hi all,
i was reading (nearly) Complete Linux loadable kernel modules
by - Pragmatic /THC Version 1.0 and found the following.
I could understand from the article that whenever system call's are made the arguments
must be in user space.Now filename is declared in Kernel space inside my modules as :
char filename[]="/home/amisim/logger.txt"
extract from the article:
#################################################################
->filename is in our kernel space; a string we just created, for example
unsigned long old_fs_value=get_fs();
1.set_fs(get_ds); /*after this we can access the user space data*/
2.open(filename, O_CREAT|O_RDWR|O_EXCL, 0640);
3.set_fs(old_fs_value); /*restore fs...*/
#################################################################
Now filename is in our kernel space, but after a call to set_fs(get_ds) the system call
works and the system call returns with a fd > 0, how is this working ?
i had tried the code without line numbers 1 and 3 (for testing purposes) but it never worked ??.
My doubts:
1. "filename" is still in kernel space right ??? 2. what happened in line 1 and 3.?
It would be great if someone could throw more light on this.I'am confused :-(.
Thanks for your time.
regards,
Amith.
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