kern_sysctl.c

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/*-
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Mike Karels at Berkeley Software Design, Inc.
 *
 * Quite extensively rewritten by Poul-Henning Kamp of the FreeBSD
 * project, to make these variables more userfriendly.
 *
 * 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.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)kern_sysctl.c       8.4 (Berkeley) 4/14/94
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include "opt_capsicum.h"
#include "opt_compat.h"
#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/fail.h>
#include <sys/systm.h>
#include <sys/capability.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/jail.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sbuf.h>
#include <sys/sx.h>
#include <sys/sysproto.h>
#include <sys/uio.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif

#include <net/vnet.h>

#include <security/mac/mac_framework.h>

#include <vm/vm.h>
#include <vm/vm_extern.h>

static MALLOC_DEFINE(M_SYSCTL, "sysctl", "sysctl internal magic");
static MALLOC_DEFINE(M_SYSCTLOID, "sysctloid", "sysctl dynamic oids");
static MALLOC_DEFINE(M_SYSCTLTMP, "sysctltmp", "sysctl temp output buffer");

/*
 * The sysctllock protects the MIB tree.  It also protects sysctl
 * contexts used with dynamic sysctls.  The sysctl_register_oid() and
 * sysctl_unregister_oid() routines require the sysctllock to already
 * be held, so the sysctl_lock() and sysctl_unlock() routines are
 * provided for the few places in the kernel which need to use that
 * API rather than using the dynamic API.  Use of the dynamic API is
 * strongly encouraged for most code.
 *
 * The sysctlmemlock is used to limit the amount of user memory wired for
 * sysctl requests.  This is implemented by serializing any userland
 * sysctl requests larger than a single page via an exclusive lock.
 */
static struct sx sysctllock;
static struct sx sysctlmemlock;

#define SYSCTL_XLOCK()          sx_xlock(&sysctllock)
#define SYSCTL_XUNLOCK()        sx_xunlock(&sysctllock)
#define SYSCTL_ASSERT_XLOCKED() sx_assert(&sysctllock, SA_XLOCKED)
#define SYSCTL_INIT()           sx_init(&sysctllock, "sysctl lock")
#define SYSCTL_SLEEP(ch, wmesg, timo)                                   \
                                sx_sleep(ch, &sysctllock, 0, wmesg, timo)

static int sysctl_root(SYSCTL_HANDLER_ARGS);

struct sysctl_oid_list sysctl__children; /* root list */

static int      sysctl_remove_oid_locked(struct sysctl_oid *oidp, int del,
                    int recurse);

static struct sysctl_oid *
sysctl_find_oidname(const char *name, struct sysctl_oid_list *list)
{
        struct sysctl_oid *oidp;

        SYSCTL_ASSERT_XLOCKED();
        SLIST_FOREACH(oidp, list, oid_link) {
                if (strcmp(oidp->oid_name, name) == 0) {
                        return (oidp);
                }
        }
        return (NULL);
}

/*
 * Initialization of the MIB tree.
 *
 * Order by number in each list.
 */
void
sysctl_lock(void)
{

        SYSCTL_XLOCK();
}

void
sysctl_unlock(void)
{

        SYSCTL_XUNLOCK();
}

void
sysctl_register_oid(struct sysctl_oid *oidp)
{
        struct sysctl_oid_list *parent = oidp->oid_parent;
        struct sysctl_oid *p;
        struct sysctl_oid *q;
        int oid_number;
        int timeout = 2;

        /*
         * First check if another oid with the same name already
         * exists in the parent's list.
         */
        SYSCTL_ASSERT_XLOCKED();
        p = sysctl_find_oidname(oidp->oid_name, parent);
        if (p != NULL) {
                if ((p->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
                        p->oid_refcnt++;
                        return;
                } else {
                        printf("can't re-use a leaf (%s)!\n", p->oid_name);
                        return;
                }
        }
        /* get current OID number */
        oid_number = oidp->oid_number;

#if (OID_AUTO >= 0)
#error "OID_AUTO is expected to be a negative value"
#endif  
        /*
         * Any negative OID number qualifies as OID_AUTO. Valid OID
         * numbers should always be positive.
         *
         * NOTE: DO NOT change the starting value here, change it in
         * <sys/sysctl.h>, and make sure it is at least 256 to
         * accomodate e.g. net.inet.raw as a static sysctl node.
         */
        if (oid_number < 0) {
                static int newoid;

                /*
                 * By decrementing the next OID number we spend less
                 * time inserting the OIDs into a sorted list.
                 */
                if (--newoid < CTL_AUTO_START)
                        newoid = 0x7fffffff;

                oid_number = newoid;
        }

        /*
         * Insert the OID into the parent's list sorted by OID number.
         */
retry:
        q = NULL;
        SLIST_FOREACH(p, parent, oid_link) {
                /* check if the current OID number is in use */
                if (oid_number == p->oid_number) {
                        /* get the next valid OID number */
                        if (oid_number < CTL_AUTO_START ||
                            oid_number == 0x7fffffff) {
                                /* wraparound - restart */
                                oid_number = CTL_AUTO_START;
                                /* don't loop forever */
                                if (!timeout--)
                                        panic("sysctl: Out of OID numbers\n");
                                goto retry;
                        } else {
                                oid_number++;
                        }
                } else if (oid_number < p->oid_number)
                        break;
                q = p;
        }
        /* check for non-auto OID number collision */
        if (oidp->oid_number >= 0 && oidp->oid_number < CTL_AUTO_START &&
            oid_number >= CTL_AUTO_START) {
                printf("sysctl: OID number(%d) is already in use for '%s'\n",
                    oidp->oid_number, oidp->oid_name);
        }
        /* update the OID number, if any */
        oidp->oid_number = oid_number;
        if (q != NULL)
                SLIST_INSERT_AFTER(q, oidp, oid_link);
        else
                SLIST_INSERT_HEAD(parent, oidp, oid_link);
}

void
sysctl_unregister_oid(struct sysctl_oid *oidp)
{
        struct sysctl_oid *p;
        int error;

