Contexts for RT debugging

[lttng-modules.git] / lttng-context-preemptible.c

diff --git a/lttng-context-preemptible.c b/lttng-context-preemptible.c
new file mode 100644 (file)
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+++ b/lttng-context-preemptible.c
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+/*
+ * lttng-context-preemptible.c
+ *
+ * LTTng preemptible context.
+ *
+ * Copyright (C) 2009-2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/irqflags.h>
+#include "lttng-events.h"
+#include "wrapper/ringbuffer/frontend_types.h"
+#include "wrapper/vmalloc.h"
+#include "lttng-tracer.h"
+
+/*
+ * We nest twice in preempt disabling within LTTng: one nesting is done
+ * by the instrumentation (tracepoint, kprobes, kretprobes, syscall
+ * tracepoint), and the second is within the lib ring buffer
+ * lib_ring_buffer_get_cpu().
+ */
+#define LTTNG_PREEMPT_DISABLE_NESTING  2
+
+static
+size_t preemptible_get_size(size_t offset)
+{
+       size_t size = 0;
+
+       size += lib_ring_buffer_align(offset, lttng_alignof(uint8_t));
+       size += sizeof(uint8_t);
+       return size;
+}
+
+static
+void preemptible_record(struct lttng_ctx_field *field,
+               struct lib_ring_buffer_ctx *ctx,
+               struct lttng_channel *chan)
+{
+       int pc = preempt_count();
+       uint8_t preemptible = 0;
+
+       WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
+       if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
+               preemptible = 1;
+       lib_ring_buffer_align_ctx(ctx, lttng_alignof(preemptible));
+       chan->ops->event_write(ctx, &preemptible, sizeof(preemptible));
+}
+
+static
+void preemptible_get_value(struct lttng_ctx_field *field,
+               struct lttng_probe_ctx *lttng_probe_ctx,
+               union lttng_ctx_value *value)
+{
+       int pc = preempt_count();
+
+       WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
+       if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
+               value->s64 = 1;
+       else
+               value->s64 = 0;
+}
+
+int lttng_add_preemptible_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, "preemptible")) {
+               lttng_remove_context_field(ctx, field);
+               return -EEXIST;
+       }
+       field->event_field.name = "preemptible";
+       field->event_field.type.atype = atype_integer;
+       field->event_field.type.u.basic.integer.size = sizeof(uint8_t) * CHAR_BIT;
+       field->event_field.type.u.basic.integer.alignment = lttng_alignof(uint8_t) * CHAR_BIT;
+       field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(uint8_t);
+       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 = preemptible_get_size;
+       field->record = preemptible_record;
+       field->get_value = preemptible_get_value;
+       lttng_context_update(*ctx);
+       wrapper_vmalloc_sync_all();
+       return 0;
+}
+EXPORT_SYMBOL_GPL(lttng_add_preemptible_to_ctx);
+
+MODULE_LICENSE("GPL and additional rights");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("Linux Trace Toolkit preemptible Context");
+MODULE_VERSION(__stringify(LTTNG_MODULES_MAJOR_VERSION) "."
+       __stringify(LTTNG_MODULES_MINOR_VERSION) "."
+       __stringify(LTTNG_MODULES_PATCHLEVEL_VERSION)
+       LTTNG_MODULES_EXTRAVERSION);