Messages in this thread | | | Date | Sat, 3 Jul 2004 22:44:35 +1000 | From | Andrew Clausen <> | Subject | Re: [RFC] Restoring HDIO_GETGEO semantics (was: Re: workaround for BIOS / CHS stuff) |
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On Sat, Jul 03, 2004 at 08:53:39AM +0100, Anton Altaparmakov wrote: > On Sat, 3 Jul 2004, Andrew Clausen wrote: > > In any case, I don't have any evidence that anything is wrong. On my > > computer, I can tell the BIOS to use CHS geometry, (as opposed to > > "Auto", "LBA" or "Large") modify the partition table to set the CHS > > start/end of the Windows partition to 0, 1024, or anything I like, and > > Windows STILL works. I can't get anything to break! > > Which version of Windows?
XP home edition (the green box)
> Does it use NTFS as both the boot and system drive?
I am using a single NTFS partition.
Note: I reversed-engineered the Windows FAT bootstrap code. My analysis is contained in the file doc/FAT in the Parted source distribution. I concluded that Windows uses LBA if the LBA flag is set in the boot partition table entry. (i.e. the partition type includes LBA in the fdisk codes - this corresponds to a bit being set)
> > So, can anyone break Windows? > > Easily. Modify any of the relevant values in the NTFS bootsector and > windows will no longer boot. So it clearly cares hugely about the > geometry. And at present there is no easy way for us to tell what it is > so mkntfs and ntfsclone cannot create bootable partitions on 2.6 kernels. > (Works fine on 2.4 using HDIO_GETGEO.) > > The relevant fields are (see linux/fs/ntfs/layout.h or > ntfsprogs/include/ntfs/layout.h) in the NTFS_BOOT_SECTOR in the > BIOS_PARAMETER_BLOCK: > > u16 sectors_per_track; /* Required to boot Windows. */ > u16 heads; /* Required to boot Windows. */ > u32 hidden_sectors; /* Offset to the start of the partition relative > to the disk in sectors. Required to boot Windows. */
I just set the first 2 of these fields to 0, and everything still works. Am I blessed? (Or perhaps cursed!)
Isn't hidden_sectors an LBA value (and hence irrelevant to this discussion)?
Cheers, Andrew
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