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Subject: Re: drivers/block/rbd.c: atomic_inc_return_safe() &
 atomic_dec_return_safe()
To:     Shuah Khan <skhan@linuxfoundation.org>, idryomov@gmail.com,
        dongsheng.yang@easystack.cn
Cc:     ceph-devel@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kees Cook <keescook@chromium.org>
References: <ce2dbec5-00f8-831b-3138-cc4f3b8fdb51@linuxfoundation.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <c2dd3223-bda1-be8c-fbc4-9c0eec63bc9d@kernel.dk>
Date:   Fri, 2 Oct 2020 17:44:22 -0600
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On 10/2/20 4:34 PM, Shuah Khan wrote:
> All,
> 
> I came across these atomic_inc_return_safe() & atomic_dec_return_safe()
> functions that hold the counters at safe values.
> 
> atomic_inc_return_safe()
> 
> If the counter is already 0 it will not be incremented.
> If the counter is already at its maximum value returns
> -EINVAL without updating it.
> 
> atomic_dec_return_safe()
> 
> Decrement the counter.  Return the resulting value, or -EINVAL
> 
> These two routines are static and only used in rbd.c.
> 
> Can these become part of atomic_t ops?

I think you just want to use refcount_t for this use case. They
have safe guards for under/overflow.

-- 
Jens Axboe