linux-kernel - Re: [PATCH 4/7] ovl: add infrastructure for intercepting file ops

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Message-ID: <CAJfpegto3K+G3wZ-atebMW_3ZwZ5fiA3r2F14DwTXwuaSu7sww@mail.gmail.com>
Date:   Thu, 24 Nov 2016 13:03:40 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        "linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] ovl: add infrastructure for intercepting file ops

On Thu, Nov 24, 2016 at 12:52 PM, Amir Goldstein <amir73il@...il.com> wrote:
> On Thu, Nov 24, 2016 at 12:55 PM, Miklos Szeredi <mszeredi@...hat.com> wrote:

>> +               /*
>> +                * These should be intercepted, but they are very unlikely to be
>> +                * a problem in practice.  Leave them alone for now.
>
> It could also be handled in vfs helpers.
> Since these ops all start with establishing that src and dest are on
> the same sb,
> then the cost of copy up of src is the cost of clone_file_range from
> lower to upper,
> so it is probably worth to copy up src and leave those fops alone.
>
>> +                */
>> +               ofop->fops.copy_file_range = orig->copy_file_range;
>> +               ofop->fops.clone_file_range = orig->clone_file_range;
>> +               ofop->fops.dedupe_file_range = orig->dedupe_file_range;

Not sure I understand.  Why should we copy up src?  Copy up is the
problem not the solution.

Thanks,
Miklos