[uml-user] Re: [uml-devel] Resizing uml filesystems

[Theodore T. <ty...@mi...>]

On Mon, Apr 08, 2002 at 10:39:43PM -0400, William Stearns wrote:
> 
> 	Run e2fsck right after the resize and you'll find that resize2fs
> 1.26 does not extend the file out to the right total length.  If you
> picture the file as (simplified):
> 
> ....MddddMddddMddddMdddd
> 
> 	where M is ext2 Metadata and d is actual data storage space,
> resize2fs performs actual writes to all of the M's, extending the file out
> to the last M, but never writes out to the last 4 d's, leaving the file 4
> d's short.
> 	I'm _way_ oversimplifying here, and run a remarkably good risk of 
> misunderstanding the problem in the first place; Ted T'so should be 
                                                       ^^^^ Ts'o :-)
> considered authoritative.


Yup, that's basically it.  resize2fs was written assuming that you
would be extending filesystems that were located in block devices ---
either real disks, or LVM devices.  So it wasn't doing anything to
extend the filesystem when it was located in a file; it merely seeked
to the right location, and wrote/modified the necessary blocks.

Hmm... it just occurred to me.  If the filesystem is being shrunk, it
would probably be a good idea if resizefs called ftruncate to shrink
the file to the correct size, too.  Hmm....

						- Ted