From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 28 Apr 2021 20:26:20 +0000 (-0400)
Subject: Refactoring: context callbacks
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=2dc781e02eb156a76554ada092a181ab2916db57;p=lttng-modules.git

Refactoring: context callbacks

Refactor the context callbacks so they take a private pointer as
argument.

Note that the callstack context internally uses a per-cpu stack across
context size calculation and recording to the ring buffer, which
requires that preemption is disabled across those operations.

The get_size_arg and _get_size callbacks are merged into a single
callback.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I7c4146481d35cb9ddef19f2cb5d61e56ebe142be
---

diff --git a/include/lttng/events.h b/include/lttng/events.h
index 8c200bdd..464adb2c 100644
--- a/include/lttng/events.h
+++ b/include/lttng/events.h
@@ -246,11 +246,10 @@ struct lttng_kernel_event_field {
 		_fields											\
 	)
 
-#define lttng_kernel_static_ctx_field(_event_field, _get_size, _get_size_arg, _record, _get_value, _destroy, _priv) \
+#define lttng_kernel_static_ctx_field(_event_field, _get_size, _record, _get_value, _destroy, _priv)	\
 	__LTTNG_COMPOUND_LITERAL(const struct lttng_kernel_ctx_field, {					\
 		.event_field = (_event_field),								\
 		.get_size = (_get_size),								\
-		.get_size_arg = (_get_size_arg),							\
 		.record = (_record),									\
 		.get_value = (_get_value),								\
 		.destroy = (_destroy),									\
@@ -303,10 +302,12 @@ struct lttng_kernel_event_field {
 		}											\
 	}),
 
-union lttng_ctx_value {
-	int64_t s64;
-	const char *str;
-	double d;
+struct lttng_ctx_value {
+	union {
+		int64_t s64;
+		const char *str;
+		double d;
+	} u;
 };
 
 /*
@@ -334,17 +335,14 @@ struct lttng_probe_ctx {
 
 struct lttng_kernel_ctx_field {
 	const struct lttng_kernel_event_field *event_field;
-	size_t (*get_size)(size_t offset);
-	size_t (*get_size_arg)(size_t offset, struct lttng_kernel_ctx_field *field,
-	                       struct lib_ring_buffer_ctx *ctx,
-	                       struct lttng_channel *chan);
-	void (*record)(struct lttng_kernel_ctx_field *field,
-		       struct lib_ring_buffer_ctx *ctx,
-		       struct lttng_channel *chan);
-	void (*get_value)(struct lttng_kernel_ctx_field *field,
-			 struct lttng_probe_ctx *lttng_probe_ctx,
-			 union lttng_ctx_value *value);
-	void (*destroy)(struct lttng_kernel_ctx_field *field);
+	size_t (*get_size)(void *priv, struct lttng_probe_ctx *probe_ctx,
+			size_t offset);
+	void (*record)(void *priv, struct lttng_probe_ctx *probe_ctx,
+			struct lib_ring_buffer_ctx *ctx,
+			struct lttng_channel *chan);
+	void (*get_value)(void *priv, struct lttng_probe_ctx *probe_ctx,
+			struct lttng_ctx_value *value);
+	void (*destroy)(void *priv);
 	void *priv;
 };
 
diff --git a/src/lttng-bytecode-interpreter.c b/src/lttng-bytecode-interpreter.c
index 0161d673..8ffe2f41 100644
--- a/src/lttng-bytecode-interpreter.c
+++ b/src/lttng-bytecode-interpreter.c
@@ -273,7 +273,7 @@ static int context_get_index(struct lttng_probe_ctx *lttng_probe_ctx,
 
 	struct lttng_kernel_ctx_field *ctx_field;
 	const struct lttng_kernel_event_field *field;
-	union lttng_ctx_value v;
+	struct lttng_ctx_value v;
 
 	ctx_field = &lttng_static_ctx->fields[idx];
 	field = ctx_field->event_field;
@@ -283,14 +283,14 @@ static int context_get_index(struct lttng_probe_ctx *lttng_probe_ctx,
 
 	switch (field->type->type) {
 	case lttng_kernel_type_integer:
-		ctx_field->get_value(ctx_field, lttng_probe_ctx, &v);
+		ctx_field->get_value(ctx_field->priv, lttng_probe_ctx, &v);
 		if (lttng_kernel_get_type_integer(field->type)->signedness) {
 			ptr->object_type = OBJECT_TYPE_S64;
-			ptr->u.s64 = v.s64;
+			ptr->u.s64 = v.u.s64;
 			ptr->ptr = &ptr->u.s64;
 		} else {
 			ptr->object_type = OBJECT_TYPE_U64;
-			ptr->u.u64 = v.s64;	/* Cast. */
+			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
 		break;
@@ -299,14 +299,14 @@ static int context_get_index(struct lttng_probe_ctx *lttng_probe_ctx,
 		const struct lttng_kernel_type_enum *enum_type = lttng_kernel_get_type_enum(field->type);
 		const struct lttng_kernel_type_integer *integer_type = lttng_kernel_get_type_integer(enum_type->container_type);
 
-		ctx_field->get_value(ctx_field, lttng_probe_ctx, &v);
+		ctx_field->get_value(ctx_field->priv, lttng_probe_ctx, &v);
 		if (integer_type->signedness) {
 			ptr->object_type = OBJECT_TYPE_SIGNED_ENUM;
-			ptr->u.s64 = v.s64;
+			ptr->u.s64 = v.u.s64;
 			ptr->ptr = &ptr->u.s64;
 		} else {
 			ptr->object_type = OBJECT_TYPE_UNSIGNED_ENUM;
-			ptr->u.u64 = v.s64;	/* Cast. */
+			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
 		break;
@@ -324,8 +324,8 @@ static int context_get_index(struct lttng_probe_ctx *lttng_probe_ctx,
 			return -EINVAL;
 		}
 		ptr->object_type = OBJECT_TYPE_STRING;
-		ctx_field->get_value(ctx_field, lttng_probe_ctx, &v);
-		ptr->ptr = v.str;
+		ctx_field->get_value(ctx_field->priv, lttng_probe_ctx, &v);
+		ptr->ptr = v.u.str;
 		break;
 	}
 	case lttng_kernel_type_sequence:
@@ -341,14 +341,14 @@ static int context_get_index(struct lttng_probe_ctx *lttng_probe_ctx,
 			return -EINVAL;
 		}
 		ptr->object_type = OBJECT_TYPE_STRING;
-		ctx_field->get_value(ctx_field, lttng_probe_ctx, &v);
-		ptr->ptr = v.str;
+		ctx_field->get_value(ctx_field->priv, lttng_probe_ctx, &v);
+		ptr->ptr = v.u.str;
 		break;
 	}
 	case lttng_kernel_type_string:
 		ptr->object_type = OBJECT_TYPE_STRING;
-		ctx_field->get_value(ctx_field, lttng_probe_ctx, &v);
-		ptr->ptr = v.str;
+		ctx_field->get_value(ctx_field->priv, lttng_probe_ctx, &v);
+		ptr->ptr = v.u.str;
 		break;
 	case lttng_kernel_type_struct:
 		printk(KERN_WARNING "LTTng: bytecode: Structure type cannot be loaded.\n");
@@ -1488,14 +1488,14 @@ int lttng_bytecode_interpret(struct lttng_bytecode_runtime *kernel_bytecode,
 			struct load_op *insn = (struct load_op *) pc;
 			struct field_ref *ref = (struct field_ref *) insn->data;
 			struct lttng_kernel_ctx_field *ctx_field;
-			union lttng_ctx_value v;
+			struct lttng_ctx_value v;
 
