/*
* lttng-context-vtid.c
*
* LTTng UST vtid context.
*
* Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; only
* version 2.1 of the License.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <sys/types.h>
#include <unistd.h>
#include <lttng/ust-events.h>
#include <lttng/ust-tracer.h>
#include <lttng/ringbuffer-config.h>
#include <lttng/ust-tid.h>
#include <urcu/tls-compat.h>
#include "lttng-tracer-core.h"
/*
* We cache the result to ensure we don't trigger a system call for
* each event.
*/
static DEFINE_URCU_TLS(pid_t, cached_vtid);
/*
* Upon fork or clone, the TID assigned to our thread is not the same as
* we kept in cache. Luckily, we are the only thread surviving in the
* child process, so we can simply clear our cached version.
*/
void lttng_context_vtid_reset(void)
{
URCU_TLS(cached_vtid) = 0;
}
static
size_t vtid_get_size(struct lttng_ctx_field *field, size_t offset)
{
size_t size = 0;
size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
size += sizeof(pid_t);
return size;
}
static
void vtid_record(struct lttng_ctx_field *field,
struct lttng_ust_lib_ring_buffer_ctx *ctx,
struct lttng_channel *chan)
{
if (caa_unlikely(!URCU_TLS(cached_vtid)))
URCU_TLS(cached_vtid) = gettid();
lib_ring_buffer_align_ctx(ctx, lttng_alignof(URCU_TLS(cached_vtid)));
chan->ops->event_write(ctx, &URCU_TLS(cached_vtid),
sizeof(URCU_TLS(cached_vtid)));
}
static
void vtid_get_value(struct lttng_ctx_field *field,
struct lttng_ctx_value *value)
{
if (caa_unlikely(!URCU_TLS(cached_vtid)))
URCU_TLS(cached_vtid) = gettid();
value->u.s64 = URCU_TLS(cached_vtid);
}
int lttng_add_vtid_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, "vtid")) {
lttng_remove_context_field(ctx, field);
return -EEXIST;
}
field->event_field.name = "vtid";
field->event_field.type.atype = atype_integer;
field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_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 = vtid_get_size;
field->record = vtid_record;
field->get_value = vtid_get_value;
lttng_context_update(*ctx);
return 0;
}
/*
* Force a read (imply TLS fixup for dlopen) of TLS variables.
*/
void lttng_fixup_vtid_tls(void)
{
asm volatile ("" : : "m" (URCU_TLS(cached_vtid)));
}