This patch overloads RINGBUF_TYPE_PADDING to provide a way to discard
events from the ring buffer, for the event-filtering mechanism
introduced in a subsequent patch.

I did the initial version but thanks to Steven Rostedt for adding
the parts that actually made it work. ;-)
Signed-off-by: NTom Zanussi <tzanussi@gmail.com>
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This patch adds a new function called ring_buffer_set_clock that
allows a tracer to assign its own clock source to the buffer.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: cleanup

The functions tracing_start/tracing_stop have been moved to kernel.h.
These are not the functions a developer most likely wants to use
when they want to insert a place to stop tracing and restart it from
user space.

tracing_start/tracing_stop was created to work with things like
suspend to ram, where even calling smp_processor_id() can crash the
system. The tracing_start/tracing_stop was used to stop the tracer from
doing anything. These are still light weight functions, but add a bit
more overhead to be able to stop the tracers. They also have no interface
back to userland. That is, if the kernel calls tracing_stop, userland
can not start tracing.

What a developer most likely wants to use is tracing_on/tracing_off.
These are very light weight functions (simply sets or clears a bit).
These functions just stop recording into the ring buffer. The tracers
don't even know that this happens except that they would receive NULL
from the ring_buffer_lock_reserve function.

Also, there's a way for the user land to enable or disable this bit.
In debugfs/tracing/tracing_on, a user may echo "0" (same as tracing_off())
or echo "1" (same as tracing_on()) into this file. This becomes handy when
a kernel developer is debugging and wants tracing to turn off when it
hits an anomaly. Then the developer can examine the trace, and restart
tracing if they want to try again (echo 1 > tracing_on).

This patch moves the prototypes for tracing_on/tracing_off to kernel.h
and comments their use, so that a kernel developer will know how
to use them.
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>

This patch adds the tracing_is_on() interface to tell if the ring
buffer is turned on or not.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: clean up.

Fix typos in the comments.
Signed-off-by: NWenji Huang <wenji.huang@oracle.com>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

tracing_off() is the fastest way to stop recording to the ring buffers.
This may be used in places like panic and die, just before the
ftrace_dump is called.

This patch adds the appropriate CPP conditionals to make it a stub
function when the ring buffer is not configured it.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

Impact: API change, cleanup

>From ring_buffer_{lock_reserve,unlock_commit}.

$ codiff /tmp/vmlinux.before /tmp/vmlinux.after
linux-2.6-tip/kernel/trace/trace.c:
  trace_vprintk              |  -14
  trace_graph_return         |  -14
  trace_graph_entry          |  -10
  trace_function             |   -8
  __ftrace_trace_stack       |   -8
  ftrace_trace_userstack     |   -8
  tracing_sched_switch_trace |   -8
  ftrace_trace_special       |  -12
  tracing_sched_wakeup_trace |   -8
 9 functions changed, 90 bytes removed, diff: -90

linux-2.6-tip/block/blktrace.c:
  __blk_add_trace |   -1
 1 function changed, 1 bytes removed, diff: -1

/tmp/vmlinux.after:
 10 functions changed, 91 bytes removed, diff: -91
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: NFrédéric Weisbecker <fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

These functions are not yet in ring_buffer.h though they seems to be
part of the API.

Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NRobert Richter <robert.richter@amd.com>

Impact: comments cleanup

fix incorrect comments for enum ring_buffer_type
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: new API to ring buffer

This patch adds a new interface into the ring buffer that allows a
page to be read from the ring buffer on a given CPU. For every page
read, one must also be given to allow for a "swap" of the pages.

 rpage = ring_buffer_alloc_read_page(buffer);
 if (!rpage)
	goto err;
 ret = ring_buffer_read_page(buffer, &rpage, cpu, full);
 if (!ret)
	goto empty;
 process_page(rpage);
 ring_buffer_free_read_page(rpage);

The caller of these functions must handle any waits that are
needed to wait for new data. The ring_buffer_read_page will simply
return 0 if there is no data, or if "full" is set and the writer
is still on the current page.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: feature to permanently disable ring buffer

This patch adds a API to the ring buffer code that will permanently
disable the ring buffer from ever recording. This should only be
called when some serious anomaly is detected, and the system
may be in an unstable state. When that happens, shutting down the
recording to the ring buffers may be appropriate.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: enable/disable ring buffer recording API added

Several kernel developers have requested that there be a way to stop
recording into the ring buffers with a simple switch that can also
be enabled from userspace. This patch addes a new kernel API to the
ring buffers called:

 tracing_on()
 tracing_off()

When tracing_off() is called, all ring buffers will not be able to record
into their buffers.

tracing_on() will enable the ring buffers again.

