linux-kernel - Re: [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter

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Message-ID: <YSkz025ncjhyRmlB@zeniv-ca.linux.org.uk>
Date:   Fri, 27 Aug 2021 18:49:55 +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 v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable

On Fri, Aug 27, 2021 at 06:49:12PM +0200, Andreas Gruenbacher wrote:
> Introduce a new fault_in_iov_iter_writeable helper for safely faulting
> in an iterator for writing.  Uses get_user_pages() to fault in the pages
> without actually writing to them, which would be destructive.
> 
> We'll use fault_in_iov_iter_writeable in gfs2 once we've determined that
> the iterator passed to .read_iter isn't in memory.

Again, the calling conventions are wrong.  Make it success/failure or
0/-EFAULT.  And it's inconsistent for iovec and non-iovec cases as it is.