linux-kernel - Re: [PATCH] kcmp: add separate Kconfig symbol for kcmp syscall

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Message-ID: <14b4a1f0-3caf-75e4-600a-3de877a92950@rasmusvillemoes.dk>
Date:   Fri, 10 Jul 2020 11:05:11 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Cyrill Gorcunov <gorcunov@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kcmp: add separate Kconfig symbol for kcmp syscall

On 10/07/2020 10.30, Cyrill Gorcunov wrote:
> On Fri, Jul 10, 2020 at 09:56:31AM +0200, Rasmus Villemoes wrote:
>> The ability to check open file descriptions for equality (without
>> resorting to unreliable fstat() and fcntl(F_GETFL) comparisons) can be
>> useful outside of the checkpoint/restore use case - for example,
>> systemd uses kcmp() to deduplicate the per-service file descriptor
>> store.
>>
>> Make it possible to have the kcmp() syscall without the full
>> CONFIG_CHECKPOINT_RESTORE.
>>
>> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
>> ---
>> I deliberately drop the ifdef in the eventpoll.h header rather than
>> replace with KCMP_SYSCALL; it's harmless to declare a function that
>> isn't defined anywhere.
> 
> Could you please point why setting #fidef KCMP_SYSCALL in eventpoll.h
> is not suitable?

It's just from a general "avoid ifdef clutter if possible" POV. The
conditional declaration of the function doesn't really serve any purpose.

> Still the overall idea is fine for me, thanks!>
> Reviewed-by: Cyrill Gorcunov <gorcunov@...il.com>

Thank you.

Rasmus