linux-kernel - Re: [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in

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Date:   Tue, 3 Aug 2021 23:38:12 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J. Wong" <djwong@...nel.org>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        cluster-devel <cluster-devel@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, ocfs2-devel@....oracle.com
Subject: Re: [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable}

On Tue, Aug 3, 2021 at 10:57 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> On Tue, Aug 03, 2021 at 09:18:09PM +0200, Andreas Gruenbacher wrote:
> > Turn fault_in_pages_{readable,writeable} into versions that return the number
> > of bytes faulted in instead of returning a non-zero value when any of the
> > requested pages couldn't be faulted in.  This supports the existing users that
> > require all pages to be faulted in, but also new users that are happy if any
> > pages can be faulted in.
> >
> > Neither of these functions is entirely trivial and it doesn't seem useful to
> > inline them, so move them to mm/gup.c.
> >
> > Rename the functions to fault_in_{readable,writeable} to make sure that code
> > that uses them can be fixed instead of breaking silently.
>
> Sigh...  We'd already discussed that; it's bloody pointless.  Making short
> fault-in return success - absolutely.  Reporting exact number of bytes is
> not going to be of any use to callers.

I'm not actually convinced that you're right about this. Let's see
what we'll end up with; we can always strip things down in the end.

Thanks,
Andreas