 			dbg_printk("get context ref offset %u type string\n",
 				ref->offset);
 			ctx_field = &lttng_static_ctx->fields[ref->offset];
-			ctx_field->get_value(ctx_field, lttng_probe_ctx, &v);
+			ctx_field->get_value(ctx_field->priv, lttng_probe_ctx, &v);
 			estack_push(stack, top, ax, bx, ax_t, bx_t);
-			estack_ax(stack, top)->u.s.str = v.str;
+			estack_ax(stack, top)->u.s.str = v.u.str;
 			if (unlikely(!estack_ax(stack, top)->u.s.str)) {
 				dbg_printk("Bytecode warning: loading a NULL string.\n");
 				ret = -EINVAL;
@@ -1516,14 +1516,14 @@ int lttng_bytecode_interpret(struct lttng_bytecode_runtime *kernel_bytecode,
 			struct load_op *insn = (struct load_op *) pc;
 			struct field_ref *ref = (struct field_ref *) insn->data;
 			struct lttng_kernel_ctx_field *ctx_field;
-			union lttng_ctx_value v;
+			struct lttng_ctx_value v;
 
 			dbg_printk("get context ref offset %u type s64\n",
 				ref->offset);
 			ctx_field = &lttng_static_ctx->fields[ref->offset];
-			ctx_field->get_value(ctx_field, lttng_probe_ctx, &v);
+			ctx_field->get_value(ctx_field->priv, lttng_probe_ctx, &v);
 			estack_push(stack, top, ax, bx, ax_t, bx_t);
-			estack_ax_v = v.s64;
+			estack_ax_v = v.u.s64;
 			estack_ax_t = REG_S64;
 			dbg_printk("ref get context s64 %lld\n",
 				(long long) estack_ax_v);
diff --git a/src/lttng-context-callstack-legacy-impl.h b/src/lttng-context-callstack-legacy-impl.h
index edd13cf5..34a977a0 100644
--- a/src/lttng-context-callstack-legacy-impl.h
+++ b/src/lttng-context-callstack-legacy-impl.h
@@ -95,19 +95,21 @@ void lttng_cs_set_init(struct lttng_cs __percpu *cs_set)
 /* Keep track of nesting inside userspace callstack context code */
 DEFINE_PER_CPU(int, callstack_user_nesting);
 
+/*
+ * Note: these callbacks expect to be invoked with preemption disabled across
+ * get_size and record due to its use of a per-cpu stack.
+ */
 static
-struct stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *field,
-					struct lib_ring_buffer_ctx *ctx)
+struct stack_trace *stack_trace_context(struct field_data *fdata, int cpu)
 {
 	int buffer_nesting, cs_user_nesting;
 	struct lttng_cs *cs;
-	struct field_data *fdata = field->priv;
 
 	/*
 	 * 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->priv.reserve_cpu);
+	cs_user_nesting = per_cpu(callstack_user_nesting, cpu);
 
 	if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 		return NULL;
@@ -119,8 +121,8 @@ 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->priv.reserve_cpu);
-	buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->priv.reserve_cpu) - 1;
+	cs = per_cpu_ptr(fdata->cs_percpu, cpu);
+	buffer_nesting = per_cpu(lib_ring_buffer_nesting, cpu) - 1;
 	if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 		return NULL;
 
@@ -128,9 +130,7 @@ struct stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *field,
 }
 
 static
-size_t lttng_callstack_length_get_size(size_t offset, struct lttng_kernel_ctx_field *field,
-				struct lib_ring_buffer_ctx *ctx,
-				struct lttng_channel *chan)
+size_t lttng_callstack_length_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t orig_offset = offset;
 
@@ -144,16 +144,15 @@ size_t lttng_callstack_length_get_size(size_t offset, struct lttng_kernel_ctx_fi
  * resulting callstack is saved to be accessed in the record step.
  */
 static
-size_t lttng_callstack_sequence_get_size(size_t offset, struct lttng_kernel_ctx_field *field,
-					struct lib_ring_buffer_ctx *ctx,
-					struct lttng_channel *chan)
+size_t lttng_callstack_sequence_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	struct stack_trace *trace;
-	struct field_data *fdata = field->priv;
+	struct field_data *fdata = (struct field_data *) priv;
 	size_t orig_offset = offset;
+	int cpu = smp_processor_id();
 
 	/* do not write data if no space is available */
-	trace = stack_trace_context(field, ctx);
+	trace = stack_trace_context(fdata, cpu);
 	if (unlikely(!trace)) {
 		offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 		return offset - orig_offset;
@@ -163,13 +162,13 @@ 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->priv.reserve_cpu);
+		++per_cpu(callstack_user_nesting, 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->priv.reserve_cpu)--;
+		per_cpu(callstack_user_nesting, cpu)--;
 
 	/*
 	 * Remove final ULONG_MAX delimiter. If we cannot find it, add
@@ -189,11 +188,13 @@ size_t lttng_callstack_sequence_get_size(size_t offset, struct lttng_kernel_ctx_
 }
 
 static
-void lttng_callstack_length_record(struct lttng_kernel_ctx_field *field,
+void lttng_callstack_length_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 			struct lib_ring_buffer_ctx *ctx,
 			struct lttng_channel *chan)
 {
-	struct stack_trace *trace = stack_trace_context(field, ctx);
+	int cpu = ctx->priv.reserve_cpu;
+	struct field_data *fdata = (struct field_data *) priv;
+	struct stack_trace *trace = stack_trace_context(fdata, cpu);
 	unsigned int nr_seq_entries;
 
 	lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
@@ -207,11 +208,13 @@ void lttng_callstack_length_record(struct lttng_kernel_ctx_field *field,
 	chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int));
 }
 static
-void lttng_callstack_sequence_record(struct lttng_kernel_ctx_field *field,
+void lttng_callstack_sequence_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 			struct lib_ring_buffer_ctx *ctx,
 			struct lttng_channel *chan)
 {
-	struct stack_trace *trace = stack_trace_context(field, ctx);
+	int cpu = ctx->priv.reserve_cpu;
+	struct field_data *fdata = (struct field_data *) priv;
+	struct stack_trace *trace = stack_trace_context(fdata, cpu);
 	unsigned int nr_seq_entries;
 
 	lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
diff --git a/src/lttng-context-callstack-stackwalk-impl.h b/src/lttng-context-callstack-stackwalk-impl.h
index a7c5a062..2e437359 100644
--- a/src/lttng-context-callstack-stackwalk-impl.h
+++ b/src/lttng-context-callstack-stackwalk-impl.h
@@ -97,19 +97,21 @@ void lttng_cs_set_init(struct lttng_cs __percpu *cs_set)
 /* Keep track of nesting inside userspace callstack context code */
 DEFINE_PER_CPU(int, callstack_user_nesting);
 
