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

From: Cornelia Huck
Subject: Re: [qemu-s390x] Interactive Boot Menu: New Fields in IPLB
Date: Fri, 8 Dec 2017 11:19:19 +0100

On Thu, 7 Dec 2017 18:56:16 -0500
"Collin L. Walling" <address@hidden> wrote:

>                        --- 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:

Hm, are we actually that constrained with space?

>   * uint8_t boot_menu_flag
>       o determines if we should show the menu or not

Should be fine. I'd recommend something along the lines of
- bit 0: show a boot menu
- bit 1-7: reserved [for future use]

>   * uint16_t boot_menu_timeout
>       o stored as milliseconds
>       o A max value of approx 65,000 gives us 65 seconds -- should be 
> plenty

65 seconds should be enough for everyone?


>       o could potentially be reduced to one byte, and we store the value
>         as seconds instead

As said, do we really need to worry about the space this is using up

> Note: these fields *only*have value in a QEMU environment.

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