Re: 64-btrfs.rules and degraded boot

[Kai Krakow <hurikhan77@gmail.com>]

Am Tue, 5 Jul 2016 12:53:02 -0600
schrieb Chris Murphy <lists@colorremedies.com>:

> For some reason I thought it was possible to do degraded Btrfs boots
> by removing root=UUID= in favor of a remaining good block device, e.g.
> root=/dev/vda2, and then adding degraded to rootflags. But this
> doesn't work either on CentOS 7.2 or Fedora Rawhide. What happens is
> systemd waits for vda2 (or by UUID) indefinitely, it doesn't even try
> to mount the volume.
> 
> I think it's due to the udev rule that's basically saying the device
> isn't ready because not all of its devices are there.
> 
> [root@f24m ~]# cat /usr/lib/udev/rules.d/64-btrfs.rules
> # do not edit this file, it will be overwritten on update
> 
> 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"

This doesn't come from the user-space tools but from the udev builtins,
I think:

# udevadm test-builtin btrfs
 
> # mark the device as not ready to be used by the system
> ENV{ID_BTRFS_READY}=="0", ENV{SYSTEMD_READY}="0"
> 
> LABEL="btrfs_end"
> 
> 
> I am kinda confused about this "btrfs ready $devnode" portion. Isn't
> it "btrfs device ready $devnode" if this is based on user space tools?
> 
> 
> 
> 



-- 
Regards,
Kai

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