xref: /src/sys/miscfs/kernfs/kernfs_vnops.c

/*	$NetBSD: kernfs_vnops.c,v 1.156.2.1 2017/04/21 16:54:03 bouyer Exp $	*/

/*
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software donated to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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. 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.
 *
 *	@(#)kernfs_vnops.c	8.15 (Berkeley) 5/21/95
 */

/*
 * Kernel parameter filesystem (/kern)
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kernfs_vnops.c,v 1.156.2.1 2017/04/21 16:54:03 bouyer Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/vmmeter.h>
#include <sys/time.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/malloc.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/buf.h>
#include <sys/dirent.h>
#include <sys/msgbuf.h>

#include <miscfs/genfs/genfs.h>
#include <miscfs/kernfs/kernfs.h>
#include <miscfs/specfs/specdev.h>

#include <uvm/uvm_extern.h>

#define KSTRING	256		/* Largest I/O available via this filesystem */
#define	UIO_MX 32

#define	READ_MODE	(S_IRUSR|S_IRGRP|S_IROTH)
#define	WRITE_MODE	(S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH)
#define	UREAD_MODE	(S_IRUSR)
#define	DIR_MODE	(S_IRUSR|S_IXUSR|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH)
#define	UDIR_MODE	(S_IRUSR|S_IXUSR)

#define N(s) sizeof(s)-1, s
const struct kern_target kern_targets[] = {
/* NOTE: The name must be less than UIO_MX-16 chars in length */
     /*        name            data          tag           type  ro/rw */
     { DT_DIR, N("."),         0,            KFSkern,        VDIR, DIR_MODE   },
     { DT_DIR, N(".."),        0,            KFSroot,        VDIR, DIR_MODE   },
     { DT_REG, N("boottime"),  &boottime.tv_sec, KFSint,     VREG, READ_MODE  },
			/* XXXUNCONST */
     { DT_REG, N("copyright"), __UNCONST(copyright),
     					     KFSstring,      VREG, READ_MODE  },
     { DT_REG, N("hostname"),  0,            KFShostname,    VREG, WRITE_MODE },
     { DT_REG, N("hz"),        &hz,          KFSint,         VREG, READ_MODE  },
     { DT_REG, N("loadavg"),   0,            KFSavenrun,     VREG, READ_MODE  },
     { DT_REG, N("msgbuf"),    0,	     KFSmsgbuf,      VREG, READ_MODE  },
     { DT_REG, N("pagesize"),  &uvmexp.pagesize, KFSint,     VREG, READ_MODE  },
     { DT_REG, N("physmem"),   &physmem,     KFSint,         VREG, READ_MODE  },
#if 0
     { DT_DIR, N("root"),      0,            KFSnull,        VDIR, DIR_MODE   },
#endif
     { DT_BLK, N("rootdev"),   &rootdev,     KFSdevice,      VBLK, READ_MODE  },
     { DT_CHR, N("rrootdev"),  &rrootdev,    KFSdevice,      VCHR, READ_MODE  },
     { DT_REG, N("time"),      0,            KFStime,        VREG, READ_MODE  },
			/* XXXUNCONST */
     { DT_REG, N("version"),   __UNCONST(version),
     					     KFSstring,      VREG, READ_MODE  },
};
const struct kern_target subdir_targets[] = {
/* NOTE: The name must be less than UIO_MX-16 chars in length */
     /*        name            data          tag           type  ro/rw */
     { DT_DIR, N("."),         0,            KFSsubdir,      VDIR, DIR_MODE   },
     { DT_DIR, N(".."),        0,            KFSkern,        VDIR, DIR_MODE   },
};
#undef N
SIMPLEQ_HEAD(,dyn_kern_target) dyn_kern_targets =
	SIMPLEQ_HEAD_INITIALIZER(dyn_kern_targets);
int nkern_targets = sizeof(kern_targets) / sizeof(kern_targets[0]);
const int static_nkern_targets = sizeof(kern_targets) / sizeof(kern_targets[0]);
int nkern_dirs = 2;

int kernfs_try_fileop(kfstype, kfsfileop, void *, int);
int kernfs_try_xread(kfstype, const struct kernfs_node *, char **,
    size_t, int);
int kernfs_try_xwrite(kfstype, const struct kernfs_node *, char *,
    size_t, int);

static int kernfs_default_xread(void *v);
static int kernfs_default_xwrite(void *v);
static int kernfs_default_fileop_getattr(void *);

