/*-
 * Copyright (c) 2004 Poul-Henning Kamp
 * All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 *
 * $FreeBSD: src/sys/kern/subr_unit.c,v 1.7 2005/03/14 06:51:29 phk Exp $
 *
 *
 * Unit number allocation functions.
 *
 * These functions implement a mixed run-length/bitmap management of unit
 * number spaces in a very memory efficient manner.
 *
 * Allocation policy is always lowest free number first.
 *
 * A return value of -1 signals that no more unit numbers are available.
 *
 * There is no cost associated with the range of unitnumbers, so unless
 * the resource really is finite, specify INT_MAX to new_unrhdr() and
 * forget about checking the return value.
 *
 * If a mutex is not provided when the unit number space is created, a
 * default global mutex is used.  The advantage to passing a mutex in, is
 * that the the alloc_unrl() function can be called with the mutex already
 * held (it will not be released by alloc_unrl()).
 *
 * The allocation function alloc_unr{l}() never sleeps (but it may block on
 * the mutex of course).
 *
 * Freeing a unit number may require allocating memory, and can therefore
 * sleep so the free_unr() function does not come in a pre-locked variant.
 *
 * A userland test program is included.
 *
 * Memory usage is a very complex function of the the exact allocation
 * pattern, but always very compact:
 *    * For the very typical case where a single unbroken run of unit
 *      numbers are allocated 44 bytes are used on x86.
 *    * For a unit number space of 1000 units and the random pattern
 *      in the usermode test program included, the worst case usage
 *      was 252 bytes on x86 for 500 allocated and 500 free units.
 *    * For a unit number space of 10000 units and the random pattern
 *      in the usermode test program included, the worst case usage
 *      was 798 bytes on x86 for 5000 allocated and 5000 free units.
 *    * The worst case is where every other unit number is allocated and
 *      the the rest are free.  In that case 44 + N/4 bytes are used where
 *      N is the number of the highest unit allocated.
 */

#include <sys/types.h>
#include <sys/queue.h>
#include <sys/bitstring.h>

#ifdef _KERNEL

#include <sys/param.h>
#include <sys/malloc.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/proc.h>

/*
 * In theory it would be smarter to allocate the individual blocks
 * with the zone allocator, but at this time the expectation is that
 * there will typically not even be enough allocations to fill a single
 * page, so we stick with malloc for now.
 */
static MALLOC_DEFINE(M_UNIT, "Unitno", "Unit number allocation");

#define Malloc(foo) kmalloc(foo, M_UNIT, M_WAITOK | M_ZERO)
#define Free(foo) kfree(foo, M_UNIT)

static struct lock unit_lock;

LOCK_SYSINIT(unit, &unit_lock, "unit# allocation", LK_CANRECURSE);

#else /* ...USERLAND */

/* No unit allocation on DragonFly's userland */

#endif /* USERLAND */

/*
 * This is our basic building block.
 *
 * It can be used in three different ways depending on the value of the ptr
 * element:
 *     If ptr is NULL, it represents a run of free items.
 *     If ptr points to the unrhdr it represents a run of allocated items.
 *     Otherwise it points to an bitstring of allocated items.
 *
 * For runs the len field is the length of the run.
 * For bitmaps the len field represents the number of allocated items.
 *
 * The bitmap is the same size as struct unr to optimize memory management.
 */
struct unr {
        TAILQ_ENTRY(unr)        list;
        u_int                   len;
        void                    *ptr;
};

struct unrb {
        u_char                  busy;
        bitstr_t                map[sizeof(struct unr) - 1];
};

CTASSERT(sizeof(struct unr) == sizeof(struct unrb));

/* Number of bits in the bitmap */
#define NBITS   ((int)sizeof(((struct unrb *)NULL)->map) * 8)

/* Header element for a unr number space. */

struct unrhdr {
        TAILQ_HEAD(unrhd,unr)   head;
        u_int                   low;    /* Lowest item */
        u_int                   high;   /* Highest item */
        u_int                   busy;   /* Count of allocated items */
        u_int                   alloc;  /* Count of memory allocations */
        u_int                   first;  /* items in allocated from start */
        u_int                   last;   /* items free at end */
        struct lock             *lock;
};


