Re: [Qemu-devel] [PATCH] util: check the return value of fcntl in qemu_set_{block, noblock}

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Dec 12, 2018 at 06:09:37PM -0800, Li Qiang wrote:
> Assert that the return value is not an error. This is like commit
> 7e6478e7d4f for qemu_set_cloexec.
> 
> Signed-off-by: Li Qiang <liq3ea@gmail.com>
> ---
>  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);

This leads to *awful* diagnostics. We need to print something
useful when it fails so we stand a chance of understanding what
is wrong.

   if (fcntl(fd, F_SETFL, f & ~O_NONBLOCK) < 0) {
       error_report("Unable to set blocking flag on fd %d: %s (errno=%d)",
                    fd, strerror(errno), errno));
       abort();
   }


> +    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);
>  }
>  
>  int socket_set_fast_reuse(int fd)
> -- 
> 2.11.0
> 
> 

Regards,
Daniel
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