set_super_anon in fs/super.c

I am working on the layered file systems. I came across a function called set_super_anon. This is a callback to the sget function to compare the superblock . This function accepts two parameters. first is superblock * and second is void *. If you look at the definition of this function, the void* is never used. Many filesystem uses this function when they are mounting the superblock. Some pass NULL and some pass actual data.I have looked till 2.6.31 but there isnt any trace of the usage of second parameter. If it is never used then why its added to the function param list? Is there any historical reason during the older kernel days? Regards, Abhijit Pawar