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Created attachment 865494 [details]
Patch to use SYSTEMD_READY=0 for uninitialized loop devices

Based on man 5 systemd.device:

SYSTEMD_READY=
           If set to 0, systemd will consider this device unplugged even if it shows up in the udev tree. If this property is unset or set to 1, the device will be considered plugged the
           moment it shows up in the udev tree. This property has no influence on the behavior when a device disappears from the udev tree. This option is useful to support devices that
           initially show up in an uninitialized state in the tree, and for which a "changed" event is generated the moment they are fully set up. Note that SYSTEMD_WANTS= (see above) is
           not acted on as long as SYSTEMD_READY=0 is set for a device.


I think we should use SYSTEMD_READY=0 for loop devices that have no file attached yet and hence they're not ready for use until some file is attached.

Otherwise, we can get into a problem when we try to bind a service to *usable* loop device (e.g. bug #1063813).

(patch attached)

If possible, please try to squeeze this patch into RHEL 7.0. Thanks!

Requesting a blocker for this one since this makes LVM on loop devices unusable when detaching and attaching again a file to a loop device.

Also, based on the definition of SYSTEMD_READY that systemd uses to declare a device as properly initialized or not, clearly, the loop device without its backing file is not initialized.

The patch is simple one-liner - it's checking the existence of loop/backing_file sysfs file existence which exists only if the loop device has a file attached and it sets SYSTEMD_READY based on this information.

Looks good to me. Care to send that patch upstream?

(In reply to Harald Hoyer from comment #4)
> Looks good to me. Care to send that patch upstream?

Sent: http://lists.freedesktop.org/archives/systemd-devel/2014-March/017647.html

This request was resolved in Red Hat Enterprise Linux 7.0.

Contact your manager or support representative in case you have further questions about the request.