        SYSCTL_ASSERT_XLOCKED();
        error = ENOENT;
        if (oidp->oid_number == OID_AUTO) {
                error = EINVAL;
        } else {
                SLIST_FOREACH(p, oidp->oid_parent, oid_link) {
                        if (p == oidp) {
                                SLIST_REMOVE(oidp->oid_parent, oidp,
                                    sysctl_oid, oid_link);
                                error = 0;
                                break;
                        }
                }
        }

        /* 
         * This can happen when a module fails to register and is
         * being unloaded afterwards.  It should not be a panic()
         * for normal use.
         */
        if (error)
                printf("%s: failed to unregister sysctl\n", __func__);
}

/* Initialize a new context to keep track of dynamically added sysctls. */
int
sysctl_ctx_init(struct sysctl_ctx_list *c)
{

        if (c == NULL) {
                return (EINVAL);
        }

        /*
         * No locking here, the caller is responsible for not adding
         * new nodes to a context until after this function has
         * returned.
         */
        TAILQ_INIT(c);
        return (0);
}

/* Free the context, and destroy all dynamic oids registered in this context */
int
sysctl_ctx_free(struct sysctl_ctx_list *clist)
{
        struct sysctl_ctx_entry *e, *e1;
        int error;

        error = 0;
        /*
         * First perform a "dry run" to check if it's ok to remove oids.
         * XXX FIXME
         * XXX This algorithm is a hack. But I don't know any
         * XXX better solution for now...
         */
        SYSCTL_XLOCK();
        TAILQ_FOREACH(e, clist, link) {
                error = sysctl_remove_oid_locked(e->entry, 0, 0);
                if (error)
                        break;
        }
        /*
         * Restore deregistered entries, either from the end,
         * or from the place where error occured.
         * e contains the entry that was not unregistered
         */
        if (error)
                e1 = TAILQ_PREV(e, sysctl_ctx_list, link);
        else
                e1 = TAILQ_LAST(clist, sysctl_ctx_list);
        while (e1 != NULL) {
                sysctl_register_oid(e1->entry);
                e1 = TAILQ_PREV(e1, sysctl_ctx_list, link);
        }
        if (error) {
                SYSCTL_XUNLOCK();
                return(EBUSY);
        }
        /* Now really delete the entries */
        e = TAILQ_FIRST(clist);
        while (e != NULL) {
                e1 = TAILQ_NEXT(e, link);
                error = sysctl_remove_oid_locked(e->entry, 1, 0);
                if (error)
                        panic("sysctl_remove_oid: corrupt tree, entry: %s",
                            e->entry->oid_name);
                free(e, M_SYSCTLOID);
                e = e1;
        }
        SYSCTL_XUNLOCK();
        return (error);
}

/* Add an entry to the context */
struct sysctl_ctx_entry *
sysctl_ctx_entry_add(struct sysctl_ctx_list *clist, struct sysctl_oid *oidp)
{
        struct sysctl_ctx_entry *e;

        SYSCTL_ASSERT_XLOCKED();
        if (clist == NULL || oidp == NULL)
                return(NULL);
        e = malloc(sizeof(struct sysctl_ctx_entry), M_SYSCTLOID, M_WAITOK);
        e->entry = oidp;
        TAILQ_INSERT_HEAD(clist, e, link);
        return (e);
}

/* Find an entry in the context */
struct sysctl_ctx_entry *
sysctl_ctx_entry_find(struct sysctl_ctx_list *clist, struct sysctl_oid *oidp)
{
        struct sysctl_ctx_entry *e;

        SYSCTL_ASSERT_XLOCKED();
        if (clist == NULL || oidp == NULL)
                return(NULL);
        TAILQ_FOREACH(e, clist, link) {
                if(e->entry == oidp)
                        return(e);
        }
        return (e);
}

/*
 * Delete an entry from the context.
 * NOTE: this function doesn't free oidp! You have to remove it
 * with sysctl_remove_oid().
 */
int
sysctl_ctx_entry_del(struct sysctl_ctx_list *clist, struct sysctl_oid *oidp)
{
        struct sysctl_ctx_entry *e;

        if (clist == NULL || oidp == NULL)
                return (EINVAL);
        SYSCTL_XLOCK();
        e = sysctl_ctx_entry_find(clist, oidp);
        if (e != NULL) {
                TAILQ_REMOVE(clist, e, link);
                SYSCTL_XUNLOCK();
                free(e, M_SYSCTLOID);
                return (0);
        } else {
                SYSCTL_XUNLOCK();
                return (ENOENT);
        }
}

/*
 * Remove dynamically created sysctl trees.
 * oidp - top of the tree to be removed
 * del - if 0 - just deregister, otherwise free up entries as well
 * recurse - if != 0 traverse the subtree to be deleted
 */
int
sysctl_remove_oid(struct sysctl_oid *oidp, int del, int recurse)
{
        int error;

        SYSCTL_XLOCK();
        error = sysctl_remove_oid_locked(oidp, del, recurse);
        SYSCTL_XUNLOCK();
        return (error);
}

int
sysctl_remove_name(struct sysctl_oid *parent, const char *name,
    int del, int recurse)
{
        struct sysctl_oid *p, *tmp;
        int error;

        error = ENOENT;
        SYSCTL_XLOCK();
        SLIST_FOREACH_SAFE(p, SYSCTL_CHILDREN(parent), oid_link, tmp) {
                if (strcmp(p->oid_name, name) == 0) {
                        error = sysctl_remove_oid_locked(p, del, recurse);
                        break;
                }
        }
        SYSCTL_XUNLOCK();

        return (error);
}


static int
sysctl_remove_oid_locked(struct sysctl_oid *oidp, int del, int recurse)
{
        struct sysctl_oid *p, *tmp;
        int error;

