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

[john . hubbard]

From: JÃrÃme Glisse <jglisse@xxxxxxxxxx>

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 JÃrÃme'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: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-block@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
 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