btrfs: rename parameter offset to disk_bytenr in submit_extent_page

The parameter offset is confusing, it's supposed to be the disk bytenr
of metadata/data.  Rename it to disk_bytenr and update the comment.

Also rename each offset passed to submit_extent_page() as @disk_bytenr
so they're consistent.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -3062,10 +3062,10 @@ struct bio *btrfs_bio_clone_partial(struct bio *orig, int offset, int size)
  * @opf:	bio REQ_OP_* and REQ_* flags as one value
  * @wbc:	optional writeback control for io accounting
  * @page:	page to add to the bio
+ * @disk_bytenr: logical bytenr where the write will be
+ * @size:	portion of page that we want to write to
  * @pg_offset:	offset of the new bio or to check whether we are adding
  *              a contiguous page to the previous one
- * @size:	portion of page that we want to write
- * @offset:	starting offset in the page
  * @bio_ret:	must be valid pointer, newly allocated bio will be stored there
  * @end_io_func:     end_io callback for new bio
  * @mirror_num:	     desired mirror to read/write
@@ -3074,7 +3074,7 @@ struct bio *btrfs_bio_clone_partial(struct bio *orig, int offset, int size)
  */
 static int submit_extent_page(unsigned int opf,
 			      struct writeback_control *wbc,
-			      struct page *page, u64 offset,
+			      struct page *page, u64 disk_bytenr,
 			      size_t size, unsigned long pg_offset,
 			      struct bio **bio_ret,
 			      bio_end_io_t end_io_func,
@@ -3086,7 +3086,7 @@ static int submit_extent_page(unsigned int opf,
 	int ret = 0;
 	struct bio *bio;
 	size_t io_size = min_t(size_t, size, PAGE_SIZE);
-	sector_t sector = offset >> 9;
+	sector_t sector = disk_bytenr >> 9;
 	struct extent_io_tree *tree = &BTRFS_I(page->mapping->host)->io_tree;
 
 	ASSERT(bio_ret);
@@ -3120,7 +3120,7 @@ static int submit_extent_page(unsigned int opf,
 		}
 	}
 
-	bio = btrfs_bio_alloc(offset);
+	bio = btrfs_bio_alloc(disk_bytenr);
 	bio_add_page(bio, page, io_size, pg_offset);
 	bio->bi_end_io = end_io_func;
 	bio->bi_private = tree;
@@ -3242,7 +3242,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 	}
 	while (cur <= end) {
 		bool force_bio_submit = false;
-		u64 offset;
+		u64 disk_bytenr;
 
 		if (cur >= last_byte) {
 			char *userpage;
@@ -3280,9 +3280,9 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 		cur_end = min(extent_map_end(em) - 1, end);
 		iosize = ALIGN(iosize, blocksize);
 		if (this_bio_flag & EXTENT_BIO_COMPRESSED)
-			offset = em->block_start;
+			disk_bytenr = em->block_start;
 		else
-			offset = em->block_start + extent_offset;
+			disk_bytenr = em->block_start + extent_offset;
 		block_start = em->block_start;
 		if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
 			block_start = EXTENT_MAP_HOLE;
@@ -3371,7 +3371,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 		}
 
 		ret = submit_extent_page(REQ_OP_READ | read_flags, NULL,
-					 page, offset, iosize,
+					 page, disk_bytenr, iosize,
 					 pg_offset, bio,
 					 end_bio_extent_readpage, 0,
 					 *bio_flags,
@@ -3548,8 +3548,8 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
 	blocksize = inode->vfs_inode.i_sb->s_blocksize;
 
 	while (cur <= end) {
+		u64 disk_bytenr;
 		u64 em_end;
-		u64 offset;
 
 		if (cur >= i_size) {
 			btrfs_writepage_endio_finish_ordered(page, cur,
@@ -3569,7 +3569,7 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
 		BUG_ON(end < cur);
 		iosize = min(em_end - cur, end - cur + 1);
 		iosize = ALIGN(iosize, blocksize);
-		offset = em->block_start + extent_offset;
+		disk_bytenr = em->block_start + extent_offset;
 		block_start = em->block_start;
 		compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
 		free_extent_map(em);
@@ -3599,7 +3599,7 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
 		}
 
 		ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
-					 page, offset, iosize, pg_offset,
+					 page, disk_bytenr, iosize, pg_offset,
 					 &epd->bio,
 					 end_bio_extent_writepage,
 					 0, 0, 0, false);
@@ -3923,7 +3923,7 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
 			struct writeback_control *wbc,
 			struct extent_page_data *epd)
 {
-	u64 offset = eb->start;
+	u64 disk_bytenr = eb->start;
 	u32 nritems;
 	int i, num_pages;
 	unsigned long start, end;
@@ -3956,7 +3956,7 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
 		clear_page_dirty_for_io(p);
 		set_page_writeback(p);
 		ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
-					 p, offset, PAGE_SIZE, 0,
+					 p, disk_bytenr, PAGE_SIZE, 0,
 					 &epd->bio,
 					 end_bio_extent_buffer_writepage,
 					 0, 0, 0, false);
@@ -3969,7 +3969,7 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
 			ret = -EIO;
 			break;
 		}
-		offset += PAGE_SIZE;
+		disk_bytenr += PAGE_SIZE;
 		update_nr_written(wbc, 1);
 		unlock_page(p);
 	}