From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 28 Apr 2021 18:56:05 +0000 (-0400)
Subject: Refactoring: ring buffer context
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=b1199bd39f4b617b99518b72ceeea644b164b901;p=lttng-modules.git

Refactoring: ring buffer context

Split the ring buffer context into:

- Public ring buffer context (initialized by probe),
- Private context (initialized by reserve callback),

Pass event recorder rather than channel as client_ctx for events
generated from instrumentation (calling ring buffer client).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Iecd23f11c54da4ba58a97c46192f775a0a74bd85
---

diff --git a/include/lttng/tracepoint-event-impl.h b/include/lttng/tracepoint-event-impl.h
index a8a438b2..dbb92b85 100644
--- a/include/lttng/tracepoint-event-impl.h
+++ b/include/lttng/tracepoint-event-impl.h
@@ -1092,8 +1092,8 @@ static void __event_probe__##_name(_data_proto)						\
 			goto __post;							\
 		}									\
 		__event_align = __event_get_align__##_name(_locvar_args);		\
-		lib_ring_buffer_ctx_init(&__ctx, __chan->chan, __event_len,		\
-					 __event_align, -1, &__lttng_probe_ctx);	\
+		lib_ring_buffer_ctx_init(&__ctx, __event_recorder, __event_len,		\
+					 __event_align, &__lttng_probe_ctx);		\
 		__ret = __chan->ops->event_reserve(&__ctx, __event_recorder->priv->id);	\
 		if (__ret < 0)								\
 			goto __post;							\
diff --git a/include/ringbuffer/backend.h b/include/ringbuffer/backend.h
index a975c7ec..5ceb4f1a 100644
--- a/include/ringbuffer/backend.h
+++ b/include/ringbuffer/backend.h
@@ -75,10 +75,10 @@ void lib_ring_buffer_write(const struct lib_ring_buffer_config *config,
 			   struct lib_ring_buffer_ctx *ctx,
 			   const void *src, size_t len)
 {
-	struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
-	struct channel_backend *chanb = &ctx->chan->backend;
+	struct lib_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
+	struct channel_backend *chanb = &ctx->priv.chan->backend;
 	size_t index, pagecpy;
-	size_t offset = ctx->buf_offset;
+	size_t offset = ctx->priv.buf_offset;
 	struct lib_ring_buffer_backend_pages *backend_pages;
 
 	if (unlikely(!len))
@@ -95,7 +95,7 @@ void lib_ring_buffer_write(const struct lib_ring_buffer_config *config,
 					src, len);
 	else
 		_lib_ring_buffer_write(bufb, offset, src, len, 0);
-	ctx->buf_offset += len;
+	ctx->priv.buf_offset += len;
 }
 
 /**
@@ -116,10 +116,10 @@ void lib_ring_buffer_memset(const struct lib_ring_buffer_config *config,
 			    struct lib_ring_buffer_ctx *ctx, int c, size_t len)
 {
 
-	struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
-	struct channel_backend *chanb = &ctx->chan->backend;
+	struct lib_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
+	struct channel_backend *chanb = &ctx->priv.chan->backend;
 	size_t index, pagecpy;
-	size_t offset = ctx->buf_offset;
+	size_t offset = ctx->priv.buf_offset;
 	struct lib_ring_buffer_backend_pages *backend_pages;
 
 	if (unlikely(!len))
@@ -135,7 +135,7 @@ void lib_ring_buffer_memset(const struct lib_ring_buffer_config *config,
 					  c, len);
 	else
 		_lib_ring_buffer_memset(bufb, offset, c, len, 0);
-	ctx->buf_offset += len;
+	ctx->priv.buf_offset += len;
 }
 
 /*
@@ -213,10 +213,10 @@ void lib_ring_buffer_strcpy(const struct lib_ring_buffer_config *config,
 			   struct lib_ring_buffer_ctx *ctx,
 			   const char *src, size_t len, int pad)
 {
-	struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
-	struct channel_backend *chanb = &ctx->chan->backend;
+	struct lib_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
+	struct channel_backend *chanb = &ctx->priv.chan->backend;
 	size_t index, pagecpy;
-	size_t offset = ctx->buf_offset;
+	size_t offset = ctx->priv.buf_offset;
 	struct lib_ring_buffer_backend_pages *backend_pages;
 
 	if (unlikely(!len))
@@ -250,7 +250,7 @@ void lib_ring_buffer_strcpy(const struct lib_ring_buffer_config *config,
 	} else {
 		_lib_ring_buffer_strcpy(bufb, offset, src, len, 0, pad);
 	}
-	ctx->buf_offset += len;
+	ctx->priv.buf_offset += len;
 }
 
 /**
@@ -271,10 +271,10 @@ void lib_ring_buffer_copy_from_user_inatomic(const struct lib_ring_buffer_config
 				    struct lib_ring_buffer_ctx *ctx,
 				    const void __user *src, size_t len)
 {
-	struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
-	struct channel_backend *chanb = &ctx->chan->backend;
+	struct lib_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
+	struct channel_backend *chanb = &ctx->priv.chan->backend;
 	size_t index, pagecpy;
-	size_t offset = ctx->buf_offset;
+	size_t offset = ctx->priv.buf_offset;
 	struct lib_ring_buffer_backend_pages *backend_pages;
 	unsigned long ret;
 
