David Howells wrote:
Nick Piggin <[email protected]> wrote:
| int atomic_inc_and_test(atomic_t *v);
| int atomic_dec_and_test(atomic_t *v);
|
| These two routines increment and decrement by 1, respectively, the
| given atomic counter. They return a boolean indicating whether the
| resulting counter value was zero or not.
|
| It requires explicit memory barrier semantics around the operation as
| above.
Note the last paragraph. "It requires" should be "They require", but the
sense would seem to be obvious. However, it's not clear on a second reading
as to whether this is an instruction to the _caller_ or an instruction to the
arch _implementer_.
Yes, I remember Dave M clarified this sometime ago (on lkml I guess). It
is a little confusing, but I think the wording is for the implementer's
point of view. Dave will pull me up if I'm wrong...
I suppose from reading the abstract at the top:
| This document is intended to serve as a guide to Linux port maintainers on
| how to implement atomic counter, bitops, and spinlock interfaces properly.
that it is meant to be read by the implementor and not the user/caller, in which
case, Nick is correct.
It seems I need to adjust my memory barrier doc, and perhaps I should adjust
atomic_ops.txt too to make it clearer.
I think that would be good. atomic_ops.txt is very useful for API users
as well, so if it can be made more general without becoming ambiguous,
I'm sure that would be appreciated.
Thanks,
Nick
--
SUSE Labs, Novell Inc.
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