Need help trying to recompile kernel with EBR functionality

[Manish Jain]

On 2020-01-01 21:09, Polytropon wrote:
> On Wed, 01 Jan 2020 06:19:33 +0000, Thomas Mueller wrote:
>>> I am a long time user of FreeBSD but have never recompiled my kernel.
>>
>>> I am trying to compile a custom 12.1 amd64 kernel with the ability
>>> to add/delete EBR partitions, but the online documentation did not
>>> help and I ended up losing EBR functionality entirely.
>>
>>> The steps I followed were as under :
>>
>>> 1) copied [/usr/src/sys/amd64/conf/]GENERIC as EBRKERNEL
>>> 2) commented out GEOM_PART_EBR_COMPAT in [/usr/src/sys/amd64/conf/]DEFAULTS
> A little sidenote: Do not change that file. All your kernel
> configurations should be in the kernel configuration file.
> In order to deviate from the defaults, use "nooption <name>"
> to disable an existing option, and (as shown correctly)
> "option <name>" to add an additional one; same for "device"
> and "nodevice".
>
>
>
>>> 3) inserted 'options GEOM_PART_EBR' into my kernel configuration
>>> file EBRKERNEL
>>> 4) cd /usr/src
>>> 5) make buildkernel KERNCONF=EBRKERNEL
>>> 6) make installkernel KERNCONF=EBRKERNEL
>>
>>> When I shutdown the system and rebooted into the new kernel, the
>>> boot process halted complaining that it could find any device
>>> /dev/ada0s5 (the EBR partition).
>>
>>> What am I doing wrong ? Any help in getting me a good custom kernel
>>> with the ability to add/delete EBR partitions would be greatly appreciated.
>>> Thank you & Regards,
>>> Manish Jain
>> I am rather confused here.  My first inclination would be to suggest
>> you switch to GPT.
> This often is not an option for multi-OS settings because it
> lacks boot selection (through FreeBSD's boot manager), and
> the support across different operating systems (for example,
> read partition of of OS 1 from OS 2) sometimes causes trouble
> when GPT is involved.
>
>
>
>> Using MBR, you get up to 4 partitions, of which one may be
>> an extended boot record.  That partition is a container for
>> logical-partition data, not a partition that can be mounted
>> or copied to or from.
> The "DOS extended partition" (which contains "logical volumes")
> is not to be addressed directly; instead the "logical volumes"
> inside it are. And that's completely okay for non-bootable
> partitions (such as data partitions). So basically there are
> 3 "DOS primary partitions" (bootable - 3 systems), one "slot"
> for the "DOS extended partition", and inside it, any further
> partitions needed, for example shared /home partitions for
> Linux.
>
> FreeBSD itself does not need any of this. ;-)
>
>
>
>> It seems to me the EBR partition would be s1, s2, s3, or s4
>> but no higher.  I'd need to see your full partition table
>> data, such as you get with "fdisk -lu" in Linux, or you can
>> use gpart with "show" in FreeBSD.
> If I remember the numbering system correctly, s1 - s4 are
> reserved for "DOS primary partitions" - slices. The "logical
> volumes" as well as the "DOS extended partition" containing
> them have a higher "s value".
>
>
>
>> Maybe you have the wrong partition name (ada0s5)?  You can
>> go to the loader prompt and get a rough idea of what's in
>> the partitions, and change the root partition to boot into.
> So if ada0s5 is the "DOS extended partition", it's absolutely
> understandable that no partition (read: slice) can be found.
> I think the problem here is that the number is wrong. It's
> worth verifying the correct numbers with gpart. The "logical
> volumes" that need to be addressed (as a "slice equivalent")
> then probably should be ada0s6 and so on.
>
>
>
>> I have created logical partitions with Linux fdisk but never
>> any BSD fdisk.  I believe there is a linuxfdisk in FreeBSD
>> ports, category would be sysutils to the best of my memory.
> In the past, I used FreeBSD's ye olde fdisk for partition
> creation, it worked, but the common suggestion was to use
> the OS that would be _using_ the partition for initializing
> it, and adding the required file systems. WIth goart, however,
> this should basically work.
>
>
>

Thomas's idea worked. sysutils/linuxfdisk is able to create/delete 
logical volumes

under FreeBSD, when FreeBSD gpart itself cannot.


And I completely agree with Polytropon that boot0 is much better for 
multi-OS systems, but boot0 works only on MBR - which is why I never use 
GPT.


Thanks.

Manish Jain