[PATCH 1/7] highmem: Add memcpy_to_folio() and memcpy_from_folio()

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

These are the folio equivalent of memcpy_to_page() and memcpy_from_page().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/highmem.h | 44 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 68da30625a6c..0280f57d4744 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -439,6 +439,50 @@ static inline void memzero_page(struct page *page, size_t offset, size_t len)
 	kunmap_local(addr);
 }
 
+static inline void memcpy_from_folio(char *to, struct folio *folio,
+		size_t offset, size_t len)
+{
+	VM_BUG_ON(offset + len > folio_size(folio));
+
+	do {
+		char *from = kmap_local_folio(folio, offset);
+		size_t chunk = len;
+
+		if (folio_test_highmem(folio) &&
+		    (chunk > (PAGE_SIZE - offset_in_page(offset))))
+			chunk = PAGE_SIZE - offset_in_page(offset);
+		memcpy(to, from, len);
+		kunmap_local(from);
+
+		from += chunk;
+		offset += chunk;
+		len -= chunk;
+	} while (len > 0);
+}
+
+static inline void memcpy_to_folio(struct folio *folio, size_t offset,
+		const char *from, size_t len)
+{
+	VM_BUG_ON(offset + len > folio_size(folio));
+
+	do {
+		char *to = kmap_local_folio(folio, offset);
+		size_t chunk = len;
+
+		if (folio_test_highmem(folio) &&
+		    (chunk > (PAGE_SIZE - offset_in_page(offset))))
+			chunk = PAGE_SIZE - offset_in_page(offset);
+		memcpy(to, from, len);
+		kunmap_local(to);
+
+		from += chunk;
+		offset += chunk;
+		len -= chunk;
+	} while (len > 0);
+
+	flush_dcache_folio(folio);
+}
+
 /**
  * memcpy_from_file_folio - Copy some bytes from a file folio.
  * @to: The destination buffer.
-- 
2.39.2