        SYSCTL_ASSERT_XLOCKED();
        if (oidp == NULL)
                return(EINVAL);
        if ((oidp->oid_kind & CTLFLAG_DYN) == 0) {
                printf("can't remove non-dynamic nodes!\n");
                return (EINVAL);
        }
        /*
         * WARNING: normal method to do this should be through
         * sysctl_ctx_free(). Use recursing as the last resort
         * method to purge your sysctl tree of leftovers...
         * However, if some other code still references these nodes,
         * it will panic.
         */
        if ((oidp->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
                if (oidp->oid_refcnt == 1) {
                        SLIST_FOREACH_SAFE(p,
                            SYSCTL_CHILDREN(oidp), oid_link, tmp) {
                                if (!recurse)
                                        return (ENOTEMPTY);
                                error = sysctl_remove_oid_locked(p, del,
                                    recurse);
                                if (error)
                                        return (error);
                        }
                        if (del)
                                free(SYSCTL_CHILDREN(oidp), M_SYSCTLOID);
                }
        }
        if (oidp->oid_refcnt > 1 ) {
                oidp->oid_refcnt--;
        } else {
                if (oidp->oid_refcnt == 0) {
                        printf("Warning: bad oid_refcnt=%u (%s)!\n",
                                oidp->oid_refcnt, oidp->oid_name);
                        return (EINVAL);
                }
                sysctl_unregister_oid(oidp);
                if (del) {
                        /*
                         * Wait for all threads running the handler to drain.
                         * This preserves the previous behavior when the
                         * sysctl lock was held across a handler invocation,
                         * and is necessary for module unload correctness.
                         */
                        while (oidp->oid_running > 0) {
                                oidp->oid_kind |= CTLFLAG_DYING;
                                SYSCTL_SLEEP(&oidp->oid_running, "oidrm", 0);
                        }
                        if (oidp->oid_descr)
                                free(__DECONST(char *, oidp->oid_descr),
                                    M_SYSCTLOID);
                        free(__DECONST(char *, oidp->oid_name), M_SYSCTLOID);
                        free(oidp, M_SYSCTLOID);
                }
        }
        return (0);
}
/*
 * Create new sysctls at run time.
 * clist may point to a valid context initialized with sysctl_ctx_init().
 */
struct sysctl_oid *
sysctl_add_oid(struct sysctl_ctx_list *clist, struct sysctl_oid_list *parent,
        int number, const char *name, int kind, void *arg1, intptr_t arg2,
        int (*handler)(SYSCTL_HANDLER_ARGS), const char *fmt, const char *descr)
{
        struct sysctl_oid *oidp;

        /* You have to hook up somewhere.. */
        if (parent == NULL)
                return(NULL);
        /* Check if the node already exists, otherwise create it */
        SYSCTL_XLOCK();
        oidp = sysctl_find_oidname(name, parent);
        if (oidp != NULL) {
                if ((oidp->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
                        oidp->oid_refcnt++;
                        /* Update the context */
                        if (clist != NULL)
                                sysctl_ctx_entry_add(clist, oidp);
                        SYSCTL_XUNLOCK();
                        return (oidp);
                } else {
                        SYSCTL_XUNLOCK();
                        printf("can't re-use a leaf (%s)!\n", name);
                        return (NULL);
                }
        }
        oidp = malloc(sizeof(struct sysctl_oid), M_SYSCTLOID, M_WAITOK|M_ZERO);
        oidp->oid_parent = parent;
        SLIST_NEXT(oidp, oid_link) = NULL;
        oidp->oid_number = number;
        oidp->oid_refcnt = 1;
        oidp->oid_name = strdup(name, M_SYSCTLOID);
        oidp->oid_handler = handler;
        oidp->oid_kind = CTLFLAG_DYN | kind;
        if ((kind & CTLTYPE) == CTLTYPE_NODE) {
                /* Allocate space for children */
                SYSCTL_CHILDREN_SET(oidp, malloc(sizeof(struct sysctl_oid_list),
                    M_SYSCTLOID, M_WAITOK));
                SLIST_INIT(SYSCTL_CHILDREN(oidp));
                oidp->oid_arg2 = arg2;
        } else {
                oidp->oid_arg1 = arg1;
                oidp->oid_arg2 = arg2;
        }
        oidp->oid_fmt = fmt;
        if (descr)
                oidp->oid_descr = strdup(descr, M_SYSCTLOID);
        /* Update the context, if used */
        if (clist != NULL)
                sysctl_ctx_entry_add(clist, oidp);
        /* Register this oid */
        sysctl_register_oid(oidp);
        SYSCTL_XUNLOCK();
        return (oidp);
}

/*
 * Rename an existing oid.
 */
void
sysctl_rename_oid(struct sysctl_oid *oidp, const char *name)
{
        char *newname;
        char *oldname;

        newname = strdup(name, M_SYSCTLOID);
        SYSCTL_XLOCK();
        oldname = __DECONST(char *, oidp->oid_name);
        oidp->oid_name = newname;
        SYSCTL_XUNLOCK();
        free(oldname, M_SYSCTLOID);
}

/*
 * Reparent an existing oid.
 */
int
sysctl_move_oid(struct sysctl_oid *oid, struct sysctl_oid_list *parent)
{
        struct sysctl_oid *oidp;

        SYSCTL_XLOCK();
        if (oid->oid_parent == parent) {
                SYSCTL_XUNLOCK();
                return (0);
        }
        oidp = sysctl_find_oidname(oid->oid_name, parent);
        if (oidp != NULL) {
                SYSCTL_XUNLOCK();
                return (EEXIST);
        }
        sysctl_unregister_oid(oid);
        oid->oid_parent = parent;
        oid->oid_number = OID_AUTO;
        sysctl_register_oid(oid);
        SYSCTL_XUNLOCK();
        return (0);
}

/*
 * Register the kernel's oids on startup.
 */
SET_DECLARE(sysctl_set, struct sysctl_oid);

static void
sysctl_register_all(void *arg)
{
        struct sysctl_oid **oidp;

        sx_init(&sysctlmemlock, "sysctl mem");
        SYSCTL_INIT();
        SYSCTL_XLOCK();
        SET_FOREACH(oidp, sysctl_set)
                sysctl_register_oid(*oidp);
        SYSCTL_XUNLOCK();
}
SYSINIT(sysctl, SI_SUB_KMEM, SI_ORDER_ANY, sysctl_register_all, 0);

