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    Subject[PATCH] ftrace: Add debug_print trace to print data from kernel to userspace
    Date
    The trace add a new interface dp_printk() which can be used
    to dump data from kernel to user space using ftrace framework.

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

    ---
    include/linux/debug_print.h | 12 +++++
    kernel/trace/Kconfig | 7 +++
    kernel/trace/Makefile | 1 +
    kernel/trace/trace_debugprint.c | 90 +++++++++++++++++++++++++++++++++++++++
    4 files changed, 110 insertions(+), 0 deletions(-)

    diff --git a/include/linux/debug_print.h b/include/linux/debug_print.h
    new file mode 100644
    index 0000000..db4397b
    --- /dev/null
    +++ b/include/linux/debug_print.h
    @@ -0,0 +1,12 @@
    +#ifndef _LINUX_DEBUGPRINT_H
    +#define _LINUX_DEBUGPRINT_H
    +#include <linux/marker.h>
    +
    +#ifdef CONFIG_DEBUG_PRINT
    +extern int do_dp_printk(const char *fmt, ...);
    +#define dp_printk(fmt, arg...) \
    + do_dp_printk(fmt, ##arg)
    +#else
    +#define dp_printk(fmt, arg...)
    +#endif
    +#endif /* _LINUX_DEBUGPRINT_H */
    diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
    index 9c89526..30eccc8 100644
    --- a/kernel/trace/Kconfig
    +++ b/kernel/trace/Kconfig
    @@ -254,4 +254,11 @@ config FTRACE_STARTUP_TEST
    functioning properly. It will do tests on all the configured
    tracers of ftrace.

    +config DEBUG_PRINT
    + bool "Trace based printk support"
    + depends on DEBUG_KERNEL
    + select TRACING
    + help
    + This tracer can be used for printk style debugging.
    +
    endmenu
    diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
    index 1a8c925..86e5869 100644
    --- a/kernel/trace/Makefile
    +++ b/kernel/trace/Makefile
    @@ -31,5 +31,6 @@ obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
    obj-$(CONFIG_BOOT_TRACER) += trace_boot.o
    obj-$(CONFIG_FUNCTION_RET_TRACER) += trace_functions_return.o
    obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
    +obj-$(CONFIG_DEBUG_PRINT) += trace_debugprint.o

    libftrace-y := ftrace.o
    diff --git a/kernel/trace/trace_debugprint.c b/kernel/trace/trace_debugprint.c
    new file mode 100644
    index 0000000..2c3ac3d
    --- /dev/null
    +++ b/kernel/trace/trace_debugprint.c
    @@ -0,0 +1,90 @@
    +/*
    + * Copyright IBM Corporation, 2008
    + * Author Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    + *
    + * This program is free software; you can redistribute it and/or modify it
    + * under the terms of version 2.1 of the GNU Lesser General Public License
    + * as published by the Free Software Foundation.
    + *
    + * This program is distributed in the hope that it would be useful, but
    + * WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    + *
    + */
    +
    +#include <linux/module.h>
    +#include <linux/fs.h>
    +#include <linux/debugfs.h>
    +#include <linux/ftrace.h>
    +
    +#include "trace.h"
    +
    +static int __read_mostly dp_tracer_enabled;
    +
    +int do_dp_printk(const char *fmt, ...)
    +{
    + int ret;
    + va_list args;
    +
    + if (!dp_tracer_enabled)
    + return 0;
    +
    + va_start(args, fmt);
    + ret = trace_vprintk(0, fmt, args);
    + va_end(args);
    + return ret;
    +}
    +EXPORT_SYMBOL(do_dp_printk);
    +
    +static void dp_reset(struct trace_array *tr)
    +{
    + int cpu;
    +
    + tr->time_start = ftrace_now(tr->cpu);
    +
    + for_each_online_cpu(cpu)
    + tracing_reset(tr, cpu);
    +}
    +
    +static void dp_trace_start(struct trace_array *tr)
    +{
    + dp_reset(tr);
    + dp_tracer_enabled = 1;
    +}
    +
    +static void dp_trace_stop(struct trace_array *tr)
    +{
    + dp_tracer_enabled = 0;
    + /* Nothing to do! */
    +}
    +
    +static void dp_trace_init(struct trace_array *tr)
    +{
    + /*
    + * enable the trace during init if
    + * we have enabled flag already set
    + */
    + if (tracing_is_enabled())
    + dp_trace_start(tr);
    +}
    +
    +static void dp_trace_reset(struct trace_array *tr)
    +{
    + if (dp_tracer_enabled)
    + dp_trace_stop(tr);
    +}
    +
    +struct tracer dp_trace __read_mostly =
    +{
    + .name = "debug_print",
    + .init = dp_trace_init,
    + .reset = dp_trace_reset,
    + .start = dp_trace_start,
    + .stop = dp_trace_stop,
    +};
    +
    +__init static int init_dp_trace(void)
    +{
    + return register_tracer(&dp_trace);
    +}
    +device_initcall(init_dp_trace);
    --
    tg: (bfb3409..) an/ftrace-dp-printk.patch (depends on: an/ftrace-dump-iterator.patch)

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