Re: [RFC PATCH] Propose a new kernel tracing framework

[Jiaying Zhang]

Hi Mathieu,

First, I apologize that I did not forward you my original email. I assumed
that the email would be noticed by interested people when it was sent
to lkml. Now I see that is a mistake.

On Fri, Mar 13, 2009 at 10:04 AM, Mathieu Desnoyers
<mathieu.desnoyers@xxxxxxxxxx> wrote:
> Hi Jiaying,
>
> I'm very interested to hear about the details of your test-case, because
> what you are talking about here, and the numbers that you get, are, at
> the very least, not representative of the current LTTng. Perharps you
> used a version right after the kernel summit and stopped following the
> improvements we have done since then ? I also wonder about the instrumentation
> set you enabled in your tests, and whether it's exactly the same in the ktrace
> and LTTng runs (especially system call tracing). Please note that following the
> Kernel Summit 2008, a more active development cycle began, and the time was not
> right for optimisation. But since then a lot of improvement has been done on
> this side.

Sorry that I omitted a lot of details in my test description. I did use an old
version of LTTng in my tests. The LTTng version I used was the 0.21 lttng
patches for 2.6.27 kernel. I used 2.6.26 kernel in my tests, with the ported
lttng-2.6.27-rc6-0.21 patches.

I enabled the same set of trace events in ktrace and LTTng runs. Here is
the list of enabled events: syscall entry/exit, irq entry/exit, trap
entry/exit,
kernel_sched_switch, kernel_process_fork, kernel_process_wait,
kernel_process_free, kernel_process_exit.

We are glad to see the improvements coming from the LTTng community.
I haven't got time to sync with the latest LTTng code and re-run my tests.
I will let you know when I have such data available.

>
> First I'd like to express my concern about the way you posted your
> numbers :
>
> 1 - You did not CC anyone from the LTTng project.
> 2 - You did not tell which LTTng version you used as a comparison basis.
> 3 - You did not look at the current state of code before posting your
>    comparison. (as shows the comment in your patch header)
That is indeed my mistake.

> 4 - You did not tell the instrumentation set that you enabled from LTTng. Is it
>    the default instrumentation ? Did you also enable system call tracing
>    with your tracer using set_kernel_trace_flag_all_tasks() ? If not, this
>    makes a huge difference on the amount of information gathered.
Yes. We also enable syscall tracing via set_kernel_trace_flag_all_tasks().

>
> So let's have a close look at them. I'm re-doing the benchmarks based on
> the current LTTng version below.
>
>> Hello All,
>>
>> We have been working on building a kernel tracer for a production environment.
>> We first considered to use the existing markers code, but found it a bit
>> heavyweight.
>
> Have you looked at :
>
> 1 - The tracepoints currently in the kernel
> 2 - The _current_ version of markers in the LTTng tree ?

I looked at the tracepoints currently in the kernel. It is great to see that
some trace instrumentation code is finally available in the mainline kernel.
But I still don't like an additional tracepoint layer on top of the
actual tracing
(ktrace or markers or ftrace) layer. That seems to add unnecessary overhead.
The markers code I referred to in my email is the current code in the mainline
kernel. I had a look at the LTTng markers code but still saw that va_list
argument is used in marker_probe_func. It sounds a nice improvement
if the LTTng markers avoids the use of va_arg whenever possible.

>
>>  So we developed a new kernel tracing prototype that shares
>> many similarities as markers but also includes several simplifications that
>> give us considerable performance benefits. For example, we pass the size of
>> trace event directly to the probe function instead of using va_arg as that
>> used in markers, which saves us the overhead of variable passing.
>
> The markers in the LTTng tree only use va_args for "debug-style"
> tracing. All the tracing fast paths are now done with custom probe
> functions which takes the arguments from the tracepoint and write them
> in the trace buffers directly in C. When the event payload size is already
> known statically, there is no dynamic computation cost at all : it's
> simply passed to the ltt-relay write function.
But this raises another concern that sub-system developers may need
to write a bunch of custom probe functions to avoid the argument parsing
overhead. Can you instead have a general probe function or macro that
does this work?

>
>>  Also, we
>> associate a single probe function to each event, so we can directly call the
>> probe function when tracing is enabled.
>
> You seem to imply that being stuck with a single probe function is
> somehow superior to have tiny per-event callbacks which then call into a
> buffer write function ? Why ?
That is indeed my thinking, because we saw that some platforms are
very sensitive to function call overhead and we haven't seen use cases
where multi probe functions prove necessary.

>
>>  Our measurements show that our
>> current tracing prototype introduces much lower overhead compared with
>> lttng (we use lttng as a comparison because markers does not provide the
>> implementation to record trace data).
>
> Why LTTng version, kernel version, LTTng config and runtime options do
> you use ?
See above for LTTng and kernel versions. I was using the default LTTng
config options and 'normal' recorder mode.

>
>> E.g., with dbench, lttng introduces
>> 20~80% overhead on our testing platforms while the overhead with our
>> kernel tracer is within 10%; with tbench, lttng usually adds more than 30%
>> overhead while the overhead added by our kernel tracer is usually within
>> 15%; with kernbench (time to compile a Linux kernel), the overhead
>> added by lttng is around 4%~18% while the overhead added by our
>> kernel tracer is within 2.5%.
>>
>
> I'm re-running the dbench and tbench tests :
>
> With LTTng 0.106, kernel 2.6.29-rc7
> 8-cores Intel(R) Xeon(R) CPU           E5405  @ 2.00GHz, 16GB ram
>
> Arming all the default LTTng instrumentation (168 tracepoints),
> Tracing in flight recorder mode, including system call entry/exit
> tracing and block I/O tracing (blktrace instrumentation), I get :
>
> Test / config    |  Vanilla kernel  |  LTTng 0.106  |  slowdown
> dbench 8 -t 200  |       1361 MB/s  |   1193 MB/s   |    12.3 %
>
> As an example of the effect of custom probe vs va_args based probes,
> let's take the tbench example
>
>                 |     Vanilla      |  LTTng 0.106  |  slowdown
> tbench 8 -t 200  |       2074 MB/s  |     997 MB/s  |      52 %
>
> The LTTng trace statistics shows the top high event rate events :
>
> Some are usual (therefore lttng already implements custom probes for them) :
>
> 42004 sched_try_wakeup
> 79754 timer_set
> 83973 sched_schedule
> 84317 softirq_exit
> 84318 softirq_entry
> 95370 page_free
> 95412 page_alloc
> 267247 syscall_entry
> 267247 syscall_exit
>
> Some are more tbench workload-specific :
>
> 16915 socket_sendmsg
> 18911 napi_complete
> 18911 napi_schedule
> 18912 dev_receive
> 18914 dev_xmit
> 18920 napi_poll
> 33831 socket_recvmsg
> 59860 read
>
>
> So let's see what happens if I implement those as custom probes and do a bit of
> tuning in the tracer hot path :
Could you give more details about the custom probe you used?
Do you need to write a custom probe for each tracepoint?