/*
 * "Staff-functions"
 *
 * These functions implement a presently undocumented interface 
 * used by the sysctl program to walk the tree, and get the type
 * so it can print the value.
 * This interface is under work and consideration, and should probably
 * be killed with a big axe by the first person who can find the time.
 * (be aware though, that the proper interface isn't as obvious as it
 * may seem, there are various conflicting requirements.
 *
 * {0,0}        printf the entire MIB-tree.
 * {0,1,...}    return the name of the "..." OID.
 * {0,2,...}    return the next OID.
 * {0,3}        return the OID of the name in "new"
 * {0,4,...}    return the kind & format info for the "..." OID.
 * {0,5,...}    return the description the "..." OID.
 */

#ifdef SYSCTL_DEBUG
static void
sysctl_sysctl_debug_dump_node(struct sysctl_oid_list *l, int i)
{
        int k;
        struct sysctl_oid *oidp;

        SYSCTL_ASSERT_XLOCKED();
        SLIST_FOREACH(oidp, l, oid_link) {

                for (k=0; k<i; k++)
                        printf(" ");

                printf("%d %s ", oidp->oid_number, oidp->oid_name);

                printf("%c%c",
                        oidp->oid_kind & CTLFLAG_RD ? 'R':' ',
                        oidp->oid_kind & CTLFLAG_WR ? 'W':' ');

                if (oidp->oid_handler)
                        printf(" *Handler");

                switch (oidp->oid_kind & CTLTYPE) {
                        case CTLTYPE_NODE:
                                printf(" Node\n");
                                if (!oidp->oid_handler) {
                                        sysctl_sysctl_debug_dump_node(
                                                oidp->oid_arg1, i+2);
                                }
                                break;
                        case CTLTYPE_INT:    printf(" Int\n"); break;
                        case CTLTYPE_UINT:   printf(" u_int\n"); break;
                        case CTLTYPE_LONG:   printf(" Long\n"); break;
                        case CTLTYPE_ULONG:  printf(" u_long\n"); break;
                        case CTLTYPE_STRING: printf(" String\n"); break;
                        case CTLTYPE_U64:    printf(" uint64_t\n"); break;
                        case CTLTYPE_S64:    printf(" int64_t\n"); break;
                        case CTLTYPE_OPAQUE: printf(" Opaque/struct\n"); break;
                        default:             printf("\n");
                }

        }
}

static int
sysctl_sysctl_debug(SYSCTL_HANDLER_ARGS)
{
        int error;

        error = priv_check(req->td, PRIV_SYSCTL_DEBUG);
        if (error)
                return (error);
        SYSCTL_XLOCK();
        sysctl_sysctl_debug_dump_node(&sysctl__children, 0);
        SYSCTL_XUNLOCK();
        return (ENOENT);
}

SYSCTL_PROC(_sysctl, 0, debug, CTLTYPE_STRING|CTLFLAG_RD,
        0, 0, sysctl_sysctl_debug, "-", "");
#endif

static int
sysctl_sysctl_name(SYSCTL_HANDLER_ARGS)
{
        int *name = (int *) arg1;
        u_int namelen = arg2;
        int error = 0;
        struct sysctl_oid *oid;
        struct sysctl_oid_list *lsp = &sysctl__children, *lsp2;
        char buf[10];

        SYSCTL_XLOCK();
        while (namelen) {
                if (!lsp) {
                        snprintf(buf,sizeof(buf),"%d",*name);
                        if (req->oldidx)
                                error = SYSCTL_OUT(req, ".", 1);
                        if (!error)
                                error = SYSCTL_OUT(req, buf, strlen(buf));
                        if (error)
                                goto out;
                        namelen--;
                        name++;
                        continue;
                }
                lsp2 = 0;
                SLIST_FOREACH(oid, lsp, oid_link) {
                        if (oid->oid_number != *name)
                                continue;

                        if (req->oldidx)
                                error = SYSCTL_OUT(req, ".", 1);
                        if (!error)
                                error = SYSCTL_OUT(req, oid->oid_name,
                                        strlen(oid->oid_name));
                        if (error)
                                goto out;

                        namelen--;
                        name++;

                        if ((oid->oid_kind & CTLTYPE) != CTLTYPE_NODE) 
                                break;

                        if (oid->oid_handler)
                                break;

                        lsp2 = SYSCTL_CHILDREN(oid);
                        break;
                }
                lsp = lsp2;
        }
        error = SYSCTL_OUT(req, "", 1);
 out:
        SYSCTL_XUNLOCK();
        return (error);
}

/*
 * XXXRW/JA: Shouldn't return name data for nodes that we don't permit in
 * capability mode.
 */
static SYSCTL_NODE(_sysctl, 1, name, CTLFLAG_RD | CTLFLAG_CAPRD,
    sysctl_sysctl_name, "");

static int
sysctl_sysctl_next_ls(struct sysctl_oid_list *lsp, int *name, u_int namelen, 
        int *next, int *len, int level, struct sysctl_oid **oidpp)
{
        struct sysctl_oid *oidp;

        SYSCTL_ASSERT_XLOCKED();
        *len = level;
        SLIST_FOREACH(oidp, lsp, oid_link) {
                *next = oidp->oid_number;
                *oidpp = oidp;

                if (oidp->oid_kind & CTLFLAG_SKIP)
                        continue;

                if (!namelen) {
                        if ((oidp->oid_kind & CTLTYPE) != CTLTYPE_NODE) 
                                return (0);
                        if (oidp->oid_handler) 
                                /* We really should call the handler here...*/
                                return (0);
                        lsp = SYSCTL_CHILDREN(oidp);
                        if (!sysctl_sysctl_next_ls(lsp, 0, 0, next+1, 
                                len, level+1, oidpp))
                                return (0);
                        goto emptynode;
                }

                if (oidp->oid_number < *name)
                        continue;

                if (oidp->oid_number > *name) {
                        if ((oidp->oid_kind & CTLTYPE) != CTLTYPE_NODE)
                                return (0);
                        if (oidp->oid_handler)
                                return (0);
                        lsp = SYSCTL_CHILDREN(oidp);
                        if (!sysctl_sysctl_next_ls(lsp, name+1, namelen-1, 
                                next+1, len, level+1, oidpp))
                                return (0);
                        goto next;
                }
                if ((oidp->oid_kind & CTLTYPE) != CTLTYPE_NODE)
                        continue;

                if (oidp->oid_handler)
                        continue;

                lsp = SYSCTL_CHILDREN(oidp);
                if (!sysctl_sysctl_next_ls(lsp, name+1, namelen-1, next+1, 
                        len, level+1, oidpp))
                        return (0);
        next:
                namelen = 1;
        emptynode:
                *len = level;
        }
        return (1);
}

static int
sysctl_sysctl_next(SYSCTL_HANDLER_ARGS)
{
        int *name = (int *) arg1;
        u_int namelen = arg2;
        int i, j, error;
        struct sysctl_oid *oid;
        struct sysctl_oid_list *lsp = &sysctl__children;
        int newoid[CTL_MAXNAME];

