Implement listing of pid tracker content

[lttng-modules.git] / lttng-tracker-pid.c

/*
 * 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.
 */
int lttng_pid_tracker_get_node_pid(const struct lttng_pid_hash_node *node)
{
	return node->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);
}