@@ -302,7 +302,7 @@ void lib_ring_buffer_copy_from_user_inatomic(const struct lib_ring_buffer_config
 		_lib_ring_buffer_copy_from_user_inatomic(bufb, offset, src, len, 0);
 	}
 	pagefault_enable();
-	ctx->buf_offset += len;
+	ctx->priv.buf_offset += len;
 
 	return;
 
@@ -338,10 +338,10 @@ void lib_ring_buffer_strcpy_from_user_inatomic(const struct lib_ring_buffer_conf
 		struct lib_ring_buffer_ctx *ctx,
 		const void __user *src, size_t len, int pad)
 {
-	struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
-	struct channel_backend *chanb = &ctx->chan->backend;
+	struct lib_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
+	struct channel_backend *chanb = &ctx->priv.chan->backend;
 	size_t index, pagecpy;
-	size_t offset = ctx->buf_offset;
+	size_t offset = ctx->priv.buf_offset;
 	struct lib_ring_buffer_backend_pages *backend_pages;
 
 	if (unlikely(!len))
@@ -382,7 +382,7 @@ void lib_ring_buffer_strcpy_from_user_inatomic(const struct lib_ring_buffer_conf
 					len, 0, pad);
 	}
 	pagefault_enable();
-	ctx->buf_offset += len;
+	ctx->priv.buf_offset += len;
 
 	return;
 
diff --git a/include/ringbuffer/backend_internal.h b/include/ringbuffer/backend_internal.h
index fd24c674..8a93ab07 100644
--- a/include/ringbuffer/backend_internal.h
+++ b/include/ringbuffer/backend_internal.h
@@ -195,9 +195,9 @@ void lib_ring_buffer_backend_get_pages(const struct lib_ring_buffer_config *conf
 			struct lib_ring_buffer_ctx *ctx,
 			struct lib_ring_buffer_backend_pages **backend_pages)
 {
-	struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
-	struct channel_backend *chanb = &ctx->chan->backend;
-	size_t sbidx, offset = ctx->buf_offset;
+	struct lib_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
+	struct channel_backend *chanb = &ctx->priv.chan->backend;
+	size_t sbidx, offset = ctx->priv.buf_offset;
 	unsigned long sb_bindex, id;
 	struct lib_ring_buffer_backend_pages *rpages;
 
@@ -206,7 +206,7 @@ void lib_ring_buffer_backend_get_pages(const struct lib_ring_buffer_config *conf
 	id = bufb->buf_wsb[sbidx].id;
 	sb_bindex = subbuffer_id_get_index(config, id);
 	rpages = bufb->array[sb_bindex];
-	CHAN_WARN_ON(ctx->chan,
+	CHAN_WARN_ON(ctx->priv.chan,
 		     config->mode == RING_BUFFER_OVERWRITE
 		     && subbuffer_id_is_noref(config, id));
 	*backend_pages = rpages;
@@ -218,7 +218,7 @@ struct lib_ring_buffer_backend_pages *
 	lib_ring_buffer_get_backend_pages_from_ctx(const struct lib_ring_buffer_config *config,
 		struct lib_ring_buffer_ctx *ctx)
 {
-	return ctx->backend_pages;
+	return ctx->priv.backend_pages;
 }
 
 /*
diff --git a/include/ringbuffer/config.h b/include/ringbuffer/config.h
index 2019e14c..bc638f94 100644
--- a/include/ringbuffer/config.h
+++ b/include/ringbuffer/config.h
@@ -20,6 +20,7 @@ struct lib_ring_buffer;
 struct channel;
 struct lib_ring_buffer_config;
 struct lib_ring_buffer_ctx;
+struct lttng_kernel_ring_buffer_ctx_private;
 
 /*
  * Ring buffer client callbacks. Only used by slow path, never on fast path.
@@ -156,6 +157,40 @@ struct lib_ring_buffer_config {
 	struct lib_ring_buffer_client_cb cb;
 };
 
