xref: /src/sys/kern/subr_hash.c

/*	$NetBSD: subr_hash.c,v 1.13 2025/08/06 11:11:34 andvar Exp $	*/

/*
 * Copyright (c) 1982, 1986, 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)kern_subr.c	8.4 (Berkeley) 2/14/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: subr_hash.c,v 1.13 2025/08/06 11:11:34 andvar Exp $");

#include <sys/param.h>
#include <sys/bitops.h>
#include <sys/kmem.h>
#include <sys/systm.h>
#include <sys/pslist.h>
#include <sys/rwlock.h>
#include <sys/sysctl.h>

static int hashstat_sysctl(SYSCTLFN_PROTO);

static size_t
hash_list_size(enum hashtype htype)
{
	LIST_HEAD(, generic) *hashtbl_list;
	SLIST_HEAD(, generic) *hashtbl_slist;
	TAILQ_HEAD(, generic) *hashtbl_tailq;
	struct pslist_head *hashtbl_pslist;
	size_t esize;

	switch (htype) {
	case HASH_LIST:
		esize = sizeof(*hashtbl_list);
		break;
	case HASH_PSLIST:
		esize = sizeof(*hashtbl_pslist);
		break;
	case HASH_SLIST:
		esize = sizeof(*hashtbl_slist);
		break;
	case HASH_TAILQ:
		esize = sizeof(*hashtbl_tailq);
		break;
	default:
		panic("hashdone: invalid table type");
	}
	return esize;
}

/*
 * General routine to allocate a hash table.
 * Allocate enough memory to hold at least `elements' list-head pointers.
 * Return a pointer to the allocated space and set *hashmask to a pattern
 * suitable for masking a value to use as an index into the returned array.
 */
void *
hashinit(u_int elements, enum hashtype htype, bool waitok, u_long *hashmask)
{
	LIST_HEAD(, generic) *hashtbl_list;
	SLIST_HEAD(, generic) *hashtbl_slist;
	TAILQ_HEAD(, generic) *hashtbl_tailq;
	struct pslist_head *hashtbl_pslist;
	u_long hashsize, i;
	size_t esize;
	void *p;

	KASSERT(elements > 0);

#define MAXELEMENTS (1U << ((sizeof(elements) * NBBY) - 1))
	if (elements > MAXELEMENTS)
		elements = MAXELEMENTS;

	hashsize = 1UL << (ilog2(elements - 1) + 1);
	esize = hash_list_size(htype);

	p = kmem_alloc(hashsize * esize, waitok ? KM_SLEEP : KM_NOSLEEP);
	if (p == NULL)
		return NULL;

	switch (htype) {
	case HASH_LIST:
		hashtbl_list = p;
		for (i = 0; i < hashsize; i++)
			LIST_INIT(&hashtbl_list[i]);
		break;
	case HASH_PSLIST:
		hashtbl_pslist = p;
		for (i = 0; i < hashsize; i++)
			PSLIST_INIT(&hashtbl_pslist[i]);
		break;
	case HASH_SLIST:
		hashtbl_slist = p;
		for (i = 0; i < hashsize; i++)
			SLIST_INIT(&hashtbl_slist[i]);
		break;
	case HASH_TAILQ:
		hashtbl_tailq = p;
		for (i = 0; i < hashsize; i++)
			TAILQ_INIT(&hashtbl_tailq[i]);
		break;
	}
	*hashmask = hashsize - 1;
	return p;
}

/*
 * Free memory from hash table previously allocated via hashinit().
 */
void
hashdone(void *hashtbl, enum hashtype htype, u_long hashmask)
{
	const size_t esize = hash_list_size(htype);
	kmem_free(hashtbl, esize * (hashmask + 1));
}

/*
 * Support for hash statistics (vmstat -H / vmstat -h hashname).
 */

struct hashstat {
	const char *hs_name;
	hashstat_func_t hs_func;
	TAILQ_ENTRY(hashstat) hs_next;
};
TAILQ_HEAD(, hashstat) hashstat_list =
    TAILQ_HEAD_INITIALIZER(hashstat_list);
static krwlock_t hashstat_lock;

void
hashstat_register(const char *name, hashstat_func_t func)
{
	struct hashstat *hs;

	hs = kmem_alloc(sizeof(*hs), KM_SLEEP);

	hs->hs_name = name;
	hs->hs_func = func;

	rw_enter(&hashstat_lock, RW_WRITER);
	TAILQ_INSERT_TAIL(&hashstat_list, hs, hs_next);
	rw_exit(&hashstat_lock);
}

/*
 * sysctl support for returning kernel hash statistics.
 *
 * We (ab)use CTL_DESCRIBE and CTL_QUERY:
 * When passed an OID of CTL_DESCRIBE, return a list and description
 * of the available hashes.
 * When passed an OID of CTL_QUERY, use the hash name passed in the
 * "new" hash input as the name of a single hash to return stats on.
 */
static int
hashstat_sysctl(SYSCTLFN_ARGS)
{
	struct hashstat_sysctl hs;
	struct hashstat *hash;
	char queryname[SYSCTL_NAMELEN];
	size_t written;
	bool fill, query;
	int error;

	if (oldp == NULL) {
		*oldlenp = 0;
		TAILQ_FOREACH(hash, &hashstat_list, hs_next)
			*oldlenp += sizeof(hs);
		return 0;
	}

	error = 0;
	written = 0;

	if (namelen > 0 && name[0] == CTL_DESCRIBE)
		fill = false;
	else
		fill = true;

	if (namelen > 0 && name[0] == CTL_QUERY) {
		const struct hashstat_sysctl *h = newp;
		size_t s;

		if (h == NULL) {
			/* Can't QUERY one hash without supplying the hash name. */
			return EINVAL;
		}
		query = true;
		error = sysctl_copyinstr(l, h->hash_name, queryname,
		    sizeof(queryname), &s);
		if (error)
			return error;
	} else {
		query = false;
	}

	sysctl_unlock();
	rw_enter(&hashstat_lock, RW_READER);
	TAILQ_FOREACH(hash, &hashstat_list, hs_next) {
		if (query && (strcmp(hash->hs_name, queryname) != 0)) {
			continue;
		}

		memset(&hs, 0, sizeof(hs));
		error = hash->hs_func(&hs, fill);
		if (error)
			break;

		error = sysctl_copyout(l, &hs, oldp, sizeof(hs));
		if (error)
			break;
		written += sizeof(hs);
		oldp = (char *)oldp + sizeof(hs);
	}
	rw_exit(&hashstat_lock);
	sysctl_relock();

	if (query && written == 0)	/* query not found? */
		error = ENOENT;

	*oldlenp = written;
	return error;
}


SYSCTL_SETUP(sysctl_hash_setup, "sysctl hash stats setup")
{

	rw_init(&hashstat_lock);	/* as good a place as any for this */

	sysctl_createv(NULL, 0, NULL, NULL,
		       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
		       CTLTYPE_STRUCT,
		       "hashstat", SYSCTL_DESCR("kernel hash statistics"),
		       hashstat_sysctl, 0, NULL, 0,
		       CTL_KERN, CTL_CREATE, CTL_EOL);
}