Re: document ext3 requirements

Pavel Machek
2009-01-04T00:17:19Z

On Sun 2009-01-04 00:01:58, Martin MOKREJŠ wrote:
> Pavel Machek wrote:
> > On Sat 2009-01-03 22:17:15, Duane Griffin wrote:
> >> [Fixed top-posting]
> >>
> >> 2009/1/3 Martin MOKREJŠ <mmokrejs@ribosome.natur.cuni.cz>:
> >>> Pavel Machek wrote:
> >>>> readonly mount does actually write to the media in some cases. Document that.
> >>>>
> >>> Can one avoid replay of the journal then if it would be unclean?
> >>> Just curious.
> >> Nope. If the underlying block device is read-only then mounting the
> >> filesystem will fail. I tried to fix this some time ago, and have a
> >> set of patches that almost always work, but "almost always" isn't good
> >> enough. Unfortunately I never managed to figure out a way to finish it
> >> off without disgusting hacks or major surgery.
> >
> > Uhuh, can you just ignore the journal and mount it anyway?
> > ...basically treating it like an ext2?
> >
> > ...ok, that will present "old" version of the filesystem to the
> > user... violating fsync() semantics.
>
> Hmm, so if my dual-boot machine does not shutdown correctly and I boot
> accidentally in M$ Win where I use ext2 IFS driver and modify some
> stuff on the ext3 drive, after a while reboot to linux and the journal
> get re-played ... Mmm ...

ext2 driver should refuse to mount dirty ext3 filesystem. (Linux ext2
driver does that).

> > Still handy for recovering badly broken filesystems, I'd say.
>
> Me as well. How about improving you doc patch with some summary of
> this thread (although it is probably not over yet)? ;-) Definitely,
> a note that one can mount it as ext2 while read-only would be helpful
> when doing some forensics on the disk.

No, you can't mount unclean ext3 as an ext2; patch to do that would be
possible but...

I believe the patch is correct & useful.
Pavel
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