Booting from symlinked kernels (was "HEADS UP: Standalone kernel debug files moving out of /boot/kernel/")

[Garrett Cooper]

On Oct 30, 2014, at 6:07, Ed Maste <emaste at freebsd.org> wrote:

> On 29 October 2014 22:32, Steve Kargl <sgk at troutmask.apl.washington.edu> wrote:
>> On Wed, Oct 29, 2014 at 03:15:50PM -0400, Ed Maste wrote:
>>> On 29 October 2014 12:49, Steven Hartland <killing at multiplay.co.uk> wrote:
>>>> Hmm not sure I like this idea as it would make it more difficult to make a
>>>> copy / backup a kernel.
>>>> 
>>>> ATM when I want to copy a kernel for debugging its a one liner, splitting
>>>> debug symbols off to /usr/lib would prevent this.
>>> 
>>> To retain the current behaviour you can set DEBUGDIR= (i.e., empty),
>>> as the debug file install path is ${DESTDIR}${DEBUGDIR}${KODIR}.
>> 
>> No, you can't.
>> 
>> su root
>> cp -pR /boot/kernel /boot/good
>> 
>> Where does DEBUGDIR enter the picture?
> 
> In your kernel build configuration (src.conf or similar ways).

If you use the kernel build infrastructure properly, the debug info should be installed to ${DEBUGDIR}/boot/${INSTKERNNAME} — not ${DEBUGDIR}/boot/kernel (the latter is broken for folks like my that have multiple kernel configs in their src.conf).

As far as the symlink trick for /boot/kernel is concerned, that only works on UFS. I used to use it on ZFS, it broke one day, I sent out an email and got some replies back stating that they weren’t really worried about the feature being broken (I can hunt down the email thread… I just don’t have it in my search results right now). Another worthwhile bug to explore/fix is: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=153996 .

Cheers!
-Garrett
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