Extract this useful helper from nilfs_page_get_nth_block()
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Acked-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
---
fs/nilfs2/page.h | 7 +------
include/linux/buffer_head.h | 22 ++++++++++++++++++++++
2 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/fs/nilfs2/page.h b/fs/nilfs2/page.h
index 21ddcdd4d63e..344d71942d36 100644
--- a/fs/nilfs2/page.h
+++ b/fs/nilfs2/page.h
@@ -55,12 +55,7 @@ unsigned long nilfs_find_uncommitted_extent(struct inode *inode,
static inline struct buffer_head *
nilfs_page_get_nth_block(struct page *page, unsigned int count)
{
- struct buffer_head *bh = page_buffers(page);
-
- while (count-- > 0)
- bh = bh->b_this_page;
- get_bh(bh);
- return bh;
+ return get_nth_bh(page_buffers(page), count);
}
#endif /* _NILFS_PAGE_H */
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 1001244a8941..3d85a0cf0ca5 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -457,6 +457,28 @@ __bread(struct block_device *bdev, sector_t block, unsigned size)
return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
}
+/**
+ * get_nth_bh - Get a reference on the n'th buffer after this one.
+ * @bh: The buffer to start counting from.
+ * @count: How many buffers to skip.
+ *
+ * This is primarily useful for finding the nth buffer in a folio; in
+ * that case you pass the head buffer and the byte offset in the folio
+ * divided by the block size. It can be used for other purposes, but
+ * it will wrap at the end of the folio rather than returning NULL or
+ * proceeding to the next folio for you.
+ *
+ * Return: The requested buffer with an elevated refcount.
+ */
+static inline __must_check
+struct buffer_head *get_nth_bh(struct buffer_head *bh, unsigned int count)
+{
+ while (count--)
+ bh = bh->b_this_page;
+ get_bh(bh);
+ return bh;
+}
+
bool block_dirty_folio(struct address_space *mapping, struct folio *folio);
#ifdef CONFIG_BUFFER_HEAD
--
2.40.1
