linux-kernel - Re: [PATCH 3/6] iov_iter: new iov_iter_pin

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Message-ID: <YwqexJOL9GcOKRg1@ZenIV>
Date:   Sat, 27 Aug 2022 23:46:28 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     John Hubbard <jhubbard@...dia.com>
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>,
        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 3/6] iov_iter: new iov_iter_pin_pages*() routines

On Sat, Aug 27, 2022 at 01:36:04AM -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().
> 
> 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().

You do realize that O_DIRECT on ITER_BVEC is possible, right?