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buffer: add get_nth_bh()

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Extract this useful helper from nilfs_page_get_nth_block()

Link: https://lkml.kernel.org/r/20231016201114.1928083-6-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-10-16 21:10:52 +01:00 committed by Andrew Morton
parent d405999367
commit 0217fbb027
2 changed files with 23 additions and 6 deletions
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7
fs/nilfs2/page.h
View file

@ -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 */

22
include/linux/buffer_head.h
View file

@ -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