mkfs: Need option to set ownership of root dir to allow user snapshot

[kdave]

Moved from https://bugzilla.kernel.org/show_bug.cgi?id=206803 :

"
When generating a btrfs image on a file using mkfs.btrfs the ownership of the root dir is always the root user.

This is problematic when automatically generating a system image as an ordinary user using for instance yocto.

There are tools like udisksctl that allow ordinary users to mount the image on /media/username/uuid.

But if the ordinary user want to take a snaphot to send/receive the system image to a remote (IIoT) device that is not allowed.

The only way is to chmod /media/username/uuid which requires root privileges,w hich in turn requires f.i. bitbake to run as sudo.

This blocks the ability to send system image updates OTA (over the air), a nice advantage of btrfs over f.i. ext.

We could use a command line switch to make the current user own the root.

There is no security penalty in this, as the generated image can always be copied to a machine that would allow the user root access (container?), but that would be cumbersome to automate.

An option like mke2fs -E root_owner would be exactly what is needed.
"