[lttng-modules.git] / lib / ringbuffer / frontend_api.h

#ifndef _LIB_RING_BUFFER_FRONTEND_API_H
#define _LIB_RING_BUFFER_FRONTEND_API_H

/*
 * lib/ringbuffer/frontend_api.h
 *
 * Ring Buffer Library Synchronization Header (buffer write API).
 *
 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; only
 * version 2.1 of the License.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Author:
 *	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * See ring_buffer_frontend.c for more information on wait-free algorithms.
 * See linux/ringbuffer/frontend.h for channel allocation and read-side API.
 */

#include "../../wrapper/ringbuffer/frontend.h"
#include "../../wrapper/percpu-defs.h"
#include <linux/errno.h>
#include <linux/prefetch.h>

/**
 * lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit.
 *
 * Disables preemption (acts as a RCU read-side critical section) and keeps a
 * ring buffer nesting count as supplementary safety net to ensure tracer client
 * code will never trigger an endless recursion. Returns the processor ID on
 * success, -EPERM on failure (nesting count too high).
 *
 * asm volatile and "memory" clobber prevent the compiler from moving
 * instructions out of the ring buffer nesting count. This is required to ensure
 * that probe side-effects which can cause recursion (e.g. unforeseen traps,
 * divisions by 0, ...) are triggered within the incremented nesting count
 * section.
 */
static inline
int lib_ring_buffer_get_cpu(const struct lib_ring_buffer_config *config)
{
	int cpu, nesting;

	rcu_read_lock_sched_notrace();
	cpu = smp_processor_id();
	nesting = ++per_cpu(lib_ring_buffer_nesting, cpu);
	barrier();

	if (unlikely(nesting > 4)) {
		WARN_ON_ONCE(1);
		per_cpu(lib_ring_buffer_nesting, cpu)--;
		rcu_read_unlock_sched_notrace();
		return -EPERM;
	} else
		return cpu;
}

/**
 * lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit.
 */
static inline
void lib_ring_buffer_put_cpu(const struct lib_ring_buffer_config *config)
{
	barrier();
	(*lttng_this_cpu_ptr(&lib_ring_buffer_nesting))--;
	rcu_read_unlock_sched_notrace();
}

/*
 * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not
 * part of the API per se.
 *
 * returns 0 if reserve ok, or 1 if the slow path must be taken.
 */
static inline
int lib_ring_buffer_try_reserve(const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer_ctx *ctx,
				unsigned long *o_begin, unsigned long *o_end,
				unsigned long *o_old, size_t *before_hdr_pad)
{
	struct channel *chan = ctx->chan;
	struct lib_ring_buffer *buf = ctx->buf;
	*o_begin = v_read(config, &buf->offset);
	*o_old = *o_begin;

	ctx->tsc = lib_ring_buffer_clock_read(chan);
	if ((int64_t) ctx->tsc == -EIO)
		return 1;

	/*
	 * Prefetch cacheline for read because we have to read the previous
	 * commit counter to increment it and commit seq value to compare it to
	 * the commit counter.
	 */
	prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);

	if (last_tsc_overflow(config, buf, ctx->tsc))
		ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC;

	if (unlikely(subbuf_offset(*o_begin, chan) == 0))
		return 1;

	ctx->slot_size = record_header_size(config, chan, *o_begin,
					    before_hdr_pad, ctx);
	ctx->slot_size +=
		lib_ring_buffer_align(*o_begin + ctx->slot_size,
				      ctx->largest_align) + ctx->data_size;
	if (unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
		     > chan->backend.subbuf_size))
		return 1;

	/*
	 * Record fits in the current buffer and we are not on a switch
	 * boundary. It's safe to write.
	 */
	*o_end = *o_begin + ctx->slot_size;

	if (unlikely((subbuf_offset(*o_end, chan)) == 0))
		/*
		 * The offset_end will fall at the very beginning of the next
		 * subbuffer.
		 */
		return 1;

	return 0;
}

/**
 * lib_ring_buffer_reserve - Reserve space in a ring buffer.
 * @config: ring buffer instance configuration.
 * @ctx: ring buffer context. (input and output) Must be already initialized.
 *
 * Atomic wait-free slot reservation. The reserved space starts at the context
 * "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc".
 *
 * Return :
 *  0 on success.
 * -EAGAIN if channel is disabled.
 * -ENOSPC if event size is too large for packet.
 * -ENOBUFS if there is currently not enough space in buffer for the event.
 * -EIO if data cannot be written into the buffer for any other reason.
 */

static inline
int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
			    struct lib_ring_buffer_ctx *ctx)
{
	struct channel *chan = ctx->chan;
	struct lib_ring_buffer *buf;
	unsigned long o_begin, o_end, o_old;
	size_t before_hdr_pad = 0;

	if (atomic_read(&chan->record_disabled))
		return -EAGAIN;

