I don't know enough about the udev rules to know which file is right. Does the builtin rule get run when LUKS devices get created too?

I'm not a udev expert, but here is the rules :

from udev :
SUBSYSTEM!="block", GOTO="btrfs_end"
ACTION=="remove", GOTO="btrfs_end"
ENV{ID_FS_TYPE}!="btrfs", GOTO="btrfs_end"

# let the kernel know about this btrfs filesystem, and check if it is complete
IMPORT{builtin}="btrfs ready $devnode"

# mark the device as not ready to be used by the system
ENV{ID_BTRFS_READY}=="0", ENV{SYSTEMD_READY}="0"

LABEL="btrfs_end"

That will cause the following code to be run: http://cgit.freedesktop.org/systemd/systemd/tree/src/udev/udev-builtin-btrfs.c 

This means it will be run on if ID_FS_TYPE is set. For LUKS devices, this should be handled by 13-dm-disk.rules with the "IMPORT{builtin}="blkid"" line.

Robert, do you confirm ?

Yes, the idea of the above rule is that if ID_FS_TYPE is not set to btrfs, the rule is skipped. Like Frederic said, blkid command should run on the device and set a couple of env variable (like ID_FS_TYPE) which udev will use in later rules.

If blkid can't get the ID_FS_TYPE or ID_FS_TYPE is set to something else then btrfs, then obviously nothing will be done.

Ok. I'll disable the udev file in btrfsprogs and we'll treat any bugs in that area as udev bugs moving forward.

Added to filesystems:btrfsprogs and forwarded to Factory as SR 200993.

This is an autogenerated message for OBS integration:
This bug (839960) was mentioned in
https://build.opensuse.org/request/show/200993 Factory / btrfsprogs

This bugfix side-effect. While installing the kernel (precisely mkinitrd), you get the following error:

cp: cannot stat ‘/usr/lib/udev/rules.d/80-btrfs.rules’: No such file or directory
Script /lib/mkinitrd/setup/11-btrfs.sh failed!

The filename in /lib/mkinitrd/scripts/setup-btrfs.sh needs to be changed to /usr/lib/udev/rules.d/64-btrfs.rules from /usr/lib/udev/rules.d/80-btrfs.rules

This is an autogenerated message for OBS integration:
This bug (839960) was mentioned in
https://build.opensuse.org/request/show/202703 Factory / btrfsprogs

openSUSE-RU-2013:1700-1: An update that has one recommended fix can now be installed.

Category: recommended (low)
Bug References: 839960
CVE References: 
Sources used:
openSUSE 13.1 (src):    btrfsprogs-0.20-4.14.1

*** Bug 842934 has been marked as a duplicate of this bug. ***