[PATCH v13 077/137] mm/filemap: Add folio_mkwrite_check_truncate()

Matthew Wilcox (Oracle)
2021-07-12T03:49:26Z

This is the folio equivalent of page_mkwrite_check_truncate().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/pagemap.h | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 319e2b486c0d..1aee9f711de8 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1121,6 +1121,34 @@ static inline unsigned long dir_pages(struct inode *inode)
PAGE_SHIFT;
}

+/**
+ * folio_mkwrite_check_truncate - check if folio was truncated
+ * @folio: the folio to check
+ * @inode: the inode to check the folio against
+ *
+ * Return: the number of bytes in the folio up to EOF,
+ * or -EFAULT if the folio was truncated.
+ */
+static inline ssize_t folio_mkwrite_check_truncate(struct folio *folio,
+ struct inode *inode)
+{
+ loff_t size = i_size_read(inode);
+ pgoff_t index = size >> PAGE_SHIFT;
+ size_t offset = offset_in_folio(folio, size);
+
+ if (!folio->mapping)
+ return -EFAULT;
+
+ /* folio is wholly inside EOF */
+ if (folio_next_index(folio) - 1 < index)
+ return folio_size(folio);
+ /* folio is wholly past EOF */
+ if (folio->index > index || !offset)
+ return -EFAULT;
+ /* folio is partially inside EOF */
+ return offset;
+}
+
/**
* page_mkwrite_check_truncate - check if page was truncated
* @page: the page to check
--
2.30.2