f2fs: support FALLOC_FL_INSERT_RANGE

index aec96d3..4d42d66 100644
@@ -1010,6 +1010,100 @@ out:
 	return ret;
 }
 
+static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
+{
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	pgoff_t pg_start, pg_end, delta, nrpages, idx;
+	loff_t new_size;
+	int ret;
+
+	if (!S_ISREG(inode->i_mode))
+		return -EINVAL;
+
+	new_size = i_size_read(inode) + len;
+	if (new_size > inode->i_sb->s_maxbytes)
+		return -EFBIG;
+
+	if (offset >= i_size_read(inode))
+		return -EINVAL;
+
+	/* insert range should be aligned to block size of f2fs. */
+	if (offset & (F2FS_BLKSIZE - 1) || len & (F2FS_BLKSIZE - 1))
+		return -EINVAL;
+
+	f2fs_balance_fs(sbi);
+
+	ret = truncate_blocks(inode, i_size_read(inode), true);
+	if (ret)
+		return ret;
+
+	/* write out all dirty pages from offset */
+	ret = filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
+	if (ret)
+		return ret;
+
+	truncate_pagecache(inode, offset);
+
+	pg_start = offset >> PAGE_CACHE_SHIFT;
+	pg_end = (offset + len) >> PAGE_CACHE_SHIFT;
+	delta = pg_end - pg_start;
+	nrpages = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
+
+	for (idx = nrpages - 1; idx >= pg_start && idx != -1; idx--) {
+		struct dnode_of_data dn;
+		struct page *ipage;
+		block_t new_addr, old_addr;
+
+		f2fs_lock_op(sbi);
+
+		set_new_dnode(&dn, inode, NULL, NULL, 0);
+		ret = get_dnode_of_data(&dn, idx, LOOKUP_NODE_RA);
+		if (ret && ret != -ENOENT) {
+			goto out;
+		} else if (ret == -ENOENT) {
+			goto next;
+		} else if (dn.data_blkaddr == NULL_ADDR) {
+			f2fs_put_dnode(&dn);
+			goto next;
+		} else {
+			new_addr = dn.data_blkaddr;
+			truncate_data_blocks_range(&dn, 1);
+			f2fs_put_dnode(&dn);
+		}
+
+		ipage = get_node_page(sbi, inode->i_ino);
+		if (IS_ERR(ipage)) {
+			ret = PTR_ERR(ipage);
+			goto out;
+		}
+
+		set_new_dnode(&dn, inode, ipage, NULL, 0);
+		ret = f2fs_reserve_block(&dn, idx + delta);
+		if (ret)
+			goto out;
+
+		old_addr = dn.data_blkaddr;
+		f2fs_bug_on(sbi, old_addr != NEW_ADDR);
+
+		if (new_addr != NEW_ADDR) {
+			struct node_info ni;
+
+			get_node_info(sbi, dn.nid, &ni);
+			f2fs_replace_block(sbi, &dn, old_addr, new_addr,
+							ni.version, true);
+		}
+		f2fs_put_dnode(&dn);
+next:
+		f2fs_unlock_op(sbi);
+	}
+
+	i_size_write(inode, new_size);
+	return 0;
+out:
+	f2fs_unlock_op(sbi);
+	return ret;
+}
+
 static int expand_inode_data(struct inode *inode, loff_t offset,
 					loff_t len, int mode)
 {

@@ -1077,11 +1171,13 @@ static long f2fs_fallocate(struct file *file, int mode,
 	struct inode *inode = file_inode(file);
 	long ret = 0;
 
-	if (f2fs_encrypted_inode(inode) && (mode & FALLOC_FL_COLLAPSE_RANGE))
+	if (f2fs_encrypted_inode(inode) &&
+		(mode & (FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_INSERT_RANGE)))
 		return -EOPNOTSUPP;
 
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
-			FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE))
+			FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
+			FALLOC_FL_INSERT_RANGE))
 		return -EOPNOTSUPP;
 
 	mutex_lock(&inode->i_mutex);

@@ -1095,6 +1191,8 @@ static long f2fs_fallocate(struct file *file, int mode,
 		ret = f2fs_collapse_range(inode, offset, len);
 	} else if (mode & FALLOC_FL_ZERO_RANGE) {
 		ret = f2fs_zero_range(inode, offset, len, mode);
+	} else if (mode & FALLOC_FL_INSERT_RANGE) {
+		ret = f2fs_insert_range(inode, offset, len);
 	} else {
 		ret = expand_inode_data(inode, offset, len, mode);
 	}