Re: Default MBR boot "manager"

On 11/11/13 15:35, Allan Jude wrote:
> On 2013-11-11 16:32, Nathan Whitehorn wrote:
>> On 11/11/13 15:19, Teske, Devin wrote:
>>> Topic: Lenovo Laptops and bsdinstall zfsboot with MBR layout...
>>>
>>> Should we do the quick patch to change the default
>>> from /boot/boot0 to /boot/mbr:
>>>
>>> Index: zfsboot
>>> ===================================================================
>>> --- zfsboot     (revision 258016)
>>> +++ zfsboot     (working copy)
>>> _at__at_ -764,7 +764,7 _at__at_ zfs_create_diskpart()
>>>                   #
>>>                   f_eval_catch $funcname gpart "$GPART_CREATE" mbr
>>> \$disk ||
>>>                                return $FAILURE
>>> -               f_eval_catch $funcname gpart "$GPART_BOOTCODE"
>>> /boot/boot0 \
>>> +               f_eval_catch $funcname gpart "$GPART_BOOTCODE"
>>> /boot/mbr \
>>>                                \$disk || return $FAILURE
>>>
>>>                   #
>>>
>>> That would fix things for Lenovo laptops for the next
>>> release until I finish up the bootcode selection menu.
>>> I'd like to take my time in making sure Allan and I design
>>> a worthy bootcode selection menu.
>> This patch looks good (I don't remember why it was boot0 in the first
>> place). I think gpart automatically installs something like /boot/mbr
>> by default, so I'd be interested to know if making the diff purely
>> negative still works.
>>
>> On another note, I think we should move away from a selector. Right
>> now, we have three kinds of boot code:
>> 1. ZFS boot code
>> 2. UFS boot code
>> 3. boot0
>>
>> Unifying 1 and 2 would help a lot -- I don't know of any reason we
>> need both except for tradition. #3 is probably best done as a
>> post-install config step ("Install FreeBSD boot manager" or
>> something), which also means it works for UFS systems.
>> -Nathan
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> You have to do down right evil things to boot ZFS on MBR. dd'ing the
> 'remainder' of the boot loader into a reserved space at the head of the
> ZFS partition. The GPT boot code is 14k, and the code to boot ZFS is
> 40k, whereas the UFS stuff is 512 bytes and fits in the intended slot.
>

We could just decide we won't support booting from ZFS on MBR. For GPT, 
there is no size limit, which simplifies everything.
-Nathan