linux-kernel - Re: [PATCH 8/9] trace: use this_cpu

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Message-ID: <5094A2CB.8040208@gmail.com>
Date:	Sat, 03 Nov 2012 12:51:23 +0800
From:	Shan Wei <shanwei88@...il.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	rostedt@...dmis.org, fweisbec@...il.com,
	Kernel-Maillist <linux-kernel@...r.kernel.org>, mingo@...hat.com
Subject: Re: [PATCH 8/9] trace: use this_cpu_ptr per-cpu helper

Christoph Lameter said, at 2012/11/3 1:53:
> 
> hmm.... what is actually returned is a pointer to char right? And buffer
> is char[1024] so I guess then you need to pass a pointer to char to
> this_cpu_read.
> 
> return this_cpu_read(&(percpu_buffer->buffer))
 
still error....

kernel/trace/trace.c: In function 'get_trace_buf':
kernel/trace/trace.c:1517: error: lvalue required as unary '&' operand
kernel/trace/trace.c:1517: warning: type defaults to 'int' in declaration of 'type name'
kernel/trace/trace.c:1517: warning: cast from pointer to integer of different size
kernel/trace/trace.c:1517: warning: return from incompatible pointer type
kernel/trace/trace.c:1498: warning: unused variable 'buffer'
kernel/trace/trace.c:1517: error: memory input 1 is not directly addressable
kernel/trace/trace.c:1517: error: memory input 1 is not directly addressable

this_cpu_read just read the actual value which a pointer point to.
some case, we just need the pointer.
It's better to use this_cpu_ptr.
return (char *)this_cpu_ptr(&percpu_buffer->buffer);

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