[SeaBIOS] Check for valid MBR before adding drive as "bootable"
steve.goodrich at se-eng.com
Wed Oct 24 14:50:59 CEST 2012
Back in July I was working on a problem that involved determining if a drive was bootable (see emails from circa 13 July 2012, "Bootorder Failover (Patch)"). I now have a few extra cycles and I'd like to try to do this the right way. What I'm trying to do is add the "drive_is_bootable()" call to the various boot_add_xxx methods, similar to the following in boot.c:
boot_add_hd(struct drive_s *drive_g, const char *desc, int prio)
if (!CONFIG_CHECK_BOOTABLE || drive_is_bootable(drive_g)) // <<<<< new code
bootentry_add(IPL_TYPE_HARDDISK, defPrio(prio, DefaultHDPrio)
, (u32)drive_g, desc);
The drive_is_bootable() function would read the MBR from the drive, check a few things to ensure that the drive is bootable, and return 0 (fail) or non-zero (success). Per the email thread referenced above, I've got my own copy of process_op() from which I've removed the ASSERT16(). Unfortunately, there are ASSERT16()'s deeper in the call tree -- specifically in the code used by process_floppy_op(), process_ata_op(), and process_cdemu_op().
I think the proper approach would be to put the processor in 16-bit mode and use the original process_op() function (returning to 32-bit mode afterward), but I'm not sure how to do that here. Can anyone offer some guidance here?
-- Steve G.
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