/*      $NetBSD: subr_extent.c,v 1.91 2026/01/04 03:17:47 riastradh Exp $       */

/*-
 * Copyright (c) 1996, 1998, 2007 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jason R. Thorpe and Matthias Drochner.
 *
 * 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * General purpose extent manager.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: subr_extent.c,v 1.91 2026/01/04 03:17:47 riastradh Exp $");

#ifdef _KERNEL
#ifdef _KERNEL_OPT
#include "opt_lockdebug.h"
#endif

#include <sys/param.h>
#include <sys/types.h>

#include <sys/extent.h>
#include <sys/kmem.h>
#include <sys/pool.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/systm.h>
#include <sys/time.h>

#include <uvm/uvm_extern.h>

#elif defined(_EXTENT_TESTING)

/*
 * user-land definitions, so it can fit into a testing harness.
 */
#include <sys/param.h>
#include <sys/pool.h>
#include <sys/extent.h>

#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

static inline void no_op(void) { return; }

/*
 * Use multi-line #defines to avoid screwing up the kernel tags file;
 * without this, ctags produces a tags file where panic() shows up
 * in subr_extent.c rather than subr_prf.c.
 */
#define \
kmem_alloc(s, flags)            malloc(s)
#define \
kmem_free(p, s)                 free(p)
#define \
cv_wait_sig(cv, lock)           (EWOULDBLOCK)
#define \
pool_get(pool, flags)           kmem_alloc((pool)->pr_size,0)
#define \
pool_put(pool, rp)              kmem_free(rp,0)
#define \
panic(a ...)                    printf(a)
#define mutex_init(a, b, c)     no_op()
#define mutex_destroy(a)        no_op()
#define mutex_enter(l)          no_op()
#define mutex_exit(l)           no_op()
#define cv_wait(cv, lock)       no_op()
#define cv_broadcast(cv)        no_op()
#define cv_init(a, b)           no_op()
#define cv_destroy(a)           no_op()
#define KMEM_IS_RUNNING                 (1)
#define IPL_VM                          (0)
#define MUTEX_DEFAULT                   (0)
#define KASSERT(exp)
#define SET_ERROR(error)        (error)
#endif

static struct pool expool;

/*
 * Macro to align to an arbitrary power-of-two boundary.
 */
#define EXTENT_ALIGN(_start, _align, _skew)             \
        (((((_start) - (_skew)) + ((_align) - 1)) & (-(_align))) + (_skew))

/*
 * Create the extent_region pool.
 */
void
extent_init(void)
{

#if defined(_KERNEL)
        pool_init(&expool, sizeof(struct extent_region), 0, 0, 0,
            "extent", NULL, IPL_VM);
#else
        expool.pr_size = sizeof(struct extent_region);
#endif
}

/*
 * Allocate an extent region descriptor.  EXTENT MUST NOT BE LOCKED.
 * We will handle any locking we may need.
 */
static struct extent_region *
extent_alloc_region_descriptor(struct extent *ex, int flags)
{
        struct extent_region *rp;
        int error;

        if (ex->ex_flags & EXF_FIXED) {
                struct extent_fixed *fex = (struct extent_fixed *)ex;

                if (!(ex->ex_flags & EXF_EARLY))
                        mutex_enter(&ex->ex_lock);
                for (;;) {
                        if ((rp = LIST_FIRST(&fex->fex_freelist)) != NULL) {
                                /*
                                 * Don't muck with flags after pulling it off
                                 * the freelist; it may have been dynamically
                                 * allocated, and kindly given to us.  We
                                 * need to remember that information.
                                 */
                                LIST_REMOVE(rp, er_link);
                                if (!(ex->ex_flags & EXF_EARLY))
                                        mutex_exit(&ex->ex_lock);
                                return (rp);
                        }
                        if (flags & EX_MALLOCOK) {
                                if (!(ex->ex_flags & EXF_EARLY))
                                        mutex_exit(&ex->ex_lock);
                                goto alloc;
                        }
                        if ((flags & EX_WAITOK) == 0) {
                                if (!(ex->ex_flags & EXF_EARLY))
                                        mutex_exit(&ex->ex_lock);
                                return (NULL);
                        }
                        KASSERT(mutex_owned(&ex->ex_lock));
                        ex->ex_flwanted = true;
                        if ((flags & EX_CATCH) != 0)
                                error = cv_wait_sig(&ex->ex_cv, &ex->ex_lock);
                        else {
                                cv_wait(&ex->ex_cv, &ex->ex_lock);
                                error = 0;
                        }
                        if (error != 0) {
                                mutex_exit(&ex->ex_lock);
                                return (NULL);
                        }
                }
        }

