Re: [Xen-devel] [PATCH] trace: Fix incorrect number of pages used for trace metadata

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 30/09/16 15:46, George Dunlap wrote:
> On 29/09/16 14:53, Igor Druzhinin wrote:
>> As long as t_info_first_offset is calculated in uint32_t offsets we need to
>> multiply it by sizeof(uint32_t) in order to get the right number of pages
>> for trace metadata. Not doing that makes it impossible to read the trace
>> buffer correctly from userspace for some corner cases.
>>
>> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> 
> Hmm, looks like we actually want to revert this c/s fbf96e6, "xentrace:
> correct formula to calculate t_info_pages".  But that one was presumably
> written (and Acked by me) because the variable name there,
> t_info_first_offset, is confusing.
> 
> The other mistake in fbf96e6 is that before t_info_words was actually
> denominated in words; but after it's denominated in bytes (which is
> again confusing).
> 
> What about something like the attached instead?  This should fix your
> problem while making the code clearer.

Obviously that comment shouldn't include the second "not bytes".  We're
not writing folk songs here...

 -George


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