Re: passing params to boot readonly

On Thu, 13 Dec 2001, Hans Reiser wrote:

> Ryan Cumming wrote:
>
> >On December 12, 2001 21:50, Stewart Allen wrote:
> >
> >>I'm in a bit of a pickle and need to find a way to pass boot params to a
> >>reiserfs rootfs to *prevent* it from replaying the journal on single-user
> >>boot. This may seem like a strange request, but I've got a degraded RAID
> >>array that I need to poke around in before deciding whether or not to send
> >>a disk off to a rehab lab. If the replay occurs, it will potentially
> >>destroy the fs since I'm using a degraded snapshot of the failed disk in
> >>hopes of reclaiming *some* of my data. The system is running 2.2.x (can't
> >>remember and can't find out w/out booting).
> >>
> >>Do I have a snowball's chance of pulling this off?
> >>
> >
> >Well, kinda. The only thing that can deter ReiserFS from replaying the
> >journal is convincing it that the physical media it's on is actually read
> >only. Some quick less/grep work revealed that there is no option that makes
> >the SCSI subsystem claim its devices are readonly (although it'd be extremely
> >useful for situations such as this).
> >
> >It'd probably be pretty easy to make a boot disk using a hacked version of
> >ReiserFS that refuses to replay the journal, by adding a "return 0;" near the
> >top of journal_read(struct super_block *) in journal.c. However, you might
> >feel more comfortable sending it off for data recovery than testing kernel
> >hacks on it ;)
> >
> >-Ryan
> >-
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> >
> why not just edit the source code directly and recompile?
>
> Hans

There are a couple of potential problems with this approach:

1. I thought the on-disk structures for ReiserFS changed sometime
   between 2.2.something (the system in question) and now. Since I
   cannot pinpoint the kernel/patch version, I'm not sure this hack
   will work.

2. I have no other systems like this one to test the read-only hack on.
   Without a fairly high degree of confidence that I'm actually booting
   in a no-replay read-only state, I'm not going to take chances with
   this data.

stewart