 alloc:
        rp = pool_get(&expool, (flags & EX_WAITOK) ? PR_WAITOK : PR_NOWAIT);

        if (rp != NULL)
                rp->er_flags = ER_ALLOC;

        return (rp);
}

/*
 * Free an extent region descriptor.  EXTENT _MUST_ BE LOCKED!
 */
static void
extent_free_region_descriptor(struct extent *ex, struct extent_region *rp)
{

        if (ex->ex_flags & EXF_FIXED) {
                struct extent_fixed *fex = (struct extent_fixed *)ex;

                /*
                 * If someone's waiting for a region descriptor,
                 * be nice and give them this one, rather than
                 * just free'ing it back to the system.
                 */
                if (rp->er_flags & ER_ALLOC) {
                        if (ex->ex_flwanted) {
                                /* Clear all but ER_ALLOC flag. */
                                rp->er_flags = ER_ALLOC;
                                LIST_INSERT_HEAD(&fex->fex_freelist, rp,
                                    er_link);
                                goto wake_em_up;
                        } else
                                pool_put(&expool, rp);
                } else {
                        /* Clear all flags. */
                        rp->er_flags = 0;
                        LIST_INSERT_HEAD(&fex->fex_freelist, rp, er_link);
                }

 wake_em_up:
                if (!(ex->ex_flags & EXF_EARLY)) {
                        ex->ex_flwanted = false;
                        cv_broadcast(&ex->ex_cv);
                }
                return;
        }

        /*
         * We know it's dynamically allocated if we get here.
         */
        pool_put(&expool, rp);
}

/*
 * Allocate and initialize an extent map.
 */
struct extent *
extent_create(const char *name, u_long start, u_long end,
    void *storage, size_t storagesize, int flags)
{
        struct extent *ex;
        char *cp = storage;
        size_t sz = storagesize;
        struct extent_region *rp;
        int fixed_extent = (storage != NULL);

#ifndef _KERNEL
        extent_init();
#endif

#ifdef DIAGNOSTIC
        /* Check arguments. */
        if (name == NULL)
                panic("extent_create: name == NULL");
        if (end < start) {
                printf("extent_create: extent `%s', start 0x%lx, end 0x%lx\n",
                    name, start, end);
                panic("extent_create: end < start");
        }
        if (fixed_extent && (storagesize < sizeof(struct extent_fixed)))
                panic("extent_create: fixed extent, bad storagesize 0x%lx",
                    (u_long)storagesize);
        if (fixed_extent == 0 && (storagesize != 0 || storage != NULL))
                panic("extent_create: storage provided for non-fixed");
#endif

        /* Allocate extent descriptor. */
        if (fixed_extent) {
                struct extent_fixed *fex;

                memset(storage, 0, storagesize);

                /*
                 * Align all descriptors on "long" boundaries.
                 */
                fex = (struct extent_fixed *)cp;
                ex = (struct extent *)fex;
                cp += ALIGN(sizeof(struct extent_fixed));
                sz -= ALIGN(sizeof(struct extent_fixed));
                fex->fex_storage = storage;
                fex->fex_storagesize = storagesize;

                /*
                 * In a fixed extent, we have to pre-allocate region
                 * descriptors and place them in the extent's freelist.
                 */
                LIST_INIT(&fex->fex_freelist);
                while (sz >= ALIGN(sizeof(struct extent_region))) {
                        rp = (struct extent_region *)cp;
                        cp += ALIGN(sizeof(struct extent_region));
                        sz -= ALIGN(sizeof(struct extent_region));
                        LIST_INSERT_HEAD(&fex->fex_freelist, rp, er_link);
                }
        } else {
                ex = kmem_alloc(sizeof(*ex),
                    (flags & EX_WAITOK) ? KM_SLEEP : KM_NOSLEEP);
                if (ex == NULL)
                        return (NULL);
        }

        /* Fill in the extent descriptor and return it to the caller. */
        if ((flags & EX_EARLY) == 0) {
                mutex_init(&ex->ex_lock, MUTEX_DEFAULT, IPL_VM);
                cv_init(&ex->ex_cv, "extent");
        }
        LIST_INIT(&ex->ex_regions);
        ex->ex_name = name;
        ex->ex_start = start;
        ex->ex_end = end;
        ex->ex_flags = 0;
        ex->ex_flwanted = false;
        if (fixed_extent)
                ex->ex_flags |= EXF_FIXED;
        if (flags & EX_NOCOALESCE)
                ex->ex_flags |= EXF_NOCOALESCE;
        if (flags & EX_EARLY)
                ex->ex_flags |= EXF_EARLY;
        return (ex);
}

