linux-kernel - Re: [RFC 1/3] procfs: fdinfo -- Extend information about epoll target files

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Date:   Tue, 21 Feb 2017 10:41:12 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:     Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...uxfoundation.org>,
        Andrew Vagin <avagin@...tuozzo.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Kirill Kolyshkin <kir@...nvz.org>,
        Jason Baron <jbaron@...mai.com>,
        Andrey Vagin <avagin@...nvz.org>
Subject: Re: [RFC 1/3] procfs: fdinfo -- Extend information about epoll target files

On Tue, Feb 21, 2017 at 8:59 AM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> Since it is possbile to have same number in tfd field (say
> file added, closed, then nother file dup'ed to same number
> and added back) it is imposible to distinguish such target
> files solely by their numbers.
>
> Strictly speaking regular applications don't need to recognize
> these targets at all but for checkpoint/restore sake we need
> to collect targets to be able to push them back on restore
> in proper order.
>
> Thus lets add file position, inode and device number where
> this target lays. This three fields can be used as a primary
> key for sorting, and together with kcmp help CRIU can find
> out an exact file target (from the whole set of processes
> being checkpointed).

I have no problem with this, but I'm wondering whether kcmp's ordered
comparisons could also be used for this purpose.