linux-kernel - Re: [PATCH-ugly] kmemtrace: casting a gfp_t requires _

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Message-ID: <20081107232535.GA3869@x200.localdomain>
Date:	Sat, 8 Nov 2008 02:25:35 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Cc:	Harvey Harrison <harvey.harrison@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH-ugly] kmemtrace: casting a gfp_t requires __force

On Sat, Nov 08, 2008 at 12:50:16AM +0200, Eduard - Gabriel Munteanu wrote:
> On Fri, Nov 07, 2008 at 10:20:29PM +0300, Alexey Dobriyan wrote:
> > On Fri, Nov 07, 2008 at 10:58:41AM -0800, Harvey Harrison wrote:
> > > --- a/include/linux/kmemtrace.h
> > > +++ b/include/linux/kmemtrace.h
> > > @@ -34,7 +34,7 @@ static inline void kmemtrace_mark_alloc_node(enum kmemtrace_type_id type_id,
> > >  		   "bytes_req %lu bytes_alloc %lu gfp_flags %lu node %d",
> > >  		   type_id, call_site, (unsigned long) ptr,
> > >  		   (unsigned long) bytes_req, (unsigned long) bytes_alloc,
> > > -		   (unsigned long) gfp_flags, node);
> > > +		   (__force unsigned long)gfp_flags, node);
> > 
> > gfp_t is "unsigned int" actually. These casts are bogus.
> > 
> > Subject: How do I printk <type> correctly?
> > 
> > If variable is of Type	use	printk format specifier.
> > ---------------------------------------------------------
> > 		int			%d or %x
> > 		unsigned int		%u or %x
> > 		long			%ld ot %lx
> > 		unsigned long		%lu or %lx
> > 		long long		%lld or %llx
> > 		unsigned long long	%llu or %llx
> > 		size_t			%zu or %zx
> > 		ssize_t			%zd or %zx
> > 
> > Raw pointer value SHOULD be printed with %p.
> > 
> > u64 SHOULD be printed with %llu/%llx, (unsigned long long):
> > 
> > 	printk("%llu", (unsigned long long)u64_var);
> > 
> > s64 SHOULD be printed with %lld/%llx, (long long):
> > 
> > 	printk("%lld", (long long)s64_var);
> > 
> > If type is dependent on config option (sector_t), use format specifier
> > of biggest type and explicitly cast to it.
> > 
> > Reminder: sizeof() result is of type size_t.
> > 
> > Thank you for your cooperation.
> 
> Hi,
> 
> Actually, "%zu" was the first thing that crossed my mind too. But we
> don't want to carry such types into the probe callbacks. It's a lot
> easier to see which u* an unsigned long fits into than it is for
> size_t. So we take care of this inside a wrapper; the sooner, the better.

Format specifiers are apparently hard.

> Also take into account that debugging code usually casts pointers to
> unsigned long. This can easily be seen by looking at _RET_IP_ definition
> or SLAB code.

You got "const void *" in this wrapper.

> I think there's a very good reason to do so, since it adds
> opacity to something that's not supposed to be used as a pointer.

What is not supposed to be used as pointer? _RET_IP_?
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