bio_vec-backed iov_iter

New variant of iov_iter - ITER_BVEC in iter->type, backed with
bio_vec array instead of iovec one.  Primitives taught to deal
with such beasts, __swap_write() switched to using that kind
of iov_iter.

Note that bio_vec is just a <page, offset, length> triple - there's
nothing block-specific about it.  I've left the definition where it
was, but took it from under ifdef CONFIG_BLOCK.

Next target: ->splice_write()...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/fuse/file.c

@@ -1288,7 +1288,7 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
 	size_t nbytes = 0;  /* # bytes already packed in req */
 
 	/* Special case for kernel I/O: can copy directly into the buffer */
-	if (ii->type & REQ_KERNEL) {
+	if (ii->type & ITER_KVEC) {
 		unsigned long user_addr = fuse_get_user_addr(ii);
 		size_t frag_size = fuse_get_frag_size(ii, *nbytesp);
 

include/linux/blk_types.h

@@ -5,8 +5,6 @@
 #ifndef __LINUX_BLK_TYPES_H
 #define __LINUX_BLK_TYPES_H
 
-#ifdef CONFIG_BLOCK
-
 #include <linux/types.h>
 
 struct bio_set;
@@ -28,6 +26,8 @@ struct bio_vec {
 	unsigned int	bv_offset;
 };
 
+#ifdef CONFIG_BLOCK
+
 struct bvec_iter {
 	sector_t		bi_sector;	/* device address in 512 byte
 						   sectors */

include/linux/uio.h

@@ -19,12 +19,21 @@ struct kvec {
 	size_t iov_len;
 };
 
+enum {
+	ITER_IOVEC = 0,
+	ITER_KVEC = 2,
+	ITER_BVEC = 4,
+};
+
 struct iov_iter {
 	int type;
-	const struct iovec *iov;
-	unsigned long nr_segs;
 	size_t iov_offset;
 	size_t count;
+	union {
+		const struct iovec *iov;
+		const struct bio_vec *bvec;
+	};
+	unsigned long nr_segs;
 };
 
 /*
@@ -54,6 +63,7 @@ static inline struct iovec iov_iter_iovec(const struct iov_iter *iter)
 }
 
 #define iov_for_each(iov, iter, start)				\
+	if (!((start).type & ITER_BVEC))			\
 	for (iter = (start);					\
 	     (iter).count &&					\
 	     ((iov = iov_iter_iovec(&(iter))), 1);		\