[PATCH] make mpage use bio_add_page()

This makes mpage use bio_add_page().  It has the added advantage that
users don't need to have deep knowledge about what the different bio
fields mean, nor does it have to abuse some of them while building the
bio.

fs/mpage.c

@@ -8,6 +8,8 @@
  *
  * 15May2002	akpm@zip.com.au
  *		Initial version
+ * 27Jun2002	axboe@suse.de
+ *		use bio_add_page() to build bio's just the right size
  */
 
 #include <linux/kernel.h>
@@ -22,12 +24,6 @@
 #include <linux/writeback.h>
 #include <linux/pagevec.h>
 
-/*
- * The largest-sized BIO which this code will assemble, in bytes.  Set this
- * to PAGE_CACHE_SIZE if your drivers are broken.
- */
-#define MPAGE_BIO_MAX_SIZE BIO_MAX_SIZE
-
 /*
  * I/O completion handler for multipage BIOs.
  *
@@ -82,8 +78,6 @@ static void mpage_end_io_write(struct bio *bio)
 
 struct bio *mpage_bio_submit(int rw, struct bio *bio)
 {
-	bio->bi_vcnt = bio->bi_idx;
-	bio->bi_idx = 0;
 	bio->bi_end_io = mpage_end_io_read;
 	if (rw == WRITE)
 		bio->bi_end_io = mpage_end_io_write;
@@ -106,11 +100,7 @@ mpage_alloc(struct block_device *bdev,
 
 	if (bio) {
 		bio->bi_bdev = bdev;
-		bio->bi_vcnt = nr_vecs;
-		bio->bi_idx = 0;
-		bio->bi_size = 0;
 		bio->bi_sector = first_sector;
-		bio->bi_io_vec[0].bv_page = NULL;
 	}
 	return bio;
 }
@@ -169,7 +159,6 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 	const unsigned blkbits = inode->i_blkbits;
 	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 	const unsigned blocksize = 1 << blkbits;
-	struct bio_vec *bvec;
 	sector_t block_in_file;
 	sector_t last_block;
 	sector_t blocks[MAX_BUF_PER_PAGE];
@@ -223,26 +212,22 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 	/*
 	 * This page will go to BIO.  Do we need to send this BIO off first?
 	 */
-	if (bio && (bio->bi_idx == bio->bi_vcnt ||
-			*last_block_in_bio != blocks[0] - 1))
+	if (bio && (*last_block_in_bio != blocks[0] - 1))
 		bio = mpage_bio_submit(READ, bio);
 
+alloc_new:
 	if (bio == NULL) {
-		unsigned nr_bvecs = MPAGE_BIO_MAX_SIZE / PAGE_CACHE_SIZE;
-
-		if (nr_bvecs > nr_pages)
-			nr_bvecs = nr_pages;
 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-					nr_bvecs, GFP_KERNEL);
+					nr_pages, GFP_KERNEL);
 		if (bio == NULL)
 			goto confused;
 	}
 
-	bvec = &bio->bi_io_vec[bio->bi_idx++];
-	bvec->bv_page = page;
-	bvec->bv_len = (first_hole << blkbits);
-	bvec->bv_offset = 0;
-	bio->bi_size += bvec->bv_len;
+	if (bio_add_page(bio, page, first_hole << blkbits, 0)) {
+		bio = mpage_bio_submit(READ, bio);
+		goto alloc_new;
+	}
+
 	if (buffer_boundary(&bh) || (first_hole != blocks_per_page))
 		bio = mpage_bio_submit(READ, bio);
 	else
@@ -330,7 +315,6 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 	const unsigned blkbits = inode->i_blkbits;
 	unsigned long end_index;
 	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
-	struct bio_vec *bvec;
 	sector_t last_block;
 	sector_t block_in_file;
 	sector_t blocks[MAX_BUF_PER_PAGE];
@@ -432,15 +416,15 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 	/*
 	 * This page will go to BIO.  Do we need to send this BIO off first?
 	 */
-	if (bio && (bio->bi_idx == bio->bi_vcnt ||
-				*last_block_in_bio != blocks[0] - 1))
+	if (bio && *last_block_in_bio != blocks[0] - 1)
 		bio = mpage_bio_submit(WRITE, bio);
 
+alloc_new:
 	if (bio == NULL) {
-		unsigned nr_bvecs = MPAGE_BIO_MAX_SIZE / PAGE_CACHE_SIZE;
+		const unsigned __nr_pages = 64;	/* FIXME */
 
 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-					nr_bvecs, GFP_NOFS|__GFP_HIGH);
+					__nr_pages, GFP_NOFS|__GFP_HIGH);
 		if (bio == NULL)
 			goto confused;
 	}
@@ -465,11 +449,11 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 			try_to_free_buffers(page);
 	}
 
-	bvec = &bio->bi_io_vec[bio->bi_idx++];
-	bvec->bv_page = page;
-	bvec->bv_len = (first_unmapped << blkbits);
-	bvec->bv_offset = 0;
-	bio->bi_size += bvec->bv_len;
+	if (bio_add_page(bio, page, first_unmapped << blkbits, 0)) {
+		bio = mpage_bio_submit(WRITE, bio);
+		goto alloc_new;
+	}
+
 	BUG_ON(PageWriteback(page));
 	SetPageWriteback(page);
 	unlock_page(page);