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From: "Gaohaifeng (A)" <gaohaifeng.gao@huawei.com>
Date: Tue, 23 Aug 2016 08:57:44 +0000
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Subject: [Qemu-devel] A question about this commit
 9894dc0cdcc397ee5b26370bc53da6d360a363c2
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To: "berrange@redhat.com" <berrange@redhat.com>, "pbonzini@redhat.com" <pbonzini@redhat.com>, "Lilijun (Jerry)" <jerry.lilijun@huawei.com>, zangchuanqiang <zangchuanqiang@huawei.com>, qemu devel <qemu-devel@nongnu.org>

Hi Daniel & Paolo,

Commit 9894dc0c "char: convert from GIOChannel to QIOChannel", about

the below code segment:

-static gboolean tcp_chr_read(GIOChannel *chan, GIOCondition cond, void *op=
aque)
+static gboolean tcp_chr_read(QIOChannel *chan, GIOCondition cond, void *op=
aque)
{
     CharDriverState *chr =3D opaque;
     TCPCharDriver *s =3D chr->opaque;
@@ -2938,9 +2801,7 @@ static gboolean tcp_chr_read(GIOChannel *chan, GIOCon=
dition cond, void *opaque)
     if (len > s->max_size)
         len =3D s->max_size;
     size =3D tcp_chr_recv(chr, (void *)buf, len);
-    if (size =3D=3D 0 ||
-        (size < 0 &&
-         socket_error() !=3D EAGAIN && socket_error() !=3D EWOULDBLOCK)) {
+    if (size =3D=3D 0 || size =3D=3D -1) {
         /* connection closed */
         tcp_chr_disconnect(chr);
     } else if (size > 0) {

The old version will not call tcp_chr_disconnect when error is not EAGAIN.
The new version will call tcp_chr_disconnect when size=3D=3D-1. From the tc=
p_chr_recv function we see EAGIN will return -1, so EAGIN will call tcp_chr=
_disconnect.

We meet an issue when Guest VM use DPDK(1.6.0) l2fwd, it may exit since lin=
k status is not up. The link is down because tcp_chr_disconnect will set it=
.

Can you explain it why EAGIN here changes the behavior ?

Thanks,
Haifeng Gao