1 files changed, 91 insertions, 0 deletions
diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
new file mode 100644
index 000000000000..b86a4881475d
--- /dev/null
+++ b/fs/btrfs/subpage.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef BTRFS_SUBPAGE_H
+#define BTRFS_SUBPAGE_H
+
+#include <linux/spinlock.h>
+
+/*
+ * Maximum page size we support is 64K, minimum sector size is 4K, u16 bitmap
+ * is sufficient. Regular bitmap_* is not used due to size reasons.
+ */
+#define BTRFS_SUBPAGE_BITMAP_SIZE	16
+
+/*
+ * Structure to trace status of each sector inside a page, attached to
+ * page::private for both data and metadata inodes.
+ */
+struct btrfs_subpage {
+	/* Common members for both data and metadata pages */
+	spinlock_t lock;
+	u16 uptodate_bitmap;
+	u16 error_bitmap;
+	union {
+		/*
+		 * Structures only used by metadata
+		 *
+		 * @eb_refs should only be operated under private_lock, as it
+		 * manages whether the subpage can be detached.
+		 */
+		atomic_t eb_refs;
+		/* Structures only used by data */
+		struct {
+			atomic_t readers;
+		};
+	};
+};
+
+enum btrfs_subpage_type {
+	BTRFS_SUBPAGE_METADATA,
+	BTRFS_SUBPAGE_DATA,
+};
+
+int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
+			 struct page *page, enum btrfs_subpage_type type);
+void btrfs_detach_subpage(const struct btrfs_fs_info *fs_info,
+			  struct page *page);
+
+/* Allocate additional data where page represents more than one sector */
+int btrfs_alloc_subpage(const struct btrfs_fs_info *fs_info,
+			struct btrfs_subpage **ret,
+			enum btrfs_subpage_type type);
+void btrfs_free_subpage(struct btrfs_subpage *subpage);
+
+void btrfs_page_inc_eb_refs(const struct btrfs_fs_info *fs_info,
+			    struct page *page);
+void btrfs_page_dec_eb_refs(const struct btrfs_fs_info *fs_info,
+			    struct page *page);
+
+void btrfs_subpage_start_reader(const struct btrfs_fs_info *fs_info,
+		struct page *page, u64 start, u32 len);
+void btrfs_subpage_end_reader(const struct btrfs_fs_info *fs_info,
+		struct page *page, u64 start, u32 len);
+
+/*
+ * Template for subpage related operations.
+ *
+ * btrfs_subpage_*() are for call sites where the page has subpage attached and
+ * the range is ensured to be inside the page.
+ *
+ * btrfs_page_*() are for call sites where the page can either be subpage
+ * specific or regular page. The function will handle both cases.
+ * But the range still needs to be inside the page.
+ */
+#define DECLARE_BTRFS_SUBPAGE_OPS(name)					\
+void btrfs_subpage_set_##name(const struct btrfs_fs_info *fs_info,	\
+		struct page *page, u64 start, u32 len);			\
+void btrfs_subpage_clear_##name(const struct btrfs_fs_info *fs_info,	\
+		struct page *page, u64 start, u32 len);			\
+bool btrfs_subpage_test_##name(const struct btrfs_fs_info *fs_info,	\
+		struct page *page, u64 start, u32 len);			\
+void btrfs_page_set_##name(const struct btrfs_fs_info *fs_info,		\
+		struct page *page, u64 start, u32 len);			\
+void btrfs_page_clear_##name(const struct btrfs_fs_info *fs_info,	\
+		struct page *page, u64 start, u32 len);			\
+bool btrfs_page_test_##name(const struct btrfs_fs_info *fs_info,	\
+		struct page *page, u64 start, u32 len);
+
+DECLARE_BTRFS_SUBPAGE_OPS(uptodate);
+DECLARE_BTRFS_SUBPAGE_OPS(error);
+
+#endif