[PATCH v3 06/13] btrfs: introduce helpers for subpage writeback status

[Qu Wenruo]

This patch introduces the following functions to handle btrfs subpage
writeback status:
- btrfs_subpage_set_writeback()
- btrfs_subpage_clear_writeback()
- btrfs_subpage_test_writeback()
  Those helpers can only be called when the range is ensured to be
  inside the page.

- btrfs_page_set_writeback()
- btrfs_page_clear_writeback()
- btrfs_page_test_writeback()
  Those helpers can handle both regular sector size and subpage without
  problem.

Signed-off-by: Qu Wenruo <w...@suse.com>
---
 fs/btrfs/subpage.c | 30 ++++++++++++++++++++++++++++++
 fs/btrfs/subpage.h |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index 183925902031..2a326d6385ed 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -260,6 +260,33 @@ void btrfs_subpage_clear_dirty(const struct btrfs_fs_info 
*fs_info,
                clear_page_dirty_for_io(page);
 }
 
+void btrfs_subpage_set_writeback(const 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->writeback_bitmap |= tmp;
+       set_page_writeback(page);
+       spin_unlock_irqrestore(&subpage->lock, flags);
+}
+
+void btrfs_subpage_clear_writeback(const 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->writeback_bitmap &= ~tmp;
+       if (subpage->writeback_bitmap == 0)
+               end_page_writeback(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.
@@ -281,6 +308,7 @@ bool btrfs_subpage_test_##name(const struct btrfs_fs_info 
*fs_info, \
 IMPLEMENT_BTRFS_SUBPAGE_TEST_OP(uptodate);
 IMPLEMENT_BTRFS_SUBPAGE_TEST_OP(error);
 IMPLEMENT_BTRFS_SUBPAGE_TEST_OP(dirty);
+IMPLEMENT_BTRFS_SUBPAGE_TEST_OP(writeback);
 
 /*
  * Note that, in selftests (extent-io-tests), we can have empty fs_info passed
@@ -319,3 +347,5 @@ IMPLEMENT_BTRFS_PAGE_OPS(uptodate, SetPageUptodate, 
ClearPageUptodate,
 IMPLEMENT_BTRFS_PAGE_OPS(error, SetPageError, ClearPageError, PageError);
 IMPLEMENT_BTRFS_PAGE_OPS(dirty, set_page_dirty, clear_page_dirty_for_io,
                         PageDirty);
+IMPLEMENT_BTRFS_PAGE_OPS(writeback, set_page_writeback, end_page_writeback,
+                       PageWriteback);
diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index adaece5ce294..fe43267e31f3 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -21,6 +21,7 @@ struct btrfs_subpage {
        u16 uptodate_bitmap;
        u16 error_bitmap;
        u16 dirty_bitmap;
+       u16 writeback_bitmap;
        union {
                /*
                 * Structures only used by metadata
@@ -89,6 +90,7 @@ bool btrfs_page_test_##name(const struct btrfs_fs_info 
*fs_info,      \
 DECLARE_BTRFS_SUBPAGE_OPS(uptodate);
 DECLARE_BTRFS_SUBPAGE_OPS(error);
 DECLARE_BTRFS_SUBPAGE_OPS(dirty);
+DECLARE_BTRFS_SUBPAGE_OPS(writeback);
 
 /*
  * Extra clear_and_test function for subpage dirty bitmap.
-- 
2.30.1