Mapping IPMI boot device selector to D-Bbus properties

[Deepak Kodihalli]

Hi,

We recently discovered an issue in the way the IPMI boot device selector 
(represented by a nibble in the boot flags) is mapped to the D-Bus model.

In the IPMI spec the boot device selector has options for both "boot 
source" (default/disk/crdom/network) and "boot mode" 
(default/bios/safe/diag). Since this isn't a bit-filed, you can't 
override for eg both the source and mode at the same time. It's probably 
debatable to say whether such a possibility is desirable or not (for eg 
I may want to set the boot source as network by default, but want to 
boot to safe mode the next boot , and revert back to network for 
subsequent boots without having to set the device again).

There are different D-Bus interfaces depicting the boot mode [1] and 
boot source [2] though. So when the IPMI boot device is changed, the 
ipmid code sets a relevant boot mode or source property. It's possible 
that both can get set when someone for eg sets the device to cdrom and 
then to bios. The issue is how should ipmid respond to a get boot 
options command - there's no way for ipmid to aggregate information from 
both D-Bus properties as in the IPMI spec only one of them can be 
represented. Today ipmid always favors the boot source property if both 
are set [3]. That's not what a user expects though, because the user 
would expect his last override to go through.

The solution I'm proposing is that if a set boot device is mapping to a 
boot source, then reset the boot mode D-Bus property to default, or vice 
versa. This way the ipmid code can determine which property is not at 
the default value. It doesn't break the behavior from an IPMI spec 
perspective because only one can be set at a point of time anyway, and 
we'll consume the latest override to the boot device. Other solutions or 
thoughts?

[1] 
https://github.com/openbmc/phosphor-dbus-interfaces/blob/master/xyz/openbmc_project/Control/Boot/Mode.interface.yaml
[2] 
https://github.com/openbmc/phosphor-dbus-interfaces/blob/master/xyz/openbmc_project/Control/Boot/Source.interface.yaml
[3] 
https://github.com/openbmc/phosphor-host-ipmid/blob/master/chassishandler.cpp#L1257

Thanks,
Deepak