block: Add bio_get_user_pages()

This replaces some of the code that was in __bio_map_user_iov(), and
soon we're going to use this helper in the dio code.

Note that this relies on the recent change to make
generic_make_request() take arbitrary sized bios - we're not using
bio_add_page() here.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>

Conflicts:
	fs/bio.c

2 files changed, 67 insertions, 0 deletions

diff --git a/fs/bio.c b/fs/bio.c
index e58eb1ee1ab7..548fb99a36af 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1234,6 +1234,71 @@ struct bio *bio_copy_user(struct request_queue *q, struct rq_map_data *map_data,
 }
 EXPORT_SYMBOL(bio_copy_user);
 
+/**
+ * bio_get_user_pages - pin user pages and add them to a biovec
+ * @bio: bio to add pages to
+ * @uaddr: start of user address
+ * @len: length in bytes
+ * @write_to_vm: bool indicating writing to pages or not
+ *
+ * Pins pages for up to @len bytes and appends them to @bio's bvec array. May
+ * pin only part of the requested pages - @bio need not have room for all the
+ * pages and can already have had pages added to it.
+ *
+ * Returns the number of bytes from @len added to @bio.
+ */
+ssize_t bio_get_user_pages(struct bio *bio, struct iov_iter *i, int write_to_vm)
+{
+	while (bio->bi_vcnt < bio->bi_max_vecs && iov_iter_count(i)) {
+		struct iovec iov = iov_iter_iovec(i);
+		int ret;
+		unsigned nr_pages, bytes;
+		unsigned offset = offset_in_page(iov.iov_base);
+		struct bio_vec *bv;
+		struct page **pages;
+
+		nr_pages = min_t(size_t,
+				 DIV_ROUND_UP(iov.iov_len + offset, PAGE_SIZE),
+				 bio->bi_max_vecs - bio->bi_vcnt);
+
+		bv = &bio->bi_io_vec[bio->bi_vcnt];
+		pages = (void *) bv;
+
+		ret = get_user_pages_fast((unsigned long) iov.iov_base,
+					  nr_pages, write_to_vm, pages);
+		if (ret < 0) {
+			if (bio->bi_vcnt)
+				return 0;
+
+			return ret;
+		}
+
+		bio->bi_vcnt += ret;
+		bytes = ret * PAGE_SIZE - offset;
+
+		while (ret--) {
+			bv[ret].bv_page = pages[ret];
+			bv[ret].bv_len = PAGE_SIZE;
+			bv[ret].bv_offset = 0;
+		}
+
+		bv[0].bv_offset += offset;
+		bv[0].bv_len -= offset;
+
+		if (bytes > iov.iov_len) {
+			bio->bi_io_vec[bio->bi_vcnt - 1].bv_len -=
+				bytes - iov.iov_len;
+			bytes = iov.iov_len;
+		}
+
+		bio->bi_iter.bi_size += bytes;
+		iov_iter_advance(i, bytes);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(bio_get_user_pages);
+
 static struct bio *__bio_map_user_iov(struct request_queue *q,
 				      struct block_device *bdev,
 				      const struct iov_iter *iter,
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 87c5cb3eab17..0074044a31c2 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -370,6 +370,8 @@ extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
 extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
 			   unsigned int, unsigned int);
 extern int bio_get_nr_vecs(struct block_device *);
+struct iov_iter;
+extern ssize_t bio_get_user_pages(struct bio *, struct iov_iter *, int);
 extern struct bio *bio_map_user(struct request_queue *, struct block_device *,
 				unsigned long, unsigned int, int, gfp_t);
 struct iov_iter;