These two act like an on/off switch. That is, there is no counting of the
number of times tracing_off or tracing_on has been called.

A new file is added to the debugfs/tracing directory called

  tracing_on

This allows for userspace applications to also flip the switch.

  echo 0 > debugfs/tracing/tracing_on

disables the tracing.

  echo 1 > /debugfs/tracing/tracing_on

enables it.

Note, this does not disable or enable any tracers. It only sets or clears
a flag that needs to be set in order for the ring buffers to write to
their buffers. It is a global flag, and affects all ring buffers.

The buffers start out with tracing_on enabled.

There are now three flags that control recording into the buffers:

 tracing_on: which affects all ring buffer tracers.

 buffer->record_disabled: which affects an allocated buffer, which may be set
     if an anomaly is detected, and tracing is disabled.

 cpu_buffer->record_disabled: which is set by tracing_stop() or if an
     anomaly is detected. tracing_start can not reenable this if
     an anomaly occurred.

The userspace debugfs/tracing/tracing_enabled is implemented with
tracing_stop() but the user space code can not enable it if the kernel
called tracing_stop().

Userspace can enable the tracing_on even if the kernel disabled it.
It is just a switch used to stop tracing if a condition was hit.
tracing_on is not for protecting critical areas in the kernel nor is
it for stopping tracing if an anomaly occurred. This is because userspace
can reenable it at any time.

Side effect: With this patch, I discovered a dead variable in ftrace.c
  called tracing_on. This patch removes it.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

The old "lock always" scheme had issues with lockdep, and was not very
efficient anyways.

This patch does a new design to be partially lockless on writes.
Writes will add new entries to the per cpu pages by simply disabling
interrupts. When a write needs to go to another page than it will
grab the lock.

A new "read page" has been added so that the reader can pull out a page
from the ring buffer to read without worrying about the writer writing over
it. This allows us to not take the lock for all reads. The lock is
now only taken when a read needs to go to a new page.

This is far from lockless, and interrupts still need to be disabled,
but it is a step towards a more lockless solution, and it also
solves a lot of the issues that were noticed by the first conversion
of ftrace to the ring buffers.

Note: the ring_buffer_{un}lock API has been removed.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This is a unified tracing buffer that implements a ring buffer that
hopefully everyone will eventually be able to use.

The events recorded into the buffer have the following structure:

  struct ring_buffer_event {
	u32 type:2, len:3, time_delta:27;
	u32 array[];
  };

The minimum size of an event is 8 bytes. All events are 4 byte
aligned inside the buffer.

There are 4 types (all internal use for the ring buffer, only
the data type is exported to the interface users).

 RINGBUF_TYPE_PADDING: this type is used to note extra space at the end
	of a buffer page.

 RINGBUF_TYPE_TIME_EXTENT: This type is used when the time between events
	is greater than the 27 bit delta can hold. We add another
	32 bits, and record that in its own event (8 byte size).

 RINGBUF_TYPE_TIME_STAMP: (Not implemented yet). This will hold data to
	help keep the buffer timestamps in sync.

RINGBUF_TYPE_DATA: The event actually holds user data.

The "len" field is only three bits. Since the data must be
4 byte aligned, this field is shifted left by 2, giving a
max length of 28 bytes. If the data load is greater than 28
bytes, the first array field holds the full length of the
data load and the len field is set to zero.

Example, data size of 7 bytes:

	type = RINGBUF_TYPE_DATA
	len = 2
	time_delta: <time-stamp> - <prev_event-time-stamp>
	array[0..1]: <7 bytes of data> <1 byte empty>

This event is saved in 12 bytes of the buffer.

