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>

1 files changed, 12 insertions, 7 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
index 313bfed..33bb38c 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -259,23 +259,28 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		struct kiocb kiocb;
 		struct file *swap_file = sis->swap_file;
 		struct address_space *mapping = swap_file->f_mapping;
-		struct iovec iov = {
-			.iov_base = kmap(page),
-			.iov_len  = PAGE_SIZE,
+		struct bio_vec bv = {
+			.bv_page = page,
+			.bv_len  = PAGE_SIZE,
+			.bv_offset = 0
+		};
+		struct iov_iter from = {
+			.type = ITER_BVEC | WRITE,
+			.count = PAGE_SIZE,
+			.iov_offset = 0,
+			.nr_segs = 1,
+			.bvec = &bv
 		};
-		struct iov_iter from;
 
 		init_sync_kiocb(&kiocb, swap_file);
 		kiocb.ki_pos = page_file_offset(page);
 		kiocb.ki_nbytes = PAGE_SIZE;
-		iov_iter_init(&from, KERNEL_WRITE, &iov, 1, PAGE_SIZE);
 
 		set_page_writeback(page);
 		unlock_page(page);
-		ret = mapping->a_ops->direct_IO(KERNEL_WRITE,
+		ret = mapping->a_ops->direct_IO(ITER_BVEC | WRITE,
 						&kiocb, &from,
 						kiocb.ki_pos);
-		kunmap(page);
 		if (ret == PAGE_SIZE) {
 			count_vm_event(PSWPOUT);
 			ret = 0;