Hi, does anybody remember in which situations the MBR or whatever else calls the FreeDOS boot sector fails to pass the drive number in DL? Because at the moment, FreeDOS defaults to ignoring DL and using the value in the boot sector, unless that value is 255. I hear that only some CDROM boot BIOS bugs and exotic boot menu systems fail to set DL, but which?
The problem is that 255 in a boot sector may look odd for disk tools plus it is not the default of our SYS. Setting 0 or 128 (0x80) is, but that causes problems when you try to boot DOS from B: or D: via boot menu, or when you boot from USB in a way where your BIOS is trying to make your boot partition show up as A: drive while it is a FAT16 partition on some USB stick ;-). So... it might be an idea to make "use DL, ignore the drive field in the boot sector" the default, but then "do use the drive field" would have to be activated by SYS by patching the boot code. To compare, for the current version you just set the drive field to any non-255 value to tell the boot sector to use it :-). Another issue is that for example mtools and old mkdosfs do not set the partition offset / hidden sectors field in the boot sector. SYS works around, but non-DOS SYS clones like sys-freedos-linux have extra hassles there: A "generic" workaround would be to check the partition table entry pointer: The MBR is supposed to give the boot sector a pointer DS:SI to the partition table item it boots (where is that documented?) and actually does seem to do so quite often... :-) For example SYSLINUX trusts this pointer if ds[si] & 7f is 0... Only the LBA "partition offset" field of the table is useful at boot. Last but not least, our boot sector uses the heads and sectors per track value from the boot sector. Is that useful? I would assume using the geometry returned by int13.8 is a lot more foolproof for harddisks (but not for overformatted floppy if anybody cares...?). By the way, we never use LBA for A: drives yet, and a comment in the source code says that BIOS cdrom boot floppy emulation can have bugs in LBA support... Eric PS: Only our FAT32-LBA boot sector has any space left, so all changes would have to be "replace style X by style Y" and not "add check for Y". ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Freedos-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freedos-devel