/*
 * Destroy an extent map.
 * Since we're freeing the data, there can't be any references
 * so we don't need any locking.
 */
void
extent_destroy(struct extent *ex)
{
        struct extent_region *rp, *orp;

#ifdef DIAGNOSTIC
        /* Check arguments. */
        if (ex == NULL)
                panic("extent_destroy: NULL extent");
#endif

        /* Free all region descriptors in extent. */
        for (rp = LIST_FIRST(&ex->ex_regions); rp != NULL; ) {
                orp = rp;
                rp = LIST_NEXT(rp, er_link);
                LIST_REMOVE(orp, er_link);
                extent_free_region_descriptor(ex, orp);
        }

        cv_destroy(&ex->ex_cv);
        mutex_destroy(&ex->ex_lock);

        /* If we're not a fixed extent, free the extent descriptor itself. */
        if ((ex->ex_flags & EXF_FIXED) == 0)
                kmem_free(ex, sizeof(*ex));
}

/*
 * Insert a region descriptor into the sorted region list after the
 * entry "after" or at the head of the list (if "after" is NULL).
 * The region descriptor we insert is passed in "rp".  We must
 * allocate the region descriptor before calling this function!
 * If we don't need the region descriptor, it will be freed here.
 */
static void
extent_insert_and_optimize(struct extent *ex, u_long start, u_long size,
    int flags, struct extent_region *after, struct extent_region *rp)
{
        struct extent_region *nextr;
        int appended = 0;

        if (after == NULL) {
                /*
                 * We're the first in the region list.  If there's
                 * a region after us, attempt to coalesce to save
                 * descriptor overhead.
                 */
                if (((ex->ex_flags & EXF_NOCOALESCE) == 0) &&
                    (LIST_FIRST(&ex->ex_regions) != NULL) &&
                    ((start + size) == LIST_FIRST(&ex->ex_regions)->er_start)) {
                        /*
                         * We can coalesce.  Prepend us to the first region.
                         */
                        LIST_FIRST(&ex->ex_regions)->er_start = start;
                        extent_free_region_descriptor(ex, rp);
                        return;
                }

                /*
                 * Can't coalesce.  Fill in the region descriptor
                 * in, and insert us at the head of the region list.
                 */
                rp->er_start = start;
                rp->er_end = start + (size - 1);
                LIST_INSERT_HEAD(&ex->ex_regions, rp, er_link);
                return;
        }

        /*
         * If EXF_NOCOALESCE is set, coalescing is disallowed.
         */
        if (ex->ex_flags & EXF_NOCOALESCE)
                goto cant_coalesce;

        /*
         * Attempt to coalesce with the region before us.
         */
        if ((after->er_end + 1) == start) {
                /*
                 * We can coalesce.  Append ourselves and make
                 * note of it.
                 */
                after->er_end = start + (size - 1);
                appended = 1;
        }

        /*
         * Attempt to coalesce with the region after us.
         */
        if ((LIST_NEXT(after, er_link) != NULL) &&
            ((start + size) == LIST_NEXT(after, er_link)->er_start)) {
                /*
                 * We can coalesce.  Note that if we appended ourselves
                 * to the previous region, we exactly fit the gap, and
                 * can free the "next" region descriptor.
                 */
                if (appended) {
                        /*
                         * Yup, we can free it up.
                         */
                        after->er_end = LIST_NEXT(after, er_link)->er_end;
                        nextr = LIST_NEXT(after, er_link);
                        LIST_REMOVE(nextr, er_link);
                        extent_free_region_descriptor(ex, nextr);
                } else {
                        /*
                         * Nope, just prepend us to the next region.
                         */
                        LIST_NEXT(after, er_link)->er_start = start;
                }

                extent_free_region_descriptor(ex, rp);
                return;
        }

        /*
         * We weren't able to coalesce with the next region, but
         * we don't need to allocate a region descriptor if we
         * appended ourselves to the previous region.
         */
        if (appended) {
                extent_free_region_descriptor(ex, rp);
                return;
        }

 cant_coalesce:

        /*
         * Fill in the region descriptor and insert ourselves
         * into the region list.
         */
        rp->er_start = start;
        rp->er_end = start + (size - 1);
        LIST_INSERT_AFTER(after, rp, er_link);
}

