Re: [Qemu-block] [RFC PATCH v2 13/18] oslib-posix: Ignore fcntl("/dev/null", F_SETFL, O_NONBLOCK) failure

[Peter Maydell]

On Tue, 29 Jan 2019 at 17:59, Philippe Mathieu-Daudé <address@hidden> wrote:
>
> Previous to OpenBSD 6.3 [1], fcntl(F_SETFL) is not permitted on
> memory devices.
> Trying this call sets errno to ENODEV ("not a memory device"):
>
>   19 ENODEV Operation not supported by device.
>     An attempt was made to apply an inappropriate function to a device,
>     for example, trying to read a write-only device such as a printer.
>
> Do not assert fcntl failures in this specific case (errno set to ENODEV)
> on OpenBSD. This fixes:
>
>   $ lm32-softmmu/qemu-system-lm32
>   assertion "f != -1" failed: file "util/oslib-posix.c", line 247, function 
> "qemu_set_nonblock"
>   Abort trap (core dumped)
>
> [1] The fix seems https://github.com/openbsd/src/commit/c2a35b387f9d3c
>   "fcntl(F_SETFL) invokes the FIONBIO and FIOASYNC ioctls internally, so
>   the memory devices (/dev/null, /dev/zero, etc) need to permit them."
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  util/oslib-posix.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 4ce1ba9ca4..2f0f27e6d9 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -244,7 +244,17 @@ void qemu_set_nonblock(int fd)
>      f = fcntl(fd, F_GETFL);
>      assert(f != -1);
>      f = fcntl(fd, F_SETFL, f | O_NONBLOCK);
> +#ifdef __OpenBSD__
> +    if (f == -1) {
> +        /*
> +         * Previous to OpenBSD 6.3, fcntl(F_SETFL) is not permitted on
> +         * memory devices and sets errno to ENODEV.
> +         */
> +        assert(errno == ENODEV);
> +    }
> +#else
>      assert(f != -1);
> +#endif

You might also add "It's OK if we fail to set O_NONBLOCK on devices
like /dev/null, because they will never block anyway."

Reviewed-by: Peter Maydell <address@hidden>

thanks
-- PMM