Re: How does the superblock/mount -t auto work? (was: Synching volumes on logout -- tune2fs)

["Monique Y. Herman" <spam@bounceswoosh.org>]

On Fri, 26 Dec 2003 at 23:59 GMT, Paul Morgan penned:
> 
> The magic number is part of the superblock.  tune2fs -l is showing you the
> superblock.  The magic number is the same for ext2 and ext3, but the
> features are different (has_journal for ext3). This is very useful:
> 
> Suppose you have an ext3 root filesystem.  If your kernel is ext3-aware
> (i.e. ext3 support compiled in or module on initrd), it will mount root as
> ext3.  If your kernel is not ext3-aware, it will mount root as ext2.
> 
> ext3 is just ext2 with a file (the journal) which is used by the ext3
> driver.  Apart from that, it is a standard ext2 filesystem.  You can also
> mount an ext3 filesystem explicitly as ext2.  Of course, you temporarily
> lose the journalling feature, but it'll work

Thank you for taking the time to respond, but the above was already
pretty clear to me.  What's not clear to me are the following points:

Since the 'auto' type for mount looks at the superblock, will an ext3
partition mounted as 'auto' be used as ext2, ie, without journalling?
(I'm guessing the answer is 'yes', but I'd still feel more warm and
fuzzy with a confirmation.)

and

Does the presence of the has_journal option imply that the driver in use
is ext3, or only that the partition itself has ext3 features, regardless
of whether they're being used?  I'm guessing the answer is "the latter,"
and that the presence of the has_journal feature does not have any
bearing on whether the ext2 or ext3 driver is being used, but again, a
confirmation would make me feel better.

Or, as an experimental solution to both of the above questions, how
would I go about determining whether an ext3 partition mounted as type
'auto' is using the ext2 or ext3 driver?

> 
> I use exclusively ext3 but just for you I created an ext2 example :)

I have all of my partitions formatted as ext3, but in researching the
original poster's question I discovered that I had for some reason put
'auto' in my fstab for the root partition (but not the others), leading
to the above questions.

-- 
monique