An event with 82 bytes of data:

	type = RINGBUF_TYPE_DATA
	len = 0
	time_delta: <time-stamp> - <prev_event-time-stamp>
	array[0]: 84 (Note the alignment)
	array[1..14]: <82 bytes of data> <2 bytes empty>

The above event is saved in 92 bytes (if my math is correct).
82 bytes of data, 2 bytes empty, 4 byte header, 4 byte length.

Do not reference the above event struct directly. Use the following
functions to gain access to the event table, since the
ring_buffer_event structure may change in the future.

ring_buffer_event_length(event): get the length of the event.
	This is the size of the memory used to record this
	event, and not the size of the data pay load.

ring_buffer_time_delta(event): get the time delta of the event
	This returns the delta time stamp since the last event.
	Note: Even though this is in the header, there should
		be no reason to access this directly, accept
		for debugging.

ring_buffer_event_data(event): get the data from the event
	This is the function to use to get the actual data
	from the event. Note, it is only a pointer to the
	data inside the buffer. This data must be copied to
	another location otherwise you risk it being written
	over in the buffer.

ring_buffer_lock: A way to lock the entire buffer.
ring_buffer_unlock: unlock the buffer.

ring_buffer_alloc: create a new ring buffer. Can choose between
	overwrite or consumer/producer mode. Overwrite will
	overwrite old data, where as consumer producer will
	throw away new data if the consumer catches up with the
	producer.  The consumer/producer is the default.

ring_buffer_free: free the ring buffer.

ring_buffer_resize: resize the buffer. Changes the size of each cpu
	buffer. Note, it is up to the caller to provide that
	the buffer is not being used while this is happening.
	This requirement may go away but do not count on it.

ring_buffer_lock_reserve: locks the ring buffer and allocates an
	entry on the buffer to write to.
ring_buffer_unlock_commit: unlocks the ring buffer and commits it to
	the buffer.

ring_buffer_write: writes some data into the ring buffer.

ring_buffer_peek: Look at a next item in the cpu buffer.
ring_buffer_consume: get the next item in the cpu buffer and
	consume it. That is, this function increments the head
	pointer.

ring_buffer_read_start: Start an iterator of a cpu buffer.
	For now, this disables the cpu buffer, until you issue
	a finish. This is just because we do not want the iterator
	to be overwritten. This restriction may change in the future.
	But note, this is used for static reading of a buffer which
	is usually done "after" a trace. Live readings would want
	to use the ring_buffer_consume above, which will not
	disable the ring buffer.

ring_buffer_read_finish: Finishes the read iterator and reenables
	the ring buffer.

ring_buffer_iter_peek: Look at the next item in the cpu iterator.
ring_buffer_read: Read the iterator and increment it.
ring_buffer_iter_reset: Reset the iterator to point to the beginning
	of the cpu buffer.
ring_buffer_iter_empty: Returns true if the iterator is at the end
	of the cpu buffer.

ring_buffer_size: returns the size in bytes of each cpu buffer.
	Note, the real size is this times the number of CPUs.

ring_buffer_reset_cpu: Sets the cpu buffer to empty
ring_buffer_reset: sets all cpu buffers to empty

ring_buffer_swap_cpu: swaps a cpu buffer from one buffer with a
	cpu buffer of another buffer. This is handy when you
	want to take a snap shot of a running trace on just one
	cpu. Having a backup buffer, to swap with facilitates this.
	Ftrace max latencies use this.

ring_buffer_empty: Returns true if the ring buffer is empty.
ring_buffer_empty_cpu: Returns true if the cpu buffer is empty.

ring_buffer_record_disable: disable all cpu buffers (read only)
ring_buffer_record_disable_cpu: disable a single cpu buffer (read only)
ring_buffer_record_enable: enable all cpu buffers.
ring_buffer_record_enabl_cpu: enable a single cpu buffer.

ring_buffer_entries: The number of entries in a ring buffer.
ring_buffer_overruns: The number of entries removed due to writing wrap.

ring_buffer_time_stamp: Get the time stamp used by the ring buffer
ring_buffer_normalize_time_stamp: normalize the ring buffer time stamp
	into nanosecs.

I still need to implement the GTOD feature. But we need support from
the cpu frequency infrastructure.  But this can be done at a later
time without affecting the ring buffer interface.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>