+/*
+ * ring buffer private context
+ *
+ * Private context passed to lib_ring_buffer_reserve(), lib_ring_buffer_commit(),
+ * lib_ring_buffer_try_discard_reserve(), lib_ring_buffer_align_ctx() and
+ * lib_ring_buffer_write().
+ *
+ * Get struct lttng_kernel_ring_buffer_ctx parent with container_of().
+ */
+
+struct lttng_kernel_ring_buffer_ctx_private {
+	/* input received by lib_ring_buffer_reserve(). */
+	struct channel *chan;			/* ring buffer channel */
+
+	/* output from lib_ring_buffer_reserve() */
+	int reserve_cpu;			/* processor id updated by the reserve */
+	size_t slot_size;			/* size of the reserved slot */
+	unsigned long buf_offset;		/* offset following the record header */
+	unsigned long pre_offset;		/*
+						 * Initial offset position _before_
+						 * the record is written. Positioned
+						 * prior to record header alignment
+						 * padding.
+						 */
+	u64 tsc;				/* time-stamp counter value */
+	unsigned int rflags;			/* reservation flags */
+
+	struct lib_ring_buffer *buf;		/*
+						 * buffer corresponding to processor id
+						 * for this channel
+						 */
+	struct lib_ring_buffer_backend_pages *backend_pages;
+};
+
 /*
  * ring buffer context
  *
@@ -164,57 +199,37 @@ struct lib_ring_buffer_config {
  * lib_ring_buffer_write().
  */
 struct lib_ring_buffer_ctx {
+	/* Private ring buffer context, set by reserve callback. */
+	struct lttng_kernel_ring_buffer_ctx_private priv;
+
 	/* input received by lib_ring_buffer_reserve(), saved here. */
-	struct channel *chan;		/* channel */
-	void *priv;			/* client private data */
+	void *client_priv;		/* Ring buffer client private data */
+
 	size_t data_size;		/* size of payload */
 	int largest_align;		/*
 					 * alignment of the largest element
 					 * in the payload
 					 */
-	int cpu;			/* processor id */
-
-	/* output from lib_ring_buffer_reserve() */
-	struct lib_ring_buffer *buf;	/*
-					 * buffer corresponding to processor id
-					 * for this channel
-					 */
-	size_t slot_size;		/* size of the reserved slot */
-	unsigned long buf_offset;	/* offset following the record header */
-	unsigned long pre_offset;	/*
-					 * Initial offset position _before_
-					 * the record is written. Positioned
-					 * prior to record header alignment
-					 * padding.
-					 */
-	u64 tsc;			/* time-stamp counter value */
-	unsigned int rflags;		/* reservation flags */
-	/* Cache backend pages pointer chasing. */
-	struct lib_ring_buffer_backend_pages *backend_pages;
+	struct lttng_probe_ctx *probe_ctx;	/* Probe context */
 };
 
 /**
  * lib_ring_buffer_ctx_init - initialize ring buffer context
  * @ctx: ring buffer context to initialize
- * @chan: channel
- * @priv: client private data
+ * @client_priv: client private data
  * @data_size: size of record data payload. It must be greater than 0.
  * @largest_align: largest alignment within data payload types
- * @cpu: processor id
  */
 static inline
 void lib_ring_buffer_ctx_init(struct lib_ring_buffer_ctx *ctx,
-			      struct channel *chan,
+			      void *client_priv,
 			      size_t data_size, int largest_align,
-			      int cpu, void *priv)
+			      struct lttng_probe_ctx *probe_ctx)
 {
-	ctx->chan = chan;
-	ctx->priv = priv;
+	ctx->client_priv = client_priv;
 	ctx->data_size = data_size;
 	ctx->largest_align = largest_align;
-	ctx->cpu = cpu;
-	ctx->rflags = 0;
-	ctx->backend_pages = NULL;
+	ctx->probe_ctx = probe_ctx;
 }
 
 /*
@@ -282,7 +297,7 @@ static inline
 void lib_ring_buffer_align_ctx(struct lib_ring_buffer_ctx *ctx,
 			   size_t alignment)
 {
-	ctx->buf_offset += lib_ring_buffer_align(ctx->buf_offset,
+	ctx->priv.buf_offset += lib_ring_buffer_align(ctx->priv.buf_offset,
 						 alignment);
 }
 
diff --git a/include/ringbuffer/frontend_api.h b/include/ringbuffer/frontend_api.h
index 3fa6c82f..1444e60a 100644
--- a/include/ringbuffer/frontend_api.h
+++ b/include/ringbuffer/frontend_api.h
@@ -75,13 +75,13 @@ int lib_ring_buffer_try_reserve(const struct lib_ring_buffer_config *config,
 				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;
+	struct channel *chan = ctx->priv.chan;
+	struct lib_ring_buffer *buf = ctx->priv.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)
+	ctx->priv.tsc = lib_ring_buffer_clock_read(chan);
+	if ((int64_t) ctx->priv.tsc == -EIO)
 		return 1;
 
 	/*
@@ -91,18 +91,18 @@ int lib_ring_buffer_try_reserve(const struct lib_ring_buffer_config *config,
 	 */
 	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 (last_tsc_overflow(config, buf, ctx->priv.tsc))
+		ctx->priv.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,
+	ctx->priv.slot_size = record_header_size(config, chan, *o_begin,
 					    before_hdr_pad, ctx, client_ctx);
-	ctx->slot_size +=
-		lib_ring_buffer_align(*o_begin + ctx->slot_size,
+	ctx->priv.slot_size +=
+		lib_ring_buffer_align(*o_begin + ctx->priv.slot_size,
 				      ctx->largest_align) + ctx->data_size;
-	if (unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
+	if (unlikely((subbuf_offset(*o_begin, chan) + ctx->priv.slot_size)
 		     > chan->backend.subbuf_size))
 		return 1;
 
@@ -110,7 +110,7 @@ int lib_ring_buffer_try_reserve(const struct lib_ring_buffer_config *config,
 	 * 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;
+	*o_end = *o_begin + ctx->priv.slot_size;
 
 	if (unlikely((subbuf_offset(*o_end, chan)) == 0))
 		/*
@@ -143,7 +143,7 @@ int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
 			    struct lib_ring_buffer_ctx *ctx,
 			    void *client_ctx)
 {
-	struct channel *chan = ctx->chan;
+	struct channel *chan = ctx->priv.chan;
 	struct lib_ring_buffer *buf;
 	unsigned long o_begin, o_end, o_old;
 	size_t before_hdr_pad = 0;
@@ -152,12 +152,12 @@ int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
 		return -EAGAIN;
 
