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Date:      Sun, 21 Apr 2013 01:36:58 +0100
From:      "Steven Hartland" <killing@multiplay.co.uk>
To:        "Joshua Isom" <jrisom@gmail.com>, <freebsd-current@freebsd.org>, <ae@freebsd.org>
Subject:   Re: Booting an alternative kernel from loader prompt fails the first time only
Message-ID:  <A09B749B8A08428BB9BE54588FA64641@multiplay.co.uk>
References:  <625362A8116D4B43AF4912773F478CB9@multiplay.co.uk> <5172C699.8020708@smeets.im> <5172CF44.1050309@gwdg.de> <201304201741.r3KHfrJe001805@pozo.com> <517327C5.5050305@gmail.com>

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----- Original Message ----- 
From: "Joshua Isom" <jrisom@gmail.com>
To: <freebsd-current@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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--- sys/boot/common/module.c.orig	2013-04-21 00:16:28.801989165 +0000=0A=
+++ sys/boot/common/module.c	2013-04-21 00:18:23.544977000 +0000=0A=
@@ -289,7 +289,8 @@=0A=
 	    break;=0A=
 	} else if (last_file_format =3D=3D i && i !=3D 0) {=0A=
 	    /* Restart from the beginning */=0A=
-	    last_file_format =3D i =3D 0;=0A=
+	    last_file_format =3D 0;=0A=
+	    i =3D -1;=0A=
 	    fp =3D NULL;=0A=
 	    continue;=0A=
 	}=0A=

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