Move liblttng-ust to 'src/lib/'

[lttng-ust.git] / src / lib / lttng-ust / lttng-context-procname.c

diff --git a/src/lib/lttng-ust/lttng-context-procname.c b/src/lib/lttng-ust/lttng-context-procname.c
new file mode 100644 (file)
index 0000000..bbc4687
--- /dev/null
+++ b/src/lib/lttng-ust/lttng-context-procname.c
@@ -0,0 +1,125 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * LTTng UST procname context.
+ */
+
+#define _LGPL_SOURCE
+#include <stddef.h>
+#include <lttng/ust-events.h>
+#include <lttng/ust-tracer.h>
+#include <lttng/ringbuffer-context.h>
+#include <urcu/tls-compat.h>
+#include <assert.h>
+#include "common/compat/pthread.h"
+#include "lttng-tracer-core.h"
+
+#include "context-internal.h"
+
+/* Maximum number of nesting levels for the procname cache. */
+#define PROCNAME_NESTING_MAX   2
+
+/*
+ * We cache the result to ensure we don't trigger a system call for
+ * each event.
+ * Upon exec, procname changes, but exec takes care of throwing away
+ * this cached version.
+ * The procname can also change by calling prctl(). The procname should
+ * be set for a thread before the first event is logged within this
+ * thread.
+ */
+typedef char procname_array[PROCNAME_NESTING_MAX][17];
+
+static DEFINE_URCU_TLS(procname_array, cached_procname);
+
+static DEFINE_URCU_TLS(int, procname_nesting);
+
+static inline
+const char *wrapper_getprocname(void)
+{
+       int nesting = CMM_LOAD_SHARED(URCU_TLS(procname_nesting));
+
+       if (caa_unlikely(nesting >= PROCNAME_NESTING_MAX))
+               return "<unknown>";
+       if (caa_unlikely(!URCU_TLS(cached_procname)[nesting][0])) {
+               CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting + 1);
+               /* Increment nesting before updating cache. */
+               cmm_barrier();
+               lttng_pthread_getname_np(URCU_TLS(cached_procname)[nesting], LTTNG_UST_ABI_PROCNAME_LEN);
+               URCU_TLS(cached_procname)[nesting][LTTNG_UST_ABI_PROCNAME_LEN - 1] = '\0';
+               /* Decrement nesting after updating cache. */
+               cmm_barrier();
+               CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting);
+       }
+       return URCU_TLS(cached_procname)[nesting];
+}
+
+/* Reset should not be called from a signal handler. */
+void lttng_ust_context_procname_reset(void)
+{
+       CMM_STORE_SHARED(URCU_TLS(cached_procname)[1][0], '\0');
+       CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1);
+       CMM_STORE_SHARED(URCU_TLS(cached_procname)[0][0], '\0');
+       CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0);
+}
+
+static
+size_t procname_get_size(void *priv __attribute__((unused)),
+               size_t offset __attribute__((unused)))
+{
+       return LTTNG_UST_ABI_PROCNAME_LEN;
+}
+
+static
+void procname_record(void *priv __attribute__((unused)),
+                struct lttng_ust_lib_ring_buffer_ctx *ctx,
+                struct lttng_ust_channel_buffer *chan)
+{
+       const char *procname;
+
+       procname = wrapper_getprocname();
+       chan->ops->event_write(ctx, procname, LTTNG_UST_ABI_PROCNAME_LEN, 1);
+}
+
+static
+void procname_get_value(void *priv __attribute__((unused)),
+               struct lttng_ust_ctx_value *value)
+{
+       value->u.str = wrapper_getprocname();
+}
+
+static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
+       lttng_ust_static_event_field("procname",
+               lttng_ust_static_type_array_text(LTTNG_UST_ABI_PROCNAME_LEN),
+               false, false),
+       procname_get_size,
+       procname_record,
+       procname_get_value,
+       NULL, NULL);
+
+int lttng_add_procname_to_ctx(struct lttng_ust_ctx **ctx)
+{
+       int ret;
+
+       if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
+               ret = -EEXIST;
+               goto error_find_context;
+       }
+       ret = lttng_ust_context_append(ctx, ctx_field);
+       if (ret)
+               return ret;
+       return 0;
+
+error_find_context:
+       return ret;
+}
+
+/*
+ * Force a read (imply TLS fixup for dlopen) of TLS variables.
+ */
+void lttng_fixup_procname_tls(void)
+{
+       asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
+}