[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: Changing root journal data mode



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.

Cheers,
 Stephen





[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]