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

[George Dunlap <george.dunlap@xxxxxxxxxx>]

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.

 -George

Attachment: 0001-xen-trace-Fix-trace-metadata-page-count-calculation-.patch
Description: Text Data

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