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In-Reply-To: <bd1ef99fc503fed492ad036f781963ca15a8596f.camel@perches.com>
From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Mon, 10 Jun 2019 02:19:49 +0900
Message-ID: <CAK7LNAT3iKOX=0GxrB__m9haM=0L+MZQRq_OvFhW5N3iaaBAPA@mail.gmail.com>
Subject: Re: [PATCH] media: do not use C++ style comments in uapi headers
To:     Joe Perches <joe@perches.com>
Cc:     Julia Lawall <julia.lawall@lip6.fr>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Randy Dunlap <rdunlap@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Sun, Jun 9, 2019 at 10:40 PM Joe Perches <joe@perches.com> wrote:
>
> On Sun, 2019-06-09 at 22:08 +0900, Masahiro Yamada wrote:
> > On Sun, Jun 9, 2019 at 8:57 PM Joe Perches <joe@perches.com> wrote:
> > > On Sun, 2019-06-09 at 16:14 +0900, Masahiro Yamada wrote:
> > > > Hi Joe,
> > > >
> > > > On Thu, Jun 6, 2019 at 2:06 AM Joe Perches <joe@perches.com> wrote:
> > > > > Perhaps a checkpatch change too:
> > > > >
> > > > > The first block updates unsigned only bitfields
> > > > > The second tests uapi definitions and suggests "__<kernel_types"
> > > >
> > > > Good.
> > > >
> > > > In addition,
> > > >
> > > > "warn if __u8, __u16, __u32, __u64 are used outside of uapi/"
> > > >
> > > > Lots of kernel-space headers use __u{8,16,32,64} instead of u{8,16,32,64}
> > > > just because developers often miss to understand when to use
> > > > the underscore-prefixed types.
> > >
> > > The problem there is that checkpatch can't know if the
> > > __<uapi_type> being used is for an actual uapi use or not.
> > >
> > > coccinelle could be much better at that.
> >
> > Why?
>
>
> Perhaps it's (somewhat) bad form to have a __uapi type in a
> structure, include that structure in a driver for something
> like a copy_to/from_user, and map the __<uapi_type> to a non
> underscore prefixed <kernel_type>

Linus Torvalds wrote 'sparse' to check this.

Any attempt to distinguish the address-space
by the presence of double-underscore-prefixes is pointless.
This is already checked by __kernel / __user.

It is absolutely correct to assign __u32 to u32, and vice versa.

If you think the following patch is wrong, please tell me why:


diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 748ac489ef7e..24c1b73d9fbd 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1132,7 +1132,7 @@ static struct binder_node *binder_init_node_ilocked(
        struct binder_node *node;
        binder_uintptr_t ptr = fp ? fp->binder : 0;
        binder_uintptr_t cookie = fp ? fp->cookie : 0;
-       __u32 flags = fp ? fp->flags : 0;
+       u32 flags = fp ? fp->flags : 0;

        assert_spin_locked(&proc->inner_lock);

@@ -4918,7 +4918,7 @@ static int
binder_ioctl_get_node_info_for_ref(struct binder_proc *proc,
 {
        struct binder_node *node;
        struct binder_context *context = proc->context;
-       __u32 handle = info->handle;
+       u32 handle = info->handle;

        if (info->strong_count || info->weak_count || info->reserved1 ||
            info->reserved2 || info->reserved3) {


>
> For instance
>
> struct flat_binder_object in drivers/android/binder.c
>
> How is checkpatch supposed to know that __u32 flags is
> inappropriate?
>
>


-- 
Best Regards
Masahiro Yamada