 	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
-		buf = per_cpu_ptr(chan->backend.buf, ctx->cpu);
+		buf = per_cpu_ptr(chan->backend.buf, ctx->priv.reserve_cpu);
 	else
 		buf = chan->backend.buf;
 	if (unlikely(atomic_read(&buf->record_disabled)))
 		return -EAGAIN;
-	ctx->buf = buf;
+	ctx->priv.buf = buf;
 
 	/*
 	 * Perform retryable operations.
@@ -166,7 +166,7 @@ int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
 						 &o_end, &o_old, &before_hdr_pad)))
 		goto slow_path;
 
-	if (unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
+	if (unlikely(v_cmpxchg(config, &ctx->priv.buf->offset, o_old, o_end)
 		     != o_old))
 		goto slow_path;
 
@@ -176,21 +176,21 @@ int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
 	 * record headers, never the opposite (missing a full TSC record header
 	 * when it would be needed).
 	 */
-	save_last_tsc(config, ctx->buf, ctx->tsc);
+	save_last_tsc(config, ctx->priv.buf, ctx->priv.tsc);
 
 	/*
 	 * Push the reader if necessary
 	 */
-	lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);
+	lib_ring_buffer_reserve_push_reader(ctx->priv.buf, chan, o_end - 1);
 
 	/*
 	 * Clear noref flag for this subbuffer.
 	 */
-	lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
+	lib_ring_buffer_clear_noref(config, &ctx->priv.buf->backend,
 				subbuf_index(o_end - 1, chan));
 
-	ctx->pre_offset = o_begin;
-	ctx->buf_offset = o_begin + before_hdr_pad;
+	ctx->priv.pre_offset = o_begin;
+	ctx->priv.buf_offset = o_begin + before_hdr_pad;
 	return 0;
 slow_path:
 	return lib_ring_buffer_reserve_slow(ctx, client_ctx);
@@ -231,9 +231,9 @@ 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;
+	struct channel *chan = ctx->priv.chan;
+	struct lib_ring_buffer *buf = ctx->priv.buf;
+	unsigned long offset_end = ctx->priv.buf_offset;
 	unsigned long endidx = subbuf_index(offset_end - 1, chan);
 	unsigned long commit_count;
 	struct commit_counters_hot *cc_hot = &buf->commit_hot[endidx];
@@ -257,7 +257,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	} else
 		smp_wmb();
 
-	v_add(config, ctx->slot_size, &cc_hot->cc);
+	v_add(config, ctx->priv.slot_size, &cc_hot->cc);
 
 	/*
 	 * commit count read can race with concurrent OOO commit count updates.
@@ -280,7 +280,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	commit_count = v_read(config, &cc_hot->cc);
 
 	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
-				      commit_count, endidx, ctx->tsc);
+				      commit_count, endidx, ctx->priv.tsc);
 	/*
 	 * Update used size at each commit. It's needed only for extracting
 	 * ring_buffer buffers from vmcore, after crash.
@@ -303,8 +303,8 @@ 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;
+	struct lib_ring_buffer *buf = ctx->priv.buf;
+	unsigned long end_offset = ctx->priv.pre_offset + ctx->priv.slot_size;
 
 	/*
 	 * We need to ensure that if the cmpxchg succeeds and discards the
@@ -320,7 +320,7 @@ int lib_ring_buffer_try_discard_reserve(const struct lib_ring_buffer_config *con
 	 */
 	save_last_tsc(config, buf, 0ULL);
 
-	if (likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
+	if (likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->priv.pre_offset)
 		   != end_offset))
 		return -EPERM;
 	else
diff --git a/src/lib/ringbuffer/ring_buffer_frontend.c b/src/lib/ringbuffer/ring_buffer_frontend.c
index 38ba05d9..d9e64dff 100644
--- a/src/lib/ringbuffer/ring_buffer_frontend.c
+++ b/src/lib/ringbuffer/ring_buffer_frontend.c
@@ -2011,14 +2011,14 @@ retry:
 	offsets->switch_old_end = 0;
 	offsets->pre_header_padding = 0;
 
-	ctx->tsc = config->cb.ring_buffer_clock_read(chan);
-	if ((int64_t) ctx->tsc == -EIO)
+	ctx->priv.tsc = config->cb.ring_buffer_clock_read(chan);
+	if ((int64_t) ctx->priv.tsc == -EIO)
 		return -EIO;
 
-	if (last_tsc_overflow(config, buf, ctx->tsc))
-		ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC;
+	if (last_tsc_overflow(config, buf, ctx->priv.tsc))
+		ctx->priv.rflags |= RING_BUFFER_RFLAG_FULL_TSC;
 
-	if (unlikely(subbuf_offset(offsets->begin, ctx->chan) == 0)) {
+	if (unlikely(subbuf_offset(offsets->begin, ctx->priv.chan) == 0)) {
 		offsets->switch_new_start = 1;		/* For offsets->begin */
 	} else {
 		offsets->size = config->cb.record_header_size(config, chan,
@@ -2175,13 +2175,13 @@ EXPORT_SYMBOL_GPL(lib_ring_buffer_lost_event_too_big);
 int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx,
 		void *client_ctx)
 {
-	struct channel *chan = ctx->chan;
+	struct channel *chan = ctx->priv.chan;
 	const struct lib_ring_buffer_config *config = &chan->backend.config;
 	struct lib_ring_buffer *buf;
 	struct switch_offsets offsets;
 	int ret;
 
