Looking for system calls implementation on linux kernel

Question

I'm looking for the implementations of open(), close(), write() and unlink(), but I can't find them anywhere! Every function I find is like sys_open, do_open, etc_open... but nothing with the interface we use. Can you help me?

I need to discover what kind of security checks they make

Answer 1

If you mean the library calls such as those found in fcntl.h, they're not part of the kernel, they're part of glibc.

If you are referring to the actual kernel calls, the system call xyzzy is usually handled by the function sys_xyzzy.

The entry.S file, at least in 2.4 (I haven't looked at later kernels), held a table mapping system call numbers to functions:

.data
  ENTRY(sys_call_table)
      .long SYMBOL_NAME(sys_ni_syscall)       /* 0  -  old "setup()" system call*/
      .long SYMBOL_NAME(sys_exit)
      .long SYMBOL_NAME(sys_fork)
      .long SYMBOL_NAME(sys_read)
      .long SYMBOL_NAME(sys_write)
      .long SYMBOL_NAME(sys_open)             /* 5 */
      .long SYMBOL_NAME(sys_close)
      .long SYMBOL_NAME(sys_waitpid)
      .long SYMBOL_NAME(sys_creat)
      .long SYMBOL_NAME(sys_link)
      .long SYMBOL_NAME(sys_unlink)           /* 10 */
      .long SYMBOL_NAME(sys_execve)
      .long SYMBOL_NAME(sys_chdir)
      .long SYMBOL_NAME(sys_time)
      .long SYMBOL_NAME(sys_mknod)
      .long SYMBOL_NAME(sys_chmod)            /* 15 */
        :
      .long SYMBOL_NAME(sys_ni_syscall)       /* sys_remap_file_pages */
      .long SYMBOL_NAME(sys_ni_syscall)       /* sys_set_tid_address */

KernelGrok seems to have a useful page showing the system calls, their names, parameters, and where to find the source. For example (slightly reformatted):

  0   sys_restart_syscall
      eax = 0x00
      kernel/signal.c:2058
  1   sys_exit
      eax = 0x01
      ebx = int error_code
      kernel/exit.c:1046
  2   sys_fork
      eax = 0x02
      ebx = struct pt_regs *
      arch/alpha/kernel/entry.S:716
  3   sys_read
      eax = 0x03
      ebx = unsigned int fd
      ecx = char __user *buf
      edx = size_t count
      fs/read_write.c:391
  4   sys_write
      eax = 0x04
      ebx = unsigned int fd
      ecx = const char __user *buf
      edx = size_t count
      fs/read_write.c:408
  :

and so on. But, being old school, I prefer to keep kernel sources local and just use grep :-)