GPT aware boot loader &mdash TODO list

Important items

1. Update documentation. Man pages: boot(8), boot.cfg(5), fdisk(8), gpt(8), installboot(8).
2. The boot(8) have memory leak somewhere, likely at exec_netbsd(). When the boot(8) tries to boot kernel many times it can end up with memory allocation problem (heap full error). Perhaps it isn't relevant to my GPT code, but needs checking (and preferably fixing).
3. The boot2() should accept 64-bit LBA. A 1st stage loader will patch boot(8) magic (set very high bit) to tell boot(8) that 64-bit LBA is passed. The biosboot.S should handle that (currently it just ignores high 32 bits of boot partition address so should working fine with any partition below 2TiB limit).
4. Implement new boot device naming scheme for boot(8): hd[0-9]gpt[0-9]+. Thus the boot(8) can access all 128 GUID partitions; hd[0-9][a-z] should still address first 26 partitions.
5. Include mbr_gpt into distribution.
6. Review the code and eliminate all introduced XXX places. Post it for public review.

Other items (for future)

• gpt(8) biosboot command should be expanded to support other selector options (like -b and -s). Also, it have somewhat fuzzy logic about boot device selection. Perhaps new -v flag and output similar to the installboot(8) should solve it.
• All other 1st stage loaders (except bootxx_fat16) should be adjusted to pass 64-bit LBA to boot(8).
• Currently only the fatboot.S can be used as primary loader.
• Include GPT loader into sysinst.

Known bugs, limitations, and caveats

• fatboot.S (bootxx_fat16) can not be used on a partition that crosses a 2TiB boundary. The higher 32 bits of LBA are not automatically adjusted on overflows at low 32 bits. Cause — no space in fatboot.S to implement this.
• fatboot.S is passing boot parameters different from struct x86_boot_params, so some features like serial console are not available. As workaround it's proposed to pass all necessary parameters via boot.cfg.