        SYSCTL_XLOCK();
        i = sysctl_sysctl_next_ls(lsp, name, namelen, newoid, &j, 1, &oid);
        SYSCTL_XUNLOCK();
        if (i)
                return (ENOENT);
        error = SYSCTL_OUT(req, newoid, j * sizeof (int));
        return (error);
}

/*
 * XXXRW/JA: Shouldn't return next data for nodes that we don't permit in
 * capability mode.
 */
static SYSCTL_NODE(_sysctl, 2, next, CTLFLAG_RD | CTLFLAG_CAPRD,
    sysctl_sysctl_next, "");

static int
name2oid(char *name, int *oid, int *len, struct sysctl_oid **oidpp)
{
        struct sysctl_oid *oidp;
        struct sysctl_oid_list *lsp = &sysctl__children;
        char *p;

        SYSCTL_ASSERT_XLOCKED();

        for (*len = 0; *len < CTL_MAXNAME;) {
                p = strsep(&name, ".");

                oidp = SLIST_FIRST(lsp);
                for (;; oidp = SLIST_NEXT(oidp, oid_link)) {
                        if (oidp == NULL)
                                return (ENOENT);
                        if (strcmp(p, oidp->oid_name) == 0)
                                break;
                }
                *oid++ = oidp->oid_number;
                (*len)++;

                if (name == NULL || *name == '\0') {
                        if (oidpp)
                                *oidpp = oidp;
                        return (0);
                }

                if ((oidp->oid_kind & CTLTYPE) != CTLTYPE_NODE)
                        break;

                if (oidp->oid_handler)
                        break;

                lsp = SYSCTL_CHILDREN(oidp);
        }
        return (ENOENT);
}

static int
sysctl_sysctl_name2oid(SYSCTL_HANDLER_ARGS)
{
        char *p;
        int error, oid[CTL_MAXNAME], len = 0;
        struct sysctl_oid *op = 0;

        if (!req->newlen) 
                return (ENOENT);
        if (req->newlen >= MAXPATHLEN)  /* XXX arbitrary, undocumented */
                return (ENAMETOOLONG);

        p = malloc(req->newlen+1, M_SYSCTL, M_WAITOK);

        error = SYSCTL_IN(req, p, req->newlen);
        if (error) {
                free(p, M_SYSCTL);
                return (error);
        }

        p [req->newlen] = '\0';

        SYSCTL_XLOCK();
        error = name2oid(p, oid, &len, &op);
        SYSCTL_XUNLOCK();

        free(p, M_SYSCTL);

        if (error)
                return (error);

        error = SYSCTL_OUT(req, oid, len * sizeof *oid);
        return (error);
}

/*
 * XXXRW/JA: Shouldn't return name2oid data for nodes that we don't permit in
 * capability mode.
 */
SYSCTL_PROC(_sysctl, 3, name2oid,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_ANYBODY | CTLFLAG_MPSAFE
    | CTLFLAG_CAPRW, 0, 0, sysctl_sysctl_name2oid, "I", "");

static int
sysctl_sysctl_oidfmt(SYSCTL_HANDLER_ARGS)
{
        struct sysctl_oid *oid;
        int error;

        SYSCTL_XLOCK();
        error = sysctl_find_oid(arg1, arg2, &oid, NULL, req);
        if (error)
                goto out;

        if (oid->oid_fmt == NULL) {
                error = ENOENT;
                goto out;
        }
        error = SYSCTL_OUT(req, &oid->oid_kind, sizeof(oid->oid_kind));
        if (error)
                goto out;
        error = SYSCTL_OUT(req, oid->oid_fmt, strlen(oid->oid_fmt) + 1);
 out:
        SYSCTL_XUNLOCK();
        return (error);
}


static SYSCTL_NODE(_sysctl, 4, oidfmt, CTLFLAG_RD|CTLFLAG_MPSAFE|CTLFLAG_CAPRD,
    sysctl_sysctl_oidfmt, "");

static int
sysctl_sysctl_oiddescr(SYSCTL_HANDLER_ARGS)
{
        struct sysctl_oid *oid;
        int error;

        SYSCTL_XLOCK();
        error = sysctl_find_oid(arg1, arg2, &oid, NULL, req);
        if (error)
                goto out;

        if (oid->oid_descr == NULL) {
                error = ENOENT;
                goto out;
        }
        error = SYSCTL_OUT(req, oid->oid_descr, strlen(oid->oid_descr) + 1);
 out:
        SYSCTL_XUNLOCK();
        return (error);
}

static SYSCTL_NODE(_sysctl, 5, oiddescr, CTLFLAG_RD|CTLFLAG_CAPRD,
    sysctl_sysctl_oiddescr, "");

/*
 * Default "handler" functions.
 */

/*
 * Handle an int, signed or unsigned.
 * Two cases:
 *     a variable:  point arg1 at it.
 *     a constant:  pass it in arg2.
 */

int
sysctl_handle_int(SYSCTL_HANDLER_ARGS)
{
        int tmpout, error = 0;

        /*
         * Attempt to get a coherent snapshot by making a copy of the data.
         */
        if (arg1)
                tmpout = *(int *)arg1;
        else
                tmpout = arg2;
        error = SYSCTL_OUT(req, &tmpout, sizeof(int));

        if (error || !req->newptr)
                return (error);

        if (!arg1)
                error = EPERM;
        else
                error = SYSCTL_IN(req, arg1, sizeof(int));
        return (error);
}

