mm: move filemap_range_needs_writeback() into header

No functional changes in this patch, just in preparation for efficiently
calling this light function from the block O_DIRECT handling.

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 29 insertions, 0 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 605246452305..274a0710f2c5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -963,6 +963,35 @@ static inline int add_to_page_cache(struct page *page,
 int __filemap_add_folio(struct address_space *mapping, struct folio *folio,
 		pgoff_t index, gfp_t gfp, void **shadowp);
 
+bool filemap_range_has_writeback(struct address_space *mapping,
+				 loff_t start_byte, loff_t end_byte);
+
+/**
+ * filemap_range_needs_writeback - check if range potentially needs writeback
+ * @mapping:           address space within which to check
+ * @start_byte:        offset in bytes where the range starts
+ * @end_byte:          offset in bytes where the range ends (inclusive)
+ *
+ * Find at least one page in the range supplied, usually used to check if
+ * direct writing in this range will trigger a writeback. Used by O_DIRECT
+ * read/write with IOCB_NOWAIT, to see if the caller needs to do
+ * filemap_write_and_wait_range() before proceeding.
+ *
+ * Return: %true if the caller should do filemap_write_and_wait_range() before
+ * doing O_DIRECT to a page in this range, %false otherwise.
+ */
+static inline bool filemap_range_needs_writeback(struct address_space *mapping,
+						 loff_t start_byte,
+						 loff_t end_byte)
+{
+	if (!mapping->nrpages)
+		return false;
+	if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
+	    !mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
+		return false;
+	return filemap_range_has_writeback(mapping, start_byte, end_byte);
+}
+
 /**
  * struct readahead_control - Describes a readahead request.
  *