Impact: improve workqueue tracer output

Currently, /sys/kernel/debug/tracing/trace_stat/workqueues can display
wrong and strange thread names.

Why?

Currently, ftrace has tracing_record_cmdline()/trace_find_cmdline()
convenience function that implements a task->comm string cache.

This can avoid unnecessary memcpy overhead and the workqueue tracer
uses it.

However, in general, any trace statistics feature shouldn't use
tracing_record_cmdline() because trace statistics can display
very old process. Then comm cache can return wrong string because
recent process overrides the cache.

Fortunately, workqueue trace guarantees that displayed processes
are live. Thus we can search comm string from PID at display time.

<before>

% cat workqueues
 # CPU  INSERTED  EXECUTED   NAME
 # |      |         |          |

   7 431913     431913       kondemand/7
   7      0          0       tail
   7     21         21       git
   7      0          0       ls
   7      9          9       cat
   7 832632     832632       unix_chkpwd
   7 236292     236292       ls

Note: tail, git, ls, cat unix_chkpwd are obiously not workqueue thread.

<after>

% cat workqueues
 # CPU  INSERTED  EXECUTED   NAME
 # |      |         |          |

   7    510        510       kondemand/7
   7      0          0       kmpathd/7
   7     15         15       ata/7
   7      0          0       aio/7
   7     11         11       kblockd/7
   7   1063       1063       work_on_cpu/7
   7    167        167       events/7
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

In a recent discussion, Andrew Morton pointed out that tracing header
should put '#' at the beginning of a line.

Then, we can easily filtered the header by following grep usage:

  cat trace | grep -v '^#'

Wakeup trace also has the same header problem.

Comparison of headers displayed:

before this patch:

 # tracer: wakeup
 #
 wakeup latency trace v1.1.5 on 2.6.29-rc7-tip-tip
 --------------------------------------------------------------------
  latency: 19059 us, #21277/21277, CPU#1 | (M:desktop VP:0, KP:0, SP:0 HP:0 #P:4)
     -----------------
     | task: kondemand/1-1644 (uid:0 nice:-5 policy:0 rt_prio:0)
     -----------------

 #                  _------=> CPU#
 #                 / _-----=> irqs-off
 #                | / _----=> need-resched
 #                || / _---=> hardirq/softirq
 #                ||| / _--=> preempt-depth
 #                |||| /
 #                |||||     delay
 #  cmd     pid   ||||| time  |   caller
 #     \   /      |||||   \   |   /
 irqbalan-1887    1d.s.    0us :   1887:120:R   + [001]  1644:115:S kondemand/1
 irqbalan-1887    1d.s.    1us : default_wake_function <-autoremove_wake_function
 irqbalan-1887    1d.s.    2us : check_preempt_wakeup <-try_to_wake_up

after this patch:

 # tracer: wakeup
 #
 # wakeup latency trace v1.1.5 on 2.6.29-rc7-tip-tip
 # --------------------------------------------------------------------
 # latency: 529 us, #530/530, CPU#0 | (M:desktop VP:0, KP:0, SP:0 HP:0 #P:4)
 #    -----------------
 #    | task: kondemand/0-1641 (uid:0 nice:-5 policy:0 rt_prio:0)
 #    -----------------
 #
 #                  _------=> CPU#
 #                 / _-----=> irqs-off
 #                | / _----=> need-resched
 #                || / _---=> hardirq/softirq
 #                ||| / _--=> preempt-depth
 #                |||| /
 #                |||||     delay
 #  cmd     pid   ||||| time  |   caller
 #     \   /      |||||   \   |   /
     sshd-2496    0d.s.    0us :   2496:120:R   + [000]  1641:115:S kondemand/0
     sshd-2496    0d.s.    1us : default_wake_function <-autoremove_wake_function
     sshd-2496    0d.s.    1us : check_preempt_wakeup <-try_to_wake_up
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <20090308124421.23C3.A69D9226@jp.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: cleanup

Remove a few leftovers and clean up the code a bit.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1236356510-8381-5-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: faster and lighter tracing

Now that we have trace_bprintk() which is faster and consume lesser
memory than trace_printk() and has the same purpose, we can now drop
the old implementation in favour of the binary one from trace_bprintk(),
which means we move all the implementation of trace_bprintk() to
trace_printk(), so the Api doesn't change except that we must now use
trace_seq_bprintk() to print the TRACE_PRINT entries.