/*
 * Based on on sysctl_handle_int() convert milliseconds into ticks.
 * Note: this is used by TCP.
 */

int
sysctl_msec_to_ticks(SYSCTL_HANDLER_ARGS)
{
        int error, s, tt;

        tt = *(int *)arg1;
        s = (int)((int64_t)tt * 1000 / hz);

        error = sysctl_handle_int(oidp, &s, 0, req);
        if (error || !req->newptr)
                return (error);

        tt = (int)((int64_t)s * hz / 1000);
        if (tt < 1)
                return (EINVAL);

        *(int *)arg1 = tt;
        return (0);
}


/*
 * Handle a long, signed or unsigned.
 * Two cases:
 *     a variable:  point arg1 at it.
 *     a constant:  pass it in arg2.
 */

int
sysctl_handle_long(SYSCTL_HANDLER_ARGS)
{
        int error = 0;
        long tmplong;
#ifdef SCTL_MASK32
        int tmpint;
#endif

        /*
         * Attempt to get a coherent snapshot by making a copy of the data.
         */
        if (arg1)
                tmplong = *(long *)arg1;
        else
                tmplong = arg2;
#ifdef SCTL_MASK32
        if (req->flags & SCTL_MASK32) {
                tmpint = tmplong;
                error = SYSCTL_OUT(req, &tmpint, sizeof(int));
        } else
#endif
                error = SYSCTL_OUT(req, &tmplong, sizeof(long));

        if (error || !req->newptr)
                return (error);

        if (!arg1)
                error = EPERM;
#ifdef SCTL_MASK32
        else if (req->flags & SCTL_MASK32) {
                error = SYSCTL_IN(req, &tmpint, sizeof(int));
                *(long *)arg1 = (long)tmpint;
        }
#endif
        else
                error = SYSCTL_IN(req, arg1, sizeof(long));
        return (error);
}

/*
 * Handle a 64 bit int, signed or unsigned.
 * Two cases:
 *     a variable:  point arg1 at it.
 *     a constant:  pass it in arg2.
 */
int
sysctl_handle_64(SYSCTL_HANDLER_ARGS)
{
        int error = 0;
        uint64_t tmpout;

        /*
         * Attempt to get a coherent snapshot by making a copy of the data.
         */
        if (arg1)
                tmpout = *(uint64_t *)arg1;
        else
                tmpout = arg2;
        error = SYSCTL_OUT(req, &tmpout, sizeof(uint64_t));

        if (error || !req->newptr)
                return (error);

        if (!arg1)
                error = EPERM;
        else
                error = SYSCTL_IN(req, arg1, sizeof(uint64_t));
        return (error);
}

/*
 * Handle our generic '\0' terminated 'C' string.
 * Two cases:
 *      a variable string:  point arg1 at it, arg2 is max length.
 *      a constant string:  point arg1 at it, arg2 is zero.
 */

int
sysctl_handle_string(SYSCTL_HANDLER_ARGS)
{
        int error=0;
        char *tmparg;
        size_t outlen;

        /*
         * Attempt to get a coherent snapshot by copying to a
         * temporary kernel buffer.
         */
retry:
        outlen = strlen((char *)arg1)+1;
        tmparg = malloc(outlen, M_SYSCTLTMP, M_WAITOK);

        if (strlcpy(tmparg, (char *)arg1, outlen) >= outlen) {
                free(tmparg, M_SYSCTLTMP);
                goto retry;
        }

        error = SYSCTL_OUT(req, tmparg, outlen);
        free(tmparg, M_SYSCTLTMP);

        if (error || !req->newptr)
                return (error);

        if ((req->newlen - req->newidx) >= arg2) {
                error = EINVAL;
        } else {
                arg2 = (req->newlen - req->newidx);
                error = SYSCTL_IN(req, arg1, arg2);
                ((char *)arg1)[arg2] = '\0';
        }

        return (error);
}

/*
 * Handle any kind of opaque data.
 * arg1 points to it, arg2 is the size.
 */

int
sysctl_handle_opaque(SYSCTL_HANDLER_ARGS)
{
        int error, tries;
        u_int generation;
        struct sysctl_req req2;

        /*
         * Attempt to get a coherent snapshot, by using the thread
         * pre-emption counter updated from within mi_switch() to
         * determine if we were pre-empted during a bcopy() or
         * copyout(). Make 3 attempts at doing this before giving up.
         * If we encounter an error, stop immediately.
         */
        tries = 0;
        req2 = *req;
retry:
        generation = curthread->td_generation;
        error = SYSCTL_OUT(req, arg1, arg2);
        if (error)
                return (error);
        tries++;
        if (generation != curthread->td_generation && tries < 3) {
                *req = req2;
                goto retry;
        }

        error = SYSCTL_IN(req, arg1, arg2);

        return (error);
}

/*
 * Transfer functions to/from kernel space.
 * XXX: rather untested at this point
 */
static int
sysctl_old_kernel(struct sysctl_req *req, const void *p, size_t l)
{
        size_t i = 0;

        if (req->oldptr) {
                i = l;
                if (req->oldlen <= req->oldidx)
                        i = 0;
                else
                        if (i > req->oldlen - req->oldidx)
                                i = req->oldlen - req->oldidx;
                if (i > 0)
                        bcopy(p, (char *)req->oldptr + req->oldidx, i);
        }
        req->oldidx += l;
        if (req->oldptr && i != l)
                return (ENOMEM);
        return (0);
}

static int
sysctl_new_kernel(struct sysctl_req *req, void *p, size_t l)
{
        if (!req->newptr)
                return (0);
        if (req->newlen - req->newidx < l)
                return (EINVAL);
        bcopy((char *)req->newptr + req->newidx, p, l);
        req->newidx += l;
        return (0);
}

int
kernel_sysctl(struct thread *td, int *name, u_int namelen, void *old,
    size_t *oldlenp, void *new, size_t newlen, size_t *retval, int flags)
{
        int error = 0;
        struct sysctl_req req;

        bzero(&req, sizeof req);

        req.td = td;
        req.flags = flags;

        if (oldlenp) {
                req.oldlen = *oldlenp;
        }
        req.validlen = req.oldlen;

        if (old) {
                req.oldptr= old;
        }

        if (new != NULL) {
                req.newlen = newlen;
                req.newptr = new;
        }

        req.oldfunc = sysctl_old_kernel;
        req.newfunc = sysctl_new_kernel;
        req.lock = REQ_UNWIRED;

