[systemd-devel] udev ATTR can have double dots and help writing a rule

Mon Nov 30 15:17:55 UTC 2020

So this is the eventual rule I ended up writing after having a lot of
trouble writing a udev rule:

`ACTION=="add", SUBSYSTEM=="ata_port", KERNEL=="ata[0-9]",
TEST=="../../power/control" ATTR{../../power/control}="auto"`

Here is the rule working:

```
Dec 01 01:33:16 arch systemd-udevd[267]: ata1:
/etc/udev/rules.d/user-powertop-tunables.rules:5 ATTR
'/sys/devices/pci0000:00/0000:00:13.0/ata1/ata_port/ata1/../../power/control'
writing 'auto'
Dec 01 01:33:16 arch systemd-udevd[258]: ata2:
/etc/udev/rules.d/user-powertop-tunables.rules:5 ATTR
'/sys/devices/pci0000:00/0000:00:13.0/ata2/ata_port/ata2/../../power/control'
writing 'auto'
```

Is this a good udev rule or even valid or is using `..` something that
shouldn't be possible?

Before settling on the above rule I was using:

`ACTION=="add", DEVPATH=="/devices/pci0000:00/0000:00:13.0",
ATTR{ata1/power/control}="auto"`

Here was that rule working:

`Nov 30 18:26:02 arch systemd-udevd[264]: ata1:
/etc/udev/rules.d/user-powertop-tunables.rules:4 ATTR
'/sys/devices/pci0000:00/0000:00:13.0/ata1/ata_port/ata1/power/control'
writing 'auto'`

Obviously I'd need to add the `TEST` and then I run into the problem
that I have to write a rule for every single number.

So can anyone help me figure this all out?

