netdev - some question about "/sys/class/net/<iface>/operstate"

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Date:   Wed, 11 Nov 2020 12:31:27 +0800 (GMT+08:00)
From:   杜英杰 <leondyj@....edu.cn>
To:     netdev@...r.kernel.org
Subject: some question about "/sys/class/net/<iface>/operstate"

I want to use inotify to monitor /sys/class/net//operstate  to detect status of a iface in real time. 
when I ifdown &amp;&amp; ifup eth3, the content of operstate changed, but the file's Modify time didn't change. 
I don't know the reason, is there any file which can be monitored by inotify to get iface status in real time? 
Much appreciation for any advice! 


below are my terminal msg:
  
[root@...gjie-4-5-0-20201109195739-1 11:10:39 0000:00:0c.0]$stat /sys/class/net/eth3/operstate 
File: ‘/sys/class/net/eth3/operstate’
Size: 4096            Blocks: 0          IO Block: 4096   regular file
Device: 14h/20d Inode: 25838       Links: 1
Access: (0444/-r--r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2020-11-10 20:42:18.592000969 +0800
Modify: 2020-11-10 20:42:18.592000969 +0800
Change: 2020-11-10 20:42:18.592000969 +0800
Birth: -
[root@...gjie-4-5-0-20201109195739-1 11:10:50 0000:00:0c.0]$cat /sys/class/net/eth3/operstate 
up
You have new mail in /var/spool/mail/root
[root@...gjie-4-5-0-20201109195739-1 11:11:06 0000:00:0c.0]$ifdown eth3
[root@...gjie-4-5-0-20201109195739-1 11:11:13 0000:00:0c.0]$cat /sys/class/net/eth3/operstate 
down
[root@...gjie-4-5-0-20201109195739-1 11:11:16 0000:00:0c.0]$stat /sys/class/net/eth3/operstate 
File: ‘/sys/class/net/eth3/operstate’
Size: 4096            Blocks: 0          IO Block: 4096   regular file
Device: 14h/20d Inode: 25838       Links: 1
Access: (0444/-r--r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2020-11-10 20:42:18.592000969 +0800
Modify: 2020-11-10 20:42:18.592000969 +0800
Change: 2020-11-10 20:42:18.592000969 +0800
Birth: -