Re: [Qemu-devel] Guest application reading from pl011 without device driver

[Jiahuan Zhang]

On 22 March 2017 at 10:37, Paolo Bonzini <address@hidden> wrote:

>
>
> On 22/03/2017 09:48, Jiahuan Zhang wrote:
> >
> >
> > On 22 March 2017 at 09:40, Paolo Bonzini <address@hidden
> > <mailto:address@hidden>> wrote:
> >
> >
> >     > > I am using a windows named pipe to get the data from a window
> >     > > host program, which uses ReadFile () in char_win.c
> >     >
> >     > OK, bugs in the windows-specific char backend would be
> >     > unsurprising.
> >     >
> >     > I'm not entirely sure how the chardev layer works, but
> >     > at the pl011 end if we return 0 from our can_receive
> >     > function then the chardev layer should decide it has
> >     > nothing to do until the pl011 later calls
> >     > qemu_chr_fe_accept_input(), I think.
> >     >
> >     > I've cc'd Paolo and Marc-André Lureau as the chardev
> >     > maintainers.
> >
> >     Windows named pipes do not support the equivalent of "select",
> >     so it's possible that they cause a busy wait.  Try using a
> >     TCP socket instead and see if the bug goes away.
> >
> >
> > Hi, I am trying to use a Windows socket for serial redirection instead
> > of Windows named pipe.
> > What do you mean "the equivalent of 'select'"?
>
> A function that lets a process sleep until data is available on the
> socket.  The solution is to rewrite Windows chardev handling in QEMU to
> use threads or overlapped I/O.
>
> Yes, socket is working well. Will you add the "select" to pipe
implementation?
Or shall I look into it and fix? Since in my case, I prefer windows pipe to
socket.
But if I do, definitly, I will spend much more effort than you, the experts.


> Paolo
>