#if defined(DIAGNOSTIC) || !defined(_KERNEL)
/*
 * Consistency check function.
 *
 * Checks the internal consistency as well as we can.
 *
 * Called at all boundaries of this API.
 */
static void
check_unrhdr(struct unrhdr *uh, int line)
{
        struct unr *up;
        struct unrb *ub;
        u_int x, y, z, w;

        y = uh->first;
        z = 0;
        TAILQ_FOREACH(up, &uh->head, list) {
                z++;
                if (up->ptr != uh && up->ptr != NULL) {
                        ub = up->ptr;
                        KASSERT (up->len <= NBITS,
                            ("UNR inconsistency: len %u max %d (line %d)\n",
                            up->len, NBITS, line));
                        z++;
                        w = 0;
                        for (x = 0; x < up->len; x++)
                                if (bit_test(ub->map, x))
                                        w++;
                        KASSERT (w == ub->busy,
                            ("UNR inconsistency: busy %u found %u (line %d)\n",
                            ub->busy, w, line));
                        y += w;
                } else if (up->ptr != NULL)
                        y += up->len;
        }
        KASSERT (y == uh->busy,
            ("UNR inconsistency: items %u found %u (line %d)\n",
            uh->busy, y, line));
        KASSERT (z == uh->alloc,
            ("UNR inconsistency: chunks %u found %u (line %d)\n",
            uh->alloc, z, line));
}

#else

static __inline void
check_unrhdr(struct unrhdr *uh, int line)
{

}

#endif


/*
 * Userland memory management.  Just use calloc and keep track of how
 * many elements we have allocated for check_unrhdr().
 */

static __inline void *
new_unr(struct unrhdr *uh, void **p1, void **p2)
{
        void *p;

        uh->alloc++;
        KASSERT(*p1 != NULL || *p2 != NULL, ("Out of cached memory"));
        if (*p1 != NULL) {
                p = *p1;
                *p1 = NULL;
                return (p);
        } else {
                p = *p2;
                *p2 = NULL;
                return (p);
        }
}

static __inline void
delete_unr(struct unrhdr *uh, void *ptr)
{

        uh->alloc--;
        Free(ptr);
}

/*
 * Allocate a new unrheader set.
 *
 * Highest and lowest valid values given as paramters.
 */

struct unrhdr *
new_unrhdr(int low, int high, struct lock *lock)
{
        struct unrhdr *uh;

        KASSERT(low <= high,
            ("UNR: use error: new_unrhdr(%u, %u)", low, high));
        uh = Malloc(sizeof *uh);
        if (lock != NULL)
                uh->lock = lock;
        else
                uh->lock = &unit_lock;
        TAILQ_INIT(&uh->head);
        uh->low = low;
        uh->high = high;
        uh->first = 0;
        uh->last = 1 + (high - low);
        check_unrhdr(uh, __LINE__);
        return (uh);
}

void
delete_unrhdr(struct unrhdr *uh)
{

        check_unrhdr(uh, __LINE__);
        KASSERT(uh->busy == 0, ("unrhdr has %u allocations", uh->busy));
        KASSERT(uh->alloc == 0, ("UNR memory leak in delete_unrhdr"));
        Free(uh);
}

static __inline int
is_bitmap(struct unrhdr *uh, struct unr *up)
{
        return (up->ptr != uh && up->ptr != NULL);
}

/*
 * Look for sequence of items which can be combined into a bitmap, if
 * multiple are present, take the one which saves most memory.
 *
 * Return (1) if a sequence was found to indicate that another call
 * might be able to do more.  Return (0) if we found no suitable sequence.
 *
 * NB: called from alloc_unr(), no new memory allocation allowed.
 */
static int
optimize_unr(struct unrhdr *uh)
{
        struct unr *up, *uf, *us;
        struct unrb *ub, *ubf;
        u_int a, l, ba;

        /*
         * Look for the run of items (if any) which when collapsed into
         * a bitmap would save most memory.
         */
        us = NULL;
        ba = 0;
        TAILQ_FOREACH(uf, &uh->head, list) {
                if (uf->len >= NBITS)
                        continue;
                a = 1;
                if (is_bitmap(uh, uf))
                        a++;
                l = uf->len;
                up = uf;
                while (1) {
                        up = TAILQ_NEXT(up, list);
                        if (up == NULL)
                                break;
                        if ((up->len + l) > NBITS)
                                break;
                        a++;
                        if (is_bitmap(uh, up))
                                a++;
                        l += up->len;
                }
                if (a > ba) {
                        ba = a;
                        us = uf;
                }
        }
        if (ba < 3)
                return (0);