+/*
+ * Note: these callbacks expect to be invoked with preemption disabled across
+ * get_size and record due to its use of a per-cpu stack.
+ */
 static
-struct lttng_stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *field,
-					struct lib_ring_buffer_ctx *ctx)
+struct lttng_stack_trace *stack_trace_context(struct field_data *fdata, int cpu)
 {
 	int buffer_nesting, cs_user_nesting;
 	struct lttng_cs *cs;
-	struct field_data *fdata = field->priv;
 
 	/*
 	 * 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->priv.reserve_cpu);
+	cs_user_nesting = per_cpu(callstack_user_nesting, cpu);
 
 	if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 		return NULL;
@@ -121,8 +123,8 @@ 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->priv.reserve_cpu);
-	buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->priv.reserve_cpu) - 1;
+	cs = per_cpu_ptr(fdata->cs_percpu, cpu);
+	buffer_nesting = per_cpu(lib_ring_buffer_nesting, cpu) - 1;
 	if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 		return NULL;
 
@@ -130,9 +132,7 @@ struct lttng_stack_trace *stack_trace_context(struct lttng_kernel_ctx_field *fie
 }
 
 static
-size_t lttng_callstack_length_get_size(size_t offset, struct lttng_kernel_ctx_field *field,
-				struct lib_ring_buffer_ctx *ctx,
-				struct lttng_channel *chan)
+size_t lttng_callstack_length_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t orig_offset = offset;
 
@@ -146,16 +146,15 @@ size_t lttng_callstack_length_get_size(size_t offset, struct lttng_kernel_ctx_fi
  * resulting callstack is saved to be accessed in the record step.
  */
 static
-size_t lttng_callstack_sequence_get_size(size_t offset, struct lttng_kernel_ctx_field *field,
-					struct lib_ring_buffer_ctx *ctx,
-					struct lttng_channel *chan)
+size_t lttng_callstack_sequence_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	struct lttng_stack_trace *trace;
-	struct field_data *fdata = field->priv;
+	struct field_data *fdata = (struct field_data *) priv;
 	size_t orig_offset = offset;
+	int cpu = smp_processor_id();
 
 	/* do not write data if no space is available */
-	trace = stack_trace_context(field, ctx);
+	trace = stack_trace_context(fdata, cpu);
 	if (unlikely(!trace)) {
 		offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 		return offset - orig_offset;
@@ -171,11 +170,11 @@ 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->priv.reserve_cpu);
+		++per_cpu(callstack_user_nesting, cpu);
 		/* do the real work and reserve space */
 		trace->nr_entries = save_func_user(trace->entries,
 						MAX_ENTRIES);
-		per_cpu(callstack_user_nesting, ctx->priv.reserve_cpu)--;
+		per_cpu(callstack_user_nesting, cpu)--;
 		break;
 	default:
 		WARN_ON_ONCE(1);
@@ -194,11 +193,13 @@ size_t lttng_callstack_sequence_get_size(size_t offset, struct lttng_kernel_ctx_
 }
 
 static
-void lttng_callstack_length_record(struct lttng_kernel_ctx_field *field,
+void lttng_callstack_length_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 			struct lib_ring_buffer_ctx *ctx,
 			struct lttng_channel *chan)
 {
-	struct lttng_stack_trace *trace = stack_trace_context(field, ctx);
+	int cpu = ctx->priv.reserve_cpu;
+	struct field_data *fdata = (struct field_data *) priv;
+	struct lttng_stack_trace *trace = stack_trace_context(fdata, cpu);
 	unsigned int nr_seq_entries;
 
 	lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
@@ -213,11 +214,13 @@ void lttng_callstack_length_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void lttng_callstack_sequence_record(struct lttng_kernel_ctx_field *field,
+void lttng_callstack_sequence_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 			struct lib_ring_buffer_ctx *ctx,
 			struct lttng_channel *chan)
 {
-	struct lttng_stack_trace *trace = stack_trace_context(field, ctx);
+	int cpu = ctx->priv.reserve_cpu;
+	struct field_data *fdata = (struct field_data *) priv;
+	struct lttng_stack_trace *trace = stack_trace_context(fdata, cpu);
 	unsigned int nr_seq_entries;
 
 	lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
diff --git a/src/lttng-context-callstack.c b/src/lttng-context-callstack.c
index e6ac2596..7e44fafa 100644
--- a/src/lttng-context-callstack.c
+++ b/src/lttng-context-callstack.c
@@ -90,9 +90,9 @@ error_alloc:
 }
 
 static
-void lttng_callstack_sequence_destroy(struct lttng_kernel_ctx_field *field)
+void lttng_callstack_sequence_destroy(void *priv)
 {
-	struct field_data *fdata = field->priv;
+	struct field_data *fdata = priv;
 
 	field_data_free(fdata);
 }
@@ -158,7 +158,7 @@ int __lttng_add_callstack_generic(struct lttng_kernel_ctx **ctx,
 	}
 	memset(&ctx_field, 0, sizeof(ctx_field));
 	ctx_field.event_field = event_fields[0];
-	ctx_field.get_size_arg = lttng_callstack_length_get_size;
+	ctx_field.get_size = lttng_callstack_length_get_size;
 	ctx_field.record = lttng_callstack_length_record;
 	ctx_field.priv = fdata;
 	ret = lttng_kernel_context_append(ctx, &ctx_field);
@@ -169,7 +169,7 @@ int __lttng_add_callstack_generic(struct lttng_kernel_ctx **ctx,
 
 	memset(&ctx_field, 0, sizeof(ctx_field));
 	ctx_field.event_field = event_fields[1];
-	ctx_field.get_size_arg = lttng_callstack_sequence_get_size;
+	ctx_field.get_size = lttng_callstack_sequence_get_size;
 	ctx_field.record = lttng_callstack_sequence_record;
 	ctx_field.destroy = lttng_callstack_sequence_destroy;
 	ctx_field.priv = fdata;
diff --git a/src/lttng-context-cgroup-ns.c b/src/lttng-context-cgroup-ns.c
index f34e9cf6..0bc345c5 100644
--- a/src/lttng-context-cgroup-ns.c
+++ b/src/lttng-context-cgroup-ns.c
@@ -25,7 +25,7 @@
 	 LTTNG_UBUNTU_KERNEL_RANGE(4,4,0,0, 4,5,0,0))
 
 static
-size_t cgroup_ns_get_size(size_t offset)
+size_t cgroup_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -35,7 +35,7 @@ size_t cgroup_ns_get_size(size_t offset)
 }
 
 static
-void cgroup_ns_record(struct lttng_kernel_ctx_field *field,
+void cgroup_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -56,9 +56,9 @@ void cgroup_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void cgroup_ns_get_value(struct lttng_kernel_ctx_field *field,
+void cgroup_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	unsigned int cgroup_ns_inum = 0;
 
