--- /dev/null
+/*
+ * 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);
+}
projects / lttng-modules.git / blobdiff