/*
 * Allocate a specific region in an extent map.
 */
int
extent_alloc_region(struct extent *ex, u_long start, u_long size, int flags)
{
        struct extent_region *rp, *last, *myrp;
        u_long end = start + (size - 1);
        int error;

#ifdef DIAGNOSTIC
        /* Check arguments. */
        if (ex == NULL)
                panic("extent_alloc_region: NULL extent");
        if (size < 1) {
                printf("extent_alloc_region: extent `%s', size 0x%lx\n",
                    ex->ex_name, size);
                panic("extent_alloc_region: bad size");
        }
        if (end < start) {
                printf(
                 "extent_alloc_region: extent `%s', start 0x%lx, size 0x%lx\n",
                 ex->ex_name, start, size);
                panic("extent_alloc_region: overflow");
        }
#endif
#ifdef LOCKDEBUG
        if (flags & EX_WAITSPACE) {
                ASSERT_SLEEPABLE();
        }
#endif

        /*
         * Make sure the requested region lies within the
         * extent.
         *
         * We don't lock to check the range, because those values
         * are never modified, and if another thread deletes the
         * extent, we're screwed anyway.
         */
        if ((start < ex->ex_start) || (end > ex->ex_end)) {
#ifdef DIAGNOSTIC
                printf("extent_alloc_region: extent `%s' (0x%lx - 0x%lx)\n",
                    ex->ex_name, ex->ex_start, ex->ex_end);
                printf("extent_alloc_region: start 0x%lx, end 0x%lx\n",
                    start, end);
                panic("extent_alloc_region: region lies outside extent");
#else
                return SET_ERROR(EINVAL);
#endif
        }

        /*
         * Allocate the region descriptor.  It will be freed later
         * if we can coalesce with another region.  Don't lock before
         * here!  This could block.
         */
        myrp = extent_alloc_region_descriptor(ex, flags);
        if (myrp == NULL) {
#ifdef DIAGNOSTIC
                printf(
                    "extent_alloc_region: can't allocate region descriptor\n");
#endif
                return SET_ERROR(ENOMEM);
        }

        if (!(ex->ex_flags & EXF_EARLY))
                mutex_enter(&ex->ex_lock);
 alloc_start:

        /*
         * Attempt to place ourselves in the desired area of the
         * extent.  We save ourselves some work by keeping the list sorted.
         * In other words, if the start of the current region is greater
         * than the end of our region, we don't have to search any further.
         */

        /*
         * Keep a pointer to the last region we looked at so
         * that we don't have to traverse the list again when
         * we insert ourselves.  If "last" is NULL when we
         * finally insert ourselves, we go at the head of the
         * list.  See extent_insert_and_optimize() for details.
         */
        last = NULL;

        LIST_FOREACH(rp, &ex->ex_regions, er_link) {
                if (rp->er_start > end) {
                        /*
                         * We lie before this region and don't
                         * conflict.
                         */
                        break;
                }

                /*
                 * The current region begins before we end.
                 * Check for a conflict.
                 */
                if (rp->er_end >= start) {
                        /*
                         * We conflict.  If we can (and want to) wait,
                         * do so.
                         */
                        if (flags & EX_WAITSPACE) {
                                KASSERT(!(ex->ex_flags & EXF_EARLY));
                                if ((flags & EX_CATCH) != 0)
                                        error = cv_wait_sig(&ex->ex_cv,
                                            &ex->ex_lock);
                                else {
                                        cv_wait(&ex->ex_cv, &ex->ex_lock);
                                        error = 0;
                                }
                                if (error == 0)
                                        goto alloc_start;
                                mutex_exit(&ex->ex_lock);
                        } else {
                                if (!(ex->ex_flags & EXF_EARLY))
                                        mutex_exit(&ex->ex_lock);
                                error = SET_ERROR(EAGAIN);
                        }
                        extent_free_region_descriptor(ex, myrp);
                        return error;
                }
                /*
                 * We don't conflict, but this region lies before
                 * us.  Keep a pointer to this region, and keep
                 * trying.
                 */
                last = rp;
        }

        /*
         * We don't conflict with any regions.  "last" points
         * to the region we fall after, or is NULL if we belong
         * at the beginning of the region list.  Insert ourselves.
         */
        extent_insert_and_optimize(ex, start, size, flags, last, myrp);
        if (!(ex->ex_flags & EXF_EARLY))
                mutex_exit(&ex->ex_lock);
        return (0);
}

/*
 * Macro to check (x + y) <= z.  This check is designed to fail
 * if an overflow occurs.
 */
#define LE_OV(x, y, z)  ((((x) + (y)) >= (x)) && (((x) + (y)) <= (z)))

