linux-kernel - Re: [PATCH] dmabuf: ensure unique directory name for dmabuf stats

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Date:   Tue, 10 May 2022 14:20:17 +0200
From:   Christian König <christian.koenig@....com>
To:     Charan Teja Kalla <quic_charante@...cinc.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     sumit.semwal@...aro.org, daniel.vetter@...ll.ch,
        tjmercier@...gle.com, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmabuf: ensure unique directory name for dmabuf stats

Am 10.05.22 um 14:16 schrieb Charan Teja Kalla:
> Thanks Christian for the inputs!!
>
> On 5/10/2022 5:05 PM, Christian König wrote:
>>> And what's to keep the seconds field from also being the same?
>> Well exporting two DMA-bufs with the same ino in the same nanosecond
>> should be basically impossible, but I would rather opt for using a 64bit
>> atomic in that function.
>>
>> This should be 100% UAPI compatible and even if we manage to create one
>> buffer ever ns we need ~500years to wrap around.
> I see that the inode->i_ctime->tv_sec is already defined as
> 64bit(time64_t tv_sec), hence used it. This way we don't need extra
> static atomic_t variable just to get a unique name.
>
> Just pasting excerpt from the reply posted to Greg about why this secs
> will always be a unique: with secs field added, to get the same
> inode-secs string, the uint should overflow in the same second which is
> impossible.
>
> Let me know If you still opt for atomic variable only.

I think just using a static atomic variable here would be cleaner, that 
is 100% unique.

Your approach should probably work as well, but it looks quite constructed.

Regards,
Christian.