@@ -72,7 +72,7 @@ void cgroup_ns_get_value(struct lttng_kernel_ctx_field *field,
 	if (current->nsproxy)
 		cgroup_ns_inum = current->nsproxy->cgroup_ns->lttng_ns_inum;
 
-	value->s64 = cgroup_ns_inum;
+	value->u.s64 = cgroup_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -80,7 +80,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	cgroup_ns_get_size,
-	NULL,
 	cgroup_ns_record,
 	cgroup_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-cpu-id.c b/src/lttng-context-cpu-id.c
index 7ae79a64..9e1d71a2 100644
--- a/src/lttng-context-cpu-id.c
+++ b/src/lttng-context-cpu-id.c
@@ -17,7 +17,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t cpu_id_get_size(size_t offset)
+size_t cpu_id_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -27,7 +27,7 @@ size_t cpu_id_get_size(size_t offset)
 }
 
 static
-void cpu_id_record(struct lttng_kernel_ctx_field *field,
+void cpu_id_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
@@ -39,11 +39,11 @@ void cpu_id_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void cpu_id_get_value(struct lttng_kernel_ctx_field *field,
+void cpu_id_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = smp_processor_id();
+	value->u.s64 = smp_processor_id();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -51,7 +51,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(int, __BYTE_ORDER, 10),
 		false, false, false),
 	cpu_id_get_size,
-	NULL,
 	cpu_id_record,
 	cpu_id_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-egid.c b/src/lttng-context-egid.c
index 027991cc..958ada67 100644
--- a/src/lttng-context-egid.c
+++ b/src/lttng-context-egid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t egid_get_size(size_t offset)
+size_t egid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t egid_get_size(size_t offset)
 }
 
 static
-void egid_record(struct lttng_kernel_ctx_field *field,
+void egid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void egid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void egid_get_value(struct lttng_kernel_ctx_field *field,
+void egid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_egid();
+	value->u.s64 = lttng_current_egid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(gid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	egid_get_size,
-	NULL,
 	egid_record,
 	egid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-euid.c b/src/lttng-context-euid.c
index 3888da1d..4bd106ae 100644
--- a/src/lttng-context-euid.c
+++ b/src/lttng-context-euid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t euid_get_size(size_t offset)
+size_t euid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t euid_get_size(size_t offset)
 }
 
 static
-void euid_record(struct lttng_kernel_ctx_field *field,
+void euid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void euid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void euid_get_value(struct lttng_kernel_ctx_field *field,
+void euid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_euid();
+	value->u.s64 = lttng_current_euid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	euid_get_size,
-	NULL,
 	euid_record,
 	euid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-gid.c b/src/lttng-context-gid.c
index 4a45bcdf..721e1a38 100644
--- a/src/lttng-context-gid.c
+++ b/src/lttng-context-gid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t gid_get_size(size_t offset)
+size_t gid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t gid_get_size(size_t offset)
 }
 
 static
-void gid_record(struct lttng_kernel_ctx_field *field,
+void gid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void gid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void gid_get_value(struct lttng_kernel_ctx_field *field,
+void gid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_gid();
+	value->u.s64 = lttng_current_gid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(gid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	gid_get_size,
-	NULL,
 	gid_record,
 	gid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-hostname.c b/src/lttng-context-hostname.c
index d00c5356..df46293b 100644
--- a/src/lttng-context-hostname.c
+++ b/src/lttng-context-hostname.c
@@ -20,7 +20,7 @@
 #define LTTNG_HOSTNAME_CTX_LEN	(__NEW_UTS_LEN + 1)
 
 static
-size_t hostname_get_size(size_t offset)
+size_t hostname_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t hostname_get_size(size_t offset)
 }
 
 static
-void hostname_record(struct lttng_kernel_ctx_field *field,
+void hostname_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -54,9 +54,9 @@ void hostname_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void hostname_get_value(struct lttng_kernel_ctx_field *field,
+void hostname_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	struct nsproxy *nsproxy;
 	struct uts_namespace *ns;
@@ -73,7 +73,7 @@ void hostname_get_value(struct lttng_kernel_ctx_field *field,
 	} else {
 		hostname = "";
 	}
-	value->str = hostname;
+	value->u.str = hostname;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -81,7 +81,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_array_text(LTTNG_HOSTNAME_CTX_LEN),
 		false, false, false),
 	hostname_get_size,
-	NULL,
 	hostname_record,
 	hostname_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-interruptible.c b/src/lttng-context-interruptible.c
index 1c78d59b..4d0596a3 100644
--- a/src/lttng-context-interruptible.c
+++ b/src/lttng-context-interruptible.c
@@ -22,7 +22,7 @@
  */
 
 static
-size_t interruptible_get_size(size_t offset)
+size_t interruptible_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -32,7 +32,7 @@ size_t interruptible_get_size(size_t offset)
 }
 
 static
-void interruptible_record(struct lttng_kernel_ctx_field *field,
+void interruptible_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
@@ -44,13 +44,13 @@ void interruptible_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void interruptible_get_value(struct lttng_kernel_ctx_field *field,
+void interruptible_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	int8_t interruptible = lttng_probe_ctx->interruptible;
 
-	value->s64 = interruptible;
+	value->u.s64 = interruptible;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -58,7 +58,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(int8_t, __BYTE_ORDER, 10),
 		false, false, false),
 	interruptible_get_size,
-	NULL,
 	interruptible_record,
 	interruptible_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-ipc-ns.c b/src/lttng-context-ipc-ns.c
index 113ffb75..278a4ae0 100644
--- a/src/lttng-context-ipc-ns.c
+++ b/src/lttng-context-ipc-ns.c
@@ -23,7 +23,7 @@
 	(LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(3,8,0))
 
 static
-size_t ipc_ns_get_size(size_t offset)
+size_t ipc_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -33,7 +33,7 @@ size_t ipc_ns_get_size(size_t offset)
 }
 
 static
-void ipc_ns_record(struct lttng_kernel_ctx_field *field,
+void ipc_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -54,9 +54,9 @@ void ipc_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void ipc_ns_get_value(struct lttng_kernel_ctx_field *field,
+void ipc_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	unsigned int ipc_ns_inum = 0;
 
@@ -70,7 +70,7 @@ void ipc_ns_get_value(struct lttng_kernel_ctx_field *field,
 	if (current->nsproxy)
 		ipc_ns_inum = current->nsproxy->ipc_ns->lttng_ns_inum;
 
