[PATCH v4 08/18] btrfs: introduce helper for subpage uptodate status

[Qu Wenruo <wqu@suse.com>]

This patch introduce the following functions to handle btrfs subpage
uptodate status:
- btrfs_subpage_set_uptodate()
- btrfs_subpage_clear_uptodate()
- btrfs_subpage_test_uptodate()
  Those helpers can only be called when the range is ensured to be
  inside the page.

- btrfs_page_set_uptodate()
- btrfs_page_clear_uptodate()
- btrfs_page_test_uptodate()
  Those helpers can handle both regular sector size and subpage without
  problem.
  Although caller should still ensure that the range is inside the page.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/subpage.h | 115 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)

diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index d8b34879368d..3373ef4ffec1 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -23,6 +23,7 @@
 struct btrfs_subpage {
 	/* Common members for both data and metadata pages */
 	spinlock_t lock;
+	u16 uptodate_bitmap;
 	union {
 		/* Structures only used by metadata */
 		bool under_alloc;
@@ -78,4 +79,118 @@ static inline void btrfs_page_end_meta_alloc(struct btrfs_fs_info *fs_info,
 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);
 
+/*
+ * Convert the [start, start + len) range into a u16 bitmap
+ *
+ * E.g. if start == page_offset() + 16K, len = 16K, we get 0x00f0.
+ */
+static inline u16 btrfs_subpage_calc_bitmap(struct btrfs_fs_info *fs_info,
+			struct page *page, u64 start, u32 len)
+{
+	int bit_start = offset_in_page(start) >> fs_info->sectorsize_bits;
+	int nbits = len >> fs_info->sectorsize_bits;
+
+	/* Basic checks */
+	ASSERT(PagePrivate(page) && page->private);
+	ASSERT(IS_ALIGNED(start, fs_info->sectorsize) &&
+	       IS_ALIGNED(len, fs_info->sectorsize));
+
+	/*
+	 * The range check only works for mapped page, we can
+	 * still have unampped page like dummy extent buffer pages.
+	 */
+	if (page->mapping)
+		ASSERT(page_offset(page) <= start &&
+			start + len <= page_offset(page) + PAGE_SIZE);
+	/*
+	 * Here nbits can be 16, thus can go beyond u16 range. Here we make the
+	 * first left shift to be calculated in unsigned long (u32), then
+	 * truncate the result to u16.
+	 */
+	return (u16)(((1UL << nbits) - 1) << bit_start);
+}
+
+static inline void btrfs_subpage_set_uptodate(struct btrfs_fs_info *fs_info,
+			struct page *page, u64 start, u32 len)
+{
+	struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
+	u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len);
+	unsigned long flags;
+
+	spin_lock_irqsave(&subpage->lock, flags);
+	subpage->uptodate_bitmap |= tmp;
+	if (subpage->uptodate_bitmap == U16_MAX)
+		SetPageUptodate(page);
+	spin_unlock_irqrestore(&subpage->lock, flags);
+}
+
+static inline void btrfs_subpage_clear_uptodate(struct btrfs_fs_info *fs_info,
+			struct page *page, u64 start, u32 len)
+{
+	struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
+	u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len);
+	unsigned long flags;
+
+	spin_lock_irqsave(&subpage->lock, flags);
+	subpage->uptodate_bitmap &= ~tmp;
+	ClearPageUptodate(page);
+	spin_unlock_irqrestore(&subpage->lock, flags);
+}
+
+/*
+ * Unlike set/clear which is dependent on each page status, for test all bits
+ * are tested in the same way.
+ */
+#define DECLARE_BTRFS_SUBPAGE_TEST_OP(name)				\
+static inline bool btrfs_subpage_test_##name(struct btrfs_fs_info *fs_info, \
+			struct page *page, u64 start, u32 len)		\
+{									\
+	struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private; \
+	u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len); \
+	unsigned long flags;						\
+	bool ret;							\
+									\
+	spin_lock_irqsave(&subpage->lock, flags);			\
+	ret = ((subpage->name##_bitmap & tmp) == tmp);			\
+	spin_unlock_irqrestore(&subpage->lock, flags);			\
+	return ret;							\
+}
+DECLARE_BTRFS_SUBPAGE_TEST_OP(uptodate);
+
+/*
+ * Note that, in selftest, especially extent-io-tests, we can have empty
+ * fs_info passed in.
+ * Thankfully in selftest, we only test sectorsize == PAGE_SIZE cases so far,
+ * thus we can fall back to regular sectorsize branch.
+ */
+#define DECLARE_BTRFS_PAGE_OPS(name, set_page_func, clear_page_func,	\
+			       test_page_func)				\
+static inline void btrfs_page_set_##name(struct btrfs_fs_info *fs_info,	\
+			struct page *page, u64 start, u32 len)		\
+{									\
+	if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE) {	\
+		set_page_func(page);					\
+		return;							\
+	}								\
+	btrfs_subpage_set_##name(fs_info, page, start, len);		\
+}									\
+static inline void btrfs_page_clear_##name(struct btrfs_fs_info *fs_info, \
+			struct page *page, u64 start, u32 len)		\
+{									\
+	if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE) {	\
+		clear_page_func(page);					\
+		return;							\
+	}								\
+	btrfs_subpage_clear_##name(fs_info, page, start, len);		\
+}									\
+static inline bool btrfs_page_test_##name(struct btrfs_fs_info *fs_info, \
+			struct page *page, u64 start, u32 len)		\
+{									\
+	if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE)	\
+		return test_page_func(page);				\
+	return btrfs_subpage_test_##name(fs_info, page, start, len);	\
+}
+DECLARE_BTRFS_PAGE_OPS(uptodate, SetPageUptodate, ClearPageUptodate,
+			PageUptodate);
+
 #endif /* BTRFS_SUBPAGE_H */
-- 
2.30.0