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Date: Mon, 25 Oct 2010 13:39:43 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: David Goulet <david.goulet@polymtl.ca>
Cc: Nils Carlson <nils.carlson@ericsson.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        ltt-dev@lists.casi.polymtl.ca
Subject: [RFC] TRACE_EVENT: mapping "=" and memcpy to macros
Message-ID: <20101025173943.GA29970@Krystal>
References: <4CC1BAA1.9070202@polymtl.ca> <913BC6918ED247478A38326BC12AAECE04D399B2@ESESSCMS0358.eemea.ericsson.se> <913BC6918ED247478A38326BC12AAECE04D399CF@ESESSCMS0358.eemea.ericsson.se> <913BC6918ED247478A38326BC12AAECE04D39AD7@ESESSCMS0358.eemea.ericsson.se> <4CC5AA98.7020308@polymtl.ca> <20101025171954.GD11891@Krystal> <4CC5BDC2.9020401@polymtl.ca>
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LTTng needs to override the assignment primitives to deal with cross-page
writes. A first step needed to move LTTng to TRACE_EVENT is to introduce the
following macros:

for ftrace and perf:

#define __assign(dest, src)                  (dest) = (src)
#define __assign_memcpy(dest, src, len)      memcpy(dest, src, len)

which would turn (e.g.)

        TP_fast_assign(
                memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
                __entry->pid    = t->pid;
        ),

into

        TP_fast_assign(
                __assign_memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
                __assign(__entry->pid, t->pid);
        ),

So LTTng (and other tracers) can override these with their own primitives. This
is a basic step required to bring the LTTng tree closer to mainline.

Thoughts ?

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com