	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
		buf = per_cpu_ptr(chan->backend.buf, ctx->cpu);
	else
		buf = chan->backend.buf;
	if (atomic_read(&buf->record_disabled))
		return -EAGAIN;
	ctx->buf = buf;

	/*
	 * Perform retryable operations.
	 */
	if (unlikely(lib_ring_buffer_try_reserve(config, ctx, &o_begin,
						 &o_end, &o_old, &before_hdr_pad)))
		goto slow_path;

	if (unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
		     != o_old))
		goto slow_path;

	/*
	 * Atomically update last_tsc. This update races against concurrent
	 * atomic updates, but the race will always cause supplementary full TSC
	 * record headers, never the opposite (missing a full TSC record header
	 * when it would be needed).
	 */
	save_last_tsc(config, ctx->buf, ctx->tsc);

	/*
	 * Push the reader if necessary
	 */
	lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);

	/*
	 * Clear noref flag for this subbuffer.
	 */
	lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
				subbuf_index(o_end - 1, chan));

	ctx->pre_offset = o_begin;
	ctx->buf_offset = o_begin + before_hdr_pad;
	return 0;
slow_path:
	return lib_ring_buffer_reserve_slow(ctx);
}

/**
 * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer.
 * @config: ring buffer instance configuration.
 * @buf: buffer
 * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH)
 *
 * This operation is completely reentrant : can be called while tracing is
 * active with absolutely no lock held.
 *
 * Note, however, that as a v_cmpxchg is used for some atomic operations and
 * requires to be executed locally for per-CPU buffers, this function must be
 * called from the CPU which owns the buffer for a ACTIVE flush, with preemption
 * disabled, for RING_BUFFER_SYNC_PER_CPU configuration.
 */
static inline
void lib_ring_buffer_switch(const struct lib_ring_buffer_config *config,
			    struct lib_ring_buffer *buf, enum switch_mode mode)
{
	lib_ring_buffer_switch_slow(buf, mode);
}

/* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */

/**
 * lib_ring_buffer_commit - Commit an record.
 * @config: ring buffer instance configuration.
 * @ctx: ring buffer context. (input arguments only)
 *
 * Atomic unordered slot commit. Increments the commit count in the
 * specified sub-buffer, and delivers it if necessary.
 */
static inline
void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
			    const struct lib_ring_buffer_ctx *ctx)
{
	struct channel *chan = ctx->chan;
	struct lib_ring_buffer *buf = ctx->buf;
	unsigned long offset_end = ctx->buf_offset;
	unsigned long endidx = subbuf_index(offset_end - 1, chan);
	unsigned long commit_count;

	/*
	 * Must count record before incrementing the commit count.
	 */
	subbuffer_count_record(config, &buf->backend, endidx);

	/*
	 * Order all writes to buffer before the commit count update that will
	 * determine that the subbuffer is full.
	 */
	if (config->ipi == RING_BUFFER_IPI_BARRIER) {
		/*
		 * Must write slot data before incrementing commit count.  This
		 * compiler barrier is upgraded into a smp_mb() by the IPI sent
		 * by get_subbuf().
		 */
		barrier();
	} else
		smp_wmb();

	v_add(config, ctx->slot_size, &buf->commit_hot[endidx].cc);

	/*
	 * commit count read can race with concurrent OOO commit count updates.
	 * This is only needed for lib_ring_buffer_check_deliver (for
	 * non-polling delivery only) and for
	 * lib_ring_buffer_write_commit_counter.  The race can only cause the
	 * counter to be read with the same value more than once, which could
	 * cause :
	 * - Multiple delivery for the same sub-buffer (which is handled
	 *   gracefully by the reader code) if the value is for a full
	 *   sub-buffer. It's important that we can never miss a sub-buffer
	 *   delivery. Re-reading the value after the v_add ensures this.
	 * - Reading a commit_count with a higher value that what was actually
	 *   added to it for the lib_ring_buffer_write_commit_counter call
	 *   (again caused by a concurrent committer). It does not matter,
	 *   because this function is interested in the fact that the commit
	 *   count reaches back the reserve offset for a specific sub-buffer,
	 *   which is completely independent of the order.
	 */
	commit_count = v_read(config, &buf->commit_hot[endidx].cc);