Jiaying

>
>                 |     Vanilla      |  LTTng 0.107  |  slowdown
> Custom probes :
> tbench 8 -t 200  |       2074 MB/s  |    1275 MB/s  |    38.5 %
>
> With tracer hot path tuning (inline hot path, function calls for slow path, will
> be in 0.108) :
> tbench 8 -t 200  |       2074 MB/s  |    1335 MB/s  |    35.6 %
>
> kernbench :
> Average Optimal load -j 32 Run
>
> Vanilla 2.6.29-rc7 :
> Elapsed Time 48.238 (0.117346)
>
> With flight recorder tracing, default lttng instrumentation, lttng 0.108 :
> Elapsed Time 50.226 (0.0750333)
>
> Slowdown : 4.1 %
>
> So except the tbench workload on LTTng 0.106, which still had a 52% performance
> impact (brought it down to 35 % for the next LTTng release) due to
> specific workload and not having specialized probes implemented, the
> dbench impact is well below your results (12.3 % vs 20-80%)
>
> So given the huge result discrepancies between your tests and mine, could you
> give us more detail about your benchmarks ? Especially knowing the enabled
> instrumentation set, and the amount of MB/s generated by both ktrace and LTTng
> runs (to make sure we are comparing the same traffic) and the LTTng versions you
> are using as a comparison basis would be good.
>
> Thanks,
>
> Mathieu
>
>
>> The patch below is the current prototype we have implemented. It uses
>> Steve's unified trace buffer code with some small extensions to support
>> buffer mmap. The patch is probably still buggy, but we would like to get
>> some early feedback from the community.
>>
>> Signed-off-by: Jiaying Zhang <jiayingz@xxxxxxxxxx>
>>
>> Index: git-linux/init/Kconfig
>> ===================================================================
>> --- git-linux.orig/init/Kconfig 2009-02-19 14:58:37.000000000 -0800
>> +++ git-linux/init/Kconfig      2009-02-19 15:50:15.000000000 -0800
>> @@ -950,6 +950,15 @@
>>          Place an empty function call at each marker site. Can be
>>          dynamically changed for a probe function.
>>
>> +config KTRACE
>> +       bool "Enable ktrace support"
>> +       select DEBUG_FS
>> +       select TRACING
>> +       select RING_BUFFER
>> +       help
>> +         Ktrace is a kernel tracing tool that allows you to trace
>> +         kernel events by inserting trace points at proper places.
>> +
>>  source "arch/Kconfig"
>>
>>  endmenu                # General setup
>> Index: git-linux/kernel/Makefile
>> ===================================================================
>> --- git-linux.orig/kernel/Makefile      2009-02-19 14:58:37.000000000 -0800
>> +++ git-linux/kernel/Makefile   2009-02-19 14:58:39.000000000 -0800
>> @@ -86,6 +86,7 @@
>>  obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o
>>  obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
>>  obj-$(CONFIG_MARKERS) += marker.o
>> +obj-$(CONFIG_KTRACE) += ktrace.o
>>  obj-$(CONFIG_TRACEPOINTS) += tracepoint.o
>>  obj-$(CONFIG_LATENCYTOP) += latencytop.o
>>  obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
>> Index: git-linux/include/asm-generic/vmlinux.lds.h
>> ===================================================================
>> --- git-linux.orig/include/asm-generic/vmlinux.lds.h    2009-02-19
>> 14:58:37.000000000 -0800
>> +++ git-linux/include/asm-generic/vmlinux.lds.h 2009-02-19
>> 14:58:39.000000000 -0800
>> @@ -73,6 +73,9 @@
>>        MEM_KEEP(init.data)                                             \
>>        MEM_KEEP(exit.data)                                             \
>>        . = ALIGN(8);                                                   \
>> +       VMLINUX_SYMBOL(__start___ktraces) = .;                          \
>> +       *(__ktrace)                                                     \
>> +       VMLINUX_SYMBOL(__stop___ktraces) = .;                           \
>>        VMLINUX_SYMBOL(__start___markers) = .;                          \
>>        *(__markers)                                                    \
>>        VMLINUX_SYMBOL(__stop___markers) = .;                           \
>> @@ -89,6 +92,7 @@
>>                VMLINUX_SYMBOL(__start_rodata) = .;                     \
>>                *(.rodata) *(.rodata.*)                                 \
>>                *(__vermagic)           /* Kernel version magic */      \
>> +               *(__ktrace_strings)     /* Ktrace: strings */           \
>>                *(__markers_strings)    /* Markers: strings */          \
>>                *(__tracepoints_strings)/* Tracepoints: strings */      \
>>        }                                                               \
>> Index: git-linux/kernel/module.c
>> ===================================================================
>> --- git-linux.orig/kernel/module.c      2009-02-19 14:58:37.000000000 -0800
>> +++ git-linux/kernel/module.c   2009-02-19 14:58:39.000000000 -0800
>> @@ -50,6 +50,7 @@
>>  #include <asm/sections.h>
>>  #include <linux/tracepoint.h>
>>  #include <linux/ftrace.h>
>> +#include <linux/ktrace.h>
>>  #include <linux/async.h>
>>
>>  #if 0
>> @@ -2145,6 +2146,10 @@
>>                                        sizeof(*mod->tracepoints),
>>                                        &mod->num_tracepoints);
>>  #endif
>> +#ifdef CONFIG_KTRACE
>> +       mod->ktrace = section_objs(hdr, sechdrs, secstrings, "__ktrace",
>> +                               sizeof(*mod->ktrace), &mod->num_ktrace);
>> +#endif
>>
>>  #ifdef CONFIG_MODVERSIONS
>>        if ((mod->num_syms && !mod->crcs)
>> Index: git-linux/include/linux/module.h
>> ===================================================================
>> --- git-linux.orig/include/linux/module.h       2009-02-19
>> 14:58:37.000000000 -0800
>> +++ git-linux/include/linux/module.h    2009-02-19 14:58:39.000000000 -0800
>> @@ -44,6 +44,7 @@
>>  };
>>
>>  struct module;
>> +struct kernel_trace;
>>
>>  struct module_attribute {
>>         struct attribute attr;
>> @@ -347,6 +348,11 @@
>>        /* Reference counts */
>>        struct module_ref ref[NR_CPUS];
>>  #endif
>> +#ifdef CONFIG_KTRACE
>> +       struct kernel_trace *ktrace;
>> +       unsigned int num_ktrace;
>> +#endif
>> +
>>  };
>>  #ifndef MODULE_ARCH_INIT
>>  #define MODULE_ARCH_INIT {}
>> Index: git-linux/include/linux/ktrace.h
