From: Christian Brauner <christian.brauner@ubuntu.com>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Al Viro <viro@zeniv.linux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
libc-alpha@sourceware.org, linux-api@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper
Date: Fri, 27 Sep 2019 10:20:17 +0200 [thread overview]
Message-ID: <20190927082016.jsis76s26uverj5r@wittgenstein> (raw)
In-Reply-To: <20190927010736.gy3vvvkjhwlybosj@yavin.dot.cyphar.com>
On Fri, Sep 27, 2019 at 11:07:36AM +1000, Aleksa Sarai wrote:
> On 2019-09-26, Christian Brauner <christian.brauner@ubuntu.com> wrote:
> > On Thu, Sep 26, 2019 at 01:03:29AM +0200, Aleksa Sarai wrote:
> > > +int is_zeroed_user(const void __user *from, size_t size)
> > > +{
> > > + unsigned long val;
> > > + uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
> > > +
> > > + if (unlikely(!size))
> > > + return true;
> >
> > You're returning "true" and another implicit boolean with (val == 0)
> > down below but -EFAULT in other places. But that function is int
> > is_zeroed_user() Would probably be good if you either switch to bool
> > is_zeroed_user() as the name suggests or rename the function and have
> > it return an int everywhere.
>
> I just checked, and in C11 (and presumably in older specs) it is
> guaranteed that "true" and "false" from <stdbool.h> have the values 1
> and 0 (respectively) [§7.18]. So this is perfectly well-defined.
>
If you declare a function as returning an int, return ints and don't mix
returning ints and "proper" C boolean types. This:
static int foo()
{
if (bla)
return true;
return -1;
}
is just messy.
>
> Personally, I think it's more readable to have:
>
> if (unlikely(size == 0))
> return true;
> /* ... */
> return (val == 0);
>
> compared to:
>
> if (unlikely(size == 0))
> return 1;
> /* ... */
> return val ? 0 : 1;
Just do:
if (unlikely(size == 0))
return 1;
/* ... */
return (val == 0);
You don't need to change the last return.
Also, as I said in a previous mail: Please wait for rc1 (that's just two
days) to be out so you can base your patchset on that as there are
changes in mainline that cause a merge conflict with your changes.
Thanks!
Christian
next prev parent reply other threads:[~2019-09-27 8:20 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-25 23:03 [PATCH v2 0/4] lib: introduce copy_struct_from_user() helper Aleksa Sarai
2019-09-25 23:03 ` [PATCH v2 1/4] " Aleksa Sarai
2019-09-25 23:07 ` Aleksa Sarai
2019-09-25 23:21 ` Christian Brauner
2019-09-27 1:07 ` Aleksa Sarai
2019-09-27 8:20 ` Christian Brauner [this message]
2019-09-26 5:49 ` kbuild test robot
2019-09-26 12:40 ` Christian Brauner
2019-09-25 23:03 ` [PATCH v2 2/4] clone3: switch to copy_struct_from_user() Aleksa Sarai
2019-09-25 23:03 ` [PATCH v2 3/4] sched_setattr: " Aleksa Sarai
2019-09-25 23:03 ` [PATCH v2 4/4] perf_event_open: " Aleksa Sarai
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