-	value->s64 = ipc_ns_inum;
+	value->u.s64 = ipc_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -78,7 +78,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	ipc_ns_get_size,
-	NULL,
 	ipc_ns_record,
 	ipc_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-migratable.c b/src/lttng-context-migratable.c
index 1695f512..19190bb9 100644
--- a/src/lttng-context-migratable.c
+++ b/src/lttng-context-migratable.c
@@ -17,7 +17,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t migratable_get_size(size_t offset)
+size_t migratable_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -27,7 +27,7 @@ size_t migratable_get_size(size_t offset)
 }
 
 static
-void migratable_record(struct lttng_kernel_ctx_field *field,
+void migratable_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
@@ -38,11 +38,11 @@ void migratable_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void migratable_get_value(struct lttng_kernel_ctx_field *field,
+void migratable_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = !current->migrate_disable;
+	value->u.s64 = !current->migrate_disable;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -50,7 +50,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uint8_t, __BYTE_ORDER, 10),
 		false, false, false),
 	migratable_get_size,
-	NULL,
 	migratable_record,
 	migratable_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-mnt-ns.c b/src/lttng-context-mnt-ns.c
index 232c5def..79b702ca 100644
--- a/src/lttng-context-mnt-ns.c
+++ b/src/lttng-context-mnt-ns.c
@@ -26,7 +26,7 @@
 #include <../fs/mount.h>
 
 static
-size_t mnt_ns_get_size(size_t offset)
+size_t mnt_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -36,7 +36,7 @@ size_t mnt_ns_get_size(size_t offset)
 }
 
 static
-void mnt_ns_record(struct lttng_kernel_ctx_field *field,
+void mnt_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -57,9 +57,9 @@ void mnt_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void mnt_ns_get_value(struct lttng_kernel_ctx_field *field,
+void mnt_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	unsigned int mnt_ns_inum = 0;
 
@@ -73,7 +73,7 @@ void mnt_ns_get_value(struct lttng_kernel_ctx_field *field,
 	if (current->nsproxy)
 		mnt_ns_inum = current->nsproxy->mnt_ns->lttng_ns_inum;
 
-	value->s64 = mnt_ns_inum;
+	value->u.s64 = mnt_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -81,7 +81,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	mnt_ns_get_size,
-	NULL,
 	mnt_ns_record,
 	mnt_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-need-reschedule.c b/src/lttng-context-need-reschedule.c
index 6f3d61d6..6984d1a4 100644
--- a/src/lttng-context-need-reschedule.c
+++ b/src/lttng-context-need-reschedule.c
@@ -18,7 +18,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t need_reschedule_get_size(size_t offset)
+size_t need_reschedule_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -28,7 +28,7 @@ size_t need_reschedule_get_size(size_t offset)
 }
 
 static
-void need_reschedule_record(struct lttng_kernel_ctx_field *field,
+void need_reschedule_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
@@ -39,11 +39,11 @@ void need_reschedule_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void need_reschedule_get_value(struct lttng_kernel_ctx_field *field,
+void need_reschedule_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = test_tsk_need_resched(current);;
+	value->u.s64 = test_tsk_need_resched(current);;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -51,7 +51,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uint8_t, __BYTE_ORDER, 10),
 		false, false, false),
 	need_reschedule_get_size,
-	NULL,
 	need_reschedule_record,
 	need_reschedule_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-net-ns.c b/src/lttng-context-net-ns.c
index 1c8adf49..a1a8d6dd 100644
--- a/src/lttng-context-net-ns.c
+++ b/src/lttng-context-net-ns.c
@@ -24,7 +24,7 @@
 	(LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(3,8,0))
 
 static
-size_t net_ns_get_size(size_t offset)
+size_t net_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -34,7 +34,7 @@ size_t net_ns_get_size(size_t offset)
 }
 
 static
-void net_ns_record(struct lttng_kernel_ctx_field *field,
+void net_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -55,9 +55,9 @@ void net_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void net_ns_get_value(struct lttng_kernel_ctx_field *field,
+void net_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	unsigned int net_ns_inum = 0;
 
@@ -71,7 +71,7 @@ void net_ns_get_value(struct lttng_kernel_ctx_field *field,
 	if (current->nsproxy)
 		net_ns_inum = current->nsproxy->net_ns->lttng_ns_inum;
 
-	value->s64 = net_ns_inum;
+	value->u.s64 = net_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -79,7 +79,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	net_ns_get_size,
-	NULL,
 	net_ns_record,
 	net_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-nice.c b/src/lttng-context-nice.c
index 22b86965..ef61570c 100644
--- a/src/lttng-context-nice.c
+++ b/src/lttng-context-nice.c
@@ -17,7 +17,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t nice_get_size(size_t offset)
+size_t nice_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -27,7 +27,7 @@ size_t nice_get_size(size_t offset)
 }
 
 static
-void nice_record(struct lttng_kernel_ctx_field *field,
+void nice_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
@@ -39,11 +39,11 @@ void nice_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void nice_get_value(struct lttng_kernel_ctx_field *field,
+void nice_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = task_nice(current);
+	value->u.s64 = task_nice(current);
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -51,7 +51,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(int, __BYTE_ORDER, 10),
 		false, false, false),
 	nice_get_size,
-	NULL,
 	nice_record,
 	nice_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-perf-counters.c b/src/lttng-context-perf-counters.c
index 53578475..44c47640 100644
--- a/src/lttng-context-perf-counters.c
+++ b/src/lttng-context-perf-counters.c
@@ -20,7 +20,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t perf_counter_get_size(size_t offset)
+size_t perf_counter_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -30,11 +30,11 @@ size_t perf_counter_get_size(size_t offset)
 }
 
 static
-void perf_counter_record(struct lttng_kernel_ctx_field *field,
+void perf_counter_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 			 struct lib_ring_buffer_ctx *ctx,
 			 struct lttng_channel *chan)
 {
-	struct lttng_perf_counter_field *perf_field = field->priv;
+	struct lttng_perf_counter_field *perf_field = (struct lttng_perf_counter_field *) priv;
 	struct perf_event *event;
 	uint64_t value;
 
@@ -77,9 +77,9 @@ void overflow_callback(struct perf_event *event, int nmi,
 #endif
 
 static
-void lttng_destroy_perf_counter_ctx_field(struct lttng_kernel_ctx_field *field)
+void lttng_destroy_perf_counter_ctx_field(void *priv)
 {
-	struct lttng_perf_counter_field *perf_field = field->priv;
+	struct lttng_perf_counter_field *perf_field = priv;
 	struct perf_event **events = perf_field->e;
 
