kernel/libc: Remove sigstack() remains.

[dragonfly.git] / sys / kern / sysv_shm.c

/*
 * Copyright (c) 1994 Adam Glass and Charles Hannum.  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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Adam Glass and Charles
 *      Hannum.
 * 4. The names of the authors may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``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 AUTHORS 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.
 */

#include "opt_sysvipc.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/shm.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/sysent.h>
#include <sys/jail.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/pmap.h>
#include <vm/vm_object.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>

static MALLOC_DEFINE(M_SHM, "shm", "SVID compatible shared memory segments");

static int shmget_allocate_segment (struct proc *p, struct shmget_args *uap, int mode);
static int shmget_existing (struct proc *p, struct shmget_args *uap, int mode, int segnum);

#define SHMSEG_FREE             0x0200
#define SHMSEG_REMOVED          0x0400
#define SHMSEG_ALLOCATED        0x0800
#define SHMSEG_WANTED           0x1000

static int shm_last_free, shm_committed, shmalloced;
int shm_nused;
static struct shmid_ds  *shmsegs;
static struct lwkt_token shm_token = LWKT_TOKEN_INITIALIZER(shm_token);

struct shm_handle {
        /* vm_offset_t kva; */
        vm_object_t shm_object;
};

struct shmmap_state {
        vm_offset_t va;
        int shmid;
};

static void shm_deallocate_segment (struct shmid_ds *);
static int shm_find_segment_by_key (key_t);
static struct shmid_ds *shm_find_segment_by_shmid (int);
static int shm_delete_mapping (struct vmspace *vm, struct shmmap_state *);
static void shmrealloc (void);
static void shminit (void *);

/*
 * Tuneable values
 */
#ifndef SHMMIN
#define SHMMIN  1
#endif
#ifndef SHMMNI
#define SHMMNI  512
#endif
#ifndef SHMSEG
#define SHMSEG  1024
#endif

struct  shminfo shminfo = {
        0,
        SHMMIN,
        SHMMNI,
        SHMSEG,
        0
};

/*
 * allow-removed    Allow a shared memory segment to be attached by its shmid
 *                  even after it has been deleted, as long as it was still
 *                  being referenced by someone.  This is a trick used by
 *                  chrome and other applications to avoid leaving shm
 *                  segments hanging around after the application is killed
 *                  or seg-faults unexpectedly.
 *
 * use-phys         Shared memory segments are to use physical memory by
 *                  default, which allows the kernel to optimize (remove)
 *                  pv_entry management structures for the related PTEs and
 *                  prevents paging.  This has distinctly different and
 *                  usually desireable characteristics verses mmap()ing
 *                  anonymous memory.
 */
static int shm_allow_removed = 1;
static int shm_use_phys = 1;

TUNABLE_LONG("kern.ipc.shmmin", &shminfo.shmmin);
TUNABLE_LONG("kern.ipc.shmmni", &shminfo.shmmni);
TUNABLE_LONG("kern.ipc.shmseg", &shminfo.shmseg);
TUNABLE_LONG("kern.ipc.shmmaxpgs", &shminfo.shmall);
TUNABLE_INT("kern.ipc.shm_use_phys", &shm_use_phys);

SYSCTL_LONG(_kern_ipc, OID_AUTO, shmmax, CTLFLAG_RW, &shminfo.shmmax, 0,
    "Max shared memory segment size");
SYSCTL_LONG(_kern_ipc, OID_AUTO, shmmin, CTLFLAG_RW, &shminfo.shmmin, 0,
    "Min shared memory segment size");
SYSCTL_LONG(_kern_ipc, OID_AUTO, shmmni, CTLFLAG_RD, &shminfo.shmmni, 0,
    "Max number of shared memory identifiers");
SYSCTL_LONG(_kern_ipc, OID_AUTO, shmseg, CTLFLAG_RW, &shminfo.shmseg, 0,
    "Max shared memory segments per process");
SYSCTL_LONG(_kern_ipc, OID_AUTO, shmall, CTLFLAG_RW, &shminfo.shmall, 0,
    "Max pages of shared memory");
SYSCTL_INT(_kern_ipc, OID_AUTO, shm_use_phys, CTLFLAG_RW, &shm_use_phys, 0,
    "Use phys pager allocation instead of swap pager allocation");
SYSCTL_INT(_kern_ipc, OID_AUTO, shm_allow_removed, CTLFLAG_RW,
    &shm_allow_removed, 0,
    "Enable/Disable attachment to attached segments marked for removal");

