Re: MBR plus emulated FAT

[Kevin Wolf]

Am 27.01.2023 um 01:00 hat Csepp geschrieben:
> 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.

Running a whole OS from a vvfat backend sounds quite adventurous...
(Running anything on vvfat, especially in read-write mode, is a little
adventurous because it's a clever, but not very supportable hack that
has known bugs, but a whole OS is a step further.) I've only ever used
it for transferring individual files.

Of course, you also need to be careful with accessing the filesystem
from the host and the guest at the same time - strictly speaking, once
you change anything from the host, a running guest sees a broken disk
than randomly changed and together with guest caches that could corrupt
everything. So avoid that if you don't want to tempt fate.

Technically it should be possible to make writes to the boot sector etc.
persistent, you just need a place to store them. I imagine an additional
special file could do the trick. If you have it in the same directory,
you would get collisions with files of the same name in the guest file
system.

So I suppose you would use an image file outside of the directory and
configure it like -blockdev vvfat,dir=/tmp/foo/,mbr=/tmp/foo_mbr.img
with a separate option specifying its path.

I'm not sure if it would be better to override parts of the image with
the actually correct data according to the generated file system.

I doubt you'll find anyone to make this hack for you, but if you feel
like it, it sounds like it should be possible.

Kevin