From Ted Phelps <phelps@dstc.edu.au>

The NFSv3 readdirplus path doesn't check to see if maxcount is less
than the size of a page before it fills it up, possibly overwriting
random bits of memory.  At least, it makes my Solaris NFSv3 client
work.

The attached patch, against 2.5.58, adds this check in a way which is
consistent with the way readdir does under both NFSv2 andNFSv3.