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Re: [libvirt] [RFC][PATCH] Growable bitmap implementation



On 02/04/2013 10:01 AM, Stefan Berger wrote:
> Add a growable bitmap implementation building on top of the 'regular'
> bitmap implementation. (no doubt, this could also be done differently...)
> 
> This patch also adds a test virgbitmaptest.c that is largely a copy of
> virbitmaptest.c with some minor modifications to test for growth of the
> bitmap.
> 
> Signed-off-by: Stefan Berger <stefanb linux vnet ibm com>
> 
> ---
> PS: This patch builds on top of a patch with a virBitmapNextClearBit
>     implementation.

In addition to Dan's comments...

virBitmapNextClearBit makes sense to add in isolation (our code should
provide symmetric handling of a bitmap; and the fact that we can iterate
over set bits but not clear bits is a wart worth fixing).  However, in
the context of fd passing, I'm not so sure we need a bitmap at all,
growable or otherwise.  It should be sufficient just to have a per-vm
single integer set to the highest fdset number allocated so far; any
time a new fdset is needed, we increment the per-vm integer (even if
that leaves gaps in lower-valued fdsets), and on libvirtd reload, the
post-processing pass would merely set the integer to one more than the
maximum fdset seen among all the devices.  Thus, I'm a bit worried that
this code is a tangent that will end up not being needed in the fdset case.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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