Re: [Qemu-devel] [PATCH] qemu-char: reset errno before qemu char write or read action

[xinhua . Cao]

在 2018/7/2 23:01, Stefan Hajnoczi 写道:
> On Mon, Jul 02, 2018 at 08:49:10AM +0800, xinhua.Cao wrote:
> > In the tcp_chr_write function, we checked errno,
> > but errno was not reset before a read or write operation.
> > Therefore, this check of errno's actions is often
> > incorrect after EAGAIN has occurred.
> > We reset errno before reading and writing to
> > ensure the correctness of errno's judgment
> >
> > Signed-off-by: xinhua.Cao <address@hidden>
> > ---
> >   chardev/char-fe.c | 1 +
> >   chardev/char.c    | 2 ++
> >   2 files changed, 3 insertions(+)
> The C11x standard "7.4 Errors <errno.h>" says that errno "is never set
> to zero by any library function".  Please follow the errno usage
> convention described in the C standard.
yes, I know that errno must be used after a negative return value.
 But if you check the return value in tcp_chr_write,
the logic is a bit more complicated. So I reset the errno in the outer 
layer.
I will check the return value at tcp_chr_write at v2 patch.
> Instead of making functions called by tcp_chr_write() clear errno,
> please fix tcp_chr_write() so that errno is only accessed when ret < 0.
>
> Thanks,
> Stefan