The patch is on top of the ext4 tree:
http://repo.or.cz/w/ext4-patch-queue.git

In this part, the i_version counter is stored into 2 32bit fields of
the ext4_inode structure osd1.linux1.l_i_version and i_version_hi.

I included the ext4_expand_inode_extra_isize patch, which does part of 
the job, checking if there is enough room for extra fields in the inode 
(i_version_hi). The other patch increments the counter on inode 
modifications and set it on inode creation.