static int
shm_find_segment_by_key(key_t key)
{
        int i;

        for (i = 0; i < shmalloced; i++) {
                if ((shmsegs[i].shm_perm.mode & SHMSEG_ALLOCATED) &&
                    shmsegs[i].shm_perm.key == key)
                        return i;
        }
        return -1;
}

static struct shmid_ds *
shm_find_segment_by_shmid(int shmid)
{
        int segnum;
        struct shmid_ds *shmseg;

        segnum = IPCID_TO_IX(shmid);
        if (segnum < 0 || segnum >= shmalloced)
                return NULL;
        shmseg = &shmsegs[segnum];
        if ((shmseg->shm_perm.mode & SHMSEG_ALLOCATED) == 0 ||
            (!shm_allow_removed &&
            (shmseg->shm_perm.mode & SHMSEG_REMOVED) != 0) ||
            shmseg->shm_perm.seq != IPCID_TO_SEQ(shmid)) {
                return NULL;
        }
        return shmseg;
}

static void
shm_deallocate_segment(struct shmid_ds *shmseg)
{
        struct shm_handle *shm_handle;
        size_t size;

        shm_handle = shmseg->shm_internal;
        vm_object_deallocate(shm_handle->shm_object);
        kfree((caddr_t)shm_handle, M_SHM);
        shmseg->shm_internal = NULL;
        size = round_page(shmseg->shm_segsz);
        shm_committed -= btoc(size);
        shm_nused--;
        shmseg->shm_perm.mode = SHMSEG_FREE;
}

static int
shm_delete_mapping(struct vmspace *vm, struct shmmap_state *shmmap_s)
{
        struct shmid_ds *shmseg;
        int segnum, result;
        size_t size;

        segnum = IPCID_TO_IX(shmmap_s->shmid);
        shmseg = &shmsegs[segnum];
        size = round_page(shmseg->shm_segsz);
        result = vm_map_remove(&vm->vm_map, shmmap_s->va, shmmap_s->va + size);
        if (result != KERN_SUCCESS)
                return EINVAL;
        shmmap_s->shmid = -1;
        shmseg->shm_dtime = time_second;
        if ((--shmseg->shm_nattch <= 0) &&
            (shmseg->shm_perm.mode & SHMSEG_REMOVED)) {
                shm_deallocate_segment(shmseg);
                shm_last_free = segnum;
        }
        return 0;
}

/*
 * MPALMOSTSAFE
 */
int
sys_shmdt(struct shmdt_args *uap)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct shmmap_state *shmmap_s;
        long i;
        int error;

        if (!jail_sysvipc_allowed && td->td_ucred->cr_prison != NULL)
                return (ENOSYS);

        lwkt_gettoken(&shm_token);
        shmmap_s = (struct shmmap_state *)p->p_vmspace->vm_shm;
        if (shmmap_s == NULL) {
                error = EINVAL;
                goto done;
        }
        for (i = 0; i < shminfo.shmseg; i++, shmmap_s++) {
                if (shmmap_s->shmid != -1 &&
                    shmmap_s->va == (vm_offset_t)uap->shmaddr)
                        break;
        }
        if (i == shminfo.shmseg)
                error = EINVAL;
        else
                error = shm_delete_mapping(p->p_vmspace, shmmap_s);
done:
        lwkt_reltoken(&shm_token);

        return (error);
}

/*
 * MPALMOSTSAFE
 */
int
sys_shmat(struct shmat_args *uap)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        int error, flags;
        long i;
        struct shmid_ds *shmseg;
        struct shmmap_state *shmmap_s = NULL;
        struct shm_handle *shm_handle;
        vm_offset_t attach_va;
        vm_prot_t prot;
        vm_size_t size;
        vm_size_t align;
        int rv;

