Re: [libvirt] race condtion in getting VNC port for libvirt
On Wed, Nov 10, 2010 at 01:21:24AM +0800, Guangya Liu wrote:
Thanks Daniel for the info.
But I still have a question, since we already make the call
qemudDomainCreate synced, why do we need to introduce a bitmap to
resolve the problem of getting VNC port conflict error? If
qemudDomainCreate is synced, then there should not any problem with VNC
port.
Previously, libvirt would call bind() on port numbers until it found
one free, then close() the socket & launch QEMU telling it to open
that port again. Thus there is a race between libvirt finding a free
port with bind()+close() for the first VM, and QEMU actually opening
it, where libvirt could then start looking for another port for a
second VM. The libvirt driver lock doesn't solve that, because the code
involves a separate QEMU process with is outside the context of the
lock
With the bitmap code, libvirt now records that it assigned this
port number to a VM, so when libvirt goes to start a second VM
it won't reuse this port, even if the first QEMU hasn't yet got
around to opening it.
Regards,
Daniel
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