Re: [PATCH 1/4] chardev/parallel: Don't close stdin on inappropriate device

[Markus Armbruster <armbru@redhat.com>]

Markus Armbruster <armbru@redhat.com> writes:

> 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 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().
>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>

[...]

> diff --git a/chardev/char-parallel.c b/chardev/char-parallel.c
> index a5164f975a..78697d7522 100644
> --- a/chardev/char-parallel.c
> +++ b/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 */
> diff --git a/tests/unit/test-char.c b/tests/unit/test-char.c
> index 649fdf64e1..76946e6f90 100644
> --- a/tests/unit/test-char.c
> +++ b/tests/unit/test-char.c
> @@ -1203,6 +1203,24 @@ 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);
> +    g_assert_null(chr);

This is wrong.

On a Linux host, qemu_chr_new_from_opts() fails, because
qemu_chr_open_pp_fd()'s attempt to PPCLAIM fails.

On a BSD host, it succeeds.

Proposed fixup appended.  Marc-André, is respinning the PR with the
fixup okay, or would you prefer a v2?

> +
> +    qemu_opts_del(opts);
> +}
> +#endif
> +
>  #ifndef _WIN32
>  static void char_file_fifo_test(void)
>  {
> @@ -1544,6 +1562,9 @@ 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);

[...]

diff --git a/tests/unit/test-char.c b/tests/unit/test-char.c
index e3b783c06b..f273ce5226 100644
--- a/tests/unit/test-char.c
+++ b/tests/unit/test-char.c
@@ -1215,7 +1215,13 @@ static void char_parallel_test(void)
     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);
 }