linux-kernel - Re: [PATCH 3/6] block, fs: assert that key paths use iovecs, and nothing else

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Message-ID: <86ce63dd-f6b0-e7b9-c4e6-6b15dc8b32a0@nvidia.com>
Date:   Sun, 27 Feb 2022 14:27:53 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Al Viro <viro@...iv.linux.org.uk>, jhubbard.send.patches@...il.com
Cc:     Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <dchinner@...hat.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Theodore Ts'o <tytso@....edu>,
        Miklos Szeredi <miklos@...redi.hu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chaitanya Kulkarni <kch@...dia.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] block, fs: assert that key paths use iovecs, and
 nothing else

On 2/27/22 14:15, Al Viro wrote:
> On Sun, Feb 27, 2022 at 01:34:31AM -0800, jhubbard.send.patches@...il.com wrote:
>> From: John Hubbard <jhubbard@...dia.com>
>>
>> Upcoming changes to Direct IO will change it from acquiring pages via
>> get_user_pages_fast(), to calling pin_user_pages_fast() instead.
>>
>> Place a few assertions at key points, that the pages are IOVEC (user
>> pages), to enforce the assumptions that there are no kernel or pipe or
>> other odd variations being passed.
> 
> Umm...  And what should happen when O_DIRECT file gets passed to splice()?

Hi Al,

First of all, full disclosure: I still haven't worked through how
splice() handles pages in all cases. I was hoping to defer it, by
limiting this series to not *all* of the original callers of
iov_iter_get_pages*().

This series leaves the splice() code pointing to iov_iter_get_pages(),
but maybe that's not possible after all.

Any advice or ideas about how to solve the O_DIRECT-to-splice() is very
welcome.


thanks,
-- 
John Hubbard
NVIDIA