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Re: [Qemu-trivial] [Qemu-devel] [PATCH] Keep pty slave file descriptor o

From: Marc-André Lureau
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] Keep pty slave file descriptor open until the master is closed
Date: Fri, 12 Feb 2016 03:29:25 +0100


On Mon, Jan 11, 2016 at 10:13 AM, Paolo Bonzini <address@hidden> wrote:
> On 11/01/2016 09:33, Michael Tokarev wrote:
>> 11.12.2015 14:29, Ashley Jonathan wrote:
>>> I have experienced a minor difficulty using QEMU with the "-serial pty" 
>>> option:
>>> If a process opens the slave pts device, writes data to it, then 
>>> immediately closes it, the data doesn't reliably get delivered to the 
>>> emulated serial port. This seems to be because a read of the master pty 
>>> device returns EIO on Linux if no process has the pts device open, even 
>>> when data is waiting "in the pipe".
>>> A fix seems to be for QEMU to keep the pts file descriptor open until the 
>>> pty is closed, as per the below patch.
>> The patch looks fine, so
>> Reviewed-by: Michael Tokarev <address@hidden>
>> but I'd love to have an ACK from the maintainer about this one,
>> or for it to pick it up.
> Ok, I'll pick it up after I've read up a bit more on PTYs.

That patch slows down qemu a lot when using -chardev
pty,id=charserial0 -device isa-serial,chardev=charserial0. I forgot a
lot about how pty/pts work, and reading some man pages didn't help me
much to understand the issue, I would suggest to revert it until a
better solution is found.

Marc-André Lureau

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