RE: Repost (from LKML): EXT3 FS and 64K blocks error

Daniel Taylor
2010-07-09T22:32:25Z

> -----Original Message-----
> From: Theodore Tso [mailto:tytso@MIT.EDU]
> Sent: Friday, July 09, 2010 5:04 AM
> To: Daniel Taylor
> Cc: linux-ext4@vger.kernel.org
> Subject: Re: Repost (from LKML): EXT3 FS and 64K blocks error
>
>
> On Jul 8, 2010, at 8:10 PM, Daniel Taylor wrote:
>
> > We're getting the following error with an EXT3 file sytem that
> > has 64K blocks (2.6.32.12, on a powerpc), although I don't see
> > any fixes for later kernels in a diff against 2.6.35-rc3):
> >
> > ext3_readdir: bad entry in directory #11: rec_len is
> smaller than minimal -
> > offset=0, inode=0, rec_len=0, name_len=0
> >
> > That message is generated in fs/ext3/dir.c:ext3_check_dir_entry()
> > when called from fs/ext3/dir.c:ext3_readdir(), AFAICT.
> >
> > Did something get missed when EXT3 handling for 64K blocks was
> > implemented or when a new feature was added?
> >
> > FWIW, I do NOT see this on EXT4.
>
> I very much doubt anyone has ever tested 64k blocks on ext3.
> There were
> some extensions made to support 64k blocks with ext4, that had to do
> with encoding the directory entry rec_len fields (which is 16
> bits and will
> overflow when trying to store the value 65536, as you have
> discovered).
>
> Bottom line, it's not so much that EXT3 handling for 64k
> blocks was ever
> *implemented*, as much as no one really thought about it much when
> they set the #define's for maximum block size supported. :-)
>
> 64k block sizes hasn't received much testing on ext4 as far
> as I know, but
> there was one developer who noted the dirent encoding problem and
> proposed a fix.

I guess we'll find out how well they work ;) we're putting them into
pre-production test now. The main reason is that we're building a NAS
that will see significant use as a media server (we hope) and we do see
a performance improvement with the larger file system blocks in our
engineering tests.

>
> Is there a particular reason why you care about this with
> ext3? Ext4 does
> provide a superset of the features in ext3...

We're switching to ext4. I just thought someone might want to take
a look at the error message. I can do some more testing, next
week, if there are suggestions of what to try.

>
> -- Ted
>
>