Some changes result of this:

- Previously, trace_bprintk depended of a single tracer and couldn't
  work without. This tracer has been dropped and the whole implementation
  of trace_printk() (like the module formats management) is now integrated
  in the tracing core (comes with CONFIG_TRACING), though we keep the file
  trace_printk (previously trace_bprintk.c) where we can find the module
  management. Thus we don't overflow trace.c

- changes some parts to use trace_seq_bprintk() to print TRACE_PRINT entries.

- change a bit trace_printk/trace_vprintk macros to support non-builtin formats
  constants, and fix 'const' qualifiers warnings. But this is all transparent for
  developers.

- etc...

V2:

- Rebase against last changes
- Fix mispell on the changelog

V3:

- Rebase against last changes (moving trace_printk() to kernel.h)
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1236356510-8381-5-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: add a generic printk() for tracing, like trace_printk()

trace_bprintk() uses the infrastructure to record events on ring_buffer.

[ fweisbec@gmail.com: ported to latest -tip, made it work if
  !CONFIG_MODULES, never free the format strings from modules
  because we can't keep track of them and conditionnaly create
  the ftrace format strings section (reported by Steven Rostedt) ]
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1236356510-8381-4-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: save on memory for tracing

Current tracers are typically using a struct(like struct ftrace_entry,
struct ctx_switch_entry, struct special_entr etc...)to record a binary
event. These structs can only record a their own kind of events.
A new kind of tracer need a new struct and a lot of code too handle it.

So we need a generic binary record for events. This infrastructure
is for this purpose.

[fweisbec@gmail.com: rebase against latest -tip, make it safe while sched
tracing as reported by Steven Rostedt]
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1236356510-8381-3-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: fix deadlock while using set_ftrace_pid

Reproducer:

	# cd /sys/kernel/debug/tracing
	# echo $$ > set_ftrace_pid

	then, console becomes hung.

Details:

when writing set_ftracepid, kernel callstack is following

	ftrace_pid_write()
		mutex_lock(&ftrace_lock);
		ftrace_update_pid_func()
			mutex_lock(&ftrace_lock);
			mutex_unlock(&ftrace_lock);
		mutex_unlock(&ftrace_lock);

then, system always deadlocks when ftrace_pid_write() is called.

In past days, ftrace_pid_write() used ftrace_start_lock, but
commit e6ea44e9 consolidated
ftrace_start_lock to ftrace_lock.
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: NLai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <srostedt@redhat.com>
LKML-Reference: <20090306151155.0778.A69D9226@jp.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

After commit 40ada30f,
"make menuconfig" doesn't display "Tracer" item.

Following modification restores it.

Impact: allow user apps to read binary format of basic ftrace entries

Currently, only defined raw events export their formats so a binary
reader can parse them. There's no reason that the default ftrace entries
can't export their formats.

This patch adds a subsystem called "ftrace" in the events directory
that includes the ftrace entries for basic ftrace recorded items.

These only have three files in the events directory:

 type             : printf
 available_types  : printf
 format           : format for the event entry

For example:

 # cat /debug/tracing/events/ftrace/wakeup/format
name: wakeup
ID: 3
format:
        field:unsigned char type;       offset:0;       size:1;
        field:unsigned char flags;      offset:1;       size:1;
        field:unsigned char preempt_count;      offset:2;       size:1;
        field:int pid;  offset:4;       size:4;
        field:int tgid; offset:8;       size:4;

        field:unsigned int prev_pid;    offset:12;      size:4;
        field:unsigned char prev_prio;  offset:16;      size:1;
        field:unsigned char prev_state; offset:17;      size:1;
        field:unsigned int next_pid;    offset:20;      size:4;
        field:unsigned char next_prio;  offset:24;      size:1;
        field:unsigned char next_state; offset:25;      size:1;
        field:unsigned int next_cpu;    offset:28;      size:4;

print fmt: "%u:%u:%u  ==+ %u:%u:%u [%03u]"
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: clean up

Move the macro that creates the event format file to a separate header.
This will allow the default ftrace events to use this same macro
to create the formats to read those events.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: cleanup

