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From: Andy Lutomirski <luto@amacapital.net>
Date: Tue, 21 Feb 2017 10:41:12 -0800
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Subject: Re: [RFC 1/3] procfs: fdinfo -- Extend information about epoll target files
To: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linuxfoundation.org>,
        Andrew Vagin <avagin@virtuozzo.com>,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Kirill Kolyshkin <kir@openvz.org>,
        Jason Baron <jbaron@akamai.com>,
        Andrey Vagin <avagin@openvz.org>
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On Tue, Feb 21, 2017 at 8:59 AM, Cyrill Gorcunov <gorcunov@openvz.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.