I have been trying to write a new system call(called sys_defclose) in the raspberry's kernel, but upon compiling i get this error:
arch/arm/kernel/built-in.o: In function `__sys_trace_return': :(.text+0xd50): undefined reference to `sys_defclose' i have modified the following file:
-include/linux/syscalls.h : where i put the prototype of my syscall
-arch/arm/include/asm/unistd.h : where i put the new raw of the syscall table:
#define __NR_sys_defclose (__NR_SYSCALL_BASE+380) -arch/arm/kernel/calls.S : where i put:
CALL(sys_defclose) -i put the source of sys_defclose in arch/arm/kernel and i have modified the makefile in the same directory with the new line
obj-y +=sys_defclose.o the kernel version is 3.6 of raspberrypi. can somebody explain me how to solve this error? thanks this is the implementation of my syscall
static struct task_struct* get_task_by_pid(pid_t pid) { return pid_task(find_pid_ns(pid, task_active_pid_ns(current)), PIDTYPE_PID); } static void close_files(struct files_struct * files) { int i, j; struct fdtable *fdt; j = 0; rcu_read_lock(); fdt = files_fdtable(files); rcu_read_unlock(); for (;;) { unsigned long set; i = j * BITS_PER_LONG; if (i >= fdt->max_fds) break; set = fdt->open_fds[j++]; while (set) { if (set & 1) { struct file * file = xchg(&fdt->fd[i], NULL); if (file) { filp_close(file, files); cond_resched(); } } i++; set >>= 1; } } } asmlinkage long sys_defclose(pid_t pid) { struct task_struct *result = NULL; rcu_read_lock(); result = get_task_by_pid(pid); rcu_read_unlock(); close_files(result->files); } 1 Answer
You should use SYSCALL_DEFINE* to define syscall (I think, this step you did wrong), then add your syscall into sys_call_table, which is architecture-dependent (arch/arm/kernel/calls.S for arm).
Change your sys_defclose to look like this:
SYSCALL_DEFINE1(defclose, pid_t, pid) { struct task_struct *result = NULL; rcu_read_lock(); result = get_task_by_pid(pid); rcu_read_unlock(); close_files(result->files); } 
