Boot Manager requirements

[vstehle]

Let's clarify the requirements on the UEFI Boot Manager to address #130.

[vstehle]

As per EBBR call of Aug 26 this must be respun with better wording for BootOptionsSupport.

[vstehle]

Changes:

• Tighten wording around Boot* variables, as per feedbacks during the EBBR call of Aug 26.
• Mention the optional Driver####, SysPrep####, OsRecovery#### and PlatformRecovery#### variables explicitly, to help searching the UEFI spec.
• Warn that BootOptionSupport will be required in the future.

[vstehle]

Reworked after @xypron's comments (thanks!) and our call of Oct. 7. Please review and let me know how you like it.

Changes:

• Require LOAD_OPTION_ACTIVE.
• Try to clarify default boot requirements a bit more.
• Explicitly require booting with EFI_SIMPLE_FILE_SYSTEM_PROTOCOL, LoadImage(), SetWatchdogTimer(), EFI_LOAD_FILE_PROTOCOL and short-form HDD paths.
• Conditionally require short form USB & URI device paths.
• Booting with EFI_BLOCK_IO_PROTOCOL and ConnectController() optional.
• Mention DriverOrder in Drivers loading description.
• Attributes other than LOAD_OPTION_ACTIVE optional.
• Mention that boot manager may treat categories as LOAD_OPTION_CATEGORY_BOOT.
• Recommend BootOptionSupport (still optional).
• Mention Key#### in Hot Keys description.
• Mention SysPrepOrder in System preparation applications description.
• Mention OsRecoveryOrder in Boot option recovery description.
• EFI_OS_INDICATIONS_START_OS_RECOVERY and EFI_OS_INDICATIONS_START_PLATFORM_RECOVERY OsIndications bits optional.
• Notifying EFI_EVENT_GROUP_READY_TO_BOOT and EFI_EVENT_GROUP_AFTER_READY_TO_BOOT optional.
• Add a note about Linux initrd, U-Boot and LOAD_FILE2.
• Remove all UEFI spec. references from the optional table.
• Shuffled around and reworded much text.
• Split-out less related section anchor and warning additions into separate commits.

[vstehle]

Rebased on CI fixes.

[xypron]

@vstehle

Concerning BootOptionSupport the UEFI spec has "If the global variable is not present, then an installer or application must act as if a value of 0 was returned."

What relevance has your warning about requiring BootOptionSupport in this context?

[vstehle]

What relevance has your warning about requiring BootOptionSupport in this context?

Hi @xypron, I think you are right; all the wording around BootOptionSupport is confusing. As this variable is optional in UEFI already, let's simply leave it as it is. While at it, we can do the same for all the other boot manager features, already optional in UEFI. I think this makes the addition lighter; let me know how you like it.

[vstehle]

Changes:

• Removed the two warnings about BootOptionSupport becoming mandatory in the future.
• List only the features we are making optional in the second table. Therefore removed the following mentions:
  • Boot menu
  • Load option categories
  • BootOptionSupport
  • Key#### hot keys
  • SysPrep* system preparation applications

[vstehle]

Rebased.

[vstehle]

Approved during the EBBR call of Oct 23.