        /*
         * If the first element is not a bitmap, make it one.
         * Trying to do so without allocating more memory complicates things
         * a bit
         */
        if (!is_bitmap(uh, us)) {
                uf = TAILQ_NEXT(us, list);
                TAILQ_REMOVE(&uh->head, us, list);
                a = us->len;
                l = us->ptr == uh ? 1 : 0;
                ub = (void *)us;
                ub->busy = 0;
                if (l) {
                        bit_nset(ub->map, 0, a);
                        ub->busy += a;
                } else {
                        bit_nclear(ub->map, 0, a);
                }
                if (!is_bitmap(uh, uf)) {
                        if (uf->ptr == NULL) {
                                bit_nclear(ub->map, a, a + uf->len - 1);
                        } else {
                                bit_nset(ub->map, a, a + uf->len - 1);
                                ub->busy += uf->len;
                        }
                        uf->ptr = ub;
                        uf->len += a;
                        us = uf;
                } else {
                        ubf = uf->ptr;
                        for (l = 0; l < uf->len; l++, a++) {
                                if (bit_test(ubf->map, l)) {
                                        bit_set(ub->map, a);
                                        ub->busy++;
                                } else {
                                        bit_clear(ub->map, a);
                                }
                        }
                        uf->len = a;
                        delete_unr(uh, uf->ptr);
                        uf->ptr = ub;
                        us = uf;
                }
        }
        ub = us->ptr;
        while (1) {
                uf = TAILQ_NEXT(us, list);
                if (uf == NULL)
                        return (1);
                if (uf->len + us->len > NBITS)
                        return (1);
                if (uf->ptr == NULL) {
                        bit_nclear(ub->map, us->len, us->len + uf->len - 1);
                        us->len += uf->len;
                        TAILQ_REMOVE(&uh->head, uf, list);
                        delete_unr(uh, uf);
                } else if (uf->ptr == uh) {
                        bit_nset(ub->map, us->len, us->len + uf->len - 1);
                        ub->busy += uf->len;
                        us->len += uf->len;
                        TAILQ_REMOVE(&uh->head, uf, list);
                        delete_unr(uh, uf);
                } else {
                        ubf = uf->ptr;
                        for (l = 0; l < uf->len; l++, us->len++) {
                                if (bit_test(ubf->map, l)) {
                                        bit_set(ub->map, us->len);
                                        ub->busy++;
                                } else {
                                        bit_clear(ub->map, us->len);
                                }
                        }
                        TAILQ_REMOVE(&uh->head, uf, list);
                        delete_unr(uh, ubf);
                        delete_unr(uh, uf);
                }
        }
}

/*
 * See if a given unr should be collapsed with a neighbor.
 *
 * NB: called from alloc_unr(), no new memory allocation allowed.
 */
static void
collapse_unr(struct unrhdr *uh, struct unr *up)
{
        struct unr *upp;
        struct unrb *ub;

        /* If bitmap is all set or clear, change it to runlength */
        if (is_bitmap(uh, up)) {
                ub = up->ptr;
                if (ub->busy == up->len) {
                        delete_unr(uh, up->ptr);
                        up->ptr = uh;
                } else if (ub->busy == 0) {
                        delete_unr(uh, up->ptr);
                        up->ptr = NULL;
                }
        }

        /* If nothing left in runlength, delete it */
        if (up->len == 0) {
                upp = TAILQ_PREV(up, unrhd, list);
                if (upp == NULL)
                        upp = TAILQ_NEXT(up, list);
                TAILQ_REMOVE(&uh->head, up, list);
                delete_unr(uh, up);
                up = upp;
        }

        /* If we have "hot-spot" still, merge with neighbor if possible */
        if (up != NULL) {
                upp = TAILQ_PREV(up, unrhd, list);
                if (upp != NULL && up->ptr == upp->ptr) {
                        up->len += upp->len;
                        TAILQ_REMOVE(&uh->head, upp, list);
                        delete_unr(uh, upp);
                        }
                upp = TAILQ_NEXT(up, list);
                if (upp != NULL && up->ptr == upp->ptr) {
                        up->len += upp->len;
                        TAILQ_REMOVE(&uh->head, upp, list);
                        delete_unr(uh, upp);
                }
        }

        /* Merge into ->first if possible */
        upp = TAILQ_FIRST(&uh->head);
        if (upp != NULL && upp->ptr == uh) {
                uh->first += upp->len;
                TAILQ_REMOVE(&uh->head, upp, list);
                delete_unr(uh, upp);
                if (up == upp)
                        up = NULL;
        }

