Bug 235380

Summary: gptzfsboot does not boot ZFS pool made from whole disks (regression)
Product: Base System Reporter: reto.haeuptli
Component: kernAssignee: freebsd-bugs mailing list <bugs>
Status: New ---    
Severity: Affects Some People CC: andrej, tsoome
Priority: --- Keywords: patch, regression
Version: 12.0-RELEASE   
Hardware: amd64   
OS: Any   

Description reto.haeuptli 2019-02-01 13:44:06 UTC
I used to boot zfs on whole disk(s) from a USB stick with a GPT partition scheme and gptzfsboot on it since FreeBSD version 9 on many testing machines and even production servers without any problems. With the release 12 this feature is broken. 

I found the reason in the source code: In the file /head/stand/i386/libi386/biosdisk.c a regression was introduced in the revisions base r37271, base r337317. Its about detecting the correct number of sectors/blocks for a block device. The change was introduced because a certain device (Mediasonic HD3-U2B PATA to USB enclosure) was not working. I tested various SASTA disks, even a 10TB disk, and USB Sticks, all detecting the wrong number of sectors instead. Reverting the change leaded to the correct detection of the number of sectors and therefore I was able to boot again. I tested also revision base r342785 of the file /head/stand/i386/libi386/biosdisk.c: The detection of the number of sectors is implemented the right way again and has improved of course.

I propose the following patch to fix the regression for FreeBSD 12

Index: stand/i386/libi386/biosdisk.c
--- stand/i386/libi386/biosdisk.c	(revision 343578)
+++ stand/i386/libi386/biosdisk.c	(working copy)
@@ -270,8 +270,8 @@
 		total = (uint64_t)params.cylinders *
 		    params.heads * params.sectors_per_track;
-		if (total > 0 && bd->bd_sectors > total)
-			bd->bd_sectors = total;
+                if (bd->bd_sectors < total)
+                        bd->bd_sectors = total;
 		ret = 1;