Re: document ext3 requirements

Theodore Tso
2009-01-04T19:37:27Z

On Sun, Jan 04, 2009 at 08:21:06PM +0100, Geert Uytterhoeven wrote:
> As mentioned before, suspending a laptop (running from hdd), running
> a live CD, and expecting everything to work fine when resuming from
> hdd?
>
> I think most people get shocked when they discover that mounting
> something read-only may actualy write to the media. This is a bit
> unexpected (hey, if I mount `read-only', I expect that no writes
> will happen), as it behaved differently before the introduction of
> journalling.

It's been this way for about a decade.... that being said, if you
really want to do this, you can today via "mount -o ro,noload /dev/XXX
/mntpt". However, the system could crash or fail because the
filesystem without having run the journal could be quite inconsistent.

> As for mounting the root file system read-only during early boot up, and
> remounting it read-write later, I guess it's quite complicated to replay the
> journal (in RAM) on read-only mount, and deferring the replay writeback until
> remounting read-write?

It's not *that* hard; if someone would like to cons up a patch, please
feel free.... but it's certainly not a high priority for me or most
of the other ext3 filesystem developers.

- Ted