Re: [Qemu-devel] [Qemu-stable] Recent patches for 2.4

[Paolo Bonzini]

On 04/08/2015 13:57, Peter Lieven wrote:
> 
> Okay, what I found out is that in aio_poll I get revents = POLLIN for
> the nfs file descriptor. But there is no data available on the socket.

Does read return 0 or EAGAIN?

If it returns EAGAIN, the bug is in the QEMU main loop or the kernel.
It should never happen that poll returns POLLIN and read returns EAGAIN.

If it returns 0, it means the other side called shutdown(fd, SHUT_WR).
Then I think the bug is in the libnfs driver or more likely libnfs.  You
should stop polling the POLLIN event after read has returned 0 once.

The same bug could be in libiscsi as well.

Paolo

> But as a consequence progress is true and we loop here forever.
> 
> I have seen that is a common bug in Linux to return POLLIN on a fd
> even there is no data available. I don't have this problem in general,
> in this case no qemu-img or qemu process would ever terminate when
> nfs is involved, but in this special case it happens reproducible.