Re: [Xen-devel] [PATCH v2 qemu-traditional] qemu: Fix race condition when opening ports

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Andrew Cooper writes ("[PATCH v2 qemu-traditional] qemu: Fix race condition 
when opening ports"):
> Two Qemus can race to bind the same VNC port.  It is valid for multiple
> bind()s on the same socket to succeed, but only the first listen() will
> succeed.

I don't think this is correct.  The SuS page for listen(2)
http://pubs.opengroup.org/onlinepubs/9699919799/functions/listen.html
doesn't list EADDRINUSE as a possible error condition.

Although wheezy's listen(2) manpage does.

> In the case that two Qemus are starting at the same time, and both trying to
> grab the next free VNC port, the second one will fail with an EADDRINUSE, and
> bail with a fatal error which renders the domain functionally useless.
> 
> In the case that listen() fails with EADDRINUSE, rebind the socket again and
> try for the next port.

My preliminary view is that this is a kernel bug.

Ian.

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