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Re: Some concern about the journal support

From: Pavel Roskin
Subject: Re: Some concern about the journal support
Date: Fri, 13 Jun 2008 11:55:59 -0400

On Fri, 2008-06-13 at 17:05 +0800, Bean wrote:
> Hi,
> I think we need to disable journal sometimes. Tools like grub-setup
> and grub-install is run in an active system, that means sectors could
> easily end up in the journal. However, journal is a temperately
> buffer, space can be reused after a while. In this case, we should
> bypass the journal and access the underlying file system directly.
> Perhaps we can use a variable like no_journal to control the journal
> support, any suggestions ?

If we are going to hardcode block locations somewhere, hardcoding a
journal location is a serious bug.  It will be overwritten.

If we are just reading from a live filesystem, there is no 100% correct
solution, but avoiding the journal seems safer to me.  We load the
mappings once, but we read from the journal when the need arises.  The
journal can be overwritten by background activity that the administrator
doesn't control.  If we ignore the journal, inconsistencies would
normally arise only if any files used by grub are modified in the
meantime.  Those should be owned by root, and no reasonable
administrator would touch them while grub-install is running.

We still want journal support for testing purposes, so perhaps
grub-fstest should have a switch to use the journal.

Pavel Roskin

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