Created attachment 1118822 [details]
Simple reproducer that works on my machine for this particular boot.

Description of problem:

udev_device_get_sysattr_value() is defined to return the contents of a sys attr file. In some cases, it doesn't.

Version-Release number of selected component (if applicable):

219

How reproducible:

Consistently, for the particular devices and attributes chosen. It is not clear what it is about the particular attribute file that causes the behavior.

Steps to Reproduce:
1. My reproducer contains two examples of devices that behave differently.
2. Run the reproducer. Note that both devices have vpg_pg83 attribute files that are non-empty (wc claims that both contain characters, and cat echos random glyphs to the terminal in both cases).
3. Note that in one case, the result of calling udev_deivce_get_sysattr_value is the empty string and that in the other case it is a non-empty string.

Actual results:

Inconsistent behavior in reading non-empty vpg_pg83 attribute file for different devices.

Expected results:

Well-documented consistency.

Additional info:

I think this also affects the behavior of udevadm info --attribute-walk for these devices. AFAIU, udevadm is defined not to show binary attributes, restricting itself to those that are matched in udev rules. For the device where the method returns a non-empty string, udevadm does not show a corresponding vpd_pg83 attribute. For the device where the function mistakenly returns an empty string, udevadm does show the attribute, apparently interpreting it, since empty, as matchable text.