Benjamin Tissoires
bb8be68d12
hid: bpf: hid_bpf_helpers: add helper for having read/write udev properties
...
We want udev-hid-bpf to be able to set udev properties by printing them
out after the BPF object has been loaded. This allows to make a query to
the device, and set a udev prop based on the answer.
Because the way udev works, the properties are cleared on bind/unbind,
and we need a way to store them. After several attempts to keep the
property alive without re-running the udev-hid-bpf tool to communicate
with the device, it came out that HID-BPF maps are pinned in the bpffs
and we can then query them.
So the following would export a UDEV property in the bpffs:
EXPORT_UDEV_PROP(HID_FOO, 32);
SEC("syscall")
int probe(struct hid_bpf_probe_args *ctx)
{
const char *foo = "foo";
UDEV_PROP_SPRINTF(HID_FOO, "%s", foo);
return 0;
}
Then, we can debug it with a simple cat:
sudo cat /sys/fs/bpf/hid/.../UDEV_PROP_HID_FOO
0: {['f','o','o',],}
This way, the property is always accessible without talking to the
device
Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/220
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org >
Signed-off-by: Jiri Kosina <jkosina@suse.com >
2026-04-08 21:46:00 +02:00
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