Re: [Xen-devel] [PATCH] include/public/io/ring.h: Remove xen_mb, xen_rmb, xen_wmb macros

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/07/2019 13:13, Paul Durrant wrote:
>> -----Original Message-----
> [snip]
>> I'm completely on Jan's side here.
>>
>> What would be possible perhaps is to split ring.h into two headers: a
>> new one with the pure ring definitions and ring.h #include-ing
>> xen-compat.h and the new header and #define-ing the xen*mb() macros.
>>
>> Not sure this would be worth it, though.
>>
> Ok. Probably not worth it, as you say. If we don't feel comfortable remove 
> old cruft like these then projects importing the headers will just have to 
> hack it or live with importing xen-compat too. Anthony already submitted a 
> patch doing the former for QEMU.

Look.

Either we expect people to copy the headers, or we expect to have a
single canonical copy which is up to date and always backwards compatible.

All documentation says "take a copy of the headers", and I have never
seen anything, except the rather weird 2.6.18 driver port in tree, use
the headers verbatim.

These headers describe an ABI, not an API.  Sure - the API is by
convention but by the time people have taken a copy, they really are
free to make modifications as they see fit, as long as they don't change
the ABI.

Insisting that everyone take a copy, *and* maintaining API compatibility
for obsolete cruft is an exercise in self-flagilation.

Given there are zero current consumers that we know of using the headers
in a verbatim way, and all we're talking about is some pieces which 
really should never have been present in the first place, I think its
entirely reasonable to make some changes and release note them.

Xen 4.13 release:
 ...
 * Some obsolete warts in the public headers have been dropped.  People
syncing to this version should be aware of:
   1) ...
   2) ...

Nothing here is rocket science, is it?

~Andrew

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