On 08.12.2017 00:56, Collin L. Walling wrote: > Hello, > > I'd like to bring up a formal discussion regarding the utilization of > reserved space > in the IPL Parameter Blocks for s390x guests. Particularly the following: > > * How should we approach "claiming" bytes so that we do not obstruct > future development? > * What would be "the best" location to store these new fields? > > I've posted some relevant information regarding this feature below. > > > --- The Fields We Need To Store --- > > Currently, we're utilizing 3 bytes out of a 77 byte reserved field in > the IPLB for > CCW and SCSI. We do this because need a way to pass the Qemu command > line options > for a boot menu (on/off and timeout) to the s390-ccw bios. We require > only two > fields in the IPLB, totaling 3 bytes: > > * uint8_t boot_menu_flag > o determines if we should show the menu or not > > * uint16_t boot_menu_timeout > o stored as milliseconds > o A max value of approx 65,000 gives us 65 seconds -- should be
1. Why on earth milliseconds. I'd rather have it remain open for 5 minutes than 1ms. 1s should really be a sufficient granularity. 2. Why not combine everything in one field? 0x00000000 -> Don't show 0x00000001 -> Show, wait 1s ... 0xffff0000 .. 0xfffffffe -> Reserved 0xffffffff -> Show, wait forever We could add another special value for "use defaults from zipl" -- Thanks, David / dhildenb
