Unable to mount btrfs filesystems spread across more than one partition with lklfuse

[Tony O]

My example has three partitions. Passing partition 1 gives "BTRFS error (device vda1): devid 2 uuid is missing". Similar for partitions 2 and 3, but "devid 1".

All these devices are on one physical disk, but passing the full disk to lklfuse obviously won't work, and I'm having trouble how to wrangle the code to find that agreeable

[Octavian Purdila]

This requires support for adding multiple disks. Then using the physical disk and multiple partitions should work. I’ll look into more details at this tomorrow.

Could you please share instructions on how to get btrfs split across multiple partitions?

[Tony O]

Assuming you have btrfsprogs, with an existing btrfs filesystem mounted at /mnt, you can add a new device as-is with btrfs device add /dev/<blk> /mnt

Thanks!

[Tony O]

Is there a plan for implementing this?

[David Disseldorp]

One option for adding devices to an existing lklfuse process at runtime is a FUSE xattr hack, e.g.:

setfattr -n lklfuse.dev.add -v /dev/sdX /mnt/

It might then also be possible to forward BTRFS_IOC_ADD_DEV ioctls through to the underlying LKL mount via a FUSE ioctl hook.