>> ===================================================================
>> --- /dev/null   1970-01-01 00:00:00.000000000 +0000
>> +++ git-linux/include/linux/ktrace.h    2009-02-19 15:36:39.000000000 -0800
>> @@ -0,0 +1,83 @@
>> +#ifndef _LINUX_KTRACE_H
>> +#define _LINUX_KTRACE_H
>> +
>> +#include <linux/types.h>
>> +
>> +struct kernel_trace;
>> +
>> +typedef void ktrace_probe_func(struct kernel_trace *, void *, size_t);
>> +
>> +struct kernel_trace {
>> +       const char      *name;
>> +       const char      *format;  /* format string describing variable list */
>> +       size_t          *stroff;  /* offsets of string variables */
>> +       /* 31 bit event_id is converted to 16 bit when entering to the buffer */
>> +       u32             enabled:1, event_id:31;
>> +       ktrace_probe_func *func;  /* probe function */
>> +       struct list_head list;  /* list head linked to the hash table entry */
>> +} __attribute__((aligned(8)));
>> +
>> +extern int ktrace_enabled;
>> +
>> +/*
>> + * Make sure the alignment of the structure in the __ktrace section will
>> + * not add unwanted padding between the beginning of the section and the
>> + * structure. Force alignment to the same alignment as the section start.
>> + */
>> +
>> +#define DEFINE_KTRACE_STRUCT(name)                     \
>> +       struct __attribute__((packed)) ktrace_struct_##name
>> +
>> +#ifdef CONFIG_KTRACE
>> +/*
>> + * DO_TRACE is the macro that is called from each trace point. Each trace
>> + * point is associated with a static ktrace object that is located in a
>> + * special __ktrace section and is uniquely identified by the event name and
>> + * event format. Take a look at the files under include/trace for example
>> + * usage. Note that we call the trace probe function only if the global
>> + * tracing is enabled and the tracing for the associated event is enabled,
>> + * so we only introduce the overhead of a predicted condition judge when
>> + * tracing is disabled.
>> + */
>> +#define DO_TRACE(name, format, args...)
>>          \
>> +       do {                                                            \
>> +               static const char __kstrtab_##name[]                    \
>> +               __attribute__((section("__ktrace_strings")))            \
>> +               = #name "\0" format;                                    \
>> +               static struct kernel_trace __ktrace_##name              \
>> +               __attribute__((section("__ktrace"), aligned(8))) =      \
>> +               { __kstrtab_##name, &__kstrtab_##name[sizeof(#name)],   \
>> +               NULL, 0, 0, NULL, LIST_HEAD_INIT(__ktrace_##name.list) }; \
>> +               __ktrace_check_format(format, ## args);                 \
>> +               if (unlikely(ktrace_enabled) &&                         \
>> +                               unlikely(__ktrace_##name.enabled)) {    \
>> +                       struct ktrace_struct_##name karg = { args };    \
>> +                       (*__ktrace_##name.func)                         \
>> +                       (&__ktrace_##name, &karg, sizeof(karg));        \
>> +               }                                                       \
>> +       } while (0)
>> +
>> +#else /* !CONFIG_KTRACE */
>> +#define DO_TRACE(name, format, args...)
>> +#endif
>> +
>> +/* To be used for string format validity checking with gcc */
>> +static inline void __printf(1, 2) ___ktrace_check_format(const char *fmt, ...)
>> +{
>> +}
>> +
>> +#define __ktrace_check_format(format, args...)                         \
>> +       do {                                                            \
>> +               if (0)                                                  \
>> +                       ___ktrace_check_format(format, ## args);        \
>> +       } while (0)
>> +
>> +
>> +/* get the trace buffer information */
>> +#define KTRACE_BUF_GET_SIZE     _IOR(0xF5, 0x00, __u32)
>> +#define KTRACE_BUF_GET_PRODUCED _IOR(0xF5, 0x01, __u32)
>> +#define KTRACE_BUF_GET_CONSUMED _IOR(0xF5, 0x02, __u32)
>> +#define KTRACE_BUF_PUT_PRODUCED _IOW(0xF5, 0x03, __u32)
>> +#define KTRACE_BUF_PUT_CONSUMED _IOW(0xF5, 0x04, __u32)
>> +
>> +#endif
>> Index: git-linux/kernel/ktrace.c
>> ===================================================================
>> --- /dev/null   1970-01-01 00:00:00.000000000 +0000
>> +++ git-linux/kernel/ktrace.c   2009-02-19 15:45:20.000000000 -0800
>> @@ -0,0 +1,872 @@
>> +/*
>> + * kernel/ktrace.c
>> + *
>> + * Implementation of the kernel tracing for linux kernel 2.6.
>> + *
>> + * Copyright 2008- Google Inc.
>> + * Original Author: Jiaying Zhang
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/kernel.h>
>> +#include <linux/bitmap.h>
>> +#include <linux/poll.h>
>> +#include <linux/errno.h>
>> +#include <linux/sched.h>
>> +#include <linux/linkage.h>
>> +#include <linux/debugfs.h>
>> +#include <linux/timer.h>
>> +#include <linux/delay.h>
>> +#include <linux/jhash.h>
>> +#include <linux/ctype.h>
>> +#include <linux/namei.h>
>> +#include <linux/ktrace.h>
>> +#include <linux/ring_buffer.h>
>> +
>> +static char *ktrace_version = "1.0.0";
>> +int ktrace_enabled;
>> +EXPORT_SYMBOL(ktrace_enabled);
>> +static uint16_t ktrace_next_id;
>> +
>> +extern struct kernel_trace __start___ktraces[];
>> +extern struct kernel_trace __stop___ktraces[];
>> +
>> +static DEFINE_MUTEX(ktrace_mutex);
>> +
>> +/* ktrace hash table entry structure and variables */
>> +struct ktrace_entry {
>> +       struct hlist_node       hlist;
>> +       char                    *name;
>> +       char                    *format;
>> +       size_t                  *stroff;
>> +       ktrace_probe_func       *func;
>> +       u32                     enabled:1, event_id:31;
>> +       struct list_head        klist;  /* list of loaded ktraces */
>> +};
>> +
>> +#define KTRACE_HASH_BITS 6
>> +#define KTRACE_HASH_SIZE (1 << KTRACE_HASH_BITS)
>> +static struct hlist_head ktrace_table[KTRACE_HASH_SIZE];
>> +
>> +/* debugfs directory variables */
>> +static struct dentry *tracedir;
>> +static struct dentry *eventdir;
>> +typedef void tracecontrol_handle_func(struct file *, unsigned long, size_t *);
>> +
>> +/* ring buffer code */
>> +static unsigned long trace_buf_size = 65536UL;
>> +struct ring_buffer *trace_buffer;
