Re: Booting an alternative kernel from loader prompt fails the first time only

----- Original Message ----- 
From: "Joshua Isom" <jrisom_at_gmail.com>
To: <freebsd-current_at_freebsd.org>
Sent: Sunday, April 21, 2013 12:41 AM
Subject: Re: Booting an alternative kernel from loader prompt fails the first time only


> On 4/20/2013 12:41 PM, Manfred Antar wrote:
>> At 10:24 AM 4/20/2013, Rainer Hurling wrote:
>>> On 20.04.2013 18:47 (UTC+2), Florian Smeets wrote:
>>>> On 20.04.13 18:05, Steven Hartland wrote:
>>>>> When trying to boot an alternative kernel from the loader prompt
>>>>> it fails the first time the command is run but succeeds the second
>>>>> time.
>>>>>
>>>>> Type '?' for a list of commands, 'help' for more detailed help.
>>>>> OK boot kernel.generic
>>>>> Booting...
>>>>> don't know how to load module '/boot/kernel.generic/kernel'
>>>>> OK boot kernel.generic
>>>>> Booting...
>>>>> /boot/kernel.generic/kernel text=0xd21288 data=......
>>>>>
>>>>
>>>> Yes, I've been seeing the same thing for about 6-12 months maybe more.
>>>> None of the people I asked were able to confirm, so I'm happy that I'm
>>>> not imagining it :)
>>>
>>> I also can confirm this behaviour for month now (on 10.0-CURRENT amd64
>>> with clang).
>>>
>>> Rainer
>>>
>>
>> Have you tried:
>> OK boot /boot/kernel.generic/kernel
>>
>> Use full path name always works for me
>> Manfred

I believe this may well have been introduced by:-
http://svnweb.freebsd.org/base?view=revision&revision=241069

When booting with a /boot/loader.conf that contains a module load line
e.g. zfs_load="YES" then this is loaded before the kernel.

Loading any module causes last_file_format to get set so when the next
file that's loaded is in fact a kernel it still try's to load it as a
"kernel module" using what was stored with last_file_format.

This fails and trips the "Restart from the beginning" case which contains:
   last_file_format = i = 0;
   fp = NULL;
   continue;

So "i" gets set to 0 but the loop then increments it to 1 before running
the next iteration, so its impossible to use first handler in the retry
case; which I suspect is the kernel loader.

This also explains why the second call to boot works as last_file_format
is now 0 due to the previous failure.

If this is the issue the attached patch should fix it. I can't test it
ATM as my current box is at the office and doesn't have remote KVM, so
I need to be in front of it.

If anyone can confirm this attached patch fixes the problem then I'll get
it committed, otherwise I'll test on Monday.

    Regards
    Steve

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