 #if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(4,10,0))
diff --git a/src/lttng-context-pid-ns.c b/src/lttng-context-pid-ns.c
index 1c3cc2bc..41c15cb5 100644
--- a/src/lttng-context-pid-ns.c
+++ b/src/lttng-context-pid-ns.c
@@ -24,7 +24,7 @@
 	(LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(3,8,0))
 
 static
-size_t pid_ns_get_size(size_t offset)
+size_t pid_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -34,7 +34,7 @@ size_t pid_ns_get_size(size_t offset)
 }
 
 static
-void pid_ns_record(struct lttng_kernel_ctx_field *field,
+void pid_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -56,9 +56,9 @@ void pid_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void pid_ns_get_value(struct lttng_kernel_ctx_field *field,
+void pid_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	struct pid_namespace *ns;
 	unsigned int pid_ns_inum = 0;
@@ -73,7 +73,7 @@ void pid_ns_get_value(struct lttng_kernel_ctx_field *field,
 	if (ns)
 		pid_ns_inum = ns->lttng_ns_inum;
 
-	value->s64 = pid_ns_inum;
+	value->u.s64 = pid_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -81,7 +81,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	pid_ns_get_size,
-	NULL,
 	pid_ns_record,
 	pid_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-pid.c b/src/lttng-context-pid.c
index 6f613725..e3e962d6 100644
--- a/src/lttng-context-pid.c
+++ b/src/lttng-context-pid.c
@@ -17,7 +17,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t pid_get_size(size_t offset)
+size_t pid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -27,7 +27,7 @@ size_t pid_get_size(size_t offset)
 }
 
 static
-void pid_record(struct lttng_kernel_ctx_field *field,
+void pid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
@@ -39,11 +39,11 @@ void pid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void pid_get_value(struct lttng_kernel_ctx_field *field,
+void pid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = task_tgid_nr(current);
+	value->u.s64 = task_tgid_nr(current);
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -51,7 +51,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	pid_get_size,
-	NULL,
 	pid_record,
 	pid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-ppid.c b/src/lttng-context-ppid.c
index 63d02b89..1494f5c7 100644
--- a/src/lttng-context-ppid.c
+++ b/src/lttng-context-ppid.c
@@ -18,7 +18,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t ppid_get_size(size_t offset)
+size_t ppid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -28,7 +28,7 @@ size_t ppid_get_size(size_t offset)
 }
 
 static
-void ppid_record(struct lttng_kernel_ctx_field *field,
+void ppid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -49,9 +49,9 @@ void ppid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void ppid_get_value(struct lttng_kernel_ctx_field *field,
+void ppid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	pid_t ppid;
 
@@ -65,7 +65,7 @@ void ppid_get_value(struct lttng_kernel_ctx_field *field,
 	rcu_read_lock();
 	ppid = task_tgid_nr(current->real_parent);
 	rcu_read_unlock();
-	value->s64 = ppid;
+	value->u.s64 = ppid;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -73,7 +73,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	ppid_get_size,
-	NULL,
 	ppid_record,
 	ppid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-prio.c b/src/lttng-context-prio.c
index b6f6c461..3eb3ff90 100644
--- a/src/lttng-context-prio.c
+++ b/src/lttng-context-prio.c
@@ -44,7 +44,7 @@ int __canary__task_prio(const struct task_struct *p)
 }
 
 static
-size_t prio_get_size(size_t offset)
+size_t prio_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -54,7 +54,7 @@ size_t prio_get_size(size_t offset)
 }
 
 static
-void prio_record(struct lttng_kernel_ctx_field *field,
+void prio_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		struct lib_ring_buffer_ctx *ctx,
 		struct lttng_channel *chan)
 {
@@ -66,11 +66,11 @@ void prio_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void prio_get_value(struct lttng_kernel_ctx_field *field,
+void prio_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = wrapper_task_prio_sym(current);
+	value->u.s64 = wrapper_task_prio_sym(current);
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -78,7 +78,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(int, __BYTE_ORDER, 10),
 		false, false, false),
 	prio_get_size,
-	NULL,
 	prio_record,
 	prio_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-procname.c b/src/lttng-context-procname.c
index 3254c2e9..94ba94e7 100644
--- a/src/lttng-context-procname.c
+++ b/src/lttng-context-procname.c
@@ -18,7 +18,7 @@
 #include <lttng/endian.h>
 
 static
-size_t procname_get_size(size_t offset)
+size_t procname_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -33,7 +33,7 @@ size_t procname_get_size(size_t offset)
  * could lead to crash in IRQ context and deadlock of the lockdep tracer.
  */
 static
-void procname_record(struct lttng_kernel_ctx_field *field,
+void procname_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void procname_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void procname_get_value(struct lttng_kernel_ctx_field *field,
+void procname_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->str = current->comm;
+	value->u.str = current->comm;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_array_text(sizeof(current->comm)),
 		false, false, false),
 	procname_get_size,
-	NULL,
 	procname_record,
 	procname_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-sgid.c b/src/lttng-context-sgid.c
index 28a44877..23d5e5bc 100644
--- a/src/lttng-context-sgid.c
+++ b/src/lttng-context-sgid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t sgid_get_size(size_t offset)
+size_t sgid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t sgid_get_size(size_t offset)
 }
 
 static
-void sgid_record(struct lttng_kernel_ctx_field *field,
+void sgid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void sgid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void sgid_get_value(struct lttng_kernel_ctx_field *field,
+void sgid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_sgid();
+	value->u.s64 = lttng_current_sgid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(gid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	sgid_get_size,
-	NULL,
 	sgid_record,
 	sgid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-suid.c b/src/lttng-context-suid.c
index 9a03468d..5a9e7beb 100644
--- a/src/lttng-context-suid.c
+++ b/src/lttng-context-suid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t suid_get_size(size_t offset)
+size_t suid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t suid_get_size(size_t offset)
 }
 
 static
-void suid_record(struct lttng_kernel_ctx_field *field,
+void suid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void suid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void suid_get_value(struct lttng_kernel_ctx_field *field,
+void suid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_suid();
+	value->u.s64 = lttng_current_suid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	suid_get_size,
-	NULL,
 	suid_record,
 	suid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-tid.c b/src/lttng-context-tid.c
index 89228a1f..5a9dee54 100644
--- a/src/lttng-context-tid.c
+++ b/src/lttng-context-tid.c
@@ -17,7 +17,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t tid_get_size(size_t offset)
+size_t tid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -27,7 +27,7 @@ size_t tid_get_size(size_t offset)
 }
 
 static
-void tid_record(struct lttng_kernel_ctx_field *field,
+void tid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -39,14 +39,14 @@ void tid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void tid_get_value(struct lttng_kernel_ctx_field *field,
+void tid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	pid_t tid;
 
 	tid = task_pid_nr(current);
-	value->s64 = tid;
+	value->u.s64 = tid;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -54,7 +54,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	tid_get_size,
-	NULL,
 	tid_record,
 	tid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-time-ns.c b/src/lttng-context-time-ns.c
index 831bbd45..355feb16 100644
--- a/src/lttng-context-time-ns.c
+++ b/src/lttng-context-time-ns.c
@@ -24,7 +24,7 @@
 #if defined(CONFIG_TIME_NS)
 
 static
-size_t time_ns_get_size(size_t offset)
+size_t time_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -34,7 +34,7 @@ size_t time_ns_get_size(size_t offset)
 }
 
 static
-void time_ns_record(struct lttng_kernel_ctx_field *field,
+void time_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -55,9 +55,9 @@ void time_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void time_ns_get_value(struct lttng_kernel_ctx_field *field,
+void time_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	unsigned int time_ns_inum = 0;
 
