Re: Default MBR boot "manager"

On 2013-11-11 16:36, Nathan Whitehorn wrote:
> 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
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With GPT you just make a partition to put the boot code in, so, there
can be a size limit, but the zfsboot script uses a generous 512kb (and
aligns the first partition to 1mb)

I had originally thought to just use GPT all the time, but there was
significant demand for ZFS on MBR. Seems people don't want to replace
their laptops just to get ZFS

-- 
Allan Jude