Re: [Xen-devel] Re: [PATCH 2/6] trace: fix T_INFO_FIRST_OFFSET

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

Here's a version that calculates t_info_first_offset during
initialization, based on the actual layout of struct t_info and
NR_CPUs.

 -George

On Wed, Jun 30, 2010 at 4:28 PM, George Dunlap
<george.dunlap@xxxxxxxxxxxxx> wrote:
> Jan Beulich wrote:
>>
>> That part your patch doesn't address either - rather than
>> sizeof(uint16_t) as the first part of the expression you'd need to
>> use sizeof(struct t_info) or offsetof(struct t_info, mfn_offset).
>>
>
> I was assuming that when someone changed struct t_info that they'd modify
> this macro as well; I suppose then that the two complaints are really
> different aspects of the same one -- that it might not be clear to the
> person who adjusts struct t_info how to translate those changes into
> T_INFO_FIRST_OFFSET.  I think this way is more clear.
>
> I suppose even better might be to calculate t_info.mfn_mfn_offset[NR_CPUS]
> (or perhaps ...[num_possible_cpus]).  Hmm... let me see what I can come up
> with.
>>
>> Btw., didn't we agree that public headers shouldn't make use of
>> language extensions? struct t_info uses a variable sized array,
>> which is an extension (standard only in C99).
>>
>
> I'm not an expert in this.  It's lot more hassle to lay out the data the way
> I'd like without it.  I'll defer judgment to Keir.
>
> -George
>
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Attachment: trace-t_info-first-offset-v3.patch
Description: Text Data

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