Re: [PATCH] kernel/itimer.c: for return value, using -EINVAL insteadof -EFAULT
From: Thomas Gleixner
Date: Thu Jun 20 2013 - 03:44:12 EST
On Thu, 20 Jun 2013, Chen Gang wrote:
> On 06/20/2013 02:59 PM, Thomas Gleixner wrote:
> > On Thu, 20 Jun 2013, Chen Gang wrote:
> >> > For the system call getitimer(), if the parameter 'value' is NULL, need
> >> > return -EINVAL, not -EFAULT.
> > Care to explain why? Because you are feeling so?
> I am not feeling so, the original implementation really just checks the parameter 'value', if it is invalid, need return, is it incorrect ??
> > I recommend reading the man page of getitimer:
> > ERRORS
> > EFAULT new_value, old_value, or curr_value is not valid a pointer.
> > And NULL is definitely NOT a valid pointer.
> > The Posix spec does not specify an explicit error value for this
> > syscall, but the general policy is:
> > [EFAULT]
> > Bad address. The system detected an invalid address in attempting
> > to use an argument of a call. The reliable detection of this error
> > cannot be guaranteed, and when not detected may result in the
> > generation of a signal, indicating an address violation, which is
> > sent to the process.
> > And we made use of this, which is correct and makes sense.
> > Returning EINVAL makes no sense at all, because EINVAL _IS_ a
> > specified error code for this syscall:
> > [EINVAL]
> > The which argument is not recognized.
> That means we need not check the parameter 'value' out side of copy_to_user().
We could do that, but that makes no sense. If we can detect it before
copy_to_user() we can return the exactly same return value which we
would return via copy_to_user(). That avoids to take a trap and run
through the fixup code.
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