How do I write a system call in linux that passes string pointers into the kernel and returns an integer value indicating the number of characters printed?

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Hi!

I am already done with simple hello world system call in linux that is when called by user level test program, passes a string to the kernel and kernel returns that string...

But, now I want the kernel to count the string length. I don't have any idea how to do that?

Posted 28-Apr-15 9:13am

keyur_raval

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Richard MacCutchan 28-Apr-15 16:56pm

You need to find a kernel function that provides that feature. Are you sure you mean the kernel, and not the C/C++ library?

keyur_raval 28-Apr-15 16:58pm

yes! I am sure about kernel, not the c/c++ library

keyur_raval 28-Apr-15 17:00pm

Well, it says I need to Modify the "_syscallx" macros found in /usr/include/asm/unistd.h where "x" is the number of parameters to pass into the kernel.
Adn then Use the example "copy_from_user()" to fetch the string from user space into a local buffer.

Richard MacCutchan 28-Apr-15 17:14pm

I've never tried that so cannot suggest anything.

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