/*
 * Allocate a region in an extent map subregion.
 *
 * If EX_FAST is specified, we return the first fit in the map.
 * Otherwise, we try to minimize fragmentation by finding the
 * smallest gap that will hold the request.
 *
 * The allocated region is aligned to "alignment", which must be
 * a power of 2.
 */
int
extent_alloc_subregion1(struct extent *ex, u_long substart, u_long subend,
    u_long size, u_long alignment, u_long skew, u_long boundary,
    int flags, u_long *result)
{
        struct extent_region *rp, *myrp, *last, *bestlast;
        u_long newstart, newend, exend, beststart, bestovh, ovh;
        u_long dontcross;
        int error;

#ifdef DIAGNOSTIC
        /*
         * Check arguments.
         *
         * We don't lock to check these, because these values
         * are never modified, and if another thread deletes the
         * extent, we're screwed anyway.
         */
        if (ex == NULL)
                panic("extent_alloc_subregion: NULL extent");
        if (result == NULL)
                panic("extent_alloc_subregion: NULL result pointer");
        if ((substart < ex->ex_start) || (substart > ex->ex_end) ||
            (subend > ex->ex_end) || (subend < ex->ex_start)) {
                printf("extent_alloc_subregion: extent `%s', ex_start 0x%lx, "
                    "ex_end 0x%lx\n", ex->ex_name, ex->ex_start, ex->ex_end);
                printf("extent_alloc_subregion: substart 0x%lx, subend 0x%lx\n",
                    substart, subend);
                panic("extent_alloc_subregion: bad subregion");
        }
        if ((size < 1) || ((size - 1) > (subend - substart))) {
                printf("extent_alloc_subregion: extent `%s', size 0x%lx\n",
                    ex->ex_name, size);
                printf("extent_alloc_subregion: substart 0x%lx, subend 0x%lx\n",
                    substart, subend);
                panic("extent_alloc_subregion: bad size");
        }
        if (alignment == 0)
                panic("extent_alloc_subregion: bad alignment");
        if (boundary && (boundary < size)) {
                printf(
                    "extent_alloc_subregion: extent `%s', size 0x%lx, "
                    "boundary 0x%lx\n", ex->ex_name, size, boundary);
                panic("extent_alloc_subregion: bad boundary");
        }
#endif
#ifdef LOCKDEBUG
        if (flags & EX_WAITSPACE) {
                ASSERT_SLEEPABLE();
        }
#endif

        /*
         * Allocate the region descriptor.  It will be freed later
         * if we can coalesce with another region.  Don't lock before
         * here!  This could block.
         */
        myrp = extent_alloc_region_descriptor(ex, flags);
        if (myrp == NULL) {
#ifdef DIAGNOSTIC
                printf(
                 "extent_alloc_subregion: can't allocate region descriptor\n");
#endif
                return SET_ERROR(ENOMEM);
        }

 alloc_start:
        mutex_enter(&ex->ex_lock);

        /*
         * Keep a pointer to the last region we looked at so
         * that we don't have to traverse the list again when
         * we insert ourselves.  If "last" is NULL when we
         * finally insert ourselves, we go at the head of the
         * list.  See extent_insert_and_optimize() for deatails.
         */
        last = NULL;

        /*
         * Keep track of size and location of the smallest
         * chunk we fit in.
         *
         * Since the extent can be as large as the numeric range
         * of the CPU (0 - 0xffffffff for 32-bit systems), the
         * best overhead value can be the maximum unsigned integer.
         * Thus, we initialize "bestovh" to 0, since we insert ourselves
         * into the region list immediately on an exact match (which
         * is the only case where "bestovh" would be set to 0).
         */
        bestovh = 0;
        beststart = 0;
        bestlast = NULL;

        /*
         * Keep track of end of free region.  This is either the end of extent
         * or the start of a region past the subend.
         */
        exend = ex->ex_end;

        /*
         * For N allocated regions, we must make (N + 1)
         * checks for unallocated space.  The first chunk we
         * check is the area from the beginning of the subregion
         * to the first allocated region after that point.
         */
        newstart = EXTENT_ALIGN(substart, alignment, skew);
        if (newstart < ex->ex_start) {
#ifdef DIAGNOSTIC
                printf(
      "extent_alloc_subregion: extent `%s' (0x%lx - 0x%lx), alignment 0x%lx\n",
                 ex->ex_name, ex->ex_start, ex->ex_end, alignment);
                mutex_exit(&ex->ex_lock);
                panic("extent_alloc_subregion: overflow after alignment");
#else
                extent_free_region_descriptor(ex, myrp);
                mutex_exit(&ex->ex_lock);
                return SET_ERROR(EINVAL);
#endif
        }

