suse man page for syscall_set_return_value

SYSCALL_SET_RETURN_V(9) 					   Machine State					   SYSCALL_SET_RETURN_V(9)

NAME
       syscall_set_return_value - change the return value of a traced system call

SYNOPSIS
       void syscall_set_return_value(struct task_struct * task, struct pt_regs * regs, int error, long val);

ARGUMENTS
       task
	   task of interest, must be blocked

       regs

	   task_pt_regs of task

       error
	   negative error code, or zero to indicate success

       val
	   user return value if error is zero

DESCRIPTION
       This changes the results of the system call that user mode will see. If error is zero, the user sees a successful system call with a return
       value of val. If error is nonzero, it's a negated errno code; the user sees a failed system call with this errno code.

       It's only valid to call this when task is stopped for tracing on exit from a system call, due to TIF_SYSCALL_TRACE or TIF_SYSCALL_AUDIT.

Kernel Hackers Manual 2.6.					     July 2010						   SYSCALL_SET_RETURN_V(9)