Re: [Xen-devel] [PATCH for-xen-4.5] libxl: Allow copying smaller bitmap into a larger one

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Tue, 2014-11-25 at 11:15 +0000, Wei Liu wrote:
> And here it is.
> 
> Boris, can you give it a shot?
> 
> ---8<---
> From 77531e31d239887b9f36c03e434300bc30683092 Mon Sep 17 00:00:00 2001
> From: Wei Liu <wei.liu2@xxxxxxxxxx>
> Date: Tue, 25 Nov 2014 10:59:47 +0000
> Subject: [PATCH] libxl: allow copying between bitmaps of different sizes
> 
> When parsing bitmap objects JSON parser will create libxl_bitmap map of the
> smallest size needed.
> 
> This can cause problems when saved image file specifies CPU affinity.  For
> example, if 'vcpu_hard_affinity' in the saved image has only the first CPU
> specified, just a single byte will be allocated and libxl_bitmap->size will be
> set to 1.
> 
> This will result in assertion in libxl_set_vcpuaffinity()->libxl_bitmap_copy()
> since the destination bitmap is created for maximum number of CPUs.
> 
> We could allocate that bitmap of the same size as the source, however, it is
> later passed to xc_vcpu_setaffinity() which expects it to be sized to the max
> number of CPUs
> 
> To fix this issue, introduce an internal function to allowing copying between
> bitmaps of different sizes. Note that this function is only used in
> libxl_set_vcpuaffinity at the moment. Though NUMA placement logic invoke
> libxl_bitmap_copy as well there's no need to replace those invocations.  NUMA
> placement logic comes into effect when no vcpu / node pinning is provided, so
> it always operates on bitmap of the same sizes (that is, size of maximum
> number of cpus /nodes).
> 
> Reported-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
>
If this end up being the approach, it can have the following:

Reviewed-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
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Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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