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looping

Posted on 2012-04-04
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Hi I am writing a kernel module.

I need a continuous loop that will look for tcp traffic and read from skb to store each source ip address from ip_hdr->saddr into an array

I can get it to read packets one at a time but I need it to loop, but when I try to implement a continuous loop the system crashes/hangs.

Can anyone offer any advice/possible fixes?

Cheers
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Question by:codey-06
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by:Anthony2000
ID: 37805980
Here is an example of using a thread in the kernel module.

http://www.scs.ch/~frey/linux/kernelthreads.html

I think your problem might be that your loop is running and using all available kernel/process time. Thus, giving the result of maybe locking up your machine. Is that what is happening?
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by:codey-06
ID: 37806049
Hi yes you are correct, the loop is using up all the kernel resources.  Is there a quick fix?
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by:Anthony2000
ID: 37806134
Have you tried some kind of sleep (I cannot remember the API call). This may give the OS and other processes time to run.
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by:codey-06
ID: 37806580
Thank you. If anyone could offer a bit more help it would be very much appreciated?
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by:sarabande
sarabande earned 250 total points
ID: 37810387
if you added an infinite or time consuming loop into a kernel module that was needed by others you were blocking all those activities dependent on those calls and the system hangs and some processes would crash or fail because of timeouts. so, the first thing you need is to start a thread where you would add the loop and the normal kernel function could proceed. of course you may not create a new thread for every call but use one thread for all requests. in the thread you would run an infinite loop and at end of loop you should add a call to usleep which would make that the thread waits a little and so other processes and threads could be scheduled by the os. the usleep takes microseconds as argument and i would use at least 1000 (1 millisecond) to not slow down the rest of the system cause that also would depend on your other actions made in the loop.

Sara
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by:Anthony2000
Anthony2000 earned 250 total points
ID: 37814353
Here is another related article.

http://www.linuxjournal.com/article/8144
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Anthony2000 earned 250 total points
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Also, if you are not familiar with this book, its also a good reference.

http://lwn.net/Kernel/LDD3/
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by:Anthony2000
ID: 37814383
Also, take a look at the functions:
set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout (signed long timeout);

See chapter 7 of the book link I provided.
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Author Closing Comment

by:codey-06
ID: 37815593
Brilliant thank you
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