Self answering below.
Op 22-02-2020 om 16:06 schreef Ferry Toth:
> Hi all,
>
> I am able to generate a rootfs image of type btrfs.
> Btrfs supports subvolumes, for instance with name @.
>
> Using subvolumes instead of partitions allow more efficient use of
the emmc compared to separate partitions. And it allows multiple
versions of the rootfs in the same pool.
>
> Manually I can create a subvolume (on the host) by loop mounting the
btrfs image and taking the snapshot. Something like this:
> mkdir tmp
> sudo mount edison-image.btrfs tmp
> sudo btrfs subvolume snapshot tmp tmp/@
>
> and then remove all dir's in root except @.
>
> mount and btrfs operations need root permissions AFAIK. Is there any
way to add these to the recipe?
Up to now I found I can use udisksctl to mount the image as ordinary user.
However, to create a snapshot it appears I need to own the root
directory and for that would need an option like mke2fs -E root_owner.
As that doesn't exist, the only workaround I find is to create an ext4
partition with -E root_owner and then convert to btrfs.
Is there really no better way?
> There is 2nd thing I want to achieve:
> Btrfs can send / receive these snapshots allowing over-the-air-updates.
>
> For this I need to:
> sudo btrfs subvolume snapshot -r tmp/@ tmp/@ota
> sudo btrfs send tmp/@ota > edison-image.snapshot
>
> And then later manually (with the device having mounted btrfs on /mnt):
>
> cat edison-image.snapshot | ssh root@edison "btrfs receive /mnt"
> ssh root@edison "btrfs property set -ts /mnt/@ota ro false"
>
> How do I automated the first steps in yocto?
>
> Ferry
>
>
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