	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
				      commit_count, endidx, ctx->tsc);
	/*
	 * Update used size at each commit. It's needed only for extracting
	 * ring_buffer buffers from vmcore, after crash.
	 */
	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
			offset_end, commit_count);
}

/**
 * lib_ring_buffer_try_discard_reserve - Try discarding a record.
 * @config: ring buffer instance configuration.
 * @ctx: ring buffer context. (input arguments only)
 *
 * Only succeeds if no other record has been written after the record to
 * discard. If discard fails, the record must be committed to the buffer.
 *
 * Returns 0 upon success, -EPERM if the record cannot be discarded.
 */
static inline
int lib_ring_buffer_try_discard_reserve(const struct lib_ring_buffer_config *config,
					const struct lib_ring_buffer_ctx *ctx)
{
	struct lib_ring_buffer *buf = ctx->buf;
	unsigned long end_offset = ctx->pre_offset + ctx->slot_size;

	/*
	 * We need to ensure that if the cmpxchg succeeds and discards the
	 * record, the next record will record a full TSC, because it cannot
	 * rely on the last_tsc associated with the discarded record to detect
	 * overflows. The only way to ensure this is to set the last_tsc to 0
	 * (assuming no 64-bit TSC overflow), which forces to write a 64-bit
	 * timestamp in the next record.
	 *
	 * Note: if discard fails, we must leave the TSC in the record header.
	 * It is needed to keep track of TSC overflows for the following
	 * records.
	 */
	save_last_tsc(config, buf, 0ULL);

	if (likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
		   != end_offset))
		return -EPERM;
	else
		return 0;
}

static inline
void channel_record_disable(const struct lib_ring_buffer_config *config,
			    struct channel *chan)
{
	atomic_inc(&chan->record_disabled);
}

static inline
void channel_record_enable(const struct lib_ring_buffer_config *config,
			   struct channel *chan)
{
	atomic_dec(&chan->record_disabled);
}

static inline
void lib_ring_buffer_record_disable(const struct lib_ring_buffer_config *config,
				    struct lib_ring_buffer *buf)
{
	atomic_inc(&buf->record_disabled);
}

static inline
void lib_ring_buffer_record_enable(const struct lib_ring_buffer_config *config,
				   struct lib_ring_buffer *buf)
{
	atomic_dec(&buf->record_disabled);
}

