Re: RO mount of ext4 filesystem causes writes

[Theodore Ts'o]

On Thu, Jun 22, 2023 at 11:18:04PM -0700, Sean Greenslade wrote:
> I perhaps should have been more explicit in my report. The issue is not
> that the image is any different after the mount; indeed, the md5sums are
> identical before and after on my machine as well. The issue is that
> something is issuing writes to the backing image, which bumps the mtime
> of the backing image. When handling the images with rsync, a difference
> in mtime causes the whole image to need to be read.

Ah, yes, your initial report said "small writes", but it didn't
specify whether the issue was that writes were modifying the image, or
just simply touching the mtime field of the backing file.  I assume
these must be largish fs images, since it must have made the increased
rsync time noticeable?

This appears to fix the problem for me, given the clarified
reproduction information.  Could you please try it on your end?

	     		   	     	    - Ted