Sometimes repairing a broken hive with a hive log does not always guarantee the hive
in question has fully recovered. In worst cases it could happen the LOG itself is even
corrupt too and that would certainly lead to a total unbootable system. This is most likely
if the victim hive is the SYSTEM hive.
This can be anyhow solved by the help of a mirror hive, or also called an "alternate hive".
Alternate hives serve the purpose as backup hives for primary hives of which there is still
a risk that is not worth taking. For now only the SYSTEM hive is granted the right to have
a backup alternate hive.
=== NOTE ===
Currently the SYSTEM hive can only base upon the alternate SYSTEM.ALT hive, which means the
corresponding LOG file never gets updated. When time comes the existing code must be adapted
to allow the possibility to use .ALT and .LOG hives simultaneously.
=== DOCUMENTATION REMARKS ===
HBOOT_TYPE_REGULAR and HBOOT_TYPE_SELF_HEAL are boot type values set up by the CMLIB library (for the BootType field respectively). HBOOT_TYPE_REGULAR indicates a normal system boot whereas HBOOT_TYPE_SELF_HEAL indicates the system boot is assisted within self healing mode.
Whether the former or the latter value is set it's governed by both the kernel and the bootloader. The bootloader and the kernel negotiate together to determine if any of the registry properties (the hive, the base block, the registry base, etc) are so severed from corruption or not. In extreme cases where
registry healing is possible, the specific base block of the damaged hive will have its flags marked with HBOOT_TYPE_SELF_HEAL. At this point the boot phase procedure is orchestrated since the boot phase no longer goes on the default path but it's assisted, as I have already said above.
HBOOT_NO_BOOT_RECOVER, HBOOT_BOOT_RECOVERED_BY_HIVE_LOG and HBOOT_BOOT_RECOVERED_BY_ALTERNATE_HIVE on the other hand are identifiers for the BootRecover field of the BASE_BLOCK header structure. These are used exclusively by FreeLdr to tell the kernel if the bootloader recovered the SYSTEM hive or not. In case where the bootloader did recover the SYSTEM hive,
the kernel will perform a flush request on the dirty data down to disk. The (almost) worse case FreeLdr could not repair the main hive by applying log data, it will load the alternate mirror version of the hive.
In addition to that, declare other miscellaneous CMLIB identifiers for log transaction writes purposes.
Correct fix was to fix the HCELL_INDEX <-> HKEY conversions, much like
is being done with UlongToHandle / HandleToUlong.
The on-disk/in-memory hive file structures are platform-independent:
their layout must not depend on whether code is compiled in 32 or 64
bits.
