linux-kernel - Re: [PATCH v7 18/19] iov_iter: Introduce nofault flag to disable page faults

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Message-ID: <YSkzSHSp8lld6dwW@zeniv-ca.linux.org.uk>
Date:   Fri, 27 Aug 2021 18:47:36 +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 18/19] iov_iter: Introduce nofault flag to disable
 page faults

On Fri, Aug 27, 2021 at 06:49:25PM +0200, Andreas Gruenbacher wrote:
> Introduce a new nofault flag to indicate to get_user_pages to use the
> FOLL_NOFAULT flag.  This will cause get_user_pages to fail when it
> would otherwise fault in a page.
> 
> Currently, the noio flag is only checked in iov_iter_get_pages and
> iov_iter_get_pages_alloc.  This is enough for iomaop_dio_rw, but it
> may make sense to check in other contexts as well.

I can live with that, but
	* direct assignments (as in the next patch) are fucking hard to
grep for.  Is it intended to be "we set it for duration of primitive",
or...?
	* it would be nice to have a description of intended semantics
for that thing.  This "may make sense to check in other contexts" really
needs to be elaborated (and agreed) upon.  Details, please.