Greetings.
What is the status of the code to start a background kernel thread to
zero the inode tables when filesystem that was created with mke2fs -E
lazy_itable_init is mounted? All I have found is a patch set posted to
this mailing list back on November 21, 2008 and some discussion of the
implementation, but nothing after that.
Is this effort still alive?
On a related note, from what I have read here, and from looking at the
ext4 kernel code, the filesystem itself never really requires the inode
tables to be zeroed out. The only reason one might want to do that is
so that fsck does not detect false errors.
But, in data=ordered mode, would not marking the inode as allocated in
the bitmap be done in the same journal transaction as populating the
inode on disk (as well as creating a directory entry pointing to it)?
And, unless the journal is broken, then either all that succeeds or none
of it does. So outside of a hardware failure, or data being overwritten
directly on the block device, it's not possible for an "actually in-use"
inode to be marked unallocated in the inode bitmap.
So, I am wondering whether we really need the complexity of a kernel
thread to zero out the itable (or the long delay of doing it during
mke2fs). Instead, would it not be better to modify fsck to ignore
garbage in unallocated inodes, at least for filesystems that have a journal.
Thanks,
Howard Cochran
On Jun 10, 2009 18:41 -0400, Howard Cochran wrote:
> What is the status of the code to start a background kernel thread to
> zero the inode tables when filesystem that was created with mke2fs -E
> lazy_itable_init is mounted? All I have found is a patch set posted to
> this mailing list back on November 21, 2008 and some discussion of the
> implementation, but nothing after that.
>
> Is this effort still alive?
I don't think anyone is currently working on it.
> On a related note, from what I have read here, and from looking at the
> ext4 kernel code, the filesystem itself never really requires the inode
> tables to be zeroed out. The only reason one might want to do that is
> so that fsck does not detect false errors.
Correct, but the risk is that the whole filesystem could become corrupted
by the old data in the inode table.
> So, I am wondering whether we really need the complexity of a kernel
> thread to zero out the itable (or the long delay of doing it during
> mke2fs). Instead, would it not be better to modify fsck to ignore
> garbage in unallocated inodes, at least for filesystems that have a
> journal.
Sure, e2fsck already does that, but this is not totally robust. If
the marker for unallocated inodes itself becomes corrupted (which
will happen eventually, or e2fsck wouldn't ever be needed) then the
aforementioned filesystem-wide corruption could ensue.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.