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

To: Brendan Cully <brendan@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] trouble with the new mmap-batch interface
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 20 Jan 2010 21:54:55 +0000
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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)?

 -- Keir



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