block: move two bvec structure into bvec.h

This patch moves 'struct bio_vec' and 'struct bvec_iter'
into 'include/linux/bvec.h', then always include this header
into 'include/linux/blk_types.h'.

With this change, both 'struct bvec_iter' and bvec iterator
helpers don't depend on CONFIG_BLOCK any more, then we can
use bvec iterator to implement iterate_bvec(): lib/iov_iter.c.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Tested-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/bio.h

@@ -31,7 +31,6 @@
 
 /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
 #include <linux/blk_types.h>
-#include <linux/bvec.h>
 
 #define BIO_DEBUG
 

include/linux/blk_types.h

@@ -6,6 +6,7 @@
 #define __LINUX_BLK_TYPES_H
 
 #include <linux/types.h>
+#include <linux/bvec.h>
 
 struct bio_set;
 struct bio;
@@ -17,28 +18,7 @@ struct cgroup_subsys_state;
 typedef void (bio_end_io_t) (struct bio *);
 typedef void (bio_destructor_t) (struct bio *);
 
-/*
- * was unsigned short, but we might as well be ready for > 64kB I/O pages
- */
-struct bio_vec {
-	struct page	*bv_page;
-	unsigned int	bv_len;
-	unsigned int	bv_offset;
-};
-
 #ifdef CONFIG_BLOCK
-
-struct bvec_iter {
-	sector_t		bi_sector;	/* device address in 512 byte
-						   sectors */
-	unsigned int		bi_size;	/* residual I/O count */
-
-	unsigned int		bi_idx;		/* current index into bvl_vec */
-
-	unsigned int            bi_bvec_done;	/* number of bytes completed in
-						   current bvec */
-};
-
 /*
  * main unit of I/O for the block layer and lower layers (ie drivers and
  * stacking drivers)

include/linux/bvec.h

@@ -20,7 +20,28 @@
 #ifndef __LINUX_BVEC_ITER_H
 #define __LINUX_BVEC_ITER_H
 
-#include <linux/blk_types.h>
+#include <linux/kernel.h>
+#include <linux/bug.h>
+
+/*
+ * was unsigned short, but we might as well be ready for > 64kB I/O pages
+ */
+struct bio_vec {
+	struct page	*bv_page;
+	unsigned int	bv_len;
+	unsigned int	bv_offset;
+};
+
+struct bvec_iter {
+	sector_t		bi_sector;	/* device address in 512 byte
+						   sectors */
+	unsigned int		bi_size;	/* residual I/O count */
+
+	unsigned int		bi_idx;		/* current index into bvl_vec */
+
+	unsigned int            bi_bvec_done;	/* number of bytes completed in
+						   current bvec */
+};
 
 /*
  * various member access, note that bio_data should of course not be used