On May 11, 2009 13:44 -0500, Eric Sandeen wrote:
> Andreas Dilger wrote:
> > The reason that the journal is zeroed is because there is some chance
> > that old (valid at the time) transaction headers and commit blocks might
> > be in the journal and could accidentally be "recovered" and cause bad
> > corruption of the filesystem.
>
> But I guess the question is, why isn't a normal internal log zeroed?
>
> If I'm reading it right only external logs get this treatment, and I
> think that's what generated the original question from Alexander.
Hmm, possibly because when ext3 was first allocated the internal journal
created was "dd if=/dev/zero of=/mnt/fs/.journal bs=1M count={jnl_size}"
on the filesystem mounted as ext2, so normal filesystem IO would handle
the zeroing of the blocks. Even today if tune2fs adds a journal to a
filesystem it does the zero filling of the journal.
Looking at the mke2fs code it also appears to be doing zeroing of the
journal inode in:
mke2fs
->ext2fs_add_journal_inode
->write_journal_inode
->ext2fs_block_iterate
->mkjournal_proc (increment zero_count)
->ext2fs_zero_blocks
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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