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Re: Changing root journal data mode



> On Sep 05, 2001  20:08 -0700, Mike Fedyk wrote:
> > Also if IIRC, tune2fs is only safe with the -j and -J options while mounted
> > because it just creates a file, and doesn't modify the super blocks.  All
> > other (still true?) options for tune2fs have to be used on an unmounted FS.
> 

On Wed, Sep 05, 2001 at 09:57:27PM -0600, Andreas Dilger wrote:
> No, in recent versions of e2fsprogs, it is possible to change most fields
> in the superblock via tune2fs on a mounted filesystem.  This doesn't
> necessarily mean that these settings will be effective immediately.  For
> example, it is possible create a journal on a mounted fs (setting the
> "HAS_JOURNAL" flag in the superblock, and creating a journal file)
> but this won't turn a mounted ext2 filesystem into ext3 until it is
> unmounted and mounted again.  Many of the superblock fields are only
> checked at mount time.
> 

Hmm, what about root reservations?  What keeps the kernel from overwriting
the changed superblocks with something from the page cache?

IIRC, tune2fs uses the buffer cache to make its changes, and they aren't
kept in sync...





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