Re: [PATCH 2/4] Remove stale archivemount support

[Stefano Brivio <sbrivio@redhat.com>]

On Sat, 6 Apr 2024 14:02:58 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, Apr 05, 2024 at 08:09:32PM +0200, Stefano Brivio wrote:
> > On Fri, 22 Mar 2024 13:27:37 +1100
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > mbuto has two ways of building the initramfs.  One is the typical approach
> > > of staging its contents in a temporary directory, then building the
> > > initramfs with cpio.  The other is to create an empty initramfs, mount
> > > it with archivemount, and copy things into the mounted archive.
> > > 
> > > However, the archivemount approach is broken.  I'm not entirely sure why,
> > > but it appears not to properly unmount the archive and retrieve the final.
> > > filled version.  The upshot is that if archivemount is installed, then
> > > mbuto generates an empty, gzip-compressed initramfs instead of whatever it
> > > was supposed to.  It looks like this has bitrotted from some earlier
> > > working version.
> > > 
> > > The archivemount approach is not necessary, and honestly a pretty strange
> > > and roundabout way of building the initramfs.  Remove it.  
> > 
> > There were two reasons behind that: first off, I mistakenly assumed
> > that the kernel could see changes made to the initramfs after boot.  
> 
> Yeah, that was never going to work.
> 
> > Second, it was actually convenient for developing this tool as I could
> > just make directories and copies in half-working images. I also had
> > half a mind about some usage with QEMU rebooting the guest, and the
> > initramfs would change across reboots without having to call mbuto
> > again, for bisections or suchlike.  
> 
> That's not really dependent on using archivemount in any case.  If
> qemu re-reads the initrd on each boot, then you can still do this by
> rebuilding the image between boots (which is all that archivemount
> would do anyway).

That was exactly my point: with archivemount, the user doesn't have to
call mbuto again -- archivemount does it, implicitly.

> If qemu doesn't re-read it, then this won't work even if you are using
> archivemount.

It looks like QEMU doesn't do that, at least not on x86, so yes, this
part never worked anyway.

-- 
Stefano