Re: [Xen-devel] trouble with the new mmap-batch interface

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 20.01.10 22:54 >>>
>On 20/01/2010 21:38, "Brendan Cully" <brendan@xxxxxxxxx> wrote:
>
>>> It seems unlikely to me that this is actual breakage, but I've built
>>> world a couple of times. Before I put printfs everywhere I thought I'd
>>> ask if anyone else had seen this or had any ideas.
>> 
>> The attached patch fixes ioemu for me.
>
>So the issue is that the kernel only writes back the err array if there was
>at least one failure in the batch. Given the alternative is pre-zeroing the
>array, shouldn't we just unconditionally copy back the array, even if it is
>all zeroes?
>
>Jan: Is it in fact a bug, because IOCTL_PRIVCMD_MMAPBATCH is similarly
>structured (but legitimately, in that case)?

Generally I intended the caller to zero the array. If that's not a good
idea, I can certainly put together patches (linux and libxc) that remove
that assumption. If you'd like to leave the assumption in, then c/s 20822
(fixing domain save) will also need another adjustment (using realloc()
inside the loop doesn't seem very nice anyway - allocating the array
where the other two arrays get allocated would be more consistent).

Jan


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