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Date: Mon, 14 Jan 2013 11:07:51 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] 100% CPU when sockfd is half-closed and unexpected
 behavior for qemu_co_send()
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To: Liu Yuan <namei.unix@gmail.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Il 14/01/2013 10:29, Liu Yuan ha scritto:
> I don't think so. I use netstat to assure that the connection is in
> closed_wait state and I added a printf in the qemu_co_send() and it
> indeed sent successfully, this can be backed by the Linux kernel
> source code:
> 
> static ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
>                                 size_t size, int flags)
> {
>          ....
>         /* Wait for a connection to finish. One exception is TCP Fast Open
>          * (passive side) where data is allowed to be sent before a connection
>          * is fully established.
>          */
>         if (((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) &&
>             !tcp_passive_fastopen(sk)) {
>                 if ((err = sk_stream_wait_connect(sk, &timeo)) != 0)
>                         goto out_err;
>         }
>         ....
> }
> 
> which will put data in the sock buf and returns successful in a
> CLOSED_WAIT state. I don't see means in Sheepdog driver code to get a
> HUP notification for a actual cut off connection.

Ok.  I guess the problem is that we use select(), not poll(), so we have
no way to get POLLHUP notifications.  But the write fd_set receives the
file descriptor because indeed writes will not block.

Stefan, Anthony, any ideas?

Paolo