linux-kernel - Re: [PATCH -next 1/5] block: add disk sequence number

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Message-ID: <CAFnufp2E8ky_q10R5=zXsU+2ca53yQ=W+XOtKAq-c654xHCoEA@mail.gmail.com>
Date:   Tue, 23 Mar 2021 18:43:34 +0100
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     JeffleXu <jefflexu@...ux.alibaba.com>
Cc:     linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lennart Poettering <lennart@...ttering.net>,
        Luca Boccassi <bluca@...ian.org>, Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Damien Le Moal <damien.lemoal@....com>,
        Tejun Heo <tj@...nel.org>,
        Javier González <javier@...igon.com>,
        Niklas Cassel <niklas.cassel@....com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH -next 1/5] block: add disk sequence number

On Tue, Mar 16, 2021 at 2:44 AM JeffleXu <jefflexu@...ux.alibaba.com> wrote:
>
> On 3/16/21 4:02 AM, Matteo Croce wrote:
> > From: Matteo Croce <mcroce@...rosoft.com>
> >
> > Add a sequence number to the disk devices. This number is put in the
> > uevent so userspace can correlate events when a driver reuses a device,
> > like the loop one.
>
> Hi, I'm quite interested in this 'seqnum'. Actually I'm also planing to
> add support for some sort of 'seqnum' when supporting IO polling for dm
> devices, so that every time dm device changes its dm table, the seqnum
> will be increased.
>

Interesting, thanks!

> As for your patch, @diskseq is declared as one static variable in
> inc_diskseq(). Then I doubt if all callers of inc_diskseq() will share
> *one* counting when inc_diskseq() is compiled as the separate call entry
> rather than inlined.
>

That would be true if the static declaration was in the .h, but being
in genhd.c it goes in vmlinux once.
Maybe you get confused by the inc_diskseq prototype in the header
file, but the function body is in the .c

Regards,



--
per aspera ad upstream