        if (!jail_sysvipc_allowed && td->td_ucred->cr_prison != NULL)
                return (ENOSYS);

        lwkt_gettoken(&shm_token);
again:
        shmmap_s = (struct shmmap_state *)p->p_vmspace->vm_shm;
        if (shmmap_s == NULL) {
                size = shminfo.shmseg * sizeof(struct shmmap_state);
                shmmap_s = kmalloc(size, M_SHM, M_WAITOK);
                for (i = 0; i < shminfo.shmseg; i++)
                        shmmap_s[i].shmid = -1;
                if (p->p_vmspace->vm_shm != NULL) {
                        kfree(shmmap_s, M_SHM);
                        goto again;
                }
                p->p_vmspace->vm_shm = (caddr_t)shmmap_s;
        }
        shmseg = shm_find_segment_by_shmid(uap->shmid);
        if (shmseg == NULL) {
                error = EINVAL;
                goto done;
        }
        error = ipcperm(p, &shmseg->shm_perm,
                        (uap->shmflg & SHM_RDONLY) ? IPC_R : IPC_R|IPC_W);
        if (error)
                goto done;
        for (i = 0; i < shminfo.shmseg; i++) {
                if (shmmap_s->shmid == -1)
                        break;
                shmmap_s++;
        }
        if (i >= shminfo.shmseg) {
                error = EMFILE;
                goto done;
        }
        size = round_page(shmseg->shm_segsz);
#ifdef VM_PROT_READ_IS_EXEC
        prot = VM_PROT_READ | VM_PROT_EXECUTE;
#else
        prot = VM_PROT_READ;
#endif
        if ((uap->shmflg & SHM_RDONLY) == 0)
                prot |= VM_PROT_WRITE;
        flags = MAP_ANON | MAP_SHARED;
        if (uap->shmaddr) {
                flags |= MAP_FIXED;
                if (uap->shmflg & SHM_RND) {
                        attach_va = (vm_offset_t)uap->shmaddr & ~(SHMLBA-1);
                } else if (((vm_offset_t)uap->shmaddr & (SHMLBA-1)) == 0) {
                        attach_va = (vm_offset_t)uap->shmaddr;
                } else {
                        error = EINVAL;
                        goto done;
                }
        } else {
                /*
                 * This is just a hint to vm_map_find() about where to put it.
                 */
                attach_va = round_page((vm_offset_t)p->p_vmspace->vm_taddr +
                                       maxtsiz + maxdsiz);
        }

        /*
         * Handle alignment.  For large memory maps it is possible
         * that the MMU can optimize the page table so align anything
         * that is a multiple of SEG_SIZE to SEG_SIZE.
         */
        if ((flags & MAP_FIXED) == 0 && (size & SEG_MASK) == 0)
                align = SEG_SIZE;
        else
                align = PAGE_SIZE;

        shm_handle = shmseg->shm_internal;
        vm_object_hold(shm_handle->shm_object);
        vm_object_chain_wait(shm_handle->shm_object, 0);
        vm_object_reference_locked(shm_handle->shm_object);
        rv = vm_map_find(&p->p_vmspace->vm_map, 
                         shm_handle->shm_object, NULL,
                         0, &attach_va, size,
                         align,
                         ((flags & MAP_FIXED) ? 0 : 1), 
                         VM_MAPTYPE_NORMAL, VM_SUBSYS_SHMEM,
                         prot, prot, 0);
        vm_object_drop(shm_handle->shm_object);
        if (rv != KERN_SUCCESS) {
                vm_object_deallocate(shm_handle->shm_object);
                error = ENOMEM;
                goto done;
        }
        vm_map_inherit(&p->p_vmspace->vm_map,
                       attach_va, attach_va + size, VM_INHERIT_SHARE);

