Re: [Xen-devel] [PATCH] xen/pciback: Update data filter intersection logic.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.06.16 at 18:23, <andrey2805@xxxxxxxxx> wrote:
> Here is printouts with applying the new logic
> 
> [  382.222213] xen-pciback: 0000:06:00.0: write request 4 bytes at 0xc = 4000
> [  382.222214] xen-pciback: 0000:06:00.0: read 1 bytes at 0xc
> [  382.222228] xen-pciback: 0000:06:00.0: read 1 bytes at 0xc = 0
> [  382.222238] xen-pciback: 0000:06:00.0: read 1 bytes at 0xd
> [  382.222281] xen-pciback: 0000:06:00.0: read 1 bytes at 0xd = 0
> [  382.222313] xen-pciback: 0000:06:00.0: read 1 bytes at 0xf
> [  382.222341] xen-pciback: 0000:06:00.0: read 1 bytes at 0xf = 0
> 
> So from prints the logic is not equivalent. 0xd is included in this case.
> 
> In original logic field 0xd is excluded because
> Not if ((req_start >= field_start && req_start < field_end)
> Nor (req_end > field_start && req_end <= field_end))  evaluate to true.
> Where request would be 4b segment starting with 0xc

Oh, I see - the current expression is screwed in two ways: For one
it has req_* and field_* the wrong way round (or should I better
say their uses are not symmetric, which for any kind of overlap
check they of course should be), and then it uses || instead of &&
(i.e. kind of, but not really checking that req is contained in field,
whereas for the purpose here we'd need the other direction). So
yes, your change is not just a simplification, but a correction.

But then on top of the previously mentioned change to your patch
you should also fix the read path in a similar manner. And the
description should of course accurately reflect the change (i.e.
no talk of quirks and overlapping filters, and a proper explanation
of what's wrong with the current expression).

Jan


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