linux-kernel - Re: [PATCHv2 05/16] atomics: prepare for atomic64_fetch_add

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Date:   Tue, 05 Jun 2018 20:54:03 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <albert@...ive.com>
Subject: Re: [PATCHv2 05/16] atomics: prepare for atomic64_fetch_add_unless()

Mark Rutland <mark.rutland@....com> writes:
> On Tue, Jun 05, 2018 at 11:26:37AM +0200, Peter Zijlstra wrote:
>> On Tue, May 29, 2018 at 04:43:35PM +0100, Mark Rutland wrote:
>> >  /**
>> > + * atomic64_add_unless - add unless the number is already a given value
>> > + * @v: pointer of type atomic_t
>> > + * @a: the amount to add to v...
>> > + * @u: ...unless v is equal to u.
>> > + *
>> > + * Atomically adds @a to @v, so long as @v was not already @u.
>> > + * Returns non-zero if @v was not @u, and zero otherwise.
>> 
>> I always get confused by that wording; would something like: "Returns
>> true if the addition was done" not be more clear?
>
> Sounds clearer to me; I just stole the wording from the existing
> atomic_add_unless().
>
> I guess you'll want similar for the conditional inc/dec ops, e.g.
>
> /**
>  * atomic_inc_not_zero - increment unless the number is zero
>  * @v: pointer of type atomic_t
>  *
>  * Atomically increments @v by 1, so long as @v is non-zero.
>  * Returns non-zero if @v was non-zero, and zero otherwise.
>  */

If we're bike-shedding .. :)

I think "so long as" is overly wordy and not helpful. It'd be clearer
just as:

  * Atomically increments @v by 1, if @v is non-zero.

cheers