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jepio
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With btrfs it's not possible in general to find a single underlying block device because there could be many, but still it is possible for our case since we have a single partition. However, rootdev failed to find it because it uses the device minor and major pair from a "stat" syscall on the mount point. This doesn't work with btrfs because it gives a logical pair instead of one belonging to a block device. Instead of using the minor and major pair, find the underlying block device of a mount point by looking it up in /proc/mounts. The existing traversal code to find the lowest backing device is kept in place by getting the minor and major pair for the found block device.
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rootdev: support btrfs
With btrfs it's not possible in general to find a single underlying
block device because there could be many, but still it is possible for
our case since we have a single partition. However, rootdev failed to
find it because it uses the device minor and major pair from a "stat"
syscall on the mount point. This doesn't work with btrfs because it
gives a logical pair instead of one belonging to a block device.
Instead of using the minor and major pair, find the underlying block
device of a mount point by looking it up in /proc/mounts. The existing
traversal code to find the lowest backing device is kept in place by
getting the minor and major pair for the found block device.
cgpt: fix cause for compiler warning
How to use/Testing done
This was built and tested with the coreos-overlay branch
kai/bootengine-verity-hashoffsetfrom flatcar-archive/coreos-overlay#1106 and flatcar-scripts branchkai/btrfs-usr-oemfrom flatcar/scripts#131 in http://jenkins.infra.kinvolk.io:8080/job/os/job/manifest/3029/cldsv/ where the Flatcar image that has a btrfs /usr partition and OEM partition.While the actual switch to a btrfs filesystem on the /usr partition is only possible when all changes are part of a Stable release because update-engine needs to know how to handle the new filesystem when updating, we can already do the switch for the OEM partition.