Re: [Qemu-devel] [PULL v2 07/49] util: check the return value of fcntl in qemu_set_{block, nonblock}

[Philippe Mathieu-Daudé]

Hi,

On 1/15/19 9:04 PM, Michael S. Tsirkin wrote:
> From: Li Qiang <address@hidden>
> 
> Assert that the return value is not an error. This is like commit
> 7e6478e7d4f for qemu_set_cloexec.
> 
> Signed-off-by: Li Qiang <address@hidden>
> Reviewed-by: Thomas Huth <address@hidden>
> Reviewed-by: Michael S. Tsirkin <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  util/oslib-posix.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index c1bee2a581..4ce1ba9ca4 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -233,14 +233,18 @@ void qemu_set_block(int fd)
>  {
>      int f;
>      f = fcntl(fd, F_GETFL);
> -    fcntl(fd, F_SETFL, f & ~O_NONBLOCK);
> +    assert(f != -1);
> +    f = fcntl(fd, F_SETFL, f & ~O_NONBLOCK);
> +    assert(f != -1);
>  }
>  
>  void qemu_set_nonblock(int fd)
>  {
>      int f;
>      f = fcntl(fd, F_GETFL);
> -    fcntl(fd, F_SETFL, f | O_NONBLOCK);
> +    assert(f != -1);
> +    f = fcntl(fd, F_SETFL, f | O_NONBLOCK);
> +    assert(f != -1);

This commit breaks OpenBSD, when trying to start QEMU I get:
assertion "f != -1" failed: file "util/oslib-posix.c", line 247,
function "qemu_set_nonblock"

Having a quick look at gdb, the last device opened is /dev/null, and
when fcntl() fails we have errno = ENODEV.

    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.

Digging further I found a recent commit which could fix this problem:
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."

Brad: Do you think this might be the fix? If so, any idea what is the
first release to contain this fix? I don't know OpenBSD and can't figure
this out... Also, what would be the cleaner QEMU fix?

Thanks,

Phil.

>  }
>  
>  int socket_set_fast_reuse(int fd)
>