Some udevadm info commands:

```
udevadm info -q all --path=/sys/bus/pci/devices/0000:00:13.0/ata1/ata_port/ata1
P: /devices/pci0000:00/0000:00:13.0/ata1/ata_port/ata1
L: 0
E: DEVPATH=/devices/pci0000:00/0000:00:13.0/ata1/ata_port/ata1
E: SUBSYSTEM=ata_port
```

```
$ udevadm info -a --path=/sys/bus/pci/devices/0000:00:13.0/ata1/ata_port/ata1

Udevadm info starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.

  looking at device '/devices/pci0000:00/0000:00:13.0/ata1/ata_port/ata1':
    KERNEL=="ata1"
    SUBSYSTEM=="ata_port"
    DRIVER==""
    ATTR{idle_irq}=="0"
    ATTR{nr_pmp_links}=="0"
    ATTR{port_no}=="1"
    ATTR{power/async}=="disabled"
    ATTR{power/control}=="auto"
    ATTR{power/runtime_active_kids}=="0"
    ATTR{power/runtime_active_time}=="0"
    ATTR{power/runtime_enabled}=="disabled"
    ATTR{power/runtime_status}=="unsupported"
    ATTR{power/runtime_suspended_time}=="0"
    ATTR{power/runtime_usage}=="0"

  looking at parent device '/devices/pci0000:00/0000:00:13.0/ata1':
    KERNELS=="ata1"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{power/async}=="enabled"
    ATTRS{power/control}=="auto"
    ATTRS{power/runtime_active_kids}=="1"
    ATTRS{power/runtime_active_time}=="1713418"
    ATTRS{power/runtime_enabled}=="enabled"
    ATTRS{power/runtime_status}=="active"
    ATTRS{power/runtime_suspended_time}=="0"
    ATTRS{power/runtime_usage}=="0"

  looking at parent device '/devices/pci0000:00/0000:00:13.0':
    KERNELS=="0000:00:13.0"
    SUBSYSTEMS=="pci"
    DRIVERS=="ahci"
    ATTRS{ari_enabled}=="0"
    ATTRS{broken_parity_status}=="0"
    ATTRS{class}=="0x010601"
    ATTRS{consistent_dma_mask_bits}=="64"
    ATTRS{d3cold_allowed}=="1"
    ATTRS{device}=="0x22a3"
    ATTRS{devspec}==""
    ATTRS{dma_mask_bits}=="64"
    ATTRS{driver_override}=="(null)"
    ATTRS{enable}=="1"
    ATTRS{irq}=="117"
    ATTRS{local_cpulist}=="0-3"
    ATTRS{local_cpus}=="f"
    ATTRS{msi_bus}=="1"
    ATTRS{msi_irqs/117}=="msi"
    ATTRS{numa_node}=="-1"
    ATTRS{power/async}=="enabled"
    ATTRS{power/control}=="auto"
    ATTRS{power/runtime_active_kids}=="1"
    ATTRS{power/runtime_active_time}=="1716855"
    ATTRS{power/runtime_enabled}=="enabled"
    ATTRS{power/runtime_status}=="active"
    ATTRS{power/runtime_suspended_time}=="0"
    ATTRS{power/runtime_usage}=="1"
    ATTRS{power/wakeup}=="disabled"
    ATTRS{power/wakeup_abort_count}==""
    ATTRS{power/wakeup_active}==""
    ATTRS{power/wakeup_active_count}==""
    ATTRS{power/wakeup_count}==""
    ATTRS{power/wakeup_expire_count}==""
    ATTRS{power/wakeup_last_time_ms}==""
    ATTRS{power/wakeup_max_time_ms}==""
    ATTRS{power/wakeup_prevent_sleep_time_ms}==""
    ATTRS{power/wakeup_total_time_ms}==""
    ATTRS{revision}=="0x35"
    ATTRS{subsystem_device}=="0x074d"
    ATTRS{subsystem_vendor}=="0x1028"
    ATTRS{vendor}=="0x8086"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{power/async}=="enabled"
    ATTRS{power/control}=="auto"
    ATTRS{power/runtime_active_kids}=="7"
    ATTRS{power/runtime_active_time}=="0"
    ATTRS{power/runtime_enabled}=="disabled"
    ATTRS{power/runtime_status}=="unsupported"
    ATTRS{power/runtime_suspended_time}=="0"
    ATTRS{power/runtime_usage}=="0"
```

```
$ udevadm info -q all --path=/sys/bus/pci/devices/0000:00:13.0/ata1
P: /devices/pci0000:00/0000:00:13.0/ata1
```

```
$ udevadm info -a --path=/sys/bus/pci/devices/0000:00:13.0/ata1

Udevadm info starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.

  looking at device '/devices/pci0000:00/0000:00:13.0/ata1':
    KERNEL=="ata1"
    SUBSYSTEM==""
    DRIVER==""
    ATTR{power/async}=="enabled"
    ATTR{power/control}=="auto"
    ATTR{power/runtime_active_kids}=="1"
    ATTR{power/runtime_active_time}=="1422356"
    ATTR{power/runtime_enabled}=="enabled"
    ATTR{power/runtime_status}=="active"
    ATTR{power/runtime_suspended_time}=="0"
    ATTR{power/runtime_usage}=="0"

  looking at parent device '/devices/pci0000:00/0000:00:13.0':
    KERNELS=="0000:00:13.0"
    SUBSYSTEMS=="pci"
    DRIVERS=="ahci"
    ATTRS{ari_enabled}=="0"
    ATTRS{broken_parity_status}=="0"
    ATTRS{class}=="0x010601"
    ATTRS{consistent_dma_mask_bits}=="64"
    ATTRS{d3cold_allowed}=="1"
    ATTRS{device}=="0x22a3"
    ATTRS{devspec}==""
    ATTRS{dma_mask_bits}=="64"
    ATTRS{driver_override}=="(null)"
    ATTRS{enable}=="1"
    ATTRS{irq}=="117"
    ATTRS{local_cpulist}=="0-3"
    ATTRS{local_cpus}=="f"
    ATTRS{msi_bus}=="1"
    ATTRS{msi_irqs/117}=="msi"
    ATTRS{numa_node}=="-1"
    ATTRS{power/async}=="enabled"
    ATTRS{power/control}=="auto"
    ATTRS{power/runtime_active_kids}=="1"
    ATTRS{power/runtime_active_time}=="1425793"
    ATTRS{power/runtime_enabled}=="enabled"
    ATTRS{power/runtime_status}=="active"
    ATTRS{power/runtime_suspended_time}=="0"
    ATTRS{power/runtime_usage}=="1"
    ATTRS{power/wakeup}=="disabled"
    ATTRS{power/wakeup_abort_count}==""
    ATTRS{power/wakeup_active}==""
    ATTRS{power/wakeup_active_count}==""
    ATTRS{power/wakeup_count}==""
    ATTRS{power/wakeup_expire_count}==""
    ATTRS{power/wakeup_last_time_ms}==""
    ATTRS{power/wakeup_max_time_ms}==""
    ATTRS{power/wakeup_prevent_sleep_time_ms}==""
    ATTRS{power/wakeup_total_time_ms}==""
    ATTRS{revision}=="0x35"
    ATTRS{subsystem_device}=="0x074d"
    ATTRS{subsystem_vendor}=="0x1028"
    ATTRS{vendor}=="0x8086"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{power/async}=="enabled"
    ATTRS{power/control}=="auto"
    ATTRS{power/runtime_active_kids}=="7"
    ATTRS{power/runtime_active_time}=="0"
    ATTRS{power/runtime_enabled}=="disabled"
    ATTRS{power/runtime_status}=="unsupported"
    ATTRS{power/runtime_suspended_time}=="0"
    ATTRS{power/runtime_usage}=="0"
```