All file_operations structures should be constant. No one is going to
change them.
Reported-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Clean up menu structure, introduce TRACING_SUPPORT switch that signals
whether an architecture supports various instrumentation mechanisms.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: decrease hangs risks with the graph tracer on slow systems

Since the function graph tracer can spend too much time on timer
interrupts, it's better now to use the more lightweight local
clock. Anyway, the function graph traces are more reliable on a
per cpu trace.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <49af243d.06e9300a.53ad.ffff840c@mx.google.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: cleanup

Use a more generic name - this also allows the prototype to move
to kernel.h and be generally available to kernel developers who
want to do some quick tracing.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The latency tracers (irqsoff, preemptoff, preemptirqsoff, and wakeup)
are pretty useless with the default output format. This patch makes them
automatically enable the latency format when they are selected. They
also record the state of the latency option, and if it was not enabled
when selected, they disable it on reset.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: clean up

Both print_lat_fmt and print_trace_fmt do pretty much the same thing
except for one different function call. This patch consolidates the
two functions and adds an if statement to perform the difference.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: clean up

The trace and latency_trace function pointers are identical for
every tracer but the function tracer. The differences in the function
tracer are trivial (latency output puts paranthesis around parent).

This patch removes the latency_trace pointer and all prints will
now just use the trace output function pointer.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

With the removal of the latency_trace file, we lost the ability
to see some of the finer details in a trace. Like the state of
interrupts enabled, the preempt count, need resched, and if we
are in an interrupt handler, softirq handler or not.

This patch simply creates an option to bring back the old format.
This also removes the warning about an unused variable that held
the latency_trace file operations.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

The buffer used by trace_seq was updated incorrectly. Instead
of consuming what was actually read, it consumed the rest of the
buffer on reads.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: fix trace read to conform to standards

Andrew Morton, Theodore Tso and H. Peter Anvin brought to my attention
that a userspace read should not return -EFAULT if it succeeded in
copying anything. It should only return -EFAULT if it failed to copy
at all.

This patch modifies the check of copy_from_user and updates the return
code appropriately.

I also used H. Peter Anvin's short cut rule to just test ret == count.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

If a partial ring_buffer_page_read happens, then some of the
incremental timestamps may be lost. This patch writes the
recent timestamp into the page that is passed back to the caller.

A partial ring_buffer_page_read is where the full page would not
be written back to the user, and instead, just part of the page
is copied to the user. A full page would be a page swap with the
ring buffer and the timestamps would be correct.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: fix to ftrace_dump output corruption

The commit: b04cc6b1
  tracing/core: introduce per cpu tracing files

added a new field to the iterator called cpu_file. This was a handle
to differentiate between the per cpu trace output files and the
all cpu "trace" file. The all cpu "trace" file required setting this
to TRACE_PIPE_ALL_CPU.

The problem is that the ftrace_dump sets up its own iterator but was
not updated to handle this change. The result was only CPU 0 printing
out on crash and a lot of "<0>"'s also being printed.
Reported-by: NThomas Gleixner <tglx@linuxtronix.de>
Tested-by: NDarren Hart <dvhtc@us.ibm.com>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Augment the traces with lock names when lockdep is available:

 1)               |  down_read_trylock() {
 1)               |    _spin_lock_irqsave() {
 1)               |      /* lock_acquire: &sem->wait_lock */
 1)   4.201 us    |    }
 1)               |    _spin_unlock_irqrestore() {
 1)               |      /* lock_release: &sem->wait_lock */
 1)   3.523 us    |    }
 1)               |  /* lock_acquire: try read &mm->mmap_sem */
 1) + 13.386 us   |  }
 1)   1.635 us    |  find_vma();
 1)               |  handle_mm_fault() {
 1)               |    __do_fault() {
 1)               |      filemap_fault() {
 1)               |        find_lock_page() {
 1)               |          find_get_page() {
 1)               |            /* lock_acquire: read rcu_read_lock */
 1)               |            /* lock_release: rcu_read_lock */
 1)   5.697 us    |          }
 1)   8.158 us    |        }
 1) + 11.079 us   |      }
 1)               |      _spin_lock() {
 1)               |        /* lock_acquire: __pte_lockptr(page) */
 1)   3.949 us    |      }
 1)   1.460 us    |      page_add_file_rmap();
 1)               |      _spin_unlock() {
 1)               |        /* lock_release: __pte_lockptr(page) */
 1)   3.115 us    |      }
 1)               |      unlock_page() {
 1)   1.421 us    |        page_waitqueue();
 1)   1.220 us    |        __wake_up_bit();
 1)   6.519 us    |      }
 1) + 34.328 us   |    }
 1) + 37.452 us   |  }
 1)               |  up_read() {
 1)               |  /* lock_release: &mm->mmap_sem */
 1)               |    _spin_lock_irqsave() {
 1)               |      /* lock_acquire: &sem->wait_lock */
 1)   3.865 us    |    }
 1)               |    _spin_unlock_irqrestore() {
 1)               |      /* lock_release: &sem->wait_lock */
 1)   8.562 us    |    }
 1) + 17.370 us   |  }
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: =?ISO-8859-1?Q?T=F6r=F6k?= Edwin <edwintorok@gmail.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1236166375.5330.7209.camel@laptop>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: new feature