        /* Merge into ->last if possible */
        upp = TAILQ_LAST(&uh->head, unrhd);
        if (upp != NULL && upp->ptr == NULL) {
                uh->last += upp->len;
                TAILQ_REMOVE(&uh->head, upp, list);
                delete_unr(uh, upp);
                if (up == upp)
                        up = NULL;
        }

        /* Try to make bitmaps */
        while (optimize_unr(uh))
                continue;
}

/*
 * Allocate a free unr.
 */
int
alloc_unrl(struct unrhdr *uh)
{
        struct unr *up;
        struct unrb *ub;
        u_int x;
        int y;

        KKASSERT(lockowned(uh->lock));
        check_unrhdr(uh, __LINE__);
        x = uh->low + uh->first;

        up = TAILQ_FIRST(&uh->head);

        /*
         * If we have an ideal split, just adjust the first+last
         */
        if (up == NULL && uh->last > 0) {
                uh->first++;
                uh->last--;
                uh->busy++;
                return (x);
        }

        /*
         * We can always allocate from the first list element, so if we have
         * nothing on the list, we must have run out of unit numbers.
         */
        if (up == NULL)
                return (-1);

        KASSERT(up->ptr != uh, ("UNR first element is allocated"));

        if (up->ptr == NULL) {  /* free run */
                uh->first++;
                up->len--;
        } else {                /* bitmap */
                ub = up->ptr;
                KASSERT(ub->busy < up->len, ("UNR bitmap confusion"));
                bit_ffc(ub->map, up->len, &y);
                KASSERT(y != -1, ("UNR corruption: No clear bit in bitmap."));
                bit_set(ub->map, y);
                ub->busy++;
                x += y;
        }
        uh->busy++;
        collapse_unr(uh, up);
        return (x);
}

int
alloc_unr(struct unrhdr *uh)
{
        int i;

        lockmgr(uh->lock, LK_EXCLUSIVE);
        i = alloc_unrl(uh);
        lockmgr(uh->lock, LK_RELEASE);
        return (i);
}

/*
 * Free a unr.
 *
 * If we can save unrs by using a bitmap, do so.
 */
static void
free_unrl(struct unrhdr *uh, u_int item, void **p1, void **p2)
{
        struct unr *up, *upp, *upn;
        struct unrb *ub;
        u_int pl;

        KASSERT(item >= uh->low && item <= uh->high,
            ("UNR: free_unr(%u) out of range [%u...%u]",
             item, uh->low, uh->high));
        check_unrhdr(uh, __LINE__);
        item -= uh->low;
        upp = TAILQ_FIRST(&uh->head);
        /*
         * Freeing in the ideal split case
         */
        if (item + 1 == uh->first && upp == NULL) {
                uh->last++;
                uh->first--;
                uh->busy--;
                check_unrhdr(uh, __LINE__);
                return;
        }
        /*
         * Freeing in the ->first section.  Create a run starting at the
         * freed item.  The code below will subdivide it.
         */
        if (item < uh->first) {
                up = new_unr(uh, p1, p2);
                up->ptr = uh;
                up->len = uh->first - item;
                TAILQ_INSERT_HEAD(&uh->head, up, list);
                uh->first -= up->len;
        }

        item -= uh->first;

        /* Find the item which contains the unit we want to free */
        TAILQ_FOREACH(up, &uh->head, list) {
                if (up->len > item)
                        break;
                item -= up->len;
        }

        /* Handle bitmap items */
        if (is_bitmap(uh, up)) {
                ub = up->ptr;
                
                KASSERT(bit_test(ub->map, item) != 0,
                    ("UNR: Freeing free item %d (bitmap)\n", item));
                bit_clear(ub->map, item);
                uh->busy--;
                ub->busy--;
                collapse_unr(uh, up);
                return;
        }

        KASSERT(up->ptr == uh, ("UNR Freeing free item %d (run))\n", item));

        /* Just this one left, reap it */
        if (up->len == 1) {
                up->ptr = NULL;
                uh->busy--;
                collapse_unr(uh, up);
                return;
        }

        /* Check if we can shift the item into the previous 'free' run */
        upp = TAILQ_PREV(up, unrhd, list);
        if (item == 0 && upp != NULL && upp->ptr == NULL) {
                upp->len++;
                up->len--;
                uh->busy--;
                collapse_unr(uh, up);
                return;
        }