>> +static DECLARE_WAIT_QUEUE_HEAD(trace_wait); /* waitqueue for trace_data_poll */
>> +static struct timer_list trace_timer; /* reader wake-up timer */
>> +#define TRACEREAD_WAKEUP_INTERVAL      1000  /* time interval in jiffies */
>> +static struct kref ktrace_kref;
>> +
>> +static void
>> +ring_buffer_probe(struct kernel_trace *kt, void *data, size_t event_size)
>> +{
>> +       struct ring_buffer_event *event;
>> +       void *trace_event;
>> +       unsigned long flag;
>> +
>> +       event = ring_buffer_lock_reserve(trace_buffer,
>> +                       sizeof(uint16_t) + event_size, &flag);
>> +       if (!event)
>> +               return;
>> +       trace_event = ring_buffer_event_data(event);
>> +       *(uint16_t *) trace_event = (uint16_t) kt->event_id;
>> +       memcpy(trace_event + sizeof(uint16_t), data, event_size);
>> +       ring_buffer_unlock_commit(trace_buffer, event, flag);
>> +}
>> +
>> +/* special probe function for events that contain string arguments */
>> +static void
>> +string_probe(struct kernel_trace *kt, void *data, size_t event_size)
>> +{
>> +       struct ring_buffer_event *event;
>> +       void *trace_event, *p;
>> +       unsigned long flag;
>> +       size_t *offset, scanned;
>> +       char *string;
>> +
>> +       /*
>> +        * Get the real length of the event, i.e., we use stroff array to
>> +        * locate string variables in the passed-in trace data and use their
>> +        * length to replace the size of the string pointers.
>> +        */
>> +       for (offset = kt->stroff; *offset != -1; offset++) {
>> +               string = *(char **) (data + *offset);
>> +               event_size += strlen(string) + 1 - sizeof(char *);
>> +       }
>> +       event = ring_buffer_lock_reserve(trace_buffer,
>> +                       sizeof(uint16_t) + event_size, &flag);
>> +       if (!event)
>> +               return;
>> +       trace_event = ring_buffer_event_data(event);
>> +       *(uint16_t *) trace_event = (uint16_t) kt->event_id;
>> +       p = trace_event + sizeof(uint16_t);
>> +       /*
>> +        * Copy the trace data into buffer. For string variables, we enter the
>> +        * string into the buffer. Otherwise, the passed in data is copied.
>> +        */
>> +       for (offset = kt->stroff, scanned = 0; *offset != -1; offset++) {
>> +               memcpy(p, data + scanned, *offset - scanned);
>> +               p += *offset - scanned;
>> +               string = *(char **) (data + *offset);
>> +               memcpy(p, string, strlen(string) + 1);
>> +               p += strlen(string) + 1;
>> +               scanned = *offset + sizeof(char *);
>> +       }
>> +       memcpy(p, data + scanned,
>> +                       trace_event + sizeof(uint16_t) + event_size - p);
>> +       ring_buffer_unlock_commit(trace_buffer, event, flag);
>> +}
>> +
>> +/* timer function used to defer ring buffer reader waking */
>> +static void wakeup_readers(unsigned long data)
>> +{
>> +       if (trace_buffer && !ring_buffer_empty(trace_buffer))
>> +               wake_up_interruptible(&trace_wait);
>> +       mod_timer(&trace_timer, jiffies + TRACEREAD_WAKEUP_INTERVAL);
>> +}
>> +
>> +/* function for reading ktrace metadata info */
>> +static void *tracing_info_start(struct seq_file *seq, loff_t *pos)
>> +{
>> +       seq_printf(seq, "version %s\n", ktrace_version);
>> +       return (*pos >= KTRACE_HASH_SIZE) ? NULL : &ktrace_table[*pos];
>> +}
>> +
>> +static void *tracing_info_next(struct seq_file *seq, void *v, loff_t *pos)
>> +{
>> +       ++*pos;
>> +       return (*pos >= KTRACE_HASH_SIZE) ? NULL : &ktrace_table[*pos];
>> +}
>> +
>> +static int tracing_info_show(struct seq_file *seq, void *v)
>> +{
>> +       struct hlist_head *head = v;
>> +       struct hlist_node *node;
>> +       struct ktrace_entry *entry;
>> +       hlist_for_each_entry(entry, node, head, hlist)
>> +               seq_printf(seq, "name '%s' format '%s' id %u %s\n",
>> +                       entry->name, entry->format, entry->event_id,
>> +                       entry->enabled ? "enabled" : "disabled");
>> +       return 0;
>> +}
>> +
>> +static void tracing_info_stop(struct seq_file *seq, void *v)
>> +{
>> +}
>> +
>> +static const struct seq_operations tracing_info_seq_ops = {
>> +       .start  = tracing_info_start,
>> +       .next   = tracing_info_next,
>> +       .show   = tracing_info_show,
>> +       .stop   = tracing_info_stop,
>> +};
>> +
>> +static int tracing_info_open(struct inode *inode, struct file *file)
>> +{
>> +       return seq_open(file, &tracing_info_seq_ops);
>> +}
>> +
>> +static const struct file_operations traceinfo_file_operations = {
>> +       .open   = tracing_info_open,
>> +       .read   = seq_read,
>> +       .llseek = seq_lseek,
>> +       .release = seq_release,
>> +};
>> +
>> +/*
>> + * wrapper function used by debugfs write operation.
>> + * func: handling function that does real work
>> + */
>> +static ssize_t trace_debugfs_write(struct file *filp, const char __user *ubuf,
>> +               size_t cnt, loff_t *ppos, tracecontrol_handle_func *func)
>> +{
>> +       int ret;
>> +       char buf[64];
>> +       unsigned long val;
>> +
>> +       if (cnt >= sizeof(buf))
>> +               return -EINVAL;
>> +       if (copy_from_user(&buf, ubuf, cnt))
>> +               return -EFAULT;
>> +       buf[cnt] = 0;
>> +
>> +       ret = strict_strtoul(buf, 10, &val);
>> +       if (ret < 0)
>> +               return ret;
>> +       val = !!val;
>> +
>> +       func(filp, val, &cnt);
>> +
>> +       filp->f_pos += cnt;
>> +       return cnt;
>> +}
>> +
>> +/* functions for reading/writing the global 'enabled' control file */
>> +static ssize_t tracing_control_read(struct file *filp, char __user *ubuf,
>> +               size_t cnt, loff_t *ppos)
>> +{
>> +       int ret;
>> +       char buf[64];
>> +       ret = snprintf(buf, 64, "%u\n", ktrace_enabled);
>> +       return simple_read_from_buffer(ubuf, cnt, ppos, buf, ret);
>> +}
>> +
>> +static void __tracing_control_write(struct file *filp,
>> +               unsigned long val, size_t *cnt)
>> +{
>> +       if (val ^ ktrace_enabled) {
>> +               if (val) {
>> +                       trace_timer.expires =
