lttng: dynamically selectable context information

Events can be augmented with context information. This is dynamically
configurable from the command line.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/lttng/ltt-context.c

@@ -0,0 +1,93 @@
+/*
+ * ltt-context.c
+ *
+ * Copyright 2011 (c) - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * LTTng trace/channel/event context management.
+ *
+ * Dual LGPL v2.1/GPL v2 license.
+ */
+
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include "wrapper/vmalloc.h"	/* for wrapper_vmalloc_sync_all() */
+#include "ltt-events.h"
+#include "ltt-tracer.h"
+
+int lttng_find_context(struct lttng_ctx *ctx, const char *name)
+{
+	unsigned int i;
+
+	for (i = 0; i < ctx->nr_fields; i++) {
+		/* Skip allocated (but non-initialized) contexts */
+		if (!ctx->fields[i].event_field.name)
+			continue;
+		if (!strcmp(ctx->fields[i].event_field.name, name))
+			return 1;
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(lttng_find_context);
+
+/*
+ * Note: as we append context information, the pointer location may change.
+ */
+struct lttng_ctx_field *lttng_append_context(struct lttng_ctx **ctx_p)
+{
+	struct lttng_ctx_field *field;
+	struct lttng_ctx *ctx;
+
+	if (!*ctx_p) {
+		*ctx_p = kzalloc(sizeof(struct lttng_ctx), GFP_KERNEL);
+		if (!*ctx_p)
+			return NULL;
+	}
+	ctx = *ctx_p;
+	if (ctx->nr_fields + 1 > ctx->allocated_fields) {
+		struct lttng_ctx_field *new_fields;
+
+		ctx->allocated_fields = max_t(size_t, 1, 2 * ctx->allocated_fields);
+		new_fields = kzalloc(ctx->allocated_fields * sizeof(struct lttng_ctx_field), GFP_KERNEL);
+		if (!new_fields)
+			return NULL;
+		if (ctx->fields)
+			memcpy(new_fields, ctx->fields, sizeof(*ctx->fields) * ctx->nr_fields);
+		kfree(ctx->fields);
+		ctx->fields = new_fields;
+	}
+	field = &ctx->fields[ctx->nr_fields];
+	ctx->nr_fields++;
+	return field;
+}
+EXPORT_SYMBOL_GPL(lttng_append_context);
+
+/*
+ * Remove last context field.
+ */
+void lttng_remove_context_field(struct lttng_ctx **ctx_p,
+				struct lttng_ctx_field *field)
+{
+	struct lttng_ctx *ctx;
+
+	ctx = *ctx_p;
+	ctx->nr_fields--;
+	WARN_ON_ONCE(&ctx->fields[ctx->nr_fields] != field);
+	memset(&ctx->fields[ctx->nr_fields], 0, sizeof(struct lttng_ctx_field));
+}
+EXPORT_SYMBOL_GPL(lttng_remove_context_field);
+
+void lttng_destroy_context(struct lttng_ctx *ctx)
+{
+	int i;
+
+	if (!ctx)
+		return;
+	for (i = 0; i < ctx->nr_fields; i++) {
+		if (ctx->fields[i].destroy)
+			ctx->fields[i].destroy(&ctx->fields[i]);
+	}
+	kfree(ctx->fields);
+	kfree(ctx);
+}

drivers/staging/lttng/lttng-context-nice.c

@@ -0,0 +1,68 @@
+/*
+ * (C) Copyright	2009-2011 -
+ * 		Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * LTTng nice context.
+ *
+ * Dual LGPL v2.1/GPL v2 license.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include "ltt-events.h"
+#include "wrapper/ringbuffer/frontend_types.h"
+#include "wrapper/vmalloc.h"
+#include "ltt-tracer.h"
+
+static
+size_t nice_get_size(size_t offset)
+{
+	size_t size = 0;
+
+	size += lib_ring_buffer_align(offset, ltt_alignof(int));
+	size += sizeof(int);
+	return size;
+}
+
+static
+void nice_record(struct lttng_ctx_field *field,
+		struct lib_ring_buffer_ctx *ctx,
+		struct ltt_channel *chan)
+{
+	int nice;
+
+	nice = task_nice(current);
+	lib_ring_buffer_align_ctx(ctx, ltt_alignof(nice));
+	chan->ops->event_write(ctx, &nice, sizeof(nice));
+}
+
+int lttng_add_nice_to_ctx(struct lttng_ctx **ctx)
+{
+	struct lttng_ctx_field *field;
+
+	field = lttng_append_context(ctx);
+	if (!field)
+		return -ENOMEM;
+	if (lttng_find_context(*ctx, "nice")) {
+		lttng_remove_context_field(ctx, field);
+		return -EEXIST;
+	}
+	field->event_field.name = "nice";
+	field->event_field.type.atype = atype_integer;
+	field->event_field.type.u.basic.integer.size = sizeof(int) * CHAR_BIT;
+	field->event_field.type.u.basic.integer.alignment = ltt_alignof(int) * CHAR_BIT;
+	field->event_field.type.u.basic.integer.signedness = is_signed_type(int);
+	field->event_field.type.u.basic.integer.reverse_byte_order = 0;
+	field->event_field.type.u.basic.integer.base = 10;
+	field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
+	field->get_size = nice_get_size;
+	field->record = nice_record;
+	wrapper_vmalloc_sync_all();
+	return 0;
+}
+EXPORT_SYMBOL_GPL(lttng_add_nice_to_ctx);
+
+MODULE_LICENSE("GPL and additional rights");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("Linux Trace Toolkit Nice Context");