[DX010] fix possible cpld race read issue

[qnos]

Why I did it

fix possible cpld race read issue between watchdog and reboot cause process

Work item tracking

• Microsoft ADO (number only):

How I did it

Use flock to limit parallel access to cpld sys file

How to verify it

It can be simulate and verified with following python script

import signal
import subprocess
import threading

exit_flag = False

def run_command(cmd):
    status = True
    result = ""
    try:
        p = subprocess.Popen(
            cmd, shell=True, universal_newlines=True,
stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        raw_data, err = p.communicate()
        if err == '':
            result = raw_data.strip()
    except:
        status = False
    return status, result

def get_cpld_reg_value(getreg_path, register):
    #cmd = "echo {1} > {0}; cat {0}".format(getreg_path, register)
    cmd = "flock {0} -c 'echo {1} > {0}; cat {0}'".format(getreg_path,
register)
    status, result = run_command(cmd)
    return result if status else None

def cpld_read(thread_num, cpld_reg):
    while not exit_flag:
        val
= get_cpld_reg_value("/sys/devices/platform/dx010_cpld/getreg",
cpld_reg)
        print(f"Thread {thread_num}: get cpld reg {cpld_reg}, value
{val}")

def signal_handler(sig, frame):
    global exit_flag
    print("Ctrl+C detected. Quitting...")
    exit_flag = True

if __name__ == '__main__':
    # Register the signal handler for Ctrl+C
    signal.signal(signal.SIGINT, signal_handler)

    t1 = threading.Thread(target=cpld_read, args=(1, '0x103',))
    t2 = threading.Thread(target=cpld_read, args=(2, '0x141',))
    t1.start()
    t2.start()
    t1.join()
    t2.join()

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211

Tested branch (Please provide the tested image version)

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[prgeor]

@qnos please raise a master branch PR

[prgeor]

@qiluo-msft Please merge for 202012

[qiluo-msft]

Is it also applicable to master and recent release branches? why only 202012?

[qnos]

Is it also applicable to master and recent release branches? why only 202012?

Is it also applicable to master and recent release branches? why only 202012?

PR #15371 already been raised for master branch.