what are st_blksize and st_blocks exactly?

[David J. MacKenzie]

The stat(2) documentation for SunOS 4.0.3 says:

	  long	    st_blksize;	   /* preferred	blocksize for file system I/O*/
	  long	    st_blocks;	   /* actual number of blocks allocated	*/

It doesn't mention what units st_blocks is measured in, but those
units don't look like they're the value of st_blksize.
How are these two fields related, if at all?
Is st_blocks always measured in 512 byte units, or is there a value
somewhere that indicates the block size for it?
--
David J. MacKenzie <djm at eng.umd.edu> <djm at ai.mit.edu>