@@ -71,7 +71,7 @@ void time_ns_get_value(struct lttng_kernel_ctx_field *field,
 	if (current->nsproxy)
 		time_ns_inum = current->nsproxy->time_ns->lttng_ns_inum;
 
-	value->s64 = time_ns_inum;
+	value->u.s64 = time_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -79,7 +79,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	time_ns_get_size,
-	NULL,
 	time_ns_record,
 	time_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-uid.c b/src/lttng-context-uid.c
index 841d2ea7..86d999af 100644
--- a/src/lttng-context-uid.c
+++ b/src/lttng-context-uid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t uid_get_size(size_t offset)
+size_t uid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t uid_get_size(size_t offset)
 }
 
 static
-void uid_record(struct lttng_kernel_ctx_field *field,
+void uid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void uid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void uid_get_value(struct lttng_kernel_ctx_field *field,
+void uid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_uid();
+	value->u.s64 = lttng_current_uid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	uid_get_size,
-	NULL,
 	uid_record,
 	uid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-user-ns.c b/src/lttng-context-user-ns.c
index bbd689df..f774d971 100644
--- a/src/lttng-context-user-ns.c
+++ b/src/lttng-context-user-ns.c
@@ -24,7 +24,7 @@
 	(LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(3,8,0))
 
 static
-size_t user_ns_get_size(size_t offset)
+size_t user_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -34,7 +34,7 @@ size_t user_ns_get_size(size_t offset)
 }
 
 static
-void user_ns_record(struct lttng_kernel_ctx_field *field,
+void user_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -48,16 +48,16 @@ void user_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void user_ns_get_value(struct lttng_kernel_ctx_field *field,
+void user_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	unsigned int user_ns_inum = 0;
 
 	if (current_user_ns())
 		user_ns_inum = current_user_ns()->lttng_ns_inum;
 
-	value->s64 = user_ns_inum;
+	value->u.s64 = user_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -65,7 +65,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	user_ns_get_size,
-	NULL,
 	user_ns_record,
 	user_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-uts-ns.c b/src/lttng-context-uts-ns.c
index 04ddc80f..204cafb6 100644
--- a/src/lttng-context-uts-ns.c
+++ b/src/lttng-context-uts-ns.c
@@ -24,7 +24,7 @@
 	(LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(3,8,0))
 
 static
-size_t uts_ns_get_size(size_t offset)
+size_t uts_ns_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -34,7 +34,7 @@ size_t uts_ns_get_size(size_t offset)
 }
 
 static
-void uts_ns_record(struct lttng_kernel_ctx_field *field,
+void uts_ns_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -55,9 +55,9 @@ void uts_ns_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void uts_ns_get_value(struct lttng_kernel_ctx_field *field,
+void uts_ns_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	unsigned int uts_ns_inum = 0;
 
@@ -71,7 +71,7 @@ void uts_ns_get_value(struct lttng_kernel_ctx_field *field,
 	if (current->nsproxy)
 		uts_ns_inum = current->nsproxy->uts_ns->lttng_ns_inum;
 
-	value->s64 = uts_ns_inum;
+	value->u.s64 = uts_ns_inum;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -79,7 +79,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(unsigned int, __BYTE_ORDER, 10),
 		false, false, false),
 	uts_ns_get_size,
-	NULL,
 	uts_ns_record,
 	uts_ns_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vegid.c b/src/lttng-context-vegid.c
index 0c775890..87c53baf 100644
--- a/src/lttng-context-vegid.c
+++ b/src/lttng-context-vegid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t vegid_get_size(size_t offset)
+size_t vegid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t vegid_get_size(size_t offset)
 }
 
 static
-void vegid_record(struct lttng_kernel_ctx_field *field,
+void vegid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void vegid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vegid_get_value(struct lttng_kernel_ctx_field *field,
+void vegid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_vegid();
+	value->u.s64 = lttng_current_vegid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(gid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vegid_get_size,
-	NULL,
 	vegid_record,
 	vegid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-veuid.c b/src/lttng-context-veuid.c
index 07968729..5b4930db 100644
--- a/src/lttng-context-veuid.c
+++ b/src/lttng-context-veuid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t veuid_get_size(size_t offset)
+size_t veuid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t veuid_get_size(size_t offset)
 }
 
 static
-void veuid_record(struct lttng_kernel_ctx_field *field,
+void veuid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void veuid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void veuid_get_value(struct lttng_kernel_ctx_field *field,
+void veuid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_veuid();
+	value->u.s64 = lttng_current_veuid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	veuid_get_size,
-	NULL,
 	veuid_record,
 	veuid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vgid.c b/src/lttng-context-vgid.c
index 00dd91d6..768ed519 100644
--- a/src/lttng-context-vgid.c
+++ b/src/lttng-context-vgid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t vgid_get_size(size_t offset)
+size_t vgid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t vgid_get_size(size_t offset)
 }
 
 static
-void vgid_record(struct lttng_kernel_ctx_field *field,
+void vgid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void vgid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vgid_get_value(struct lttng_kernel_ctx_field *field,
+void vgid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_vgid();
+	value->u.s64 = lttng_current_vgid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(gid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vgid_get_size,
-	NULL,
 	vgid_record,
 	vgid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vpid.c b/src/lttng-context-vpid.c
index 4732f280..dfc56751 100644
--- a/src/lttng-context-vpid.c
+++ b/src/lttng-context-vpid.c
@@ -17,7 +17,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t vpid_get_size(size_t offset)
+size_t vpid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -27,7 +27,7 @@ size_t vpid_get_size(size_t offset)
 }
 
 static
-void vpid_record(struct lttng_kernel_ctx_field *field,
+void vpid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -45,9 +45,9 @@ void vpid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vpid_get_value(struct lttng_kernel_ctx_field *field,
+void vpid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	pid_t vpid;
 
