2 files changed, 41 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cf7982336103..630068184265 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -954,7 +954,7 @@ extern void truncate_pagecache(struct inode *inode, loff_t old, loff_t new);
 extern void truncate_setsize(struct inode *inode, loff_t newsize);
 extern int vmtruncate(struct inode *inode, loff_t offset);
 extern int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end);
-
+void truncate_pagecache_range(struct inode *inode, loff_t offset, loff_t end);
 int truncate_inode_page(struct address_space *mapping, struct page *page);
 int generic_error_remove_page(struct address_space *mapping, struct page *page);
 
diff --git a/mm/truncate.c b/mm/truncate.c
index 18aded3a89fc..61a183b89df6 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -626,3 +626,43 @@ int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend)
 
         return 0;
 }
+
+/**
+ * truncate_pagecache_range - unmap and remove pagecache that is hole-punched
+ * @inode: inode
+ * @lstart: offset of beginning of hole
+ * @lend: offset of last byte of hole
+ *
+ * This function should typically be called before the filesystem
+ * releases resources associated with the freed range (eg. deallocates
+ * blocks). This way, pagecache will always stay logically coherent
+ * with on-disk format, and the filesystem would not have to deal with
+ * situations such as writepage being called for a page that has already
+ * had its underlying blocks deallocated.
+ */
+void truncate_pagecache_range(struct inode *inode, loff_t lstart, loff_t lend)
+{
+        struct address_space *mapping = inode->i_mapping;
+        loff_t unmap_start = round_up(lstart, PAGE_SIZE);
+        loff_t unmap_end = round_down(1 + lend, PAGE_SIZE) - 1;
+        /*
+         * This rounding is currently just for example: unmap_mapping_range
+         * expands its hole outwards, whereas we want it to contract the hole
+         * inwards.  However, existing callers of truncate_pagecache_range are
+         * doing their own page rounding first; and truncate_inode_pages_range
+         * currently BUGs if lend is not pagealigned-1 (it handles partial
+         * page at start of hole, but not partial page at end of hole).  Note
+         * unmap_mapping_range allows holelen 0 for all, and we allow lend -1.
+         */
+
+        /*
+         * Unlike in truncate_pagecache, unmap_mapping_range is called only
+         * once (before truncating pagecache), and without "even_cows" flag:
+         * hole-punching should not remove private COWed pages from the hole.
+         */
+        if ((u64)unmap_end > (u64)unmap_start)
+                unmap_mapping_range(mapping, unmap_start,
+                                    1 + unmap_end - unmap_start, 0);
+        truncate_inode_pages_range(mapping, lstart, lend);
+}
+EXPORT_SYMBOL(truncate_pagecache_range);