#endif /* _LIB_RING_BUFFER_FRONTEND_API_H */
Commit	Line	Data
886d51a3 MD	1	#ifndef _LIB_RING_BUFFER_FRONTEND_API_H
886d51a3 MD	2	#define _LIB_RING_BUFFER_FRONTEND_API_H
f3bc08c5 MD	3
f3bc08c5 MD	4	/*
886d51a3	5	* lib/ringbuffer/frontend_api.h
f3bc08c5 MD	6	*
	7	* Ring Buffer Library Synchronization Header (buffer write API).
	8	*
886d51a3 MD	9	* Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	10	*
	11	* This library is free software; you can redistribute it and/or
	12	* modify it under the terms of the GNU Lesser General Public
	13	* License as published by the Free Software Foundation; only
	14	* version 2.1 of the License.
	15	*
	16	* This library is distributed in the hope that it will be useful,
	17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	19	* Lesser General Public License for more details.
	20	*
	21	* You should have received a copy of the GNU Lesser General Public
	22	* License along with this library; if not, write to the Free Software
	23	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	24	*
f3bc08c5 MD	25	* Author:
	26	* Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	27	*
	28	* See ring_buffer_frontend.c for more information on wait-free algorithms.
	29	* See linux/ringbuffer/frontend.h for channel allocation and read-side API.
f3bc08c5 MD	30	*/
	31
	32	#include "../../wrapper/ringbuffer/frontend.h"
e6b06d7d	33	#include "../../wrapper/percpu-defs.h"
f3bc08c5	34	#include <linux/errno.h>
dfbc2ec7	35	#include <linux/prefetch.h>
f3bc08c5 MD	36
	37	/**
	38	* lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit.
	39	*
	40	* Disables preemption (acts as a RCU read-side critical section) and keeps a
	41	* ring buffer nesting count as supplementary safety net to ensure tracer client
	42	* code will never trigger an endless recursion. Returns the processor ID on
	43	* success, -EPERM on failure (nesting count too high).
	44	*
	45	* asm volatile and "memory" clobber prevent the compiler from moving
	46	* instructions out of the ring buffer nesting count. This is required to ensure
	47	* that probe side-effects which can cause recursion (e.g. unforeseen traps,
	48	* divisions by 0, ...) are triggered within the incremented nesting count
	49	* section.
	50	*/
	51	static inline
	52	int lib_ring_buffer_get_cpu(const struct lib_ring_buffer_config *config)
	53	{
	54	int cpu, nesting;
	55
	56	rcu_read_lock_sched_notrace();
	57	cpu = smp_processor_id();
	58	nesting = ++per_cpu(lib_ring_buffer_nesting, cpu);
	59	barrier();
	60
	61	if (unlikely(nesting > 4)) {
	62	WARN_ON_ONCE(1);
	63	per_cpu(lib_ring_buffer_nesting, cpu)--;
	64	rcu_read_unlock_sched_notrace();
	65	return -EPERM;
	66	} else
	67	return cpu;
	68	}
	69
	70	/**
	71	* lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit.
	72	*/
	73	static inline
	74	void lib_ring_buffer_put_cpu(const struct lib_ring_buffer_config *config)
	75	{
	76	barrier();
e6b06d7d	77	(*lttng_this_cpu_ptr(&lib_ring_buffer_nesting))--;
f3bc08c5 MD	78	rcu_read_unlock_sched_notrace();
	79	}
	80
	81	/*
	82	* lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not
	83	* part of the API per se.
	84	*
	85	* returns 0 if reserve ok, or 1 if the slow path must be taken.
	86	*/
	87	static inline
	88	int lib_ring_buffer_try_reserve(const struct lib_ring_buffer_config *config,
	89	struct lib_ring_buffer_ctx *ctx,
	90	unsigned long o_begin, unsigned long o_end,
	91	unsigned long o_old, size_t before_hdr_pad)
	92	{
	93	struct channel *chan = ctx->chan;
	94	struct lib_ring_buffer *buf = ctx->buf;
	95	*o_begin = v_read(config, &buf->offset);
	96	o_old = o_begin;
	97
	98	ctx->tsc = lib_ring_buffer_clock_read(chan);
97ca2c54 MD	99	if ((int64_t) ctx->tsc == -EIO)
97ca2c54 MD	100	return 1;
f3bc08c5 MD	101
	102	/*
	103	* Prefetch cacheline for read because we have to read the previous
	104	* commit counter to increment it and commit seq value to compare it to
	105	* the commit counter.
	106	*/
	107	prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);
	108
	109	if (last_tsc_overflow(config, buf, ctx->tsc))
64c796d8	110	ctx->rflags \|= RING_BUFFER_RFLAG_FULL_TSC;
f3bc08c5 MD	111
	112	if (unlikely(subbuf_offset(*o_begin, chan) == 0))
	113	return 1;
	114
	115	ctx->slot_size = record_header_size(config, chan, *o_begin,
64c796d8	116	before_hdr_pad, ctx);
f3bc08c5 MD	117	ctx->slot_size +=
	118	lib_ring_buffer_align(*o_begin + ctx->slot_size,
	119	ctx->largest_align) + ctx->data_size;