>> +                               jiffies + TRACEREAD_WAKEUP_INTERVAL;
>> +                       add_timer(&trace_timer);
>> +                       ktrace_enabled = 1;
>> +               } else {
>> +                       ktrace_enabled = 0;
>> +                       del_timer_sync(&trace_timer);
>> +                       if (trace_buffer && !ring_buffer_empty(trace_buffer))
>> +                               wake_up_interruptible(&trace_wait);
>> +               }
>> +       }
>> +}
>> +
>> +static ssize_t tracing_control_write(struct file *filp, const char
>> __user *ubuf,
>> +               size_t cnt, loff_t *ppos)
>> +{
>> +       return trace_debugfs_write(filp, ubuf, cnt, ppos,
>> +                       __tracing_control_write);
>> +}
>> +
>> +static const struct file_operations tracecontrol_file_operations = {
>> +       .read   = tracing_control_read,
>> +       .write  = tracing_control_write,
>> +};
>> +
>> +/* functions for reading/writing a trace event file */
>> +static int update_ktrace(struct ktrace_entry *entry,
>> +               ktrace_probe_func *func, int enabled)
>> +{
>> +       struct kernel_trace *iter;
>> +       /* no need to update the list if the tracing is not initialized */
>> +       if (!tracedir)
>> +               return 0;
>> +       entry->enabled = enabled;
>> +       entry->func = func;
>> +       list_for_each_entry(iter, &entry->klist, list) {
>> +               iter->stroff = entry->stroff;
>> +               iter->func = func;
>> +               iter->enabled = enabled;
>> +       }
>> +       return 0;
>> +}
>> +
>> +static int ktrace_probe_register(struct ktrace_entry *entry,
>> +               ktrace_probe_func *probefunc)
>> +{
>> +       return update_ktrace(entry, probefunc, 1);
>> +}
>> +
>> +static int ktrace_probe_unregister(struct ktrace_entry *entry)
>> +{
>> +       return update_ktrace(entry, NULL, 0);
>> +}
>> +
>> +static int ktrace_control_open(struct inode *inode, struct file *filp)
>> +{
>> +       filp->private_data = inode->i_private;
>> +       return 0;
>> +}
>> +
>> +static ssize_t ktrace_control_read(struct file *filp, char __user *ubuf,
>> +               size_t cnt, loff_t *ppos)
>> +{
>> +       int ret;
>> +       char buf[64];
>> +       struct ktrace_entry *entry = filp->private_data;
>> +
>> +       ret = snprintf(buf, 64, "%u\n", entry->enabled);
>> +       return simple_read_from_buffer(ubuf, cnt, ppos, buf, ret);
>> +}
>> +
>> +/*
>> + * Check whether the event contains string arguments. Return 0 if not;
>> + * otherwise record the offsets of the string arguments in the ktrace
>> + * structure according to the event format and return 1.
>> + * The offset info is later used to store the string arguments into
>> + * the trace buffer during trace probe.
>> + */
>> +static int contain_string_arguments(struct ktrace_entry *entry)
>> +{
>> +       int count = 0;
>> +       char *fmt;
>> +       int qualifier;          /* 'h', 'l', or 'L' for integer fields */
>> +       size_t offset = 0;
>> +
>> +       for (fmt = strstr(entry->format, "%s"); fmt; fmt = strstr(++fmt, "%s"))
>> +               count++;
>> +       if (!count)
>> +               return 0;
>> +       entry->stroff = kmalloc(sizeof(size_t) * (count + 1), GFP_KERNEL);
>> +       if (!entry->stroff)
>> +               return -ENOMEM;
>> +
>> +       for (fmt = entry->format, count = 0; *fmt ; ++fmt) {
>> +               if (*fmt != '%')
>> +                       continue;
>> +repeat:
>> +               ++fmt;
>> +               switch (*fmt) {
>> +               case '-':
>> +               case '+':
>> +               case ' ':
>> +               case '#':
>> +               case '0':
>> +                       ++fmt;
>> +                       goto repeat;
>> +               }
>> +
>> +               while (isdigit(*fmt))
>> +                       fmt++;
>> +
>> +               /* get the conversion qualifier */
>> +               qualifier = -1;
>> +               if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L') {
>> +                       qualifier = *fmt;
>> +                       ++fmt;
>> +                       if (qualifier == 'l' && *fmt == 'l') {
>> +                               qualifier = 'L';
>> +                               ++fmt;
>> +                       }
>> +               }
>> +
>> +               switch (*fmt) {
>> +               case 'c':
>> +                       offset += sizeof(char);
>> +                       continue;
>> +               case 's':
>> +                       entry->stroff[count] = offset;
>> +                       count++;
>> +                       offset += sizeof(char *);
>> +                       continue;
>> +               case 'p':
>> +                       offset += sizeof(void *);
>> +                       continue;
>> +               case 'd':
>> +               case 'i':
>> +               case 'o':
>> +               case 'u':
>> +               case 'x':
>> +               case 'X':
>> +                       switch (qualifier) {
>> +                       case 'L':
>> +                               offset += sizeof(long long);
>> +                               break;
>> +                       case 'l':
>> +                               offset += sizeof(long);
>> +                               break;
>> +                       case 'h':
>> +                               offset += sizeof(short);
>> +                               break;
>> +                       default:
>> +                               offset += sizeof(int);
>> +                               break;
>> +                       }
>> +                       break;
>> +               default:
>> +                       printk(KERN_WARNING "unknown format '%c'", *fmt);
>> +                       continue;
>> +               }
>> +       }
>> +       entry->stroff[count] = -1;
>> +       return 1;
>> +}
>> +
>> +static void __ktrace_control_write(struct file *filp,
>> +               unsigned long val, size_t *cnt)
>> +{
>> +       struct ktrace_entry *entry = filp->private_data;
>> +       int ret;
>> +
>> +       mutex_lock(&ktrace_mutex);
>> +       if (val ^ entry->enabled) {
>> +               if (val) {