-	ctx->buf = buf = get_current_buf(chan, ctx->cpu);
+	ctx->priv.buf = buf = get_current_buf(chan, ctx->priv.reserve_cpu);
 	offsets.size = 0;
 
 	do {
@@ -2199,7 +2199,7 @@ int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx,
 	 * records, never the opposite (missing a full TSC record when it would
 	 * be needed).
 	 */
-	save_last_tsc(config, buf, ctx->tsc);
+	save_last_tsc(config, buf, ctx->priv.tsc);
 
 	/*
 	 * Push the reader if necessary
@@ -2218,21 +2218,21 @@ int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx,
 	if (unlikely(offsets.switch_old_end)) {
 		lib_ring_buffer_clear_noref(config, &buf->backend,
 					    subbuf_index(offsets.old - 1, chan));
-		lib_ring_buffer_switch_old_end(buf, chan, &offsets, ctx->tsc);
+		lib_ring_buffer_switch_old_end(buf, chan, &offsets, ctx->priv.tsc);
 	}
 
 	/*
 	 * Populate new subbuffer.
 	 */
 	if (unlikely(offsets.switch_new_start))
-		lib_ring_buffer_switch_new_start(buf, chan, &offsets, ctx->tsc);
+		lib_ring_buffer_switch_new_start(buf, chan, &offsets, ctx->priv.tsc);
 
 	if (unlikely(offsets.switch_new_end))
-		lib_ring_buffer_switch_new_end(buf, chan, &offsets, ctx->tsc);
+		lib_ring_buffer_switch_new_end(buf, chan, &offsets, ctx->priv.tsc);
 
-	ctx->slot_size = offsets.size;
-	ctx->pre_offset = offsets.begin;
-	ctx->buf_offset = offsets.begin + offsets.pre_header_padding;
+	ctx->priv.slot_size = offsets.size;
+	ctx->priv.pre_offset = offsets.begin;
+	ctx->priv.buf_offset = offsets.begin + offsets.pre_header_padding;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_reserve_slow);
diff --git a/src/lttng-context-callstack-legacy-impl.h b/src/lttng-context-callstack-legacy-impl.h
index b74b966a..edd13cf5 100644
--- a/src/lttng-context-callstack-legacy-impl.h
+++ b/src/lttng-context-callstack-legacy-impl.h
@@ -107,7 +107,7 @@ struct stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *field,
 	 * Do not gather the userspace callstack context when the event was
 	 * triggered by the userspace callstack context saving mechanism.
 	 */
-	cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu);
+	cs_user_nesting = per_cpu(callstack_user_nesting, ctx->priv.reserve_cpu);
 
 	if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 		return NULL;
@@ -119,8 +119,8 @@ struct stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *field,
 	 * max nesting is checked in lib_ring_buffer_get_cpu().
 	 * Check it again as a safety net.
 	 */
-	cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
-	buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
+	cs = per_cpu_ptr(fdata->cs_percpu, ctx->priv.reserve_cpu);
+	buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->priv.reserve_cpu) - 1;
 	if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 		return NULL;
 
@@ -163,13 +163,13 @@ size_t lttng_callstack_sequence_get_size(size_t offset, struct lttng_kernel_ctx_
 	trace->nr_entries = 0;
 
 	if (fdata->mode == CALLSTACK_USER)
-		++per_cpu(callstack_user_nesting, ctx->cpu);
+		++per_cpu(callstack_user_nesting, ctx->priv.reserve_cpu);
 
 	/* do the real work and reserve space */
 	cs_types[fdata->mode].save_func(trace);
 
 	if (fdata->mode == CALLSTACK_USER)
-		per_cpu(callstack_user_nesting, ctx->cpu)--;
+		per_cpu(callstack_user_nesting, ctx->priv.reserve_cpu)--;
 
 	/*
 	 * Remove final ULONG_MAX delimiter. If we cannot find it, add
diff --git a/src/lttng-context-callstack-stackwalk-impl.h b/src/lttng-context-callstack-stackwalk-impl.h
index 7c452491..a7c5a062 100644
--- a/src/lttng-context-callstack-stackwalk-impl.h
+++ b/src/lttng-context-callstack-stackwalk-impl.h
@@ -109,7 +109,7 @@ struct lttng_stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *fie
 	 * Do not gather the userspace callstack context when the event was
 	 * triggered by the userspace callstack context saving mechanism.
 	 */
-	cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu);
+	cs_user_nesting = per_cpu(callstack_user_nesting, ctx->priv.reserve_cpu);
 
 	if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 		return NULL;
@@ -121,8 +121,8 @@ struct lttng_stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *fie
 	 * max nesting is checked in lib_ring_buffer_get_cpu().
 	 * Check it again as a safety net.
 	 */
-	cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
-	buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
+	cs = per_cpu_ptr(fdata->cs_percpu, ctx->priv.reserve_cpu);
+	buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->priv.reserve_cpu) - 1;
 	if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 		return NULL;
 