        /*
         * Find the first allocated region that begins on or after
         * the subregion start, advancing the "last" pointer along
         * the way.
         */
        LIST_FOREACH(rp, &ex->ex_regions, er_link) {
                if (rp->er_start >= newstart)
                        break;
                last = rp;
        }

        /*
         * Relocate the start of our candidate region to the end of
         * the last allocated region (if there was one overlapping
         * our subrange).
         */
        if (last != NULL && last->er_end >= newstart)
                newstart = EXTENT_ALIGN((last->er_end + 1), alignment, skew);

        for (; rp != NULL; rp = LIST_NEXT(rp, er_link)) {
                /*
                 * If the region pasts the subend, bail out and see
                 * if we fit against the subend.
                 */
                if (rp->er_start > subend) {
                        exend = rp->er_start;
                        break;
                }

                /*
                 * Check the chunk before "rp".  Note that our
                 * comparison is safe from overflow conditions.
                 */
                if (LE_OV(newstart, size, rp->er_start)) {
                        /*
                         * Do a boundary check, if necessary.  Note
                         * that a region may *begin* on the boundary,
                         * but it must end before the boundary.
                         */
                        if (boundary) {
                                newend = newstart + (size - 1);

                                /*
                                 * Calculate the next boundary after the start
                                 * of this region.
                                 */
                                dontcross = EXTENT_ALIGN(newstart+1, boundary,
                                    (flags & EX_BOUNDZERO) ? 0 : ex->ex_start)
                                    - 1;

#if 0
                                printf("newstart=%lx newend=%lx ex_start=%lx ex_end=%lx boundary=%lx dontcross=%lx\n",
                                    newstart, newend, ex->ex_start, ex->ex_end,
                                    boundary, dontcross);
#endif

                                /* Check for overflow */
                                if (dontcross < ex->ex_start)
                                        dontcross = ex->ex_end;
                                else if (newend > dontcross) {
                                        /*
                                         * Candidate region crosses boundary.
                                         * Throw away the leading part and see
                                         * if we still fit.
                                         */
                                        newstart = dontcross + 1;
                                        newend = newstart + (size - 1);
                                        dontcross += boundary;
                                        if (!LE_OV(newstart, size, rp->er_start))
                                                goto skip;
                                }

                                /*
                                 * If we run past the end of
                                 * the extent or the boundary
                                 * overflows, then the request
                                 * can't fit.
                                 */
                                if (newstart + size - 1 > ex->ex_end ||
                                    dontcross < newstart)
                                        goto fail;
                        }

                        /*
                         * We would fit into this space.  Calculate
                         * the overhead (wasted space).  If we exactly
                         * fit, or we're taking the first fit, insert
                         * ourselves into the region list.
                         */
                        ovh = rp->er_start - newstart - size;
                        if ((flags & EX_FAST) || (ovh == 0))
                                goto found;

                        /*
                         * Don't exactly fit, but check to see
                         * if we're better than any current choice.
                         */
                        if ((bestovh == 0) || (ovh < bestovh)) {
                                bestovh = ovh;
                                beststart = newstart;
                                bestlast = last;
                        }
                }

skip:
                /*
                 * Skip past the current region and check again.
                 */
                newstart = EXTENT_ALIGN((rp->er_end + 1), alignment, skew);
                if (newstart < rp->er_end) {
                        /*
                         * Overflow condition.  Don't error out, since
                         * we might have a chunk of space that we can
                         * use.
                         */
                        goto fail;
                }

                last = rp;
        }

        /*
         * The final check is from the current starting point to the
         * end of the subregion.  If there were no allocated regions,
         * "newstart" is set to the beginning of the subregion, or
         * just past the end of the last allocated region, adjusted
         * for alignment in either case.
         */
        if (LE_OV(newstart, (size - 1), subend)) {
                /*
                 * Do a boundary check, if necessary.  Note
                 * that a region may *begin* on the boundary,
                 * but it must end before the boundary.
                 */
                if (boundary) {
                        newend = newstart + (size - 1);

                        /*
                         * Calculate the next boundary after the start
                         * of this region.
                         */
                        dontcross = EXTENT_ALIGN(newstart+1, boundary,
                            (flags & EX_BOUNDZERO) ? 0 : ex->ex_start)
                            - 1;

