Re: Why system call need to copy the date from the userspace before using it

[Hacksaw <hacksaw@hacksaw.org>]

Sorry if this bugs anyone, but I'm learning things here.

What I would expect the kernel to do is this:

system_call_data_prep (userdata, size){	

   if !4G/4G {
      for each page from userdata to userdata+size
      {
 	if the page is swapped out, swap it in
	if the page is not owned by the user process, return -ENOWAYMAN
	otherwise, lock the page
      }
      return userdata;
    }
    else { //kernel land and userland are mutually exclusive
	   copy the data into kernel land
	   return kernelland_copy_of_userdata;
          }
}

(And then the syscall would need to run the opposite function 
sys_call_data_unprep to unlock pages.)

Hmm, maybe that interface sucks.

Is it anything close to that? 
   
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