xref: /illumos-gate/usr/src/common/idspace/id_space.c (revision 01aad269)

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include <sys/types.h>
#include <sys/id_space.h>
#include <sys/debug.h>

/*
 * ID Spaces
 *
 *   The id_space_t provides a simple implementation of a managed range of
 *   integer identifiers using a vmem arena.  An ID space guarantees that the
 *   next identifer returned by an allocation is larger than the previous one,
 *   unless there are no larger slots remaining in the range.  In this case,
 *   the ID space will return the first available slot in the lower part of the
 *   range (viewing the previous identifier as a partitioning element).  If no
 *   slots are available, id_alloc()/id_allocff() will sleep until an
 *   identifier becomes available.  Accordingly, id_space allocations must be
 *   initiated from contexts where sleeping is acceptable.  id_alloc_nosleep()/
 *   id_allocff_nosleep() will return -1 if no slots are available or if the
 *   system is low on memory.  If id_alloc_nosleep() fails, callers should
 *   not try to extend the ID space.  This is to avoid making a possible
 *   low-memory situation worse.
 *
 *   As an ID space is designed for representing a range of id_t's, there
 *   is a preexisting maximal range: [0, MAXUID].  ID space requests outside
 *   that range will fail on a DEBUG kernel.  The id_allocff*() functions
 *   return the first available id, and should be used when there is benefit
 *   to having a compact allocated range.
 *
 *   (Presently, the id_space_t abstraction supports only direct allocations; ID
 *   reservation, in which an ID is allocated but placed in a internal
 *   dictionary for later use, should be added when a consuming subsystem
 *   arrives.)
 *
 *   This code is also shared with userland. In userland, we don't have the same
 *   ability to have sleeping variants, so we effectively turn the normal
 *   versions without _nosleep into _nosleep.
 */

#define	ID_TO_ADDR(id) ((void *)(uintptr_t)(id + 1))
#define	ADDR_TO_ID(addr) ((id_t)((uintptr_t)addr - 1))

/*
 * Create an arena to represent the range [low, high).
 * Caller must be in a context in which VM_SLEEP is legal,
 * for the kernel. Always VM_NOSLEEP in userland.
 */
id_space_t *
id_space_create(const char *name, id_t low, id_t high)
{
#ifdef _KERNEL
	int flag = VM_SLEEP;
#else
	int flag = VM_NOSLEEP;
#endif
	ASSERT(low >= 0);
	ASSERT(low < high);

	return (vmem_create(name, ID_TO_ADDR(low), high - low, 1,
	    NULL, NULL, NULL, 0, flag | VMC_IDENTIFIER));
}

/*
 * Destroy a previously created ID space.
 * No restrictions on caller's context.
 */
void
id_space_destroy(id_space_t *isp)
{
	vmem_destroy(isp);
}

void
id_space_extend(id_space_t *isp, id_t low, id_t high)
{
#ifdef _KERNEL
	int flag = VM_SLEEP;
#else
	int flag = VM_NOSLEEP;
#endif
	(void) vmem_add(isp, ID_TO_ADDR(low), high - low, flag);
}

/*
 * Allocate an id_t from specified ID space.
 * Caller must be in a context in which VM_SLEEP is legal.
 */
id_t
id_alloc(id_space_t *isp)
{
#ifdef _KERNEL
	int flag = VM_SLEEP;
#else
	int flag = VM_NOSLEEP;
#endif
	return (ADDR_TO_ID(vmem_alloc(isp, 1, flag | VM_NEXTFIT)));
}

/*
 * Allocate an id_t from specified ID space.
 * Returns -1 on failure (see module block comments for more information on
 * failure modes).
 */
id_t
id_alloc_nosleep(id_space_t *isp)
{
	return (ADDR_TO_ID(vmem_alloc(isp, 1, VM_NOSLEEP | VM_NEXTFIT)));
}

/*
 * Allocate an id_t from specified ID space using FIRSTFIT.
 * Caller must be in a context in which VM_SLEEP is legal.
 */
id_t
id_allocff(id_space_t *isp)
{
#ifdef _KERNEL
	int flag = VM_SLEEP;
#else
	int flag = VM_NOSLEEP;
#endif
	return (ADDR_TO_ID(vmem_alloc(isp, 1, flag | VM_FIRSTFIT)));
}

/*
 * Allocate an id_t from specified ID space using FIRSTFIT
 * Returns -1 on failure (see module block comments for more information on
 * failure modes).
 */
id_t
id_allocff_nosleep(id_space_t *isp)
{
	return (ADDR_TO_ID(vmem_alloc(isp, 1, VM_NOSLEEP | VM_FIRSTFIT)));
}

/*
 * Allocate a specific identifier if possible, returning the id if
 * successful, or -1 on failure.
 */
id_t
id_alloc_specific_nosleep(id_space_t *isp, id_t id)
{
	void *minaddr = ID_TO_ADDR(id);
	void *maxaddr = ID_TO_ADDR(id + 1);

	/*
	 * Note that even though we're vmem_free()ing this later, it
	 * should be OK, since there's no quantum cache.
	 */
	return (ADDR_TO_ID(vmem_xalloc(isp, 1, 1, 0, 0,
	    minaddr, maxaddr, VM_NOSLEEP)));
}

/*
 * Free a previously allocated ID.
 * No restrictions on caller's context.
 */
void
id_free(id_space_t *isp, id_t id)
{
	vmem_free(isp, ID_TO_ADDR(id), 1);
}