#if 0
                        printf("newstart=%lx newend=%lx ex_start=%lx ex_end=%lx boundary=%lx dontcross=%lx\n",
                            newstart, newend, ex->ex_start, ex->ex_end,
                            boundary, dontcross);
#endif

                        /* Check for overflow */
                        if (dontcross < ex->ex_start)
                                dontcross = ex->ex_end;
                        else if (newend > dontcross) {
                                /*
                                 * Candidate region crosses boundary.
                                 * Throw away the leading part and see
                                 * if we still fit.
                                 */
                                newstart = dontcross + 1;
                                newend = newstart + (size - 1);
                                dontcross += boundary;
                                if (!LE_OV(newstart, (size - 1), subend))
                                        goto fail;
                        }

                        /*
                         * If we run past the end of
                         * the extent or the boundary
                         * overflows, then the request
                         * can't fit.
                         */
                        if (newstart + size - 1 > ex->ex_end ||
                            dontcross < newstart)
                                goto fail;
                }

                /*
                 * We would fit into this space.  Calculate
                 * the overhead (wasted space).  If we exactly
                 * fit, or we're taking the first fit, insert
                 * ourselves into the region list.
                 */
                ovh = exend - newstart - (size - 1);
                if ((flags & EX_FAST) || (ovh == 0))
                        goto found;

                /*
                 * Don't exactly fit, but check to see
                 * if we're better than any current choice.
                 */
                if ((bestovh == 0) || (ovh < bestovh)) {
                        bestovh = ovh;
                        beststart = newstart;
                        bestlast = last;
                }
        }

 fail:
        /*
         * One of the following two conditions have
         * occurred:
         *
         *      There is no chunk large enough to hold the request.
         *
         *      If EX_FAST was not specified, there is not an
         *      exact match for the request.
         *
         * Note that if we reach this point and EX_FAST is
         * set, then we know there is no space in the extent for
         * the request.
         */
        if (((flags & EX_FAST) == 0) && (bestovh != 0)) {
                /*
                 * We have a match that's "good enough".
                 */
                newstart = beststart;
                last = bestlast;
                goto found;
        }

        /*
         * No space currently available.  Wait for it to free up,
         * if possible.
         */
        if (flags & EX_WAITSPACE) {
                if ((flags & EX_CATCH) != 0) {
                        error = cv_wait_sig(&ex->ex_cv, &ex->ex_lock);
                } else {
                        cv_wait(&ex->ex_cv, &ex->ex_lock);
                        error = 0;
                }
                if (error == 0)
                        goto alloc_start;
                mutex_exit(&ex->ex_lock);
        } else {
                mutex_exit(&ex->ex_lock);
                error = SET_ERROR(EAGAIN);
        }

        extent_free_region_descriptor(ex, myrp);
        return error;

 found:
        /*
         * Insert ourselves into the region list.
         */
        extent_insert_and_optimize(ex, newstart, size, flags, last, myrp);
        mutex_exit(&ex->ex_lock);
        *result = newstart;
        return (0);
}

int
extent_alloc_subregion(struct extent *ex, u_long start, u_long end, u_long size,
    u_long alignment, u_long boundary, int flags, u_long *result)
{

        return (extent_alloc_subregion1(ex, start, end, size, alignment,
                                        0, boundary, flags, result));
}

int
extent_alloc(struct extent *ex, u_long size, u_long alignment, u_long boundary,
    int flags, u_long *result)
{

        return (extent_alloc_subregion1(ex, ex->ex_start, ex->ex_end,
                                        size, alignment, 0, boundary,
                                        flags, result));
}

int
extent_alloc1(struct extent *ex, u_long size, u_long alignment, u_long skew,
    u_long boundary, int flags, u_long *result)
{

        return (extent_alloc_subregion1(ex, ex->ex_start, ex->ex_end,
                                        size, alignment, skew, boundary,
                                        flags, result));
}

int
extent_free(struct extent *ex, u_long start, u_long size, int flags)
{
        struct extent_region *rp, *nrp = NULL;
        u_long end = start + (size - 1);

#ifdef DIAGNOSTIC
        /*
         * Check arguments.
         *
         * We don't lock to check these, because these values
         * are never modified, and if another thread deletes the
         * extent, we're screwed anyway.
         */
        if (ex == NULL)
                panic("extent_free: NULL extent");
        if ((start < ex->ex_start) || (end > ex->ex_end)) {
                extent_print(ex);
                printf("extent_free: extent `%s', start 0x%lx, size 0x%lx\n",
                    ex->ex_name, start, size);
                panic("extent_free: extent `%s', region not within extent",
                    ex->ex_name);
        }
        /* Check for an overflow. */
        if (end < start) {
                extent_print(ex);
                printf("extent_free: extent `%s', start 0x%lx, size 0x%lx\n",
                    ex->ex_name, start, size);
                panic("extent_free: overflow");
        }
#endif

