[systemd-devel] Out of order events

[Lennart Poettering]

On Tue, 29.03.16 18:15, Nathaniel McCallum (npmccallum at redhat.com) wrote:

> I have a rule like this:
> 
> ACTION=="add", SUBSYSTEM=="block", ENV{ID_FS_TYPE}=="crypto_LUKS",
> ENV{ID_FS_VERSION}="1", RUN+="sh -c 'echo password | cryptsetup open
> $devnode luks-$env{ID_FS_UUID_ENC}'"
> 
> Okay, my real rule isn't so security braindead, but the above will
> suffice for concept. :)
> 
> What I find interesting is that the udev events happen backwards in
> this case. First, two udev events are generated for the new plaintext
> block device and then finally I get the add event for the ciphertext
> block device. For instance:

udev dispatches events in an undefined order generally, with one
exception: parent devices are processed before child devices.

Since in the udev tree the DM devices and the backing devices are not
in a parent/child relationship (in fact any relationship at all) their
events may be dispatched in any order.

Lennart

-- 
Lennart Poettering, Red Hat