root/lib/syscall.c

DEFINITIONS

1. collect_syscall
2. task_current_syscall

#include <linux/ptrace.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <asm/syscall.h>

static int collect_syscall(struct task_struct *target, long *callno,
                           unsigned long args[6], unsigned int maxargs,
                           unsigned long *sp, unsigned long *pc)
{
        struct pt_regs *regs = task_pt_regs(target);
        if (unlikely(!regs))
                return -EAGAIN;

        *sp = user_stack_pointer(regs);
        *pc = instruction_pointer(regs);

        *callno = syscall_get_nr(target, regs);
        if (*callno != -1L && maxargs > 0)
                syscall_get_arguments(target, regs, 0, maxargs, args);

        return 0;
}

/**
 * task_current_syscall - Discover what a blocked task is doing.
 * @target:             thread to examine
 * @callno:             filled with system call number or -1
 * @args:               filled with @maxargs system call arguments
 * @maxargs:            number of elements in @args to fill
 * @sp:                 filled with user stack pointer
 * @pc:                 filled with user PC
 *
 * If @target is blocked in a system call, returns zero with *@callno
 * set to the the call's number and @args filled in with its arguments.
 * Registers not used for system call arguments may not be available and
 * it is not kosher to use &struct user_regset calls while the system
 * call is still in progress.  Note we may get this result if @target
 * has finished its system call but not yet returned to user mode, such
 * as when it's stopped for signal handling or syscall exit tracing.
 *
 * If @target is blocked in the kernel during a fault or exception,
 * returns zero with *@callno set to -1 and does not fill in @args.
 * If so, it's now safe to examine @target using &struct user_regset
 * get() calls as long as we're sure @target won't return to user mode.
 *
 * Returns -%EAGAIN if @target does not remain blocked.
 *
 * Returns -%EINVAL if @maxargs is too large (maximum is six).
 */
int task_current_syscall(struct task_struct *target, long *callno,
                         unsigned long args[6], unsigned int maxargs,
                         unsigned long *sp, unsigned long *pc)
{
        long state;
        unsigned long ncsw;

        if (unlikely(maxargs > 6))
                return -EINVAL;

        if (target == current)
                return collect_syscall(target, callno, args, maxargs, sp, pc);

        state = target->state;
        if (unlikely(!state))
                return -EAGAIN;

        ncsw = wait_task_inactive(target, state);
        if (unlikely(!ncsw) ||
            unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
            unlikely(wait_task_inactive(target, state) != ncsw))
                return -EAGAIN;

        return 0;
}
EXPORT_SYMBOL_GPL(task_current_syscall);