@@ -58,7 +58,7 @@ void vpid_get_value(struct lttng_kernel_ctx_field *field,
 		vpid = 0;
 	else
 		vpid = task_tgid_vnr(current);
-	value->s64 = vpid;
+	value->u.s64 = vpid;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -66,7 +66,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vpid_get_size,
-	NULL,
 	vpid_record,
 	vpid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vppid.c b/src/lttng-context-vppid.c
index 714cf664..5f72a064 100644
--- a/src/lttng-context-vppid.c
+++ b/src/lttng-context-vppid.c
@@ -18,7 +18,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t vppid_get_size(size_t offset)
+size_t vppid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -28,7 +28,7 @@ size_t vppid_get_size(size_t offset)
 }
 
 static
-void vppid_record(struct lttng_kernel_ctx_field *field,
+void vppid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		  struct lib_ring_buffer_ctx *ctx,
 		  struct lttng_channel *chan)
 {
@@ -60,9 +60,9 @@ void vppid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vppid_get_value(struct lttng_kernel_ctx_field *field,
+void vppid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	struct task_struct *parent;
 	pid_t vppid;
@@ -87,7 +87,7 @@ void vppid_get_value(struct lttng_kernel_ctx_field *field,
 	else
 		vppid = task_tgid_vnr(parent);
 	rcu_read_unlock();
-	value->s64 = vppid;
+	value->u.s64 = vppid;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -95,7 +95,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vppid_get_size,
-	NULL,
 	vppid_record,
 	vppid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vsgid.c b/src/lttng-context-vsgid.c
index 0ca4f088..d95b2a1d 100644
--- a/src/lttng-context-vsgid.c
+++ b/src/lttng-context-vsgid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t vsgid_get_size(size_t offset)
+size_t vsgid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t vsgid_get_size(size_t offset)
 }
 
 static
-void vsgid_record(struct lttng_kernel_ctx_field *field,
+void vsgid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void vsgid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vsgid_get_value(struct lttng_kernel_ctx_field *field,
+void vsgid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_vsgid();
+	value->u.s64 = lttng_current_vsgid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(gid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vsgid_get_size,
-	NULL,
 	vsgid_record,
 	vsgid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vsuid.c b/src/lttng-context-vsuid.c
index 82a8a472..38b0a71e 100644
--- a/src/lttng-context-vsuid.c
+++ b/src/lttng-context-vsuid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t vsuid_get_size(size_t offset)
+size_t vsuid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t vsuid_get_size(size_t offset)
 }
 
 static
-void vsuid_record(struct lttng_kernel_ctx_field *field,
+void vsuid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void vsuid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vsuid_get_value(struct lttng_kernel_ctx_field *field,
+void vsuid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_vsuid();
+	value->u.s64 = lttng_current_vsuid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vsuid_get_size,
-	NULL,
 	vsuid_record,
 	vsuid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vtid.c b/src/lttng-context-vtid.c
index 76750adc..ba597efc 100644
--- a/src/lttng-context-vtid.c
+++ b/src/lttng-context-vtid.c
@@ -17,7 +17,7 @@
 #include <lttng/tracer.h>
 
 static
-size_t vtid_get_size(size_t offset)
+size_t vtid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -27,7 +27,7 @@ size_t vtid_get_size(size_t offset)
 }
 
 static
-void vtid_record(struct lttng_kernel_ctx_field *field,
+void vtid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -45,9 +45,9 @@ void vtid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vtid_get_value(struct lttng_kernel_ctx_field *field,
+void vtid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
 	pid_t vtid;
 
@@ -58,7 +58,7 @@ void vtid_get_value(struct lttng_kernel_ctx_field *field,
 		vtid = 0;
 	else
 		vtid = task_pid_vnr(current);
-	value->s64 = vtid;
+	value->u.s64 = vtid;
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -66,7 +66,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vtid_get_size,
-	NULL,
 	vtid_record,
 	vtid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context-vuid.c b/src/lttng-context-vuid.c
index ef9a4928..e3c946c9 100644
--- a/src/lttng-context-vuid.c
+++ b/src/lttng-context-vuid.c
@@ -19,7 +19,7 @@
 #include <wrapper/user_namespace.h>
 
 static
-size_t vuid_get_size(size_t offset)
+size_t vuid_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 {
 	size_t size = 0;
 
@@ -29,7 +29,7 @@ size_t vuid_get_size(size_t offset)
 }
 
 static
-void vuid_record(struct lttng_kernel_ctx_field *field,
+void vuid_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 		 struct lib_ring_buffer_ctx *ctx,
 		 struct lttng_channel *chan)
 {
@@ -41,11 +41,11 @@ void vuid_record(struct lttng_kernel_ctx_field *field,
 }
 
 static
-void vuid_get_value(struct lttng_kernel_ctx_field *field,
+void vuid_get_value(void *priv,
 		struct lttng_probe_ctx *lttng_probe_ctx,
-		union lttng_ctx_value *value)
+		struct lttng_ctx_value *value)
 {
-	value->s64 = lttng_current_vuid();
+	value->u.s64 = lttng_current_vuid();
 }
 
 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
@@ -53,7 +53,6 @@ static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_
 		lttng_kernel_static_type_integer_from_type(uid_t, __BYTE_ORDER, 10),
 		false, false, false),
 	vuid_get_size,
-	NULL,
 	vuid_record,
 	vuid_get_value,
 	NULL, NULL);
diff --git a/src/lttng-context.c b/src/lttng-context.c
index 0176dd94..6f39ee06 100644
--- a/src/lttng-context.c
+++ b/src/lttng-context.c
@@ -201,7 +201,7 @@ void lttng_kernel_destroy_context(struct lttng_kernel_ctx *ctx)
 		return;
 	for (i = 0; i < ctx->nr_fields; i++) {
 		if (ctx->fields[i].destroy)
-			ctx->fields[i].destroy(&ctx->fields[i]);
+			ctx->fields[i].destroy(ctx->fields[i].priv);
 	}
 	lttng_kvfree(ctx->fields);
 	kfree(ctx);
diff --git a/src/lttng-ring-buffer-client.h b/src/lttng-ring-buffer-client.h
index 9ac2cfe9..cec656af 100644
--- a/src/lttng-ring-buffer-client.h
+++ b/src/lttng-ring-buffer-client.h
@@ -99,11 +99,8 @@ void ctx_get_struct_size(struct lttng_kernel_ctx *ctx, size_t *ctx_len,
 		return;
 	}
 	for (i = 0; i < ctx->nr_fields; i++) {
-		if (ctx->fields[i].get_size)
-			offset += ctx->fields[i].get_size(offset);
-		if (ctx->fields[i].get_size_arg)
-			offset += ctx->fields[i].get_size_arg(offset,
-					&ctx->fields[i], bufctx, chan);
+		offset += ctx->fields[i].get_size(ctx->fields[i].priv,
+				bufctx->probe_ctx, offset);
 	}
 	*ctx_len = offset;
 }
@@ -119,7 +116,8 @@ void ctx_record(struct lib_ring_buffer_ctx *bufctx,
 		return;
 	lib_ring_buffer_align_ctx(bufctx, ctx->largest_align);
 	for (i = 0; i < ctx->nr_fields; i++)
-		ctx->fields[i].record(&ctx->fields[i], bufctx, chan);
+		ctx->fields[i].record(ctx->fields[i].priv, bufctx->probe_ctx,
+				bufctx, chan);
 }
 
 /*