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

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Message-ID: <cf3a80e3-301d-7c61-54ab-d63fd355dd48@quicinc.com>
Date:   Tue, 10 May 2022 17:46:50 +0530
From:   Charan Teja Kalla <quic_charante@...cinc.com>
To:     Christian König <christian.koenig@....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

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.