How to understand code or programming written for linux hooking system calls?

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C

Linux

I have found materials on how hooking system call is done but the programming done is not understood by me for e.g:

include<ASM / cacheflush.h> 
  #IFDEF KERN_2_6_24 
  #include LT& ASM / semaphore.h> 
  INT set_page_rw (long unsigned integer _addr) 
  { 
  Structure page * Pico; 
  Pgprot_t PROT; 
  PG = virt_to_page(_addr); 
  Prot.pgprot = VM_READ | VM_WRITE; 
  Return change_page_attr(PG,1,PROT); 
  }INT set_page_ro (long unsigned integer _addr) 
  { 
  Structure page * Pico; 
  Pgprot_t PROT; 
  PG = virt_to_page(_addr); 
  Prot.pgprot = VM_READ; 
  Return change_page_attr(PG,1,PROT); 
  }#Other #includes LT& Linux/semaphore.h> 
  INT set_page_rw (long unsigned integer _addr) 
  { 

...etc

most of these functions or any thing is un understand able for me as i am very new to this can any one guide me what are steps i should take to understand this programmatically.

What I have tried:

tried to understand hook system call programs but new to this so not fully understanding what functions are doing..