This patch creates a directory of files that correspond to the
per CPU ring buffers. These are binary files and are made to
be used with splice. This is the fastest way to extract data from
the ftrace ring buffers.

Thanks to Jiaying Zhang for pushing me to get this code fixed,
 and to Eduard - Gabriel Munteanu for his splice code that helped
 me debug my code.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: dont leave holes in read buffer page

The ring_buffer_read_page swaps a given page with the reader page
of the ring buffer, if certain conditions are set:

 1) requested length is big enough to hold entire page data

 2) a writer is not currently on the page

 3) the page is not partially consumed.

Instead of swapping with the supplied page. It copies the data to
the supplied page instead. But currently the data is copied in the
same offset as the source page. This causes a hole at the start
of the reader page. This complicates the use of this function.
Instead, it should copy the data at the beginning of the function
and update the index fields accordingly.

Other small clean ups are also done in this patch.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: fix to possible alignment problems on some archs.

Some arch compilers include an NULL char array in the sizeof field.
Since the ring_buffer_event type includes one of these, it is better
to use the "offsetof" instead, to avoid strange bugs on these archs.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

The ring_buffer_read_page was broken if it were to only copy part
of the page. This patch fixes that up as well as adds a parameter
to allow a length field, in order to only copy part of the buffer page.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: fix ring_buffer_read_page

After a page is swapped into the ring buffer, the write field must
also be reset.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

The registering of events had the return value check backwards.
A zero returned is success, the check had it as a failure.

This patch also fixes a missing "\n" in the warning that the check
failed.
Reported-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

This patch adds the internal print format used to print the raw events
to the event trace point format file.

 # cat /debug/tracing/events/sched/sched_switch/format
name: sched_switch
ID: 29
format:
        field:unsigned char type;       offset:0;       size:1;
        field:unsigned char flags;      offset:1;       size:1;
        field:unsigned char preempt_count;      offset:2;       size:1;
        field:int pid;  offset:4;       size:4;
        field:int tgid; offset:8;       size:4;

        field:pid_t prev_pid;   offset:12;      size:4;
        field:int prev_prio;    offset:16;      size:4;
        field special:char next_comm[TASK_COMM_LEN];    offset:20;      size:16;
        field:pid_t next_pid;   offset:36;      size:4;
        field:int next_prio;    offset:40;      size:4;

print fmt: "prev %d:%d ==> next %s:%d:%d"
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

To be able to identify the trace in the binary format output, the
id of the trace event (which is dynamically assigned) must also be listed.

This patch adds the name of the trace point as well as the id assigned.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

This patch includes the ftrace header to the event formats files:

 # cat /debug/tracing/events/sched/sched_switch/format
        field:unsigned char type;       offset:0;       size:1;
        field:unsigned char flags;      offset:1;       size:1;
        field:unsigned char preempt_count;      offset:2;       size:1;
        field:int pid;  offset:4;       size:4;
        field:int tgid; offset:8;       size:4;

        field:pid_t prev_pid;   offset:12;      size:4;
        field:int prev_prio;    offset:16;      size:4;
        field special:char next_comm[TASK_COMM_LEN];    offset:20;      size:16;
        field:pid_t next_pid;   offset:36;      size:4;
        field:int next_prio;    offset:40;      size:4;

A blank line is used as a deliminator between the ftrace header and the
trace point fields.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

This patch adds the "format" file to the trace point event directory.
This is based off of work by Tom Zanussi, in which a file is exported
to be tread from user land such that a user space app may read the
binary record stored in the ring buffer.

