linux-kernel - [PATCH 02/12] iov_iter: add helper to test if an iter would use GUP v2

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Date:   Tue, 23 Jul 2019 21:25:08 -0700
From:   john.hubbard@...il.com
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "David S . Miller" <davem@...emloft.net>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Latchesar Ionkov <lucho@...kov.net>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>, ceph-devel@...r.kernel.org,
        kvm@...r.kernel.org, linux-block@...r.kernel.org,
        linux-cifs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-rdma@...r.kernel.org,
        netdev@...r.kernel.org, samba-technical@...ts.samba.org,
        v9fs-developer@...ts.sourceforge.net,
        virtualization@...ts.linux-foundation.org,
        Jérôme Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>, Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Ming Lei <ming.lei@...hat.com>,
        Dave Chinner <david@...morbit.com>
Subject: [PATCH 02/12] iov_iter: add helper to test if an iter would use GUP v2

From: Jérôme Glisse <jglisse@...hat.com>

Add a helper to test if call to iov_iter_get_pages*() with a given
iter would result in calls to GUP (get_user_pages*()). We want to
use different tracking of page references if they are coming from
GUP (get_user_pages*()) and thus  we need to know when GUP is used
for a given iter.

Changes since Jérôme's original patch:

* iov_iter_get_pages_use_gup(): do not return true for the ITER_PIPE
case, because iov_iter_get_pages() calls pipe_get_pages(), which in
turn uses get_page(), not get_user_pages().

* Remove some obsolete code, as part of rebasing onto Linux 5.3.

* Fix up the kerneldoc comment to "Return:" rather than "Returns:",
and a few other grammatical tweaks.

Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
Signed-off-by: John Hubbard <jhubbard@...dia.com>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-block@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Johannes Thumshirn <jthumshirn@...e.de>
Cc: Christoph Hellwig <hch@....de>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Ming Lei <ming.lei@...hat.com>
Cc: Dave Chinner <david@...morbit.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: Matthew Wilcox <willy@...radead.org>
---
 include/linux/uio.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index ab5f523bc0df..2a179af8e5a7 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -86,6 +86,17 @@ static inline unsigned char iov_iter_rw(const struct iov_iter *i)
 	return i->type & (READ | WRITE);
 }
 
+/**
+ * iov_iter_get_pages_use_gup - report if iov_iter_get_pages(i) uses GUP
+ * @i: iterator
+ * Return: true if a call to iov_iter_get_pages*() with the iter provided in
+ *          the argument would result in the use of get_user_pages*()
+ */
+static inline bool iov_iter_get_pages_use_gup(const struct iov_iter *i)
+{
+	return iov_iter_type(i) == ITER_IOVEC;
+}
+
 /*
  * Total number of bytes covered by an iovec.
  *
-- 
2.22.0