	120	if (unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
	121	> chan->backend.subbuf_size))
	122	return 1;
	123
	124	/*
	125	* Record fits in the current buffer and we are not on a switch
	126	* boundary. It's safe to write.
	127	*/
	128	o_end = o_begin + ctx->slot_size;
f5ea5800 MD	129
	130	if (unlikely((subbuf_offset(*o_end, chan)) == 0))
	131	/*
	132	* The offset_end will fall at the very beginning of the next
	133	* subbuffer.
	134	*/
	135	return 1;
	136
f3bc08c5 MD	137	return 0;
	138	}
	139
	140	/**
	141	* lib_ring_buffer_reserve - Reserve space in a ring buffer.
	142	* @config: ring buffer instance configuration.
	143	* @ctx: ring buffer context. (input and output) Must be already initialized.
	144	*
	145	* Atomic wait-free slot reservation. The reserved space starts at the context
	146	* "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc".
	147	*
97ca2c54 MD	148	* Return :
	149	* 0 on success.
	150	* -EAGAIN if channel is disabled.
	151	* -ENOSPC if event size is too large for packet.
	152	* -ENOBUFS if there is currently not enough space in buffer for the event.
	153	* -EIO if data cannot be written into the buffer for any other reason.
f3bc08c5 MD	154	*/
	155
	156	static inline
	157	int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
	158	struct lib_ring_buffer_ctx *ctx)
	159	{
	160	struct channel *chan = ctx->chan;
	161	struct lib_ring_buffer *buf;
	162	unsigned long o_begin, o_end, o_old;
	163	size_t before_hdr_pad = 0;
	164
	165	if (atomic_read(&chan->record_disabled))
	166	return -EAGAIN;
	167
	168	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
	169	buf = per_cpu_ptr(chan->backend.buf, ctx->cpu);
	170	else
	171	buf = chan->backend.buf;
	172	if (atomic_read(&buf->record_disabled))
	173	return -EAGAIN;
	174	ctx->buf = buf;
	175
	176	/*
	177	* Perform retryable operations.
	178	*/
	179	if (unlikely(lib_ring_buffer_try_reserve(config, ctx, &o_begin,
	180	&o_end, &o_old, &before_hdr_pad)))
	181	goto slow_path;
	182
	183	if (unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
	184	!= o_old))
	185	goto slow_path;
	186
	187	/*
	188	* Atomically update last_tsc. This update races against concurrent
	189	* atomic updates, but the race will always cause supplementary full TSC
	190	* record headers, never the opposite (missing a full TSC record header
	191	* when it would be needed).
	192	*/
	193	save_last_tsc(config, ctx->buf, ctx->tsc);
	194
	195	/*
	196	* Push the reader if necessary
	197	*/
	198	lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);
	199
	200	/*
	201	* Clear noref flag for this subbuffer.
	202	*/
	203	lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
	204	subbuf_index(o_end - 1, chan));
	205
	206	ctx->pre_offset = o_begin;
	207	ctx->buf_offset = o_begin + before_hdr_pad;
	208	return 0;
	209	slow_path:
	210	return lib_ring_buffer_reserve_slow(ctx);
	211	}
	212
	213	/**
	214	* lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer.
	215	* @config: ring buffer instance configuration.
	216	* @buf: buffer
	217	* @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH)
218	*
219	* This operation is completely reentrant : can be called while tracing is
220	* active with absolutely no lock held.
221	*
222	* Note, however, that as a v_cmpxchg is used for some atomic operations and
223	* requires to be executed locally for per-CPU buffers, this function must be
224	* called from the CPU which owns the buffer for a ACTIVE flush, with preemption
225	* disabled, for RING_BUFFER_SYNC_PER_CPU configuration.
226	*/
227	static inline
228	void lib_ring_buffer_switch(const struct lib_ring_buffer_config *config,
229	struct lib_ring_buffer *buf, enum switch_mode mode)
230	{
231	lib_ring_buffer_switch_slow(buf, mode);
232	}
233
234	/* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */
235
236	/**
237	* lib_ring_buffer_commit - Commit an record.
238	* @config: ring buffer instance configuration.
239	* @ctx: ring buffer context. (input arguments only)
240	*
241	* Atomic unordered slot commit. Increments the commit count in the
242	* specified sub-buffer, and delivers it if necessary.
243	*/
244	static inline
245	void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
246	const struct lib_ring_buffer_ctx *ctx)
247	{
248	struct channel *chan = ctx->chan;
249	struct lib_ring_buffer *buf = ctx->buf;
250	unsigned long offset_end = ctx->buf_offset;
251	unsigned long endidx = subbuf_index(offset_end - 1, chan);