 # cat /debug/tracing/events/sched/sched_switch/format
        field:pid_t prev_pid;   offset:12;      size:4;
        field:int prev_prio;    offset:16;      size:4;
        field special:char next_comm[TASK_COMM_LEN];    offset:20;      size:16;
        field:pid_t next_pid;   offset:36;      size:4;
        field:int next_prio;    offset:40;      size:4;

Idea-from: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: clean up

The trace_seq functions may be used separately outside of the ftrace
iterator. The trace_seq_reset is needed for these operations.

This patch also renames trace_seq_reset to the more appropriate
trace_seq_init.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

The trace event objects are currently not proctected against
reentrancy. This patch adds a mutex around the modifications of
the trace event fields.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Tom Zanussi pointed out that the simple TRACE_FIELD was not enough to
record trace data that required memcpy. This patch addresses this issue
by adding a TRACE_FIELD_SPECIAL. The format is similar to TRACE_FIELD
but looks like so:

  TRACE_FIELD_SPECIAL(type_item, item, cmd)

What TRACE_FIELD gave was:

  TRACE_FIELD(type, item, assign)

The TRACE_FIELD would be used in declaring a structure:

  struct {
	type	item;
  };

And later assign it via:

  entry->item = assign;

What TRACE_FIELD_SPECIAL gives us is:

In the declaration of the structure:

  struct {
	type_item;
  };

And the assignment:

  cmd;

This change log will explain the one example used in the patch:

 TRACE_EVENT_FORMAT(sched_switch,
	TPPROTO(struct rq *rq, struct task_struct *prev,
		struct task_struct *next),
	TPARGS(rq, prev, next),
	TPFMT("task %s:%d ==> %s:%d",
	      prev->comm, prev->pid, next->comm, next->pid),
	TRACE_STRUCT(
		TRACE_FIELD(pid_t, prev_pid, prev->pid)
		TRACE_FIELD(int, prev_prio, prev->prio)
		TRACE_FIELD_SPECIAL(char next_comm[TASK_COMM_LEN],
				    next_comm,
				    TPCMD(memcpy(TRACE_ENTRY->next_comm,
						 next->comm,
						 TASK_COMM_LEN)))
		TRACE_FIELD(pid_t, next_pid, next->pid)
		TRACE_FIELD(int, next_prio, next->prio)
	),
	TPRAWFMT("prev %d:%d ==> next %s:%d:%d")
	);

 The struct will be create as:

  struct {
	pid_t		prev_pid;
	int		prev_prio;
	char next_comm[TASK_COMM_LEN];
	pid_t		next_pid;
	int		next_prio;
  };

Note the TRACE_ENTRY in the cmd part of TRACE_SPECIAL. TRACE_ENTRY will
be set by the tracer to point to the structure inside the trace buffer.

  entry->prev_pid	= prev->pid;
  entry->prev_prio	= prev->prio;
  memcpy(entry->next_comm, next->comm, TASK_COMM_LEN);
  entry->next_pid	= next->pid;
  entry->next_prio	= next->prio
Reported-by: NTom Zanussi <tzanussi@gmail.com>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

This patch adds the interface to enable the C style trace points.
In the directory /debugfs/tracing/events/subsystem/event
We now have three files:

 enable : values 0 or 1 to enable or disable the trace event.

 available_types: values 'raw' and 'printf' which indicate the tracing
       types available for the trace point. If a developer does not
       use the TRACE_EVENT_FORMAT macro and just uses the TRACE_FORMAT
       macro, then only 'printf' will be available. This file is
       read only.

 type: values 'raw' or 'printf'. This indicates which type of tracing
       is active for that trace point. 'printf' is the default and
       if 'raw' is not available, this file is read only.

