Re: "Some devices missing" only while not mounted

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On 01/22/2016 12:40 PM, Chris Murphy wrote:
On Thu, Jan 21, 2016 at 8:55 PM, Anand Jain <anand.jain@xxxxxxxxxx> wrote:

   'btrfs dev ready':
      - cannot be fixed without breaking the API rules.
      May be we would obsolete this cli to a sysfs interface or
      something else.


Wait, so 'btrfs dev ready' will always exit 1 (not ready) any time a
device has been made missing or replaced?

 And therefore now the
system can't boot anymore since udev+systemd won't mount a Btrfs root
fs that's not ready? That's kindof a nasty bug.

 In the case here, its not a problem as kernel doesn't think there
 is a missing device. So with that 'btrfs dev ready' should return 0,
 unless user is providing a device which was deleted in the btrfs
 device tree but failed to wipe the SB in the deleted device.

 However there are some cases where 'btrfs dev ready' will never
 return 0, especially in the cases of seed/sprout devices. So if
 system boot depends on that, then yes boot will fail. (I am not
 sure if there are some real use cases).

 Next. Even with a missing device some pools are mountable with
 degrade option. Discussion on this before preferred boot to
 ask for the user choice. Since its alway challenging to know
 if the device is really missing OR its just +1s slower than
 our timeout in waiting for it.

Thanks, Anand


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