        KKASSERT(shmmap_s->shmid == -1);
        shmmap_s->va = attach_va;
        shmmap_s->shmid = uap->shmid;
        shmseg->shm_lpid = p->p_pid;
        shmseg->shm_atime = time_second;
        shmseg->shm_nattch++;
        uap->sysmsg_resultp = (void *)attach_va;
        error = 0;
done:
        lwkt_reltoken(&shm_token);

        return error;
}

/*
 * MPALMOSTSAFE
 */
int
sys_shmctl(struct shmctl_args *uap)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        int error;
        struct shmid_ds inbuf;
        struct shmid_ds *shmseg;

        if (!jail_sysvipc_allowed && td->td_ucred->cr_prison != NULL)
                return (ENOSYS);

        lwkt_gettoken(&shm_token);
        shmseg = shm_find_segment_by_shmid(uap->shmid);
        if (shmseg == NULL) {
                error = EINVAL;
                goto done;
        }

        switch (uap->cmd) {
        case IPC_STAT:
                error = ipcperm(p, &shmseg->shm_perm, IPC_R);
                if (error == 0)
                        error = copyout(shmseg, uap->buf, sizeof(inbuf));
                break;
        case IPC_SET:
                error = ipcperm(p, &shmseg->shm_perm, IPC_M);
                if (error == 0)
                        error = copyin(uap->buf, &inbuf, sizeof(inbuf));
                if (error == 0) {
                        shmseg->shm_perm.uid = inbuf.shm_perm.uid;
                        shmseg->shm_perm.gid = inbuf.shm_perm.gid;
                        shmseg->shm_perm.mode =
                            (shmseg->shm_perm.mode & ~ACCESSPERMS) |
                            (inbuf.shm_perm.mode & ACCESSPERMS);
                        shmseg->shm_ctime = time_second;
                }
                break;
        case IPC_RMID:
                error = ipcperm(p, &shmseg->shm_perm, IPC_M);
                if (error == 0) {
                        shmseg->shm_perm.key = IPC_PRIVATE;
                        shmseg->shm_perm.mode |= SHMSEG_REMOVED;
                        if (shmseg->shm_nattch <= 0) {
                                shm_deallocate_segment(shmseg);
                                shm_last_free = IPCID_TO_IX(uap->shmid);
                        }
                }
                break;
#if 0
        case SHM_LOCK:
        case SHM_UNLOCK:
#endif
        default:
                error = EINVAL;
                break;
        }
done:
        lwkt_reltoken(&shm_token);

        return error;
}

static int
shmget_existing(struct proc *p, struct shmget_args *uap, int mode, int segnum)
{
        struct shmid_ds *shmseg;
        int error;

        shmseg = &shmsegs[segnum];
        if (shmseg->shm_perm.mode & SHMSEG_REMOVED) {
                /*
                 * This segment is in the process of being allocated.  Wait
                 * until it's done, and look the key up again (in case the
                 * allocation failed or it was freed).
                 */
                shmseg->shm_perm.mode |= SHMSEG_WANTED;
                error = tsleep((caddr_t)shmseg, PCATCH, "shmget", 0);
                if (error)
                        return error;
                return EAGAIN;
        }
        if ((uap->shmflg & (IPC_CREAT | IPC_EXCL)) == (IPC_CREAT | IPC_EXCL))
                return EEXIST;
        error = ipcperm(p, &shmseg->shm_perm, mode);
        if (error)
                return error;
        if (uap->size && uap->size > shmseg->shm_segsz)
                return EINVAL;
        uap->sysmsg_result = IXSEQ_TO_IPCID(segnum, shmseg->shm_perm);
        return 0;
}

static int
shmget_allocate_segment(struct proc *p, struct shmget_args *uap, int mode)
{
        int i, segnum, shmid;
        size_t size;
        struct ucred *cred = p->p_ucred;
        struct shmid_ds *shmseg;
        struct shm_handle *shm_handle;

