@ static void char_serial_test(void)
 }
 #endif
 
+#if defined(HAVE_CHARDEV_PARALLEL) && !defined(WIN32)
+static void char_parallel_test(void)
+{
+    QemuOpts *opts;
+    Chardev *chr;
+
+    opts = qemu_opts_create(qemu_find_opts("chardev"), "parallel-id",
+                            1, &error_abort);
+    qemu_opt_set(opts, "backend", "parallel", &error_abort);
+    qemu_opt_set(opts, "path", "/dev/null", &error_abort);
+
+    chr = qemu_chr_new_from_opts(opts, NULL, NULL);
+#ifdef __linux__
+    /* fails to PPCLAIM, see qemu_chr_open_pp_fd() */
+    g_assert_null(chr);
+#else
+    g_assert_nonnull(chr);
+    object_unparent(OBJECT(chr));
+#endif
+
+    qemu_opts_del(opts);
+}
+#endif
+
 #ifndef _WIN32
 static void char_file_fifo_test(void)
 {
@@ -1545,6 +1569,9 @@ int main(int argc, char **argv)
 #if defined(HAVE_CHARDEV_SERIAL) && !defined(WIN32)
     g_test_add_func("/char/serial", char_serial_test);
 #endif
+#if defined(HAVE_CHARDEV_PARALLEL) && !defined(WIN32)
+    g_test_add_func("/char/parallel", char_parallel_test);
+#endif
     g_test_add_func("/char/hotswap", char_hotswap_test);
     g_test_add_func("/char/websocket", char_websock_test);