X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=lttng-tracker-pid.c;fp=lttng-tracker-pid.c;h=f8f0a51dcc1e738727286b69e28f343ac43476e1;hb=e0130fabb0cbec05e19fcc7fe955fe9d8d8bc91e;hp=0000000000000000000000000000000000000000;hpb=cd955ba27283657df9a7903660343fd94948d30d;p=lttng-modules.git

diff --git a/lttng-tracker-pid.c b/lttng-tracker-pid.c
new file mode 100644
index 00000000..f8f0a51d
--- /dev/null
+++ b/lttng-tracker-pid.c
@@ -0,0 +1,157 @@
+/*
+ * lttng-tracker-pid.c
+ *
+ * LTTng Process ID trackering.
+ *
+ * Copyright (C) 2014 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/err.h>
+#include <linux/seq_file.h>
+#include <linux/stringify.h>
+#include <linux/rculist.h>
+#include <linux/hash.h>
+#include <linux/rcupdate.h>
+
+#include "wrapper/tracepoint.h"
+#include "lttng-events.h"
+
+/*
+ * Hash table is allocated and freed when there are no possible
+ * concurrent lookups (ensured by the alloc/free caller). However,
+ * there can be concurrent RCU lookups vs add/del operations.
+ *
+ * Concurrent updates of the PID hash table are forbidden: the caller
+ * must ensure mutual exclusion. This is currently done by holding the
+ * sessions_mutex across calls to create, destroy, add, and del
+ * functions of this API.
+ */
+struct lttng_pid_hash_node {
+	struct hlist_node hlist;
+	int pid;
+};
+
+/*
+ * Lookup performed from RCU read-side critical section (RCU sched),
+ * protected by preemption off at the tracepoint call site.
+ * Return 1 if found, 0 if not found.
+ */
+bool lttng_pid_tracker_lookup(struct lttng_pid_tracker *lpf, int pid)
+{
+	struct hlist_head *head;
+	struct lttng_pid_hash_node *e;
+	uint32_t hash = hash_32(pid, 32);
+
+	head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
+	hlist_for_each_entry_rcu_notrace(e, head, hlist) {
+		if (pid == e->pid)
+			return 1;	/* Found */
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(lttng_pid_tracker_lookup);
+
+/*
+ * Tracker add and del operations support concurrent RCU lookups.
+ */
+int lttng_pid_tracker_add(struct lttng_pid_tracker *lpf, int pid)
+{
+	struct hlist_head *head;
+	struct lttng_pid_hash_node *e;
+	uint32_t hash = hash_32(pid, 32);
+
+	head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
+	hlist_for_each_entry(e, head, hlist) {
+		if (pid == e->pid)
+			return -EEXIST;
+	}
+	e = kmalloc(sizeof(struct lttng_pid_hash_node), GFP_KERNEL);
+	if (!e)
+		return -ENOMEM;
+	e->pid = pid;
+	hlist_add_head_rcu(&e->hlist, head);
+	return 0;
+}
+
+static
+void pid_tracker_del_node_rcu(struct lttng_pid_hash_node *e)
+{
+	hlist_del_rcu(&e->hlist);
+	/*
+	 * We choose to use a heavyweight synchronize on removal here,
+	 * since removal of a PID from the tracker mask is a rare
+	 * operation, and we don't want to use more cache lines than
+	 * what we really need when doing the PID lookups, so we don't
+	 * want to afford adding a rcu_head field to those pid hash
+	 * node.
+	 */
+	synchronize_trace();
+	kfree(e);
+}
+
+/*
+ * This removal is only used on destroy, so it does not need to support
+ * concurrent RCU lookups.
+ */
+static
+void pid_tracker_del_node(struct lttng_pid_hash_node *e)
+{
+	hlist_del(&e->hlist);
+	kfree(e);
+}
+
+int lttng_pid_tracker_del(struct lttng_pid_tracker *lpf, int pid)
+{
+	struct hlist_head *head;
+	struct lttng_pid_hash_node *e;
+	uint32_t hash = hash_32(pid, 32);
+
+	head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
+	/*
+	 * No need of _safe iteration, because we stop traversal as soon
+	 * as we remove the entry.
+	 */
+	hlist_for_each_entry(e, head, hlist) {
+		if (pid == e->pid) {
+			pid_tracker_del_node_rcu(e);
+			return 0;
+		}
+	}
+	return -ENOENT;	/* Not found */
+}
+
+struct lttng_pid_tracker *lttng_pid_tracker_create(void)
+{
+	return kzalloc(sizeof(struct lttng_pid_tracker), GFP_KERNEL);
+}
+
+void lttng_pid_tracker_destroy(struct lttng_pid_tracker *lpf)
+{
+	int i;
+
+	for (i = 0; i < LTTNG_PID_TABLE_SIZE; i++) {
+		struct hlist_head *head = &lpf->pid_hash[i];
+		struct lttng_pid_hash_node *e;
+		struct hlist_node *tmp;
+
+		hlist_for_each_entry_safe(e, tmp, head, hlist)
+			pid_tracker_del_node(e);
+	}
+	kfree(lpf);
+}