Re: MBR plus emulated FAT

[Richard W.M. Jones]

On Sat, Jan 28, 2023 at 08:48:13PM +0100, Csepp wrote:
> 
> Eric Blake <eblake@redhat.com> writes:
> 
> > On Fri, Jan 27, 2023 at 01:00:05AM +0100, Csepp wrote:
> >> Hi!
> >> 
> >> Would it be possible to store the metadata for emulated FAT partitions
> >> backed by host directories?  It would make installing Windows 98 much
> >> more seamless, since it would be able to set the boot flag during
> >> install. I have a 9front install that uses no block devices and gets its
> >> root file system via a simple 9P server, I've found that extremely
> >> useful, since it lets me back up or modify files directly from the host.
> >> 
> >> I don't have that much free time, but if it wouldn't be too difficult to
> >> implement this and someone helped, I could try to do it myself.  But
> >> honestly I would be super thankful if someone else implemented it
> >> instead.
> >
> > I wonder if you can already accomplish this using nbdkit-floppy-plugin
> > (expose a directory as a FAT file system over NBD), then connect qemu
> > as an NBD client, rather than having to implement this all in qemu
> > proper.
> 
> Didn't know abut that program, thanks!  Unfortunately:
> > The plugin does not support writes.
> https://manpages.debian.org/bullseye/nbdkit/nbdkit-floppy-plugin.1.en.html

(Late reply - Eric just told me about this thread)

You can place the COW filter on top to make this plugin writable.
However that doesn't persist the changes back to the disk (VVFAT is
kind of crazy).

$ nbdkit --filter=cow floppy /directory

Rich.

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