>> +                       ret = contain_string_arguments(entry);
>> +                       if (ret == 0)
>> +                               ktrace_probe_register(entry, ring_buffer_probe);
>> +                       else if (ret > 0)
>> +                               ktrace_probe_register(entry, string_probe);
>> +                       else
>> +                               *cnt = ret;
>> +               } else
>> +                       ktrace_probe_unregister(entry);
>> +       }
>> +       mutex_unlock(&ktrace_mutex);
>> +}
>> +
>> +static ssize_t ktrace_control_write(struct file *filp, const char __user *ubuf,
>> +               size_t cnt, loff_t *ppos)
>> +{
>> +       return trace_debugfs_write(filp, ubuf, cnt, ppos,
>> +                       __ktrace_control_write);
>> +}
>> +
>> +static const struct file_operations ktracecontrol_file_operations = {
>> +       .open   = ktrace_control_open,
>> +       .read   = ktrace_control_read,
>> +       .write  = ktrace_control_write,
>> +};
>> +
>> +/* functions for adding/removing a trace event. Protected by mutex lock.
>> + * Called during initialization or after loading a module */
>> +static struct ktrace_entry *add_ktrace(struct kernel_trace *ktrace)
>> +{
>> +       struct ktrace_entry *entry;
>> +       size_t name_len = strlen(ktrace->name) + 1;
>> +       u32 hash = jhash(ktrace->name, name_len-1, 0);
>> +       struct hlist_head *head;
>> +       struct hlist_node *node;
>> +       struct dentry *dentry;
>> +
>> +       if (!tracedir)
>> +               return 0;
>> +       head = &ktrace_table[hash & ((1 << KTRACE_HASH_BITS)-1)];
>> +       hlist_for_each_entry(entry, node, head, hlist) {
>> +               if (!strcmp(ktrace->name, entry->name)) {
>> +                       if (strcmp(ktrace->format, entry->format)) {
>> +                               printk(KERN_WARNING "the format of tracepoint "
>> +                                       "\'%s\' changes from \'%s\' to \'%s\'."
>> +                                       "Dynamic changing of trace format is "
>> +                                       "not supported yet!\n",
>> +                                       ktrace->name, entry->format,
>> +                                       ktrace->format);
>> +                               return ERR_PTR(-EINVAL);
>> +                       }
>> +                       ktrace->enabled = entry->enabled;
>> +                       ktrace->func = entry->func;
>> +                       ktrace->event_id = entry->event_id;
>> +                       if (list_empty(&entry->klist))
>> +                               goto add_head;
>> +                       list_add_tail(&ktrace->list, &entry->klist);
>> +                       return entry;
>> +               }
>> +       }
>> +       entry = kmalloc(sizeof(struct ktrace_entry), GFP_KERNEL);
>> +       if (!entry)
>> +               return ERR_PTR(-ENOMEM);
>> +       entry->name = kmalloc(name_len, GFP_KERNEL);
>> +       if (!entry->name) {
>> +               kfree(entry);
>> +               return ERR_PTR(-ENOMEM);
>> +       }
>> +       memcpy(entry->name, ktrace->name, name_len);
>> +       if (ktrace->format) {
>> +               size_t format_len = strlen(ktrace->format) + 1;
>> +               entry->format = kmalloc(format_len, GFP_KERNEL);
>> +               if (!entry->format) {
>> +                       kfree(entry->name);
>> +                       kfree(entry);
>> +                       return ERR_PTR(-ENOMEM);
>> +               }
>> +               memcpy(entry->format, ktrace->format, format_len);
>> +       } else
>> +               entry->format = NULL;
>> +       entry->func = ktrace->func;
>> +       entry->enabled = 0;
>> +       ktrace->event_id = entry->event_id = ktrace_next_id++;
>> +       entry->stroff = NULL;
>> +       INIT_LIST_HEAD(&entry->klist);
>> +       hlist_add_head(&entry->hlist, head);
>> +add_head:
>> +       list_add(&ktrace->list, &entry->klist);
>> +       dentry = debugfs_create_file(entry->name, 0660, eventdir,
>> +                               entry, &ktracecontrol_file_operations);
>> +       if (!dentry)
>> +               printk(KERN_WARNING "Couldn't create debugfs '%s' entry\n",
>> +                                                       entry->name);
>> +       return entry;
>> +}
>> +
>> +static int remove_ktrace(struct kernel_trace *ktrace, int free)
>> +{
>> +       struct ktrace_entry *entry;
>> +       size_t name_len = strlen(ktrace->name) + 1;
>> +       u32 hash = jhash(ktrace->name, name_len-1, 0);
>> +       struct hlist_head *head;
>> +       struct hlist_node *node, *temp;
>> +       struct dentry *dentry;
>> +
>> +       if (!tracedir)
>> +               return 0;
>> +       list_del(&ktrace->list);
>> +       head = &ktrace_table[hash & ((1 << KTRACE_HASH_BITS)-1)];
>> +       hlist_for_each_entry_safe(entry, node, temp, head, hlist)
>> +               if (!strcmp(ktrace->name, entry->name)) {
>> +                       if (list_empty(&entry->klist)) {
>> +                               dentry = lookup_one_len(entry->name,
>> +                                       eventdir, strlen(entry->name));
>> +                               if (dentry && !IS_ERR(dentry)) {
>> +                                       debugfs_remove(dentry);
>> +                                       dput(dentry);
>> +                               }
>> +                               entry->enabled = 0;
>> +                               if (free) {
>> +                                       hlist_del(&entry->hlist);
>> +                                       kfree(entry->name);
>> +                                       kfree(entry->format);
>> +                                       kfree(entry->stroff);
>> +                                       kfree(entry);
>> +                               }
>> +                       }
>> +                       return 0;
>> +               }
>> +       return -1;
>> +}
>> +
>> +/* Add/remove tracepoints contained in a module to the ktrace hash table.
>> + * Called at the end of module load/unload. */
>> +static int ktrace_module_notify(struct notifier_block *self,
>> +               unsigned long val, void *data)
>> +{
