Re: ext2 caches

From: Theodore Y. Ts'o (tytso@MIT.EDU)
Date: Fri Sep 29 2000 - 22:33:08 EST


   Date: Fri, 29 Sep 2000 19:24:01 +0200
   From: Frederic Magniette <Frederic.Magniette@lri.fr>

   We would like to do some operations on a ext2 disk while it is
   mounted read-only. The problem is that our operations have no
   effects because everithing is cached. Is it possible to shrink all
   the caches, especially the superblock caches and to reload the
   changes? We used prune_dcache (kernel 2.2.14) and dev_fsync . It
   has some effect but none on the superblock and the root of the disk.
   Thanks by advance

It is not safe to modify an ext2 filesystem via external means while it
is mounted, even if it is mounted read-only. You can panic the kernel
that way. (Well, tune2fs works while the filesystem mounted, but that's
a special case.)

Basically, no, it's not safe to do this for just about any filesystem.

                                                        - Ted
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