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"cat /proc/20502/wchan" vs strace vs man page

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From: Johan Walles <johan.walles@...>
To: <linux-kernel@...>
Subject: "cat /proc/20502/wchan" vs strace vs man page
Date: Monday, September 24, 2007 - 3:54 am

Try this:

1. At one prompt, do "cat".

Now, switch to another prompt and...

2. Do "pstree -p|grep cat" to find out the PID of your cat command.  I

get 20502.

3. Do "cat /proc/20502/wchan".  I get "0" here.

4. Do "strace -p 20502".  I get "read(0,  <unfinished ...>" here.


So wchan says cat is waiting for "0".  Strace says cat is waiting for

read (which sounds much more probable to me).


Is "0" the correct contents of /proc/20502/wchan?  I expected it to

say something about "read".


According to "man proc", wchan "is the "channel" in which the process

is waiting.  It is the address of a system call".  "0" doesn't seem to

fit that description.  Is "0" or the man page wrong?


I'm on Ubuntu 7.04 Feisty, i686, have manpages "2.39-1", kernel "Linux

version 2.6.20-16-generic (root@terranova) (gcc version 4.1.2 (Ubuntu

4.1.2-0ubuntu4)) #2 SMP Fri Aug 31 00:55:27 UTC 2007".


I'm not subscribed to the list, please CC me on replies.


  Cheers //Johan

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Previous thread: [PATCH] include/linux/mutex.h: unclear reference to convention by Matti Linnanvuori on Monday, September 24, 2007 - 3:38 am. (2 messages)

Next thread: What's in mmc.git for 2.6.24 by Pierre Ossman on Monday, September 24, 2007 - 4:28 am. (3 messages)