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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 30.06.10 at 16:52, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> Good catch.  This fix produces the correct index, but:
> * It's not as clear, IMHO, where the math is coming from
> * I think it may give the wrong result if the t_info struct ever
> changes (e.g., more data before the cpu offset list)

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).

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).

> The bug in the original math was that I should have added 3 to round
> up, rather than 1.

Correct.

> I'm attaching a patch that will hopefully fix the bug and make it more
> clear.  Thoughts?

Leaving aside the comment above this looks okay to me.

Jan


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