        SYSCTL_XLOCK();
        error = sysctl_root(0, name, namelen, &req);
        SYSCTL_XUNLOCK();

        if (req.lock == REQ_WIRED && req.validlen > 0)
                vsunlock(req.oldptr, req.validlen);

        if (error && error != ENOMEM)
                return (error);

        if (retval) {
                if (req.oldptr && req.oldidx > req.validlen)
                        *retval = req.validlen;
                else
                        *retval = req.oldidx;
        }
        return (error);
}

int
kernel_sysctlbyname(struct thread *td, char *name, void *old, size_t *oldlenp,
    void *new, size_t newlen, size_t *retval, int flags)
{
        int oid[CTL_MAXNAME];
        size_t oidlen, plen;
        int error;

        oid[0] = 0;             /* sysctl internal magic */
        oid[1] = 3;             /* name2oid */
        oidlen = sizeof(oid);

        error = kernel_sysctl(td, oid, 2, oid, &oidlen,
            (void *)name, strlen(name), &plen, flags);
        if (error)
                return (error);

        error = kernel_sysctl(td, oid, plen / sizeof(int), old, oldlenp,
            new, newlen, retval, flags);
        return (error);
}

/*
 * Transfer function to/from user space.
 */
static int
sysctl_old_user(struct sysctl_req *req, const void *p, size_t l)
{
        size_t i, len, origidx;
        int error;

        origidx = req->oldidx;
        req->oldidx += l;
        if (req->oldptr == NULL)
                return (0);
        /*
         * If we have not wired the user supplied buffer and we are currently
         * holding locks, drop a witness warning, as it's possible that
         * write operations to the user page can sleep.
         */
        if (req->lock != REQ_WIRED)
                WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
                    "sysctl_old_user()");
        i = l;
        len = req->validlen;
        if (len <= origidx)
                i = 0;
        else {
                if (i > len - origidx)
                        i = len - origidx;
                if (req->lock == REQ_WIRED) {
                        error = copyout_nofault(p, (char *)req->oldptr +
                            origidx, i);
                } else
                        error = copyout(p, (char *)req->oldptr + origidx, i);
                if (error != 0)
                        return (error);
        }
        if (i < l)
                return (ENOMEM);
        return (0);
}

static int
sysctl_new_user(struct sysctl_req *req, void *p, size_t l)
{
        int error;

        if (!req->newptr)
                return (0);
        if (req->newlen - req->newidx < l)
                return (EINVAL);
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
            "sysctl_new_user()");
        error = copyin((char *)req->newptr + req->newidx, p, l);
        req->newidx += l;
        return (error);
}

/*
 * Wire the user space destination buffer.  If set to a value greater than
 * zero, the len parameter limits the maximum amount of wired memory.
 */
int
sysctl_wire_old_buffer(struct sysctl_req *req, size_t len)
{
        int ret;
        size_t wiredlen;

        wiredlen = (len > 0 && len < req->oldlen) ? len : req->oldlen;
        ret = 0;
        if (req->lock != REQ_WIRED && req->oldptr &&
            req->oldfunc == sysctl_old_user) {
                if (wiredlen != 0) {
                        ret = vslock(req->oldptr, wiredlen);
                        if (ret != 0) {
                                if (ret != ENOMEM)
                                        return (ret);
                                wiredlen = 0;
                        }
                }
                req->lock = REQ_WIRED;
                req->validlen = wiredlen;
        }
        return (0);
}

int
sysctl_find_oid(int *name, u_int namelen, struct sysctl_oid **noid,
    int *nindx, struct sysctl_req *req)
{
        struct sysctl_oid_list *lsp;
        struct sysctl_oid *oid;
        int indx;

        SYSCTL_ASSERT_XLOCKED();
        lsp = &sysctl__children;
        indx = 0;
        while (indx < CTL_MAXNAME) {
                SLIST_FOREACH(oid, lsp, oid_link) {
                        if (oid->oid_number == name[indx])
                                break;
                }
                if (oid == NULL)
                        return (ENOENT);

                indx++;
                if ((oid->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
                        if (oid->oid_handler != NULL || indx == namelen) {
                                *noid = oid;
                                if (nindx != NULL)
                                        *nindx = indx;
                                KASSERT((oid->oid_kind & CTLFLAG_DYING) == 0,
                                    ("%s found DYING node %p", __func__, oid));
                                return (0);
                        }
                        lsp = SYSCTL_CHILDREN(oid);
                } else if (indx == namelen) {
                        *noid = oid;
                        if (nindx != NULL)
                                *nindx = indx;
                        KASSERT((oid->oid_kind & CTLFLAG_DYING) == 0,
                            ("%s found DYING node %p", __func__, oid));
                        return (0);
                } else {
                        return (ENOTDIR);
                }
        }
        return (ENOENT);
}

/*
 * Traverse our tree, and find the right node, execute whatever it points
 * to, and return the resulting error code.
 */

static int
sysctl_root(SYSCTL_HANDLER_ARGS)
{
        struct sysctl_oid *oid;
        int error, indx, lvl;

        SYSCTL_ASSERT_XLOCKED();

        error = sysctl_find_oid(arg1, arg2, &oid, &indx, req);
        if (error)
                return (error);

        if ((oid->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
                /*
                 * You can't call a sysctl when it's a node, but has
                 * no handler.  Inform the user that it's a node.
                 * The indx may or may not be the same as namelen.
                 */
                if (oid->oid_handler == NULL)
                        return (EISDIR);
        }

        /* Is this sysctl writable? */
        if (req->newptr && !(oid->oid_kind & CTLFLAG_WR))
                return (EPERM);

        KASSERT(req->td != NULL, ("sysctl_root(): req->td == NULL"));

#ifdef CAPABILITY_MODE
        /*
         * If the process is in capability mode, then don't permit reading or
         * writing unless specifically granted for the node.
         */
        if (IN_CAPABILITY_MODE(req->td)) {
                if (req->oldptr && !(oid->oid_kind & CTLFLAG_CAPRD))
                        return (EPERM);
                if (req->newptr && !(oid->oid_kind & CTLFLAG_CAPWR))
                        return (EPERM);
        }
#endif

