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-rw-r--r--include/linux/pagemap.h28
1 files changed, 28 insertions, 0 deletions
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 37a4d9e32cd3..ccb14b6a16b5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -636,4 +636,32 @@ static inline unsigned long dir_pages(struct inode *inode)
PAGE_SHIFT;
}
+/**
+ * page_mkwrite_check_truncate - check if page was truncated
+ * @page: the page to check
+ * @inode: the inode to check the page against
+ *
+ * Returns the number of bytes in the page up to EOF,
+ * or -EFAULT if the page was truncated.
+ */
+static inline int page_mkwrite_check_truncate(struct page *page,
+ struct inode *inode)
+{
+ loff_t size = i_size_read(inode);
+ pgoff_t index = size >> PAGE_SHIFT;
+ int offset = offset_in_page(size);
+
+ if (page->mapping != inode->i_mapping)
+ return -EFAULT;
+
+ /* page is wholly inside EOF */
+ if (page->index < index)
+ return PAGE_SIZE;
+ /* page is wholly past EOF */
+ if (page->index > index || !offset)
+ return -EFAULT;
+ /* page is partially inside EOF */
+ return offset;
+}
+
#endif /* _LINUX_PAGEMAP_H */