>> +#ifdef CONFIG_MODULES
>> +       struct kernel_trace *iter;
>> +       struct module *mod = data;
>> +
>> +       if (val != MODULE_STATE_COMING && val != MODULE_STATE_GOING)
>> +               return 0;
>> +       mutex_lock(&ktrace_mutex);
>> +       for (iter = mod->ktrace; iter < mod->ktrace + mod->num_ktrace; iter++)
>> +               if (val == MODULE_STATE_COMING)
>> +                       add_ktrace(iter);
>> +               else
>> +                       remove_ktrace(iter, 0);
>> +       mutex_unlock(&ktrace_mutex);
>> +#endif
>> +       return 0;
>> +}
>> +
>> +static struct notifier_block ktrace_module_nb = {
>> +       .notifier_call  = ktrace_module_notify,
>> +};
>> +
>> +/* functions for user-space programs to read data from tracing buffer */
>> +static int trace_data_open(struct inode *inode, struct file *filp)
>> +{
>> +       filp->private_data = inode->i_private;
>> +       kref_get(&ktrace_kref);
>> +       return 0;
>> +}
>> +
>> +static void release_trace_buffer(struct kref *kref)
>> +{
>> +       ring_buffer_free(trace_buffer);
>> +       trace_buffer = NULL;
>> +}
>> +
>> +static int trace_data_release(struct inode *inode, struct file *filp)
>> +{
>> +       kref_put(&ktrace_kref, release_trace_buffer);
>> +       return 0;
>> +}
>> +
>> +static unsigned int trace_data_poll(struct file *filp, poll_table *poll_table)
>> +{
>> +       struct ring_buffer_per_cpu *cpu_buffer = filp->private_data;
>> +       if (filp->f_mode & FMODE_READ) {
>> +               if (!ring_buffer_per_cpu_empty(cpu_buffer))
>> +                       return POLLIN | POLLRDNORM;
>> +               poll_wait(filp, &trace_wait, poll_table);
>> +               if (!ring_buffer_per_cpu_empty(cpu_buffer))
>> +                       return POLLIN | POLLRDNORM;
>> +       }
>> +       return 0;
>> +}
>> +
>> +static int trace_buf_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>> +{
>> +       struct ring_buffer_per_cpu *cpu_buffer = vma->vm_private_data;
>> +       pgoff_t pgoff = vmf->pgoff;
>> +       struct page *page;
>> +
>> +       if (!trace_buffer)
>> +               return VM_FAULT_OOM;
>> +       page = ring_buffer_get_page(cpu_buffer, pgoff);
>> +       if (page == NULL)
>> +               return VM_FAULT_SIGBUS;
>> +       get_page(page);
>> +       vmf->page = page;
>> +       return 0;
>> +}
>> +
>> +static struct vm_operations_struct trace_data_mmap_ops = {
>> +       .fault = trace_buf_fault,
>> +};
>> +
>> +static int trace_data_mmap(struct file *filp, struct vm_area_struct *vma)
>> +{
>> +       struct ring_buffer_per_cpu *cpu_buffer = filp->private_data;
>> +
>> +       vma->vm_ops = &trace_data_mmap_ops;
>> +       vma->vm_flags |= VM_DONTEXPAND;
>> +       vma->vm_private_data = cpu_buffer;
>> +       return 0;
>> +}
>> +
>> +static int trace_data_ioctl(struct inode *inode, struct file *filp,
>> +               unsigned int cmd, unsigned long arg)
>> +{
>> +       u32 __user *argp = (u32 __user *)arg;
>> +       struct ring_buffer_per_cpu *cpu_buffer = filp->private_data;
>> +
>> +       if (!trace_buffer || !tracedir)
>> +               return -EINVAL;
>> +       switch (cmd) {
>> +       case KTRACE_BUF_GET_SIZE:
>> +       {
>> +               unsigned long bufsize;
>> +               bufsize = ring_buffer_size(trace_buffer);
>> +               return put_user((u32)bufsize, argp);
>> +       }
>> +       case KTRACE_BUF_GET_PRODUCED:
>> +               return put_user(ring_buffer_get_produced(cpu_buffer), argp);
>> +       case KTRACE_BUF_GET_CONSUMED:
>> +               return put_user(ring_buffer_get_consumed(cpu_buffer), argp);
>> +       case KTRACE_BUF_PUT_CONSUMED:
>> +       {
>> +               u32 consumed, consumed_old;
>> +               int ret;
>> +
>> +               ret = get_user(consumed, argp);
>> +               if (ret) {
>> +                       printk(KERN_WARNING
>> +                               "error getting consumed value: %d\n", ret);
>> +                       return ret;
>> +               }
>> +               consumed_old = ring_buffer_get_consumed(cpu_buffer);
>> +               if (consumed == consumed_old)
>> +                       return 0;
>> +               ring_buffer_advance_reader(cpu_buffer, consumed - consumed_old);
>> +               return 0;
>> +       }
>> +       default:
>> +               return -ENOIOCTLCMD;
>> +       }
>> +       return 0;
>> +}
>> +
>> +static const struct file_operations tracedata_file_operations = {
>> +       .open           = trace_data_open,
>> +       .poll           = trace_data_poll,
>> +       .mmap           = trace_data_mmap,
>> +       .ioctl          = trace_data_ioctl,
>> +       .release        = trace_data_release,
>> +};
>> +
>> +/* function to report the number of lost events due to buffer overflow */
>> +static ssize_t trace_overflow_read(struct file *filp, char __user *ubuf,
>> +               size_t cnt, loff_t *ppos)
>> +{
>> +       int ret;
>> +       char buf[64];
>> +       ret = snprintf(buf, 64, "%lu\n", ring_buffer_overruns(trace_buffer));
>> +       return simple_read_from_buffer(ubuf, cnt, ppos, buf, ret);
>> +}
>> +
>> +static const struct file_operations traceoverflow_file_operations = {
>> +       .read           = trace_overflow_read,
>> +};
>> +
>> +/* function to re-initialize trace buffer */
>> +static void __trace_buffer_reset(struct file *filp,
>> +               unsigned long val, size_t *cnt)
>> +{
>> +       if (val && trace_buffer)
>> +               ring_buffer_reset(trace_buffer);
>> +}
>> +
>> +static ssize_t trace_buffer_reset(struct file *filp, const char __user *ubuf,
>> +               size_t cnt, loff_t *ppos)
>> +{
>> +       return trace_debugfs_write(filp, ubuf, cnt, ppos,
>> +                       __trace_buffer_reset);
>> +}
>> +
>> +static const struct file_operations tracereset_file_operations = {
>> +       .write          = trace_buffer_reset,
>> +};
>> +
>> +/*
>> + * We use debugfs for kernel-user communication. All of the control/info
>> + * files are under debugfs/ktrace directory.
>> + */
>> +static int create_debugfs(void)
>> +{
>> +       struct dentry *entry, *bufdir;
>> +       struct ring_buffer_per_cpu *cpu_buffer;
>> +       char *tmpname;