        /*
         * If we're allowing coalescing, we must allocate a region
         * descriptor now, since it might block.
         */
        const bool coalesce = (ex->ex_flags & EXF_NOCOALESCE) == 0;

        if (coalesce) {
                /* Allocate a region descriptor. */
                nrp = extent_alloc_region_descriptor(ex, flags);
                if (nrp == NULL)
                        return SET_ERROR(ENOMEM);
        }

        if (!(ex->ex_flags & EXF_EARLY))
                mutex_enter(&ex->ex_lock);

        /*
         * Find region and deallocate.  Several possibilities:
         *
         *      1. (start == er_start) && (end == er_end):
         *         Free descriptor.
         *
         *      2. (start == er_start) && (end < er_end):
         *         Adjust er_start.
         *
         *      3. (start > er_start) && (end == er_end):
         *         Adjust er_end.
         *
         *      4. (start > er_start) && (end < er_end):
         *         Fragment region.  Requires descriptor alloc.
         *
         * Cases 2, 3, and 4 require that the EXF_NOCOALESCE flag
         * is not set.
         */
        LIST_FOREACH(rp, &ex->ex_regions, er_link) {
                /*
                 * Save ourselves some comparisons; does the current
                 * region end before chunk to be freed begins?  If so,
                 * then we haven't found the appropriate region descriptor.
                 */
                if (rp->er_end < start)
                        continue;

                /*
                 * Save ourselves some traversal; does the current
                 * region begin after the chunk to be freed ends?  If so,
                 * then we've already passed any possible region descriptors
                 * that might have contained the chunk to be freed.
                 */
                if (rp->er_start > end)
                        break;

                /* Case 1. */
                if ((start == rp->er_start) && (end == rp->er_end)) {
                        LIST_REMOVE(rp, er_link);
                        extent_free_region_descriptor(ex, rp);
                        goto done;
                }

                /*
                 * The following cases all require that EXF_NOCOALESCE
                 * is not set.
                 */
                if (!coalesce)
                        continue;

                /* Case 2. */
                if ((start == rp->er_start) && (end < rp->er_end)) {
                        rp->er_start = (end + 1);
                        goto done;
                }

                /* Case 3. */
                if ((start > rp->er_start) && (end == rp->er_end)) {
                        rp->er_end = (start - 1);
                        goto done;
                }

                /* Case 4. */
                if ((start > rp->er_start) && (end < rp->er_end)) {
                        /* Fill in new descriptor. */
                        nrp->er_start = end + 1;
                        nrp->er_end = rp->er_end;

                        /* Adjust current descriptor. */
                        rp->er_end = start - 1;

                        /* Insert new descriptor after current. */
                        LIST_INSERT_AFTER(rp, nrp, er_link);

                        /* We used the new descriptor, so don't free it below */
                        nrp = NULL;
                        goto done;
                }
        }

        /* Region not found, or request otherwise invalid. */
        if (!(ex->ex_flags & EXF_EARLY))
                mutex_exit(&ex->ex_lock);
        extent_print(ex);
        printf("extent_free: start 0x%lx, end 0x%lx\n", start, end);
        panic("extent_free: region not found");

 done:
        if (nrp != NULL)
                extent_free_region_descriptor(ex, nrp);
        if (!(ex->ex_flags & EXF_EARLY)) {
                cv_broadcast(&ex->ex_cv);
                mutex_exit(&ex->ex_lock);
        }
        return (0);
}

void
extent_print(struct extent *ex)
{
        struct extent_region *rp;

        if (ex == NULL)
                panic("extent_print: NULL extent");

        if (!(ex->ex_flags & EXF_EARLY))
                mutex_enter(&ex->ex_lock);

        printf("extent `%s' (0x%lx - 0x%lx), flags = 0x%x\n", ex->ex_name,
            ex->ex_start, ex->ex_end, ex->ex_flags);

        LIST_FOREACH(rp, &ex->ex_regions, er_link)
                printf("     0x%lx - 0x%lx\n", rp->er_start, rp->er_end);

        if (!(ex->ex_flags & EXF_EARLY))
                mutex_exit(&ex->ex_lock);
}