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From:   Matteo Croce <mcroce@linux.microsoft.com>
Date:   Wed, 23 Jun 2021 15:10:21 +0200
Message-ID: <CAFnufp1gdag0rGQ8K4_2oB6_aC+EZgfgwd2eL4-AxpG0mK+_qQ@mail.gmail.com>
Subject: Re: [PATCH v3 1/6] block: add disk sequence number
To:     Christoph Hellwig <hch@infradead.org>
Cc:     linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Jens Axboe <axboe@kernel.dk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Lennart Poettering <lennart@poettering.net>,
        Luca Boccassi <bluca@debian.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Damien Le Moal <damien.lemoal@wdc.com>,
        Tejun Heo <tj@kernel.org>,
        "Javier Gonz??lez" <javier@javigon.com>,
        Niklas Cassel <niklas.cassel@wdc.com>,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>,
        Hannes Reinecke <hare@suse.de>,
        Matthew Wilcox <willy@infradead.org>,
        JeffleXu <jefflexu@linux.alibaba.com>
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On Wed, Jun 23, 2021 at 1:49 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Wed, Jun 23, 2021 at 12:58:53PM +0200, Matteo Croce wrote:
> > +void inc_diskseq(struct gendisk *disk)
> > +{
> > +     static atomic64_t diskseq;
>
> Please don't hide file scope variables in functions.
>

I just didn't want to clobber that file namespace, as that is the only
point where it's used.

> 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.

-- 
per aspera ad upstream