        if (uap->size < shminfo.shmmin || uap->size > shminfo.shmmax)
                return EINVAL;
        if (shm_nused >= shminfo.shmmni) /* any shmids left? */
                return ENOSPC;
        size = round_page(uap->size);
        if (shm_committed + btoc(size) > shminfo.shmall)
                return ENOMEM;
        if (shm_last_free < 0) {
                shmrealloc();   /* maybe expand the shmsegs[] array */
                for (i = 0; i < shmalloced; i++) {
                        if (shmsegs[i].shm_perm.mode & SHMSEG_FREE)
                                break;
                }
                if (i == shmalloced)
                        return ENOSPC;
                segnum = i;
        } else  {
                segnum = shm_last_free;
                shm_last_free = -1;
        }
        shmseg = &shmsegs[segnum];
        /*
         * In case we sleep in malloc(), mark the segment present but deleted
         * so that noone else tries to create the same key.
         */
        shmseg->shm_perm.mode = SHMSEG_ALLOCATED | SHMSEG_REMOVED;
        shmseg->shm_perm.key = uap->key;
        shmseg->shm_perm.seq = (shmseg->shm_perm.seq + 1) & 0x7fff;
        shm_handle = kmalloc(sizeof(struct shm_handle), M_SHM, M_WAITOK);
        shmid = IXSEQ_TO_IPCID(segnum, shmseg->shm_perm);
        
        /*
         * We make sure that we have allocated a pager before we need
         * to.
         */
        if (shm_use_phys) {
                shm_handle->shm_object =
                   phys_pager_alloc(NULL, size, VM_PROT_DEFAULT, 0);
        } else {
                shm_handle->shm_object =
                   swap_pager_alloc(NULL, size, VM_PROT_DEFAULT, 0);
        }
        vm_object_clear_flag(shm_handle->shm_object, OBJ_ONEMAPPING);
        vm_object_set_flag(shm_handle->shm_object, OBJ_NOSPLIT);

        shmseg->shm_internal = shm_handle;
        shmseg->shm_perm.cuid = shmseg->shm_perm.uid = cred->cr_uid;
        shmseg->shm_perm.cgid = shmseg->shm_perm.gid = cred->cr_gid;
        shmseg->shm_perm.mode = (shmseg->shm_perm.mode & SHMSEG_WANTED) |
            (mode & ACCESSPERMS) | SHMSEG_ALLOCATED;
        shmseg->shm_segsz = uap->size;
        shmseg->shm_cpid = p->p_pid;
        shmseg->shm_lpid = shmseg->shm_nattch = 0;
        shmseg->shm_atime = shmseg->shm_dtime = 0;
        shmseg->shm_ctime = time_second;
        shm_committed += btoc(size);
        shm_nused++;

        /*
         * If a physical mapping is desired and we have a ton of free pages
         * we pre-allocate the pages here in order to avoid on-the-fly
         * allocation later.  This has a big effect on database warm-up
         * times since DFly supports concurrent page faults coming from the
         * same VM object for pages which already exist.
         *
         * This can hang the kernel for a while so only do it if shm_use_phys
         * is set to 2 or higher.
         */
        if (shm_use_phys > 1) {
                vm_pindex_t pi, pmax;
                vm_page_t m;

                pmax = round_page(shmseg->shm_segsz) >> PAGE_SHIFT;
                vm_object_hold(shm_handle->shm_object);
                if (pmax > vmstats.v_free_count)
                        pmax = vmstats.v_free_count;
                for (pi = 0; pi < pmax; ++pi) {
                        m = vm_page_grab(shm_handle->shm_object, pi,
                                         VM_ALLOC_SYSTEM | VM_ALLOC_NULL_OK |
                                         VM_ALLOC_ZERO);
                        if (m == NULL)
                                break;
                        vm_pager_get_page(shm_handle->shm_object, &m, 1);
                        vm_page_activate(m);
                        vm_page_wakeup(m);
                        lwkt_yield();
                }
                vm_object_drop(shm_handle->shm_object);
        }

        if (shmseg->shm_perm.mode & SHMSEG_WANTED) {
                /*
                 * Somebody else wanted this key while we were asleep.  Wake
                 * them up now.
                 */
                shmseg->shm_perm.mode &= ~SHMSEG_WANTED;
                wakeup((caddr_t)shmseg);
        }
        uap->sysmsg_result = shmid;
        return 0;
}

