linux-kernel - Re: [PATCH v2 4/7] iov_iter: new iov_iter_pin

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Message-ID: <85a8a0e1-72dd-e37c-85c5-77fab21acde4@nvidia.com>
Date:   Wed, 31 Aug 2022 18:48:59 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Miklos Szeredi <miklos@...redi.hu>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, Jan Kara <jack@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/7] iov_iter: new iov_iter_pin_pages*() routines

On 8/31/22 17:42, Al Viro wrote:
> On Tue, Aug 30, 2022 at 09:18:40PM -0700, John Hubbard wrote:
>> Provide two new wrapper routines that are intended for user space pages
>> only:
>>
>>     iov_iter_pin_pages()
>>     iov_iter_pin_pages_alloc()
>>
>> Internally, these routines call pin_user_pages_fast(), instead of
>> get_user_pages_fast(), for user_backed_iter(i) and iov_iter_bvec(i)
>> cases.
>>
>> As always, callers must use unpin_user_pages() or a suitable FOLL_PIN
>> variant, to release the pages, if they actually were acquired via
>> pin_user_pages_fast().
>>
>> This is a prerequisite to converting bio/block layers over to use
>> pin_user_pages_fast().
> 
> What of ITER_PIPE (splice from O_DIRECT fd to a to pipe, for filesystem
> that uses generic_file_splice_read())?

Yes. And it turns out that I sent this v2 just a little too early: it
does not include Jan Kara's latest idea [1] of including ITER_PIPE and
ITER_XARRAY. That should fix this up.


[1] https://lore.kernel.org/r/20220831094349.boln4jjajkdtykx3@quack3

thanks,

-- 
John Hubbard
NVIDIA