@@ -171,11 +171,11 @@ size_t lttng_callstack_sequence_get_size(size_t offset, struct lttng_kernel_ctx_
 						MAX_ENTRIES, 0);
 		break;
 	case CALLSTACK_USER:
-		++per_cpu(callstack_user_nesting, ctx->cpu);
+		++per_cpu(callstack_user_nesting, ctx->priv.reserve_cpu);
 		/* do the real work and reserve space */
 		trace->nr_entries = save_func_user(trace->entries,
 						MAX_ENTRIES);
-		per_cpu(callstack_user_nesting, ctx->cpu)--;
+		per_cpu(callstack_user_nesting, ctx->priv.reserve_cpu)--;
 		break;
 	default:
 		WARN_ON_ONCE(1);
diff --git a/src/lttng-context-cpu-id.c b/src/lttng-context-cpu-id.c
index 47c4aa20..7ae79a64 100644
--- a/src/lttng-context-cpu-id.c
+++ b/src/lttng-context-cpu-id.c
@@ -33,7 +33,7 @@ void cpu_id_record(struct lttng_kernel_ctx_field *field,
 {
 	int cpu;
 
-	cpu = ctx->cpu;
+	cpu = ctx->priv.reserve_cpu;
 	lib_ring_buffer_align_ctx(ctx, lttng_alignof(cpu));
 	chan->ops->event_write(ctx, &cpu, sizeof(cpu));
 }
diff --git a/src/lttng-context-interruptible.c b/src/lttng-context-interruptible.c
index 5cc64b2b..1c78d59b 100644
--- a/src/lttng-context-interruptible.c
+++ b/src/lttng-context-interruptible.c
@@ -36,7 +36,7 @@ void interruptible_record(struct lttng_kernel_ctx_field *field,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
-	struct lttng_probe_ctx *lttng_probe_ctx = ctx->priv;
+	struct lttng_probe_ctx *lttng_probe_ctx = ctx->probe_ctx;
 	int8_t interruptible = lttng_probe_ctx->interruptible;
 
 	lib_ring_buffer_align_ctx(ctx, lttng_alignof(interruptible));
diff --git a/src/lttng-context-perf-counters.c b/src/lttng-context-perf-counters.c
index e637bb75..53578475 100644
--- a/src/lttng-context-perf-counters.c
+++ b/src/lttng-context-perf-counters.c
@@ -38,7 +38,7 @@ void perf_counter_record(struct lttng_kernel_ctx_field *field,
 	struct perf_event *event;
 	uint64_t value;
 
-	event = perf_field->e[ctx->cpu];
+	event = perf_field->e[ctx->priv.reserve_cpu];
 	if (likely(event)) {
 		if (unlikely(event->state == PERF_EVENT_STATE_ERROR)) {
 			value = 0;
diff --git a/src/lttng-event-notifier-notification.c b/src/lttng-event-notifier-notification.c
index ce5a670f..e5bd172a 100644
--- a/src/lttng-event-notifier-notification.c
+++ b/src/lttng-event-notifier-notification.c
@@ -401,7 +401,7 @@ void notification_send(struct lttng_event_notifier_notification *notif,
 	kernel_notif.capture_buf_size = capture_buffer_content_len;
 
 	lib_ring_buffer_ctx_init(&ctx, event_notifier_group->chan, reserve_size,
-			lttng_alignof(kernel_notif), -1, NULL);
+			lttng_alignof(kernel_notif), NULL);
 	ret = event_notifier_group->ops->event_reserve(&ctx, 0);
 	if (ret < 0) {
 		record_error(event_notifier);
diff --git a/src/lttng-events.c b/src/lttng-events.c
index 51c5cb39..4c266466 100644
--- a/src/lttng-events.c
+++ b/src/lttng-events.c
@@ -2882,7 +2882,7 @@ int lttng_metadata_output_channel(struct lttng_metadata_stream *stream,
 			stream->transport->ops.packet_avail_size(chan),
 			len);
 	lib_ring_buffer_ctx_init(&ctx, chan, reserve_len,
-			sizeof(char), -1, NULL);
+			sizeof(char), NULL);
 	/*
 	 * If reservation failed, return an error to the caller.
 	 */
diff --git a/src/lttng-ring-buffer-client.h b/src/lttng-ring-buffer-client.h
index 26034e92..ff404368 100644
--- a/src/lttng-ring-buffer-client.h
+++ b/src/lttng-ring-buffer-client.h
@@ -149,7 +149,7 @@ size_t record_header_size(const struct lib_ring_buffer_config *config,
 	case 1:	/* compact */
 		padding = lib_ring_buffer_align(offset, lttng_alignof(uint32_t));
 		offset += padding;
-		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
+		if (!(ctx->priv.rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
 			offset += sizeof(uint32_t);	/* id and timestamp */
 		} else {
 			/* Minimum space taken by LTTNG_COMPACT_EVENT_BITS id */
@@ -165,7 +165,7 @@ size_t record_header_size(const struct lib_ring_buffer_config *config,
 		padding = lib_ring_buffer_align(offset, lttng_alignof(uint16_t));
 		offset += padding;
 		offset += sizeof(uint16_t);
-		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
+		if (!(ctx->priv.rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
 			offset += lib_ring_buffer_align(offset, lttng_alignof(uint32_t));
 			offset += sizeof(uint32_t);	/* timestamp */
 		} else {
@@ -207,9 +207,9 @@ void lttng_write_event_header(const struct lib_ring_buffer_config *config,
 			    struct lib_ring_buffer_ctx *ctx,
 			    uint32_t event_id)
 {
-	struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
+	struct lttng_channel *lttng_chan = channel_get_private(ctx->priv.chan);
 
