D10203: loader: zfs reader should check all labels

Hi!

Sorry about forward, but this patch is something a bit more complicated and if we have some people willing to test, it would be really nice:) I have had it around for my illumos port for some time now, but those small details about the zfsboot/gptzfsboot etc sometimes do count a lot… 

thanks,
toomas

> Begin forwarded message:
> 
> From: "tsoome (Toomas Soome)" <phabric-noreply_at_FreeBSD.org>
> Subject: [Differential] D10203: loader: zfs reader should check all labels
> Date: 30. märts 2017 18:39.44 GMT+3
> To: tsoome_at_me.com
> Reply-To: D10203+574+d76c8a36ba3c3f0a_at_reviews.freebsd.org
> 
> tsoome created this revision.
> Herald added a subscriber: delphij.
> 
> REVISION SUMMARY
>  The current zfs reader is only checking first label from each device, however,
>  we do have 4 labels on device and we should check all 4 to be protected
>  against disk failures and incomplete label updates.
> 
>  The difficulty is about the fact that 2 label copies are in front of the
>  pool data, and 2 are at the end, which means, we have to know the size of
>  the pool data area.
> 
>  Since we have now the mechanism from common/disk.c to use the partition
>  information, it does help us in this task; however, there are still some
>  corner cases.
> 
>  Namely, if the pool is created without partition, directly on the disk,
>  and firmware will give us the wrong size for the disk, we only can check
>  the first two label copies.
> 
> REPOSITORY
>  rS FreeBSD src repository
> 
> REVISION DETAIL
>  https://reviews.freebsd.org/D10203
> 
> AFFECTED FILES
>  sys/boot/efi/boot1/zfs_module.c
>  sys/boot/efi/loader/main.c
>  sys/boot/i386/common/drv.h
>  sys/boot/i386/loader/main.c
>  sys/boot/i386/zfsboot/zfsboot.c
>  sys/boot/zfs/libzfs.h
>  sys/boot/zfs/zfsimpl.c
> 
> EMAIL PREFERENCES
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> 
> To: tsoome, allanjude, imp, avg
> Cc: delphij