linux-kernel - [RFC PATCH 0/2] iov_iter: Provide a function to extract/pin/get pages from an iteraor

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Date:   Mon, 31 Oct 2022 14:49:32 +0000
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     linux-mm@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        linux-fsdevel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>, dhowells@...hat.com,
        smfrench@...il.com, torvalds@...ux-foundation.org,
        linux-cifs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 0/2] iov_iter: Provide a function to extract/pin/get pages
 from an iteraor

Hi Al,

Here's a patch to provide a function to extract a list of pages from an
iterator, getting pins of refs on them as appropriate.

I added a macro by which you can query an iterator to find out how the
extraction function will treat the pages (it returns 0, FOLL_GET or FOLL_PIN
as appropriate).  Note that it's a macro to avoid #inclusion of linux/mm.h in
linux/uio.h.

I've added another crude, incomplete patch to make cifs use it a bit as an
example.  Note that cifs won't work properly with this under all
circumstances, particularly if it decides to split the rdata or wdata record -
but it seems to work for small I/Os.

David
---
David Howells (2):
      iov_iter: Add a function to extract a page list from an iterator
      cifs: Test use of iov_iter_extract_pages() and iov_iter_extract_mode()

 fs/cifs/cifsglob.h  |   2 +
 fs/cifs/file.c      |  93 +++++++++----
 include/linux/uio.h |  26 ++++
 lib/iov_iter.c      | 333 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 427 insertions(+), 27 deletions(-)