[PATCH 03/14] btrfs: extent_io: introduce the skeleton of btrfs_subpage structure

[Qu Wenruo <wqu@suse.com>]

For btrfs subpage support, we need a structure for record extra info for
a page so that we can know things like which sector in the page is
uptodate/dirty.

This patch will introduce the skeleton structure for future btrfs
subpage support.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 32 ++++++++++++++++++++++++++++++++
 fs/btrfs/extent_io.h |  8 ++++++++
 2 files changed, 40 insertions(+)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 759d2f2292ed..2eaf09ff59ca 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5279,6 +5279,38 @@ static struct extent_buffer *grab_extent_buffer_from_page(struct page *page)
 	return NULL;
 }
 
+int btrfs_attach_subpage(struct btrfs_fs_info *fs_info, struct page *page)
+{
+	struct btrfs_subpage *subpage;
+
+	ASSERT(PageLocked(page));
+	/* Either not subpage, or the page already has private attached */
+	if (!btrfs_is_subpage(fs_info) || PagePrivate(page))
+		return 0;
+
+	subpage = kzalloc(sizeof(*subpage), GFP_NOFS);
+	if (!subpage)
+		return -ENOMEM;
+
+	spin_lock_init(&subpage->lock);
+	attach_page_private(page, subpage);
+	return 0;
+}
+
+void btrfs_detach_subpage(struct btrfs_fs_info *fs_info, struct page *page)
+{
+	struct btrfs_subpage *subpage;
+
+	/* Either not subpage, or already detached */
+	if (!btrfs_is_subpage(fs_info) || !PagePrivate(page))
+		return;
+
+	subpage = (struct btrfs_subpage *)detach_page_private(page);
+	ASSERT(subpage && bitmap_empty(subpage->tree_block_bitmap,
+				       BTRFS_SUBPAGE_BITMAP_SIZE));
+	kfree(subpage);
+}
+
 struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 					  u64 start, u64 owner_root, int level)
 {
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 0123c75ee203..4251bef25aac 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -307,6 +307,14 @@ blk_status_t btrfs_submit_read_repair(struct inode *inode,
 				      u64 start, u64 end, int failed_mirror,
 				      submit_bio_hook_t *submit_bio_hook);
 
+#define BTRFS_SUBPAGE_BITMAP_SIZE	(SZ_64K / SZ_4K)
+struct btrfs_subpage {
+	spinlock_t lock;
+	DECLARE_BITMAP(tree_block_bitmap, BTRFS_SUBPAGE_BITMAP_SIZE);
+};
+
+int btrfs_attach_subpage(struct btrfs_fs_info *fs_info, struct page *page);
+void btrfs_detach_subpage(struct btrfs_fs_info *fs_info, struct page *page);
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 bool find_lock_delalloc_range(struct inode *inode,
 			     struct page *locked_page, u64 *start,
-- 
2.29.2