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. 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.
2. Use a persistent daemon.
It might be possible to have a persistent Type=oneshot .service via ENV{SYSTEMD_WANTS}, with RefuseManualStop. Not sure if that's a good idea. I'm not using systemd as PID 1, so this definitely isn't an option :).
It seems that a persistent daemon is the technically correct way to do this, but it's a lot of extra complexity. That's unfortunate, but it somewhat makes sense. -- Sincerely, Demi Marie Obenour (she/her/hers)