VFS: Cannot open root device "(null)" or unknown-block(0, 0): error -2

[Valdis Kl=?utf-8?Q?=c4=93?=tnieks]

On Fri, 13 Aug 2021 18:08:38 -0600, jim.cromie at gmail.com said:

> then I added BTRFS_FS, since thats the host fs.
> of course it didnt work.

> VFS: Cannot open root device "(null)" or unknown-block(0,0): error -2
> Please append a correct "root=" boot option; here are the available partitions:
> Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
> CPU: 0 PID: 1 Comm: swapper Tainted: G        W         5.14.0-rc4+ #5

And it didn't find any usable btrfs (or other fs it knew about)

> Heres a working  kernel (if overlarge config)

> VFS: Mounted root (9p filesystem) readonly on device 0:20.

> Anybody see any clues ?

That '9p filesystem' should be a really big clue.  If that's the root fs that you
actually want to use, you need to do two things:

a) point at it with root=
b) have 9p filesystem support in the kernel
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