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Re: [Xen-devel] [PATCH 4/8] xen/arm: Add support for read-only foreign mappings


On 11/15/18 1:19 PM, Andrii Anisov wrote:
So I would prefer to stick with _t which is quite common within the p2m
code base so far.

I've found a similar code only in one place - p2m_get_entry()
function. And it is, at least, somehow commented there:
     /* Allow t to be NULL */
     t = t ?: &_t;

     *t = p2m_invalid;

And in x86 code...

But IMO, it is really confusing to write a code to calculate and store
a value which clearly is not needed by a caller.

I disagree, you directly know that t can be NULL. Although, I agree that a comment would help to understand.

 From another hand, I'm not sure if a compiler would be intelligent
enough to factor out the odd code from execution pass on the incoming
null pointer.

You can't assume the compiler will inline even with the inline keyword.

I'm sorry, but I can't pass my RB for `_t`.

I think this request is unreasonable because this is a matter of taste.

While this is a nice feature to have in Xen 4.12 and address a long standing open issue on Arm. I don't require it and I am not inclined to address bikeshedding.

So I will keep aside for now until someone cares about it.


Julien Grall

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