-	if (unlikely(ctx->rflags))
+	if (unlikely(ctx->priv.rflags))
 		goto slow_path;
 
 	switch (lttng_chan->header_type) {
@@ -224,13 +224,13 @@ void lttng_write_event_header(const struct lib_ring_buffer_config *config,
 		bt_bitfield_write(&id_time, uint32_t,
 				LTTNG_COMPACT_EVENT_BITS,
 				LTTNG_COMPACT_TSC_BITS,
-				ctx->tsc);
+				ctx->priv.tsc);
 		lib_ring_buffer_write(config, ctx, &id_time, sizeof(id_time));
 		break;
 	}
 	case 2:	/* large */
 	{
-		uint32_t timestamp = (uint32_t) ctx->tsc;
+		uint32_t timestamp = (uint32_t) ctx->priv.tsc;
 		uint16_t id = event_id;
 
 		lib_ring_buffer_write(config, ctx, &id, sizeof(id));
@@ -256,11 +256,11 @@ void lttng_write_event_header_slow(const struct lib_ring_buffer_config *config,
 				 struct lib_ring_buffer_ctx *ctx,
 				 uint32_t event_id)
 {
-	struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
+	struct lttng_channel *lttng_chan = channel_get_private(ctx->priv.chan);
 
 	switch (lttng_chan->header_type) {
 	case 1:	/* compact */
-		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
+		if (!(ctx->priv.rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
 			uint32_t id_time = 0;
 
 			bt_bitfield_write(&id_time, uint32_t,
@@ -269,11 +269,11 @@ void lttng_write_event_header_slow(const struct lib_ring_buffer_config *config,
 					event_id);
 			bt_bitfield_write(&id_time, uint32_t,
 					LTTNG_COMPACT_EVENT_BITS,
-					LTTNG_COMPACT_TSC_BITS, ctx->tsc);
+					LTTNG_COMPACT_TSC_BITS, ctx->priv.tsc);
 			lib_ring_buffer_write(config, ctx, &id_time, sizeof(id_time));
 		} else {
 			uint8_t id = 0;
-			uint64_t timestamp = ctx->tsc;
+			uint64_t timestamp = ctx->priv.tsc;
 
 			bt_bitfield_write(&id, uint8_t,
 					0,
@@ -289,8 +289,8 @@ void lttng_write_event_header_slow(const struct lib_ring_buffer_config *config,
 		break;
 	case 2:	/* large */
 	{
-		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
-			uint32_t timestamp = (uint32_t) ctx->tsc;
+		if (!(ctx->priv.rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
+			uint32_t timestamp = (uint32_t) ctx->priv.tsc;
 			uint16_t id = event_id;
 
 			lib_ring_buffer_write(config, ctx, &id, sizeof(id));
@@ -298,7 +298,7 @@ void lttng_write_event_header_slow(const struct lib_ring_buffer_config *config,
 			lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
 		} else {
 			uint16_t id = 65535;
-			uint64_t timestamp = ctx->tsc;
+			uint64_t timestamp = ctx->priv.tsc;
 
 			lib_ring_buffer_write(config, ctx, &id, sizeof(id));
 			/* Align extended struct on largest member */
@@ -607,14 +607,17 @@ static
 int lttng_event_reserve(struct lib_ring_buffer_ctx *ctx,
 		      uint32_t event_id)
 {
-	struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
+	struct lttng_kernel_event_recorder *event_recorder = ctx->client_priv;
+	struct lttng_channel *lttng_chan = event_recorder->chan;
 	struct lttng_client_ctx client_ctx;
 	int ret, cpu;
 
 	cpu = lib_ring_buffer_get_cpu(&client_config);
 	if (unlikely(cpu < 0))
 		return -EPERM;
-	ctx->cpu = cpu;
+	memset(&ctx->priv, 0, sizeof(ctx->priv));
+	ctx->priv.chan = lttng_chan->chan;
+	ctx->priv.reserve_cpu = cpu;
 
 	/* Compute internal size of context structures. */
 	ctx_get_struct_size(lttng_chan->ctx, &client_ctx.packet_context_len, lttng_chan, ctx);
@@ -622,11 +625,11 @@ int lttng_event_reserve(struct lib_ring_buffer_ctx *ctx,
 	switch (lttng_chan->header_type) {
 	case 1:	/* compact */
 		if (event_id > 30)
-			ctx->rflags |= LTTNG_RFLAG_EXTENDED;
+			ctx->priv.rflags |= LTTNG_RFLAG_EXTENDED;
 		break;
 	case 2:	/* large */
 		if (event_id > 65534)
-			ctx->rflags |= LTTNG_RFLAG_EXTENDED;
+			ctx->priv.rflags |= LTTNG_RFLAG_EXTENDED;
 		break;
 	default:
 		WARN_ON_ONCE(1);
@@ -636,7 +639,7 @@ int lttng_event_reserve(struct lib_ring_buffer_ctx *ctx,
 	if (unlikely(ret))
 		goto put;
 	lib_ring_buffer_backend_get_pages(&client_config, ctx,
-			&ctx->backend_pages);
+			&ctx->priv.backend_pages);
 	lttng_write_event_header(&client_config, ctx, event_id);
 	return 0;
 put:
diff --git a/src/lttng-ring-buffer-event-notifier-client.h b/src/lttng-ring-buffer-event-notifier-client.h
index b5e91c55..993c96da 100644
--- a/src/lttng-ring-buffer-event-notifier-client.h
+++ b/src/lttng-ring-buffer-event-notifier-client.h
@@ -303,13 +303,17 @@ void lttng_write_event_notifier_header(const struct lib_ring_buffer_config *conf
 static
 int lttng_event_reserve(struct lib_ring_buffer_ctx *ctx, uint32_t event_id)
 {
+	struct channel *chan = ctx->client_priv;
 	int ret;
 
