freebsd-update 6.2-R -> 6.3-B1 rollback failed

[Miroslav Lachman]

Colin Percival wrote:
> Jan Henrik Sylvester wrote:
> 
>>>In short, as long as you don't build a custom kernel but call it
>>>"GENERIC" or
>>>"SMP", FreeBSD Update should automatically DTRT.
>>
>>That is exactly my question. On 6.2-RELEASE, I sometimes used a modified
>>ld-elf.so.1 or a single patched module without recompiling the kernel.
>>What does using freebsd-update (accidentally or deliberately) do in that
>>case?  By accident, I discovered that it does not always fail. Does it
>>skip the modified files, overwrite them with new versions, or overwrite
>>them with an unpredictable bdiff merge that is likely garbage?
> 
> 
> Depending on the UpdateIfUnmodified option in freebsd-update.conf, it will
> either update files to "clean" new versions or print a warning message and
> not touch them.
> 
> There's also an IgnorePaths directive which you can use to tell FreeBSD
> Update not to touch some files (even if they haven't been modified locally).
> 
> FreeBSD Update will never produce mangled files as a result of applying a
> bsdiff patch to the wrong file -- it checks file hashes before and after
> applying patches and gracefully falls back to downloading complete files
> if it can't generate a file via patching.

Is it possible to configure freebsd-update to not remove old kernel 
directory and just rename it to kernel.old or something else?
Two times I end up with unbootable machine (upgraded from 6.3 to 7.0 - 
7.x version kernel always hangs on this machine, even with CD boot) and 
then I must use bootable CD / flashdisk with old 6.x kernel to be able 
to run freebsd-update rollback.
It will be useful if one can choose to leave old kernel in boot 
directory to be able to boot it if something goes wrong.

Miroslav Lachman