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Date: Thu, 19 Apr 2018 21:33:07 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [LSF/MM] schedule suggestion
Message-ID: <20180419203307.GJ30522@ZenIV.linux.org.uk>
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To: Jerome Glisse <jglisse@redhat.com>
Cc: Jeff Layton <jlayton@kernel.org>, Matthew Wilcox <willy@infradead.org>, Dave Chinner <david@fromorbit.com>, linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org, linux-fsdevel <linux-fsdevel@vger.kernel.org>, linux-block@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>

On Thu, Apr 19, 2018 at 01:26:10PM -0400, Jerome Glisse wrote:

> Basicly i want a callback in __fd_install(), do_dup2(), dup_fd() and
> add void * *private_data; to struct fdtable (also a default array to
> struct files_struct). The callback would be part of struct file_operations.
> and only call if it exist (os overhead is only for device driver that
> care).

Hell, *NO*.  This is insane - you would need to maintain extra counts
("how many descriptors refer to this struct file... for this descriptor
table").

Besides, _what_ private_data?  What would own and maintain it?  A specific
driver?  What if more than one of them wants that thing?
 
> Did i miss something fundamental ? copy_files() call dup_fd() so i
> should be all set here.

That looks like an extremely misguided kludge for hell knows what purpose,
almost certainly architecturally insane.  What are you actually trying to
achieve?