[bug #46763] allow multibooting of windows-xp 32bit or lower on >2TB discs

[Piotr Sawuk]

Follow-up Comment #2, bug #46763 (project grub):

first off, gptsync by design wont work with extended mbr-partitions. the
parent-partition must encompass all its sub-partitions, and therefore no
gpt-partition can hold the extended mbr-entry while at the same time the
individual extended sub-partitions are mirrorred on gpt. this could "easily"
be changed  by extending gptsync to management of actual extended mbr. less
intuitive but slightly easier to implement is to detect extended partitions
while they're being attatched to mbr by gptsync and altering the
partition-size accordingly. but neither of these solutions really is of much
use for the ordinary user.

fact is, my use-case is a prepared mirroring of gpt to mbr, and I want to keep
it. additionally to that upgraded windows-xp refuses to work if the first
partition is a protected one for gpt, I must un-protect it first. I didn't
manage to get it to work and nowhere on the net I found a solution. but if I
turn off gpt then the boot-partition is gone and I can't load any modules nor
do there exist any partitions at all. that's what my patches fixed. what's
still missing for this bug is support in config-creation, and be it a
command-line option. and actual distinction between OS requiring gpt or mbr
partitions would be nice too...

if you say gptsync is sufficient, try it out! somehow I doubt it even works
without my patches. and even if it does, the mbr.patch is needed along with
the gpt-hybrid.patch to actually alter msdos1 from 0xee to 0x6e for
windows-xp. well, I didn't try to swap protective mbr entry with some other
partition, so maybe that would have worked. (i.e. maybe internally windos-xp
omits a number if partition-type is 0xee and therefore my boot.ini was
faulty.) as someone else complained here, changing boot.ini doesn't help, the
partition table must be returned to the state where windows was installed or
else windows probably wont boot.

and the 3rd point where my patches are needed is to change the active flag
while booting from gpt partitions. old windows uses that flag to determine
what is drive c:, so when installing multiple windows versions you need my
mbr.patch!

also there is the point of interface-flexibility. fact is gpt and mbr are two
partition tables for the same disc. this should be reflected in code. gpt is
what grub should use by default, but the other possibility should be up to the
user. IMHO gpt is an ugly hack, so its standard shouldn't be obeyed that
strictly. hence the gpt.patch for making use of gpt even if it doesn't exist
according to mbr! the OS should obey standards, not the boot-loader...

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