linux-kernel - Re: [PATCH v3 1/6] block: add disk sequence number

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Date:   Wed, 23 Jun 2021 15:28:43 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Matteo Croce <mcroce@...ux.microsoft.com>
Cc:     Christoph Hellwig <hch@...radead.org>, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lennart Poettering <lennart@...ttering.net>,
        Luca Boccassi <bluca@...ian.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Damien Le Moal <damien.lemoal@....com>,
        Tejun Heo <tj@...nel.org>,
        Javier Gonz??lez <javier@...igon.com>,
        Niklas Cassel <niklas.cassel@....com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Hannes Reinecke <hare@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        JeffleXu <jefflexu@...ux.alibaba.com>
Subject: Re: [PATCH v3 1/6] block: add disk sequence number

On Wed, Jun 23, 2021 at 03:10:21PM +0200, Matteo Croce wrote:
> I just didn't want to clobber that file namespace, as that is the only
> point where it's used.

It doesn't really clobber the file namespace.  Declaring it normally
at the top of the file makes it very clear we have global state.
Hiding it in a function just causes obsfucation.

> > Can you explain a little more why we need a global sequence count vs
> > a per-disk one here?
> 
> The point of the whole series is to have an unique sequence number for
> all the disks.
> Events can arrive to the userspace delayed or out-of-order, so this
> helps to correlate events to the disk.
> It might seem strange, but there isn't a way to do this yet, so I come
> up with a global, monotonically incrementing number.

Maybe add a comment to explain that?