>> +       int cpu;
>> +
>> +       tracedir = debugfs_create_dir("ktrace", NULL);
>> +       if (!tracedir) {
>> +               printk(KERN_WARNING "Couldn't create debugfs directory\n");
>> +               return -ENOMEM;
>> +       }
>> +
>> +       /* 'buffers' is the directory that holds trace buffer debugfs files */
>> +       bufdir = debugfs_create_dir("buffers", tracedir);
>> +       if (!bufdir) {
>> +               printk(KERN_WARNING "Couldn't create 'buffers' directory\n");
>> +               return -ENOMEM;
>> +       }
>> +
>> +       tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
>> +       if (!tmpname)
>> +               return -ENOMEM;
>> +       /* create a debugfs file for each cpu buffer */
>> +       for_each_possible_cpu(cpu) {
>> +               snprintf(tmpname, NAME_MAX, "%s%d", "cpu", cpu);
>> +               cpu_buffer = ring_buffer_cpu(trace_buffer, cpu);
>> +               entry = debugfs_create_file(tmpname, 0440, bufdir, cpu_buffer,
>> +                       &tracedata_file_operations);
>> +               if (!entry) {
>> +                       printk(KERN_WARNING
>> +                               "Couldn't create debugfs \'%s\' entry\n",
>> +                                       tmpname);
>> +                       return -ENOMEM;
>> +               }
>> +       }
>> +       kfree(tmpname);
>> +
>> +       /* the control file for users to enable/disable global tracing. */
>> +       entry = debugfs_create_file("enabled", 0664, tracedir, NULL,
>> +                       &tracecontrol_file_operations);
>> +       if (!entry) {
>> +               printk(KERN_WARNING
>> +                       "Couldn't create debugfs 'enabled' entry\n");
>> +               return -ENOMEM;
>> +       }
>> +
>> +       /*
>> +        * the debugfs file that displays the name, format etc. of every
>> +        * supported trace event. The file is to be used by the user-space
>> +        * trace parser to analyze the collected trace data.
>> +        */
>> +       entry = debugfs_create_file("info", 0444, tracedir, NULL,
>> +                       &traceinfo_file_operations);
>> +       if (!entry) {
>> +               printk(KERN_WARNING "Couldn't create debugfs 'info' entry\n");
>> +               return -ENOMEM;
>> +       }
>> +
>> +       /*
>> +        * the debugfs file that reports the number of events
>> +        * lost due to buffer overflow
>> +        */
>> +       entry = debugfs_create_file("overflow", 0444, tracedir, NULL,
>> +                       &traceoverflow_file_operations);
>> +       if (!entry) {
>> +               printk(KERN_WARNING
>> +                       "Couldn't create debugfs 'overflow' entry\n");
>> +               return -ENOMEM;
>> +       }
>> +
>> +       /* the debugfs file that resets trace buffer upon write */
>> +       entry = debugfs_create_file("reset", 0220, tracedir, NULL,
>> +                       &tracereset_file_operations);
>> +       if (!entry) {
>> +               printk(KERN_WARNING "Couldn't create debugfs 'reset' entry\n");
>> +               return -ENOMEM;
>> +       }
>> +
>> +       /* create the directory that holds the control files for every event */
>> +       eventdir = debugfs_create_dir("events", tracedir);
>> +       if (!eventdir) {
>> +               printk(KERN_WARNING "Couldn't create 'events' directory\n");
>> +               return -ENOMEM;
>> +       }
>> +       return 0;
>> +}
>> +
>> +static void remove_debugfs_file(struct dentry *dir, char *name)
>> +{
>> +       struct dentry *dentry;
>> +       dentry = lookup_one_len(name, dir, strlen(name));
>> +       if (dentry && !IS_ERR(dentry)) {
>> +               debugfs_remove(dentry);
>> +               dput(dentry);
>> +       }
>> +}
>> +
>> +static int remove_debugfs(void)
>> +{
>> +       struct dentry *bufdir;
>> +       char *tmpname;
>> +       int cpu;
>> +
>> +       bufdir = lookup_one_len("buffers", tracedir, strlen("buffers"));
>> +       if (!bufdir || IS_ERR(bufdir))
>> +               return -EIO;
>> +       tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
>> +       if (!tmpname)
>> +               return -ENOMEM;
>> +       for_each_possible_cpu(cpu) {
>> +               snprintf(tmpname, NAME_MAX, "%s%d", "cpu", cpu);
>> +               remove_debugfs_file(bufdir, tmpname);
>> +       }
>> +       kfree(tmpname);
>> +       debugfs_remove(bufdir);
>> +
>> +       remove_debugfs_file(tracedir, "enabled");
>> +       remove_debugfs_file(tracedir, "info");
>> +       debugfs_remove(eventdir);
>> +       debugfs_remove(tracedir);
>> +       return 0;
>> +}
>> +
>> +static int __init init_ktrace(void)
>> +{
>> +       struct kernel_trace *iter;
>> +       int i, err;
>> +
>> +       ktrace_next_id = 0;
>> +       kref_set(&ktrace_kref, 1);
>> +       trace_buffer = ring_buffer_alloc(trace_buf_size, RB_FL_OVERWRITE);
>> +       if (trace_buffer == NULL)
>> +               return -ENOMEM;
>> +       setup_timer(&trace_timer, wakeup_readers, 0);
>> +       for (i = 0; i < KTRACE_HASH_SIZE; i++)
>> +               INIT_HLIST_HEAD(&ktrace_table[i]);
>> +
>> +       mutex_lock(&ktrace_mutex);
>> +       err = create_debugfs();
>> +       if (err != 0)
>> +               goto out;
>> +       for (iter = __start___ktraces; iter < __stop___ktraces; iter++)
>> +               add_ktrace(iter);
>> +       err = register_module_notifier(&ktrace_module_nb);
>> +out:
>> +       mutex_unlock(&ktrace_mutex);
>> +       return err;
>> +}
>> +module_init(init_ktrace);
>> +
>> +static void __exit exit_ktrace(void)
>> +{
>> +       struct kernel_trace *iter;
>> +
>> +       if (ktrace_enabled) {
>> +               ktrace_enabled = 0;
>> +               del_timer_sync(&trace_timer);
>> +       }
>> +       mutex_lock(&ktrace_mutex);
>> +       for (iter = __start___ktraces; iter < __stop___ktraces; iter++)
>> +               remove_ktrace(iter, 1);
>> +       unregister_module_notifier(&ktrace_module_nb);
>> +       remove_debugfs();
>> +       mutex_unlock(&ktrace_mutex);
>> +
>> +       kref_put(&ktrace_kref, release_trace_buffer);
>> +}
>
> --
> Mathieu Desnoyers
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
>
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