Re: Mystery empty file

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On 6/6/19 13:45, Adam Williamson wrote:
On Thu, 2019-06-06 at 11:15 -0600, Chris Murphy wrote:
On Thu, Jun 6, 2019 at 9:49 AM Richard Ryniker <ryniker@xxxxxxxxxxxx> wrote:
I think you will find the file is not truly empty.  /sys is not an actual
file system, merely an interface to kernel information.  There is no
directory structure that records the length or other attributes of a file,
as is the case for data on real media such as disks.

If you read the /sys/kernel/debug/usb/devices file, you should find the
data you seek.

[root@fmac ~]# ls -l /sys/kernel/debug/usb/devices
-r--r--r--. 1 root root 0 Jun  6 10:11 /sys/kernel/debug/usb/devices
[root@fmac ~]# cat /sys/kernel/debug/usb/devices
cat: /sys/kernel/debug/usb/devices: Operation not permitted
[root@fmac ~]#

5.2.0-0.rc3.git1.1.fc31.x86_64

Try it with enforcing=0 ?


I just tried permissive mode with the same result. I've just looked through of the "files" in debug and they are all empty; so I'm guessing that the kernel folks turned this off.

That's okay, it was a reach given how things have been changing and I wouldn't want to be running in permissive mode to get the info. I hear there is a new interface to get information on connected USB devices that ordinary users can access. I think I will investigate that. Who knows, I may end up writing a little code that someone else might find useful.

Thanks everyone for trying to help.


	Have a Great Day!

	Pat	(tablepc)
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