illumos gate

So I've seen this now on:

• Dell PE R710, latest BIOS and previous release
• Dell PE 2950, latest BIOS
• Dell PE R815, unknown (possibly oldish) BIOS

With USB sticks:

• Kingston DT3 16GB
• A no-name 4GB

Booting from the USB stick produces the following output:

GRUB Loading stage 1.5.

GRUB loading, please wait...
Error 21

Error 21 corresponds to ERR_NO_DISK -- in this particular case using printf it can be seen that the failing call is to get_diskinfo, which is returning error code 0x60. This error code is produced in stage2/asm.S after calling int 13h with ah = 0x08, when %cl & 0x3f == 0 -- ie, the BIOS is claiming that there is a disk there, but its sectors per track is zero, which GRUB interprets as "you're lying to me, there's no disk there", thanks to ancient BIOS bugs.

However, in the same function in stage2/bios.c, GRUB has already called int 13h with ax = 0x4800 (an extended BIOS call) and gotten valid data back, including the "real" CHS geometry for this disk.

So there's two parts to this:

• The Dell BIOS should not be returning 0 sectors per track in ah=0x08
• But GRUB should probably trust the geometry data it already got from the extended call -- at least in this case

Just for testing, I patched GRUB to never made the ah=0x08 call if it got CHS geometry with the ax=0x4800 first, and it successfully boots into Illumos on all the affected BIOSes listed above. Patch is attached, but may not be appropriate for merging -- just because the Dell BIOS returns valid data in that extended call for CHS doesn't mean everybody does...