252	unsigned long commit_count;
253
254	/*
255	* Must count record before incrementing the commit count.
256	*/
257	subbuffer_count_record(config, &buf->backend, endidx);
258
259	/*
260	* Order all writes to buffer before the commit count update that will
261	* determine that the subbuffer is full.
262	*/
263	if (config->ipi == RING_BUFFER_IPI_BARRIER) {
264	/*
265	* Must write slot data before incrementing commit count. This
266	* compiler barrier is upgraded into a smp_mb() by the IPI sent
267	* by get_subbuf().
268	*/
269	barrier();
270	} else
271	smp_wmb();
272
273	v_add(config, ctx->slot_size, &buf->commit_hot[endidx].cc);
274
275	/*
276	* commit count read can race with concurrent OOO commit count updates.
277	* This is only needed for lib_ring_buffer_check_deliver (for
278	* non-polling delivery only) and for
279	* lib_ring_buffer_write_commit_counter. The race can only cause the
280	* counter to be read with the same value more than once, which could
281	* cause :
282	* - Multiple delivery for the same sub-buffer (which is handled
283	* gracefully by the reader code) if the value is for a full
284	* sub-buffer. It's important that we can never miss a sub-buffer
285	* delivery. Re-reading the value after the v_add ensures this.
286	* - Reading a commit_count with a higher value that what was actually
287	* added to it for the lib_ring_buffer_write_commit_counter call
288	* (again caused by a concurrent committer). It does not matter,
289	* because this function is interested in the fact that the commit
290	* count reaches back the reserve offset for a specific sub-buffer,
291	* which is completely independent of the order.
292	*/
293	commit_count = v_read(config, &buf->commit_hot[endidx].cc);
294
295	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
635e457c	296	commit_count, endidx, ctx->tsc);
f3bc08c5 MD	297	/*
	298	* Update used size at each commit. It's needed only for extracting
	299	* ring_buffer buffers from vmcore, after crash.
	300	*/
	301	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
7915e163	302	offset_end, commit_count);
f3bc08c5 MD	303	}
	304
	305	/**
	306	* lib_ring_buffer_try_discard_reserve - Try discarding a record.
	307	* @config: ring buffer instance configuration.
	308	* @ctx: ring buffer context. (input arguments only)
	309	*
	310	* Only succeeds if no other record has been written after the record to
	311	* discard. If discard fails, the record must be committed to the buffer.
	312	*
	313	* Returns 0 upon success, -EPERM if the record cannot be discarded.
	314	*/
	315	static inline
	316	int lib_ring_buffer_try_discard_reserve(const struct lib_ring_buffer_config *config,
	317	const struct lib_ring_buffer_ctx *ctx)
	318	{
	319	struct lib_ring_buffer *buf = ctx->buf;
	320	unsigned long end_offset = ctx->pre_offset + ctx->slot_size;
	321
	322	/*
	323	* We need to ensure that if the cmpxchg succeeds and discards the
	324	* record, the next record will record a full TSC, because it cannot
	325	* rely on the last_tsc associated with the discarded record to detect
	326	* overflows. The only way to ensure this is to set the last_tsc to 0
	327	* (assuming no 64-bit TSC overflow), which forces to write a 64-bit
	328	* timestamp in the next record.
	329	*
	330	* Note: if discard fails, we must leave the TSC in the record header.
	331	* It is needed to keep track of TSC overflows for the following
	332	* records.
	333	*/
	334	save_last_tsc(config, buf, 0ULL);
	335
	336	if (likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
	337	!= end_offset))
	338	return -EPERM;
	339	else
	340	return 0;
	341	}
	342
	343	static inline
	344	void channel_record_disable(const struct lib_ring_buffer_config *config,
	345	struct channel *chan)
	346	{
	347	atomic_inc(&chan->record_disabled);
	348	}
	349
	350	static inline
	351	void channel_record_enable(const struct lib_ring_buffer_config *config,
	352	struct channel *chan)
	353	{
	354	atomic_dec(&chan->record_disabled);
	355	}
	356
	357	static inline
	358	void lib_ring_buffer_record_disable(const struct lib_ring_buffer_config *config,
	359	struct lib_ring_buffer *buf)
	360	{
	361	atomic_inc(&buf->record_disabled);
	362	}
	363
	364	static inline
	365	void lib_ring_buffer_record_enable(const struct lib_ring_buffer_config *config,
	366	struct lib_ring_buffer *buf)
367	{
368	atomic_dec(&buf->record_disabled);
369	}
370
886d51a3	371	#endif /* _LIB_RING_BUFFER_FRONTEND_API_H */