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Date: Tue, 1 Jul 2014 17:54:18 +0400 (MSK)
From: Kirill Batuzov <batuzovk@ispras.ru>
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Subject: Re: [Qemu-devel] [PATCH] Handle G_IO_HUP in tcp_chr_read for tcp
 chardev
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To: =?ISO-8859-15?Q?Alex_Benn=E9e?= <alex.bennee@linaro.org>
Cc: Antonios Motakis <a.motakis@virtualopensystems.com>, Nikita Belov <zodiac@ispras.ru>, qemu-devel@nongnu.org, Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>, "Michael S. Tsirkin" <mst@redhat.com>

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On Tue, 1 Jul 2014, Alex Benn=C3=A9e wrote:

>=20
> Kirill Batuzov writes:
>=20
> > Due to GLib limitations it is not possible to create several watches =
on one
> > channel on Windows hosts. See bug #338943 in GNOME bugzilla for detai=
ls:
> > https://bugzilla.gnome.org/show_bug.cgi?id=3D338943
> >
> > Handle G_IO_HUP in tcp_chr_read. It is already watched by correspondi=
ng watch.
> > Also remove the second watch with its handler.
> >
> > This reverts commit cdaa86a54b232572bba594bf87a7416e527e460c.
> > ("Add G_IO_HUP handler for socket chardev") but keeps its functionali=
ty.
> <snip>
> > --- a/qemu-char.c
> > +++ b/qemu-char.c
> > @@ -2673,6 +2673,12 @@ static gboolean tcp_chr_read(GIOChannel *chan,=
 GIOCondition cond, void *opaque)
> >      uint8_t buf[READ_BUF_LEN];
> >      int len, size;
> > =20
> > +    if (cond & G_IO_HUP) {
> > +        /* connection closed */
> > +        tcp_chr_disconnect(chr);
> > +        return TRUE;
> > +    }
>=20
> Is this right. AIUI we could return FALSE here to remove the watch for
> the now closed channel.
>=20
>
tcp_chr_disconnect will remove the watch and perform other non-obvious
cleanup. Also we already have tcp_chr_disconnect followed by return TRUE
in tcp_chr_read:

    size =3D tcp_chr_recv(chr, (void *)buf, len);
    if (size =3D=3D 0) {
        /* connection closed */
        tcp_chr_disconnect(chr);
    } else if (size > 0) {
	    /* ... */
    }

    return TRUE;

Actually I'm not sure that tcp_chr_read handles all corner cases
correctly. For eaxmple, should not it be "size <=3D 0" instead of
"size =3D=3D 0" in the above code? tcp_chr_recv may return negative value=
 on error.
Should not tcp_chr_recv handle G_IO_ERR condition? It is watched in
corresponding watch.

But since we are in soft-freeze before 2.1 I decided to keep the patch as
simple as possible and not to fix theoretical bugs for which I do not
have real examples.

--=20
Kirill
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