I just had an interesting experience. Someone wrote me with a suggested improvement to the iplvol script I wrote, based on Rob van der Heij's tip about where the IPL volume subchannel information was stored. I went to test it on a system, and it failed. Once I investigated far enough, I discovered that I have two different systems, both at kernel 2.4.19, one of which has the correct value stored at 0x10404, and one which has all zeroes stored there.
Rob, anyone, do you have any idea what other software needs to be at a particular level for that value to be stored at that address? Mark Post
