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

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Message-ID: <CAFnufp1gdag0rGQ8K4_2oB6_aC+EZgfgwd2eL4-AxpG0mK+_qQ@mail.gmail.com>
Date:   Wed, 23 Jun 2021 15:10:21 +0200
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     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 1:49 PM Christoph Hellwig <hch@...radead.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