Re: [systemd-devel] Non-idempotent RUN+= scripts

[Andrei Borzenkov <arvidjaar@gmail.com>]

24.09.2025 23:46, Demi Marie Obenour wrote:
> On 9/24/25 13:46, Mantas Mikulėnas wrote:
>> On Wed, Sep 24, 2025 at 8:27 PM Demi Marie Obenour <demiobenour@gmail.com>
>> wrote:
>>
>>> There are cases where a RUN+= script needs to do something
>>> exactly once each time a device appears, such as binding a
>>> different driver to the device.  If the udev rule matches
>>> based on a property (such as PCI device information) that
>>> is set only by the kernel, is it okay to use ACTION=="add"
>>> in the rule?  The only other options I know of are to either
>>>
>>
>> Such events can still be caused by the admin doing "udevadm trigger
>> --action=". Not sure why one might do that, but probably better to not rely
>> on nobody doing that.
> 
> In *this* case that should never happen, as Spectrum OS's host
> is basically an appliance and ideally nobody would be able to
> run commands like that.
> 

systemd-udev-trigger.service does it

> Will an ACTION=="add" event always come before any other events?
> 
>>> 1. Add additional code to the script to make sure it is
>>>     idempotent.  This might require adding a lock.
>>>
>>
>> Maybe not necessarily a lock as I *think* udev event processing is
>> serialized (for a given device at least); a flag file in /run or an xattr
>> on the /dev node might be enough.
> 
> These are PCI devices with no driver.  The difficulty with a flag file
> is that it needs to be reliably removed.
> 

You may try adding device property and importing it in events (IMPORT{db}).