        /* Is this sysctl sensitive to securelevels? */
        if (req->newptr && (oid->oid_kind & CTLFLAG_SECURE)) {
                lvl = (oid->oid_kind & CTLMASK_SECURE) >> CTLSHIFT_SECURE;
                error = securelevel_gt(req->td->td_ucred, lvl);
                if (error)
                        return (error);
        }

        /* Is this sysctl writable by only privileged users? */
        if (req->newptr && !(oid->oid_kind & CTLFLAG_ANYBODY)) {
                int priv;

                if (oid->oid_kind & CTLFLAG_PRISON)
                        priv = PRIV_SYSCTL_WRITEJAIL;
#ifdef VIMAGE
                else if ((oid->oid_kind & CTLFLAG_VNET) &&
                     prison_owns_vnet(req->td->td_ucred))
                        priv = PRIV_SYSCTL_WRITEJAIL;
#endif
                else
                        priv = PRIV_SYSCTL_WRITE;
                error = priv_check(req->td, priv);
                if (error)
                        return (error);
        }

        if (!oid->oid_handler)
                return (EINVAL);

        if ((oid->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
                arg1 = (int *)arg1 + indx;
                arg2 -= indx;
        } else {
                arg1 = oid->oid_arg1;
                arg2 = oid->oid_arg2;
        }
#ifdef MAC
        error = mac_system_check_sysctl(req->td->td_ucred, oid, arg1, arg2,
            req);
        if (error != 0)
                return (error);
#endif
        oid->oid_running++;
        SYSCTL_XUNLOCK();

        if (!(oid->oid_kind & CTLFLAG_MPSAFE))
                mtx_lock(&Giant);
        error = oid->oid_handler(oid, arg1, arg2, req);
        if (!(oid->oid_kind & CTLFLAG_MPSAFE))
                mtx_unlock(&Giant);

        KFAIL_POINT_ERROR(_debug_fail_point, sysctl_running, error);

        SYSCTL_XLOCK();
        oid->oid_running--;
        if (oid->oid_running == 0 && (oid->oid_kind & CTLFLAG_DYING) != 0)
                wakeup(&oid->oid_running);
        return (error);
}

#ifndef _SYS_SYSPROTO_H_
struct sysctl_args {
        int     *name;
        u_int   namelen;
        void    *old;
        size_t  *oldlenp;
        void    *new;
        size_t  newlen;
};
#endif
int
sys___sysctl(struct thread *td, struct sysctl_args *uap)
{
        int error, i, name[CTL_MAXNAME];
        size_t j;

        if (uap->namelen > CTL_MAXNAME || uap->namelen < 2)
                return (EINVAL);

        error = copyin(uap->name, &name, uap->namelen * sizeof(int));
        if (error)
                return (error);

        error = userland_sysctl(td, name, uap->namelen,
                uap->old, uap->oldlenp, 0,
                uap->new, uap->newlen, &j, 0);
        if (error && error != ENOMEM)
                return (error);
        if (uap->oldlenp) {
                i = copyout(&j, uap->oldlenp, sizeof(j));
                if (i)
                        return (i);
        }
        return (error);
}

/*
 * This is used from various compatibility syscalls too.  That's why name
 * must be in kernel space.
 */
int
userland_sysctl(struct thread *td, int *name, u_int namelen, void *old,
    size_t *oldlenp, int inkernel, void *new, size_t newlen, size_t *retval,
    int flags)
{
        int error = 0, memlocked;
        struct sysctl_req req;

        bzero(&req, sizeof req);

        req.td = td;
        req.flags = flags;

        if (oldlenp) {
                if (inkernel) {
                        req.oldlen = *oldlenp;
                } else {
                        error = copyin(oldlenp, &req.oldlen, sizeof(*oldlenp));
                        if (error)
                                return (error);
                }
        }
        req.validlen = req.oldlen;

        if (old) {
                if (!useracc(old, req.oldlen, VM_PROT_WRITE))
                        return (EFAULT);
                req.oldptr= old;
        }

        if (new != NULL) {
                if (!useracc(new, newlen, VM_PROT_READ))
                        return (EFAULT);
                req.newlen = newlen;
                req.newptr = new;
        }

        req.oldfunc = sysctl_old_user;
        req.newfunc = sysctl_new_user;
        req.lock = REQ_UNWIRED;

#ifdef KTRACE
        if (KTRPOINT(curthread, KTR_SYSCTL))
                ktrsysctl(name, namelen);
#endif

        if (req.oldlen > PAGE_SIZE) {
                memlocked = 1;
                sx_xlock(&sysctlmemlock);
        } else
                memlocked = 0;
        CURVNET_SET(TD_TO_VNET(td));

        for (;;) {
                req.oldidx = 0;
                req.newidx = 0;
                SYSCTL_XLOCK();
                error = sysctl_root(0, name, namelen, &req);
                SYSCTL_XUNLOCK();
                if (error != EAGAIN)
                        break;
                kern_yield(PRI_USER);
        }

        CURVNET_RESTORE();

        if (req.lock == REQ_WIRED && req.validlen > 0)
                vsunlock(req.oldptr, req.validlen);
        if (memlocked)
                sx_xunlock(&sysctlmemlock);

        if (error && error != ENOMEM)
                return (error);

        if (retval) {
                if (req.oldptr && req.oldidx > req.validlen)
                        *retval = req.validlen;
                else
                        *retval = req.oldidx;
        }
        return (error);
}

/*
 * Drain into a sysctl struct.  The user buffer should be wired if a page
 * fault would cause issue.
 */
static int
sbuf_sysctl_drain(void *arg, const char *data, int len)
{
        struct sysctl_req *req = arg;
        int error;

        error = SYSCTL_OUT(req, data, len);
        KASSERT(error >= 0, ("Got unexpected negative value %d", error));
        return (error == 0 ? len : -error);
}

struct sbuf *
sbuf_new_for_sysctl(struct sbuf *s, char *buf, int length,
    struct sysctl_req *req)
{

        s = sbuf_new(s, buf, length, SBUF_FIXEDLEN);
        sbuf_set_drain(s, sbuf_sysctl_drain, req);
        return (s);
}