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

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Message-ID: <YQmtnuqDwBIBf4N+@zeniv-ca.linux.org.uk>
Date:   Tue, 3 Aug 2021 20:57:02 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Andreas Gruenbacher <agruenba@...hat.com>
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@...hat.com,
        linux-fsdevel@...r.kernel.org, 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 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.

Please, don't.