+	memset(&ctx->priv, 0, sizeof(ctx->priv));
+	ctx->priv.chan = chan;
+
 	ret = lib_ring_buffer_reserve(&client_config, ctx, NULL);
 	if (ret)
 		return ret;
 	lib_ring_buffer_backend_get_pages(&client_config, ctx,
-			&ctx->backend_pages);
+			&ctx->priv.backend_pages);
 
 	lttng_write_event_notifier_header(&client_config, ctx);
 	return 0;
diff --git a/src/lttng-ring-buffer-metadata-client.h b/src/lttng-ring-buffer-metadata-client.h
index 6fa0c2b1..7e418001 100644
--- a/src/lttng-ring-buffer-metadata-client.h
+++ b/src/lttng-ring-buffer-metadata-client.h
@@ -302,13 +302,17 @@ void lttng_buffer_read_close(struct lib_ring_buffer *buf)
 static
 int lttng_event_reserve(struct lib_ring_buffer_ctx *ctx, uint32_t event_id)
 {
+	struct channel *chan = ctx->client_priv;
 	int ret;
 
+	memset(&ctx->priv, 0, sizeof(ctx->priv));
+	ctx->priv.chan = chan;
+
 	ret = lib_ring_buffer_reserve(&client_config, ctx, NULL);
 	if (ret)
 		return ret;
 	lib_ring_buffer_backend_get_pages(&client_config, ctx,
-			&ctx->backend_pages);
+			&ctx->priv.backend_pages);
 	return 0;
 
 }
diff --git a/src/probes/lttng-kprobes.c b/src/probes/lttng-kprobes.c
index 238441f5..39de7d3d 100644
--- a/src/probes/lttng-kprobes.c
+++ b/src/probes/lttng-kprobes.c
@@ -63,8 +63,8 @@ int lttng_kprobes_event_handler_pre(struct kprobe *p, struct pt_regs *regs)
 		struct lib_ring_buffer_ctx ctx;
 		int ret;
 
-		lib_ring_buffer_ctx_init(&ctx, chan->chan, sizeof(data),
-					 lttng_alignof(data), -1, &lttng_probe_ctx);
+		lib_ring_buffer_ctx_init(&ctx, event_recorder, sizeof(data),
+					 lttng_alignof(data), &lttng_probe_ctx);
 		ret = chan->ops->event_reserve(&ctx, event_recorder->priv->id);
 		if (ret < 0)
 			return 0;
diff --git a/src/probes/lttng-kretprobes.c b/src/probes/lttng-kretprobes.c
index 378a0e83..03561703 100644
--- a/src/probes/lttng-kretprobes.c
+++ b/src/probes/lttng-kretprobes.c
@@ -81,8 +81,8 @@ int _lttng_kretprobes_handler(struct kretprobe_instance *krpi,
 		payload.ip = (unsigned long) lttng_get_kretprobe(krpi)->kp.addr;
 		payload.parent_ip = (unsigned long) krpi->ret_addr;
 
-		lib_ring_buffer_ctx_init(&ctx, chan->chan, sizeof(payload),
-					 lttng_alignof(payload), -1, &lttng_probe_ctx);
+		lib_ring_buffer_ctx_init(&ctx, event_recorder, sizeof(payload),
+					 lttng_alignof(payload), &lttng_probe_ctx);
 		ret = chan->ops->event_reserve(&ctx, event_recorder->priv->id);
 		if (ret < 0)
 			return 0;
diff --git a/src/probes/lttng-uprobes.c b/src/probes/lttng-uprobes.c
index 233813f0..20865889 100644
--- a/src/probes/lttng-uprobes.c
+++ b/src/probes/lttng-uprobes.c
@@ -68,8 +68,8 @@ int lttng_uprobes_event_handler_pre(struct uprobe_consumer *uc, struct pt_regs *
 		struct lib_ring_buffer_ctx ctx;
 		int ret;
 
-		lib_ring_buffer_ctx_init(&ctx, chan->chan,
-			sizeof(payload), lttng_alignof(payload), -1, &lttng_probe_ctx);
+		lib_ring_buffer_ctx_init(&ctx, event_recorder,
+			sizeof(payload), lttng_alignof(payload), &lttng_probe_ctx);
 
 		ret = chan->ops->event_reserve(&ctx, event_recorder->priv->id);
 		if (ret < 0)