 # echo raw > /debug/tracing/events/sched/sched_wakeup/type
 # echo 1 > /debug/tracing/events/sched/sched_wakeup/enable

 Will enable the C style tracing for the sched_wakeup trace point.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: lower overhead tracing

The current event tracer can automatically pick up trace points
that are registered with the TRACE_FORMAT macro. But it required
a printf format string and parsing. Although, this adds the ability
to get guaranteed information like task names and such, it took
a hit in overhead processing. This processing can add about 500-1000
nanoseconds overhead, but in some cases that too is considered
too much and we want to shave off as much from this overhead as
possible.

Tom Zanussi recently posted tracing patches to lkml that are based
on a nice idea about capturing the data via C structs using
STRUCT_ENTER, STRUCT_EXIT type of macros.

I liked that method very much, but did not like the implementation
that required a developer to add data/code in several disjoint
locations.

This patch extends the event_tracer macros to do a similar "raw C"
approach that Tom Zanussi did. But instead of having the developers
needing to tweak a bunch of code all over the place, they can do it
all in one macro - preferably placed near the code that it is
tracing. That makes it much more likely that tracepoints will be
maintained on an ongoing basis by the code they modify.

The new macro TRACE_EVENT_FORMAT is created for this approach. (Note,
a developer may still utilize the more low level DECLARE_TRACE macros
if they don't care about getting their traces automatically in the event
tracer.)

They can also use the existing TRACE_FORMAT if they don't need to code
the tracepoint in C, but just want to use the convenience of printf.

So if the developer wants to "hardwire" a tracepoint in the fastest
possible way, and wants to acquire their data via a user space utility
in a raw binary format, or wants to see it in the trace output but not
sacrifice any performance, then they can implement the faster but
more complex TRACE_EVENT_FORMAT macro.

Here's what usage looks like:

  TRACE_EVENT_FORMAT(name,
	TPPROTO(proto),
	TPARGS(args),
	TPFMT(fmt, fmt_args),
	TRACE_STUCT(
		TRACE_FIELD(type1, item1, assign1)
		TRACE_FIELD(type2, item2, assign2)
			[...]
	),
	TPRAWFMT(raw_fmt)
	);

Note name, proto, args, and fmt, are all identical to what TRACE_FORMAT
uses.

 name: is the unique identifier of the trace point
 proto: The proto type that the trace point uses
 args: the args in the proto type
 fmt: printf format to use with the event printf tracer
 fmt_args: the printf argments to match fmt

 TRACE_STRUCT starts the ability to create a structure.
 Each item in the structure is defined with a TRACE_FIELD

  TRACE_FIELD(type, item, assign)

 type: the C type of item.
 item: the name of the item in the stucture
 assign: what to assign the item in the trace point callback

 raw_fmt is a way to pretty print the struct. It must match
  the order of the items are added in TRACE_STUCT

 An example of this would be:

 TRACE_EVENT_FORMAT(sched_wakeup,
	TPPROTO(struct rq *rq, struct task_struct *p, int success),
	TPARGS(rq, p, success),
	TPFMT("task %s:%d %s",
	      p->comm, p->pid, success?"succeeded":"failed"),
	TRACE_STRUCT(
		TRACE_FIELD(pid_t, pid, p->pid)
		TRACE_FIELD(int, success, success)
	),
	TPRAWFMT("task %d success=%d")
	);

 This creates us a unique struct of:

 struct {
	pid_t		pid;
	int		success;
 };

 And the way the call back would assign these values would be:

	entry->pid = p->pid;
	entry->success = success;

The nice part about this is that the creation of the assignent is done
via macro magic in the event tracer.  Once the TRACE_EVENT_FORMAT is
created, the developer will then have a faster method to record
into the ring buffer. They do not need to worry about the tracer itself.

The developer would only need to touch the files in include/trace/*.h

Again, I would like to give special thanks to Tom Zanussi for this
nice idea.

Idea-from: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Right now all tracers must manage their own trace buffers. This was
to enforce tracers to be independent in case we finally decide to
allow each tracer to have their own trace buffer.

But now we are adding event tracing that writes to the current tracer's
buffer. This adds an interface to allow events to write to the current
tracer buffer without having to manage its own. Since event tracing
has no "tracer", and is just a way to hook into any other tracer.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

This patch makes the event files, set_event and available_events
aware of the subsystem.

Now you can enable an entire subsystem with:

  echo 'irq:*' > set_event

Note: the '*' is not needed.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>