Re: [Qemu-devel] [PATCH 2/3] Always use nonblocking mode for qemu_chr_open_fd.

[Anthony Liguori <anthony@codemonkey.ws>]

Hi,

Ian Jackson wrote:
> The rest of qemu assumes that IO operations on a CharDriverState do
> not block.  Currently there are a couple of cases where such a driver
> was set up but the calls to set nonblocking mode were missing:
>  * qemu_chr_open_pty
>  * qemu_chr_open_pipe
>  * qemu_chr_open_stdio
>
> This is fixed by adding two calls to socket_set_nonblock to
> qemu_chr_open_fd.
>   

This changes semantics a bit.  Previously, using a pty would guarantee 
that data is always written as qemu_chr_write does not perform any sort 
of buffering.

Now, that data will be silently dropped instead of causing QEMU to 
block.  I don't think it's perfectly clear that one behaviour is clearly 
better than the other.

Regards,

Anthony Liguori

> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
> ---
>  vl.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/vl.c b/vl.c
> index 4f31288..c428c7e 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2090,6 +2090,9 @@ static CharDriverState *qemu_chr_open_fd(int fd_in, int fd_out)
>      CharDriverState *chr;
>      FDCharDriver *s;
>  
> +    socket_set_nonblock(fd_in);
> +    socket_set_nonblock(fd_out);
> +
>      chr = qemu_mallocz(sizeof(CharDriverState));
>      if (!chr)
>          return NULL;
>