How to find system call implementations in Linux/Android 2.6.29?

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http://unix.stackexchange.com – I want to modify some system calls for tracing purposes. To be specific, whenever a system call open is made, I want to print some messages. I have been looking into the internet and the code and I found open.c in kernel/goldfish/fs/ directory. And there are many functions in this file. How would I know which function is being called exactly. I could have written some printk call in all these functions to find it but I have to do it for other system calls also. So, I have a few questions, 1) What is the best way to find implementation details of system calls? 2) I am using Kernel 2.6.29 (HowTos)