[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [qemu-s390x] Interactive Boot Menu: New Fields in IPLB

From: David Hildenbrand
Subject: Re: [qemu-s390x] Interactive Boot Menu: New Fields in IPLB
Date: Fri, 8 Dec 2017 12:59:37 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

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"



David / dhildenb

reply via email to

[Prev in Thread] Current Thread [Next in Thread]