        /* Check if we can shift the item to the next 'free' run */
        upn = TAILQ_NEXT(up, list);
        if (item == up->len - 1 && upn != NULL && upn->ptr == NULL) {
                upn->len++;
                up->len--;
                uh->busy--;
                collapse_unr(uh, up);
                return;
        }

        /* Split off the tail end, if any. */
        pl = up->len - (1 + item);
        if (pl > 0) {
                upp = new_unr(uh, p1, p2);
                upp->ptr = uh;
                upp->len = pl;
                TAILQ_INSERT_AFTER(&uh->head, up, upp, list);
        }

        /* Split off head end, if any */
        if (item > 0) {
                upp = new_unr(uh, p1, p2);
                upp->len = item;
                upp->ptr = uh;
                TAILQ_INSERT_BEFORE(up, upp, list);
        }
        up->len = 1;
        up->ptr = NULL;
        uh->busy--;
        collapse_unr(uh, up);
}

void
free_unr(struct unrhdr *uh, u_int item)
{
        void *p1, *p2;

        p1 = Malloc(sizeof(struct unr));
        p2 = Malloc(sizeof(struct unr));
        lockmgr(uh->lock, LK_EXCLUSIVE);
        free_unrl(uh, item, &p1, &p2);
        lockmgr(uh->lock, LK_RELEASE);
        if (p1 != NULL)
                Free(p1);
        if (p2 != NULL)
                Free(p2);
}

#ifndef _KERNEL /* USERLAND test driver */

/*
 * Simple stochastic test driver for the above functions
 */

static void
print_unr(struct unrhdr *uh, struct unr *up)
{
        u_int x;
        struct unrb *ub;

        printf("  %p len = %5u ", up, up->len);
        if (up->ptr == NULL)
                printf("free\n");
        else if (up->ptr == uh)
                printf("alloc\n");
        else {
                ub = up->ptr;
                printf("bitmap(%d) [", ub->busy);
                for (x = 0; x < up->len; x++) {
                        if (bit_test(ub->map, x))
                                printf("#");
                        else
                                printf(" ");
                }
                printf("]\n");
        }
}

static void
print_unrhdr(struct unrhdr *uh)
{
        struct unr *up;
        u_int x;

        printf(
            "%p low = %u high = %u first = %u last = %u busy %u chunks = %u\n",
            uh, uh->low, uh->high, uh->first, uh->last, uh->busy, uh->alloc);
        x = uh->low + uh->first;
        TAILQ_FOREACH(up, &uh->head, list) {
                printf("  from = %5u", x);
                print_unr(uh, up);
                if (up->ptr == NULL || up->ptr == uh)
                        x += up->len;
                else
                        x += NBITS;
        }
}

/* Number of unrs to test */
#define NN      10000

int
main(int argc __unused, const char **argv __unused)
{
        struct unrhdr *uh;
        u_int i, x, m, j;
        char a[NN];

        setbuf(stdout, NULL);
        uh = new_unrhdr(0, NN - 1, NULL);
        print_unrhdr(uh);

        memset(a, 0, sizeof a);

        fprintf(stderr, "sizeof(struct unr) %d\n", sizeof (struct unr));
        fprintf(stderr, "sizeof(struct unrb) %d\n", sizeof (struct unrb));
        fprintf(stderr, "sizeof(struct unrhdr) %d\n", sizeof (struct unrhdr));
        fprintf(stderr, "NBITS %d\n", NBITS);
        x = 1;
        for (m = 0; m < NN * 100; m++) {
                j = random();
                i = (j >> 1) % NN;
#if 0
                if (a[i] && (j & 1))
                        continue;
#endif
                if (a[i]) {
                        printf("F %u\n", i);
                        free_unr(uh, i);
                        a[i] = 0;
                } else {
                        no_alloc = 1;
                        i = alloc_unr(uh);
                        if (i != -1) {
                                a[i] = 1;
                                printf("A %u\n", i);
                        }
                        no_alloc = 0;
                }
                if (1)  /* XXX: change this for detailed debug printout */
                        print_unrhdr(uh);
                check_unrhdr(uh, __LINE__);
        }
        for (i = 0; i < NN; i++) {
                if (a[i]) {
                        printf("C %u\n", i);
                        free_unr(uh, i);
                        print_unrhdr(uh);
                }
        }
        print_unrhdr(uh);
        delete_unrhdr(uh);
        return (0);
}
#endif