There may be a confusion about which strings are supposed to be raw and which are escaped.

Unit names are escaped strings, because some unit names are generated from path names. That's why I have a unit called "sys-devices-virtual-block-dm\x2d0.device" here (just an example).

But if that's the case, shouldn't a name such as "lvm2-pvscan@/dev/dm-0.service" be considered invalid? The "/" character should not appear in an escaped string.
An escaped name would be "lvm2-pvscan@dev-dm\x2d0.service". But I don't think we provide a tool to perform easy (un-)escaping in shell scripts.

As a RFE, systemd-udev could provide not only $devnode, but also an escaped form of the same.

(In reply to Michal Schmidt from comment #2)
> An escaped name would be "lvm2-pvscan@dev-dm\x2d0.service". But I don't
> think we provide a tool to perform easy (un-)escaping in shell scripts.

bash:

dev_unit_name()
{
    _name="${1%%/}"
    _name="${_name##/}"
    _name="${_name//-/\x2d}"
    _name="${_name//\//-}"
    echo "$_name"
}

$ dev_unit_name /dev/dm/0
dev-dm-0

$ dev_unit_name /dev/dm-0
dev-dm\x2d0

(In reply to Michal Schmidt from comment #2)
> As a RFE, systemd-udev could provide not only $devnode, but also an escaped
> form of the same.

I agree

Finally, I've changed major:minor instead of device name for the instantiated service. But still, please, provide the escaped form of $devnode in udev as well for anybody else who could hit this problem again...

Note that SYSTEMD_WANTS in udev rules expects properly escape unit names, but also takes unescaped ones, which when that is detected are automatically escaped. This follows the same rules as "systemctl status <foobar>" will automatically escape <foobar> if it is detected not to be already escaped.

Then, from inside the unit files there is %i and %I, one to access the escpaed, ant the other to access the unescaped instance part of the name.

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the next release of Red Hat Enterprise Linux.

(In reply to Lennart Poettering from comment #6)
> Note that SYSTEMD_WANTS in udev rules expects properly escape unit names,
> but also takes unescaped ones, which when that is detected are automatically
> escaped. This follows the same rules as "systemctl status <foobar>" will
> automatically escape <foobar> if it is detected not to be already escaped.
> 
> Then, from inside the unit files there is %i and %I, one to access the
> escpaed, ant the other to access the unescaped instance part of the name.

Does not work for "-" in the original name, because that will be converted to "/" in the unescaped "%I" version.