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]

chardev/char-parallel.c

@@ -164,13 +164,13 @@ static void qemu_chr_open_pp_fd(Chardev *chr,
 {
     ParallelChardev *drv = PARALLEL_CHARDEV(chr);
 
+    drv->fd = fd;
+
     if (ioctl(fd, PPCLAIM) < 0) {
         error_setg_errno(errp, errno, "not a parallel port");
-        close(fd);
         return;
     }
 
-    drv->fd = fd;
     drv->mode = IEEE1284_MODE_COMPAT;
 }
 #endif /* __linux__ */
@@ -238,6 +238,7 @@ static void qemu_chr_open_pp_fd(Chardev *chr,
 }
 #endif
 
+#ifdef HAVE_CHARDEV_PARALLEL
 static void qmp_chardev_open_parallel(Chardev *chr,
                                       ChardevBackend *backend,
                                       bool *be_opened,
@@ -306,3 +307,5 @@ static void register_types(void)
 }
 
 type_init(register_types);
+
+#endif  /* HAVE_CHARDEV_PARALLEL */

chardev/meson.build

@@ -21,11 +21,9 @@ if host_os == 'windows'
 else
   chardev_ss.add(files(
       'char-fd.c',
+      'char-parallel.c',
       'char-pty.c',
     ), util)
-  if host_os in ['linux', 'gnu/kfreebsd', 'freebsd', 'dragonfly']
-    chardev_ss.add(files('char-parallel.c'))
-  endif
 endif
 
 chardev_ss = chardev_ss.apply({})

include/qemu/osdep.h

@@ -508,11 +508,18 @@ void qemu_anon_ram_free(void *ptr, size_t size);
 
 #ifdef _WIN32
 #define HAVE_CHARDEV_SERIAL 1
-#elif defined(__linux__) || defined(__sun__) || defined(__FreeBSD__)    \
+#define HAVE_CHARDEV_PARALLEL 1
+#else
+#if defined(__linux__) || defined(__sun__) || defined(__FreeBSD__)   \
     || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__) \
     || defined(__GLIBC__) || defined(__APPLE__)
 #define HAVE_CHARDEV_SERIAL 1
 #endif
+#if defined(__linux__) || defined(__FreeBSD__) \
+    || defined(__FreeBSD_kernel__) || defined(__DragonFly__)
+#define HAVE_CHARDEV_PARALLEL 1
+#endif
+#endif
 
 #if defined(__HAIKU__)
 #define SIGIO SIGPOLL

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)
 {
@@ -1544,6 +1568,9 @@ int main(int argc, char **argv)
     g_test_add_func("/char/udp", char_udp_test);
 #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);