/*
 * MPALMOSTSAFE
 */
int
sys_shmget(struct shmget_args *uap)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        int segnum, mode, error;

        if (!jail_sysvipc_allowed && td->td_ucred->cr_prison != NULL)
                return (ENOSYS);

        mode = uap->shmflg & ACCESSPERMS;

        lwkt_gettoken(&shm_token);

        if (uap->key != IPC_PRIVATE) {
        again:
                segnum = shm_find_segment_by_key(uap->key);
                if (segnum >= 0) {
                        error = shmget_existing(p, uap, mode, segnum);
                        if (error == EAGAIN)
                                goto again;
                        goto done;
                }
                if ((uap->shmflg & IPC_CREAT) == 0) {
                        error = ENOENT;
                        goto done;
                }
        }
        error = shmget_allocate_segment(p, uap, mode);
done:
        lwkt_reltoken(&shm_token);

        return (error);
}

void
shmfork(struct proc *p1, struct proc *p2)
{
        struct shmmap_state *shmmap_s;
        size_t size;
        int i;

        lwkt_gettoken(&shm_token);
        size = shminfo.shmseg * sizeof(struct shmmap_state);
        shmmap_s = kmalloc(size, M_SHM, M_WAITOK);
        bcopy((caddr_t)p1->p_vmspace->vm_shm, (caddr_t)shmmap_s, size);
        p2->p_vmspace->vm_shm = (caddr_t)shmmap_s;
        for (i = 0; i < shminfo.shmseg; i++, shmmap_s++) {
                if (shmmap_s->shmid != -1)
                        shmsegs[IPCID_TO_IX(shmmap_s->shmid)].shm_nattch++;
        }
        lwkt_reltoken(&shm_token);
}

void
shmexit(struct vmspace *vm)
{
        struct shmmap_state *base, *shm;
        int i;

        if ((base = (struct shmmap_state *)vm->vm_shm) != NULL) {
                vm->vm_shm = NULL;
                lwkt_gettoken(&shm_token);
                for (i = 0, shm = base; i < shminfo.shmseg; i++, shm++) {
                        if (shm->shmid != -1)
                                shm_delete_mapping(vm, shm);
                }
                kfree(base, M_SHM);
                lwkt_reltoken(&shm_token);
        }
}

static void
shmrealloc(void)
{
        int i;
        struct shmid_ds *newsegs;

        if (shmalloced >= shminfo.shmmni)
                return;

        newsegs = kmalloc(shminfo.shmmni * sizeof(*newsegs), M_SHM, M_WAITOK);
        for (i = 0; i < shmalloced; i++)
                bcopy(&shmsegs[i], &newsegs[i], sizeof(newsegs[0]));
        for (; i < shminfo.shmmni; i++) {
                shmsegs[i].shm_perm.mode = SHMSEG_FREE;
                shmsegs[i].shm_perm.seq = 0;
        }
        kfree(shmsegs, M_SHM);
        shmsegs = newsegs;
        shmalloced = shminfo.shmmni;
}

static void
shminit(void *dummy)
{
        int i;

        /*
         * If not overridden by a tunable set the maximum shm to
         * 2/3 of main memory.
         */
        if (shminfo.shmall == 0)
                shminfo.shmall = (size_t)vmstats.v_page_count * 2 / 3;

        shminfo.shmmax = shminfo.shmall * PAGE_SIZE;
        shmalloced = shminfo.shmmni;
        shmsegs = kmalloc(shmalloced * sizeof(shmsegs[0]), M_SHM, M_WAITOK);
        for (i = 0; i < shmalloced; i++) {
                shmsegs[i].shm_perm.mode = SHMSEG_FREE;
                shmsegs[i].shm_perm.seq = 0;
        }
        shm_last_free = 0;
        shm_nused = 0;
        shm_committed = 0;
}
SYSINIT(sysv_shm, SI_SUB_SYSV_SHM, SI_ORDER_FIRST, shminit, NULL);