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Re: Changing root journal data mode



On Thu, Sep 06, 2001 at 10:06:45AM +0100, Stephen C. Tweedie wrote:
> On Wed, Sep 05, 2001 at 09:06:03PM -0700, Mike Fedyk wrote:
> > On Wed, Sep 05, 2001 at 09:57:27PM -0600, Andreas Dilger wrote:
> > > 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...
> 
> The kernel also uses the buffer cache when dealing with the
> superblock.  There are still some cache aliasing problems --- the
> kernel will read several superblock fields from the buffer cache and
> store them in the internal ext2/3 superblock struct at times, mainly
> to avoid constant byte-swapping when accessing those fields, but the
> fields where that is done tend to be mostly readonly so if tune2fs
> modifies a few bytes of the buffer-cache superblock, those values
> won't be overwritten by the kernel.  They won't be *read* by the
> kernel until next mount, but they will survive on disk.
> 

Ok, great.  Was this true on 2.2 and 2.0 kernels also?

Were there any fields that the kernel didn't treat as read only?  I can
imagine that the FS_CLEAN flag would be written...

Also, I noticed that on 2.4.9-ac7 if I run tune2fs -l:

 tune2fs 1.22, 22-Jun-2001 for EXT2 FS 0.5b, 95/08/09
 Filesystem volume name:   <none>
 Last mounted on:          <not available>
 Filesystem UUID:          f5719854-d253-4809-9504-84850c44a796
 Filesystem magic number:  0xEF53
 Filesystem revision #:    1 (dynamic)
 Filesystem features:      has_journal filetype needs_recovery sparse_super
 Filesystem state:         clean
                           ^^^^^^

This is my root FS, and it is mounted, should this be clean?

Mike





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