ext4: Add flag to files with blocks intentionally past EOF

fallocate() may potentially instantiate blocks past EOF, depending
on the flags used when it is called.

e2fsck currently has a test for blocks past i_size, and it
sometimes trips up - noticeably on xfstests 013 which runs fsstress.

This patch from Jiayang does fix it up - it (along with
e2fsprogs updates and other patches recently from Aneesh) has
survived many fsstress runs in a row.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index b63d193..2220feb 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -92,6 +92,15 @@
 			flags &= ~EXT4_EXTENTS_FL;
 		}
 
+		if (flags & EXT4_EOFBLOCKS_FL) {
+			/* we don't support adding EOFBLOCKS flag */
+			if (!(oldflags & EXT4_EOFBLOCKS_FL)) {
+				err = -EOPNOTSUPP;
+				goto flags_out;
+			}
+		} else if (oldflags & EXT4_EOFBLOCKS_FL)
+			ext4_truncate(inode);
+
 		handle = ext4_journal_start(inode, 1);
 		if (IS_ERR(handle)) {
 			err = PTR_ERR(handle);