1-line Summary: Some laptops don't have a disk activity LED, and that just won't do! This project aims to reuse an existing LED as a disk activity indicator.
NOTE ! Specifically coded to support a Lenovo (IBM) Thinkpad T460 laptop; we use the Power LED #0 as the disk activity LED.
I got the idea when reading a reddit post talking about similar stuff [3].
Hey, check out the YouTube video screencast for diskled here!
We'd like to simulate this using software, and an LED on the laptop that we do have control over (eg., the Power Led #0 over the procfs interface; details below).
A REQUEST
Pl try this on a similar laptop and let me know if it works, or what your experience is.
HOWTO: TRY IT
- git clone (or git pull)
- cd [diskled-folder]
- make
- ./diskled.sh
Theory of Operation
We require a source for disk IO activity; we use /proc/diskstats . Eg.
$ cat /proc/diskstats
8 0 sda 40565749 1001718 918480123 318424600 12437524 6232361 260453890 2635848839 **4** 193643664 2954393124
8 1 sda1 554 774 12711 7291 2 0 2 196 0 6616 7487
8 2 sda2 145 0 12432 2659 0 0 0 0 0 2192 2659
[...]
$
The first line is all we capture; the fields in the first line are:
Device major#, device minor#, device name,
reads: completed, merged, sectors read, ms spent reading,
writes: completed, merged, sectors written, ms spent writing,
**ios_in_progress**, ios ms total, ios ms weighted.
Details: see [1]
The important field for us is the "ios_in_progress"; it's the only field that is not cumulative and could go to zero. It's an indication of the current number of IOs in progress. So, we use it to determine whether to turn On or Off the LED; the way it's currently setup: the 1st parameter to led_putios is the "led_turnon_threshold"; we use the value 2 as of now..
The program is built architected as a producer-consumer model: producer | consumer
- led_getios : the producer: this 'C' code fetches and isolates the 'ios_in_progress' integer, and writes it to stdout followed by a newline '\n'.
- led_putios : the consumer: this 'C' code reads from stdin - thus fetching the output of the producer (the IOs in progress) as it's on the RHS of the pipe - and will switch On/Off the LED based on the value it reads.
Tips:
- to see the actual value of the key variable "ios_in_progress", you can modify the wrapper shell script to run led_putios in verbose mode. Alternatively, and even better, sending SIGUSR1 to the led_putios process (it's PID is displayed), will cause it to toggle the verbosity! Careful- don't do this when it's running in the background, else redirect it's stderr appropriately.
Ref: [1] https://www.kernel.org/doc/Documentation/iostats.txt [2] https://www.kernel.org/doc/Documentation/laptops/thinkpad-acpi.txt [3] https://www.reddit.com/r/linux/comments/25teew/turn_your_scroll_lock_into_disk_activity_indicator/ [4] https://youtu.be/ELmu6sTYD08
- Partially written with StackEdit.*