/* must include all fileop's */
const struct kernfs_fileop kernfs_default_fileops[] = {
  { .kf_fileop = KERNFS_XREAD },
  { .kf_fileop = KERNFS_XWRITE },
  { .kf_fileop = KERNFS_FILEOP_OPEN },
  { .kf_fileop = KERNFS_FILEOP_GETATTR,
    .kf_vop = kernfs_default_fileop_getattr },
  { .kf_fileop = KERNFS_FILEOP_IOCTL },
  { .kf_fileop = KERNFS_FILEOP_CLOSE },
  { .kf_fileop = KERNFS_FILEOP_READ,
    .kf_vop = kernfs_default_xread },
  { .kf_fileop = KERNFS_FILEOP_WRITE,
    .kf_vop = kernfs_default_xwrite },
};

int	kernfs_lookup(void *);
#define	kernfs_create	genfs_eopnotsupp
#define	kernfs_mknod	genfs_eopnotsupp
int	kernfs_open(void *);
int	kernfs_close(void *);
int	kernfs_access(void *);
int	kernfs_getattr(void *);
int	kernfs_setattr(void *);
int	kernfs_read(void *);
int	kernfs_write(void *);
#define	kernfs_fcntl	genfs_fcntl
int	kernfs_ioctl(void *);
#define	kernfs_poll	genfs_poll
#define kernfs_revoke	genfs_revoke
#define	kernfs_fsync	genfs_nullop
#define	kernfs_seek	genfs_nullop
#define	kernfs_remove	genfs_eopnotsupp
int	kernfs_link(void *);
#define	kernfs_rename	genfs_eopnotsupp
#define	kernfs_mkdir	genfs_eopnotsupp
#define	kernfs_rmdir	genfs_eopnotsupp
int	kernfs_symlink(void *);
int	kernfs_readdir(void *);
#define	kernfs_readlink	genfs_eopnotsupp
#define	kernfs_abortop	genfs_abortop
int	kernfs_inactive(void *);
int	kernfs_reclaim(void *);
#define	kernfs_lock	genfs_lock
#define	kernfs_unlock	genfs_unlock
#define	kernfs_bmap	genfs_badop
#define	kernfs_strategy	genfs_badop
int	kernfs_print(void *);
#define	kernfs_islocked	genfs_islocked
int	kernfs_pathconf(void *);
#define	kernfs_advlock	genfs_einval
#define	kernfs_bwrite	genfs_eopnotsupp
#define	kernfs_putpages	genfs_putpages

static int	kernfs_xread(struct kernfs_node *, int, char **,
				size_t, size_t *);
static int	kernfs_xwrite(const struct kernfs_node *, char *, size_t);

int (**kernfs_vnodeop_p)(void *);
const struct vnodeopv_entry_desc kernfs_vnodeop_entries[] = {
	{ &vop_default_desc, vn_default_error },
	{ &vop_lookup_desc, kernfs_lookup },		/* lookup */
	{ &vop_create_desc, kernfs_create },		/* create */
	{ &vop_mknod_desc, kernfs_mknod },		/* mknod */
	{ &vop_open_desc, kernfs_open },		/* open */
	{ &vop_close_desc, kernfs_close },		/* close */
	{ &vop_access_desc, kernfs_access },		/* access */
	{ &vop_getattr_desc, kernfs_getattr },		/* getattr */
	{ &vop_setattr_desc, kernfs_setattr },		/* setattr */
	{ &vop_read_desc, kernfs_read },		/* read */
	{ &vop_write_desc, kernfs_write },		/* write */
	{ &vop_fallocate_desc, genfs_eopnotsupp },	/* fallocate */
	{ &vop_fdiscard_desc, genfs_eopnotsupp },	/* fdiscard */
	{ &vop_fcntl_desc, kernfs_fcntl },		/* fcntl */
	{ &vop_ioctl_desc, kernfs_ioctl },		/* ioctl */
	{ &vop_poll_desc, kernfs_poll },		/* poll */
	{ &vop_revoke_desc, kernfs_revoke },		/* revoke */
	{ &vop_fsync_desc, kernfs_fsync },		/* fsync */
	{ &vop_seek_desc, kernfs_seek },		/* seek */
	{ &vop_remove_desc, kernfs_remove },		/* remove */
	{ &vop_link_desc, kernfs_link },		/* link */
	{ &vop_rename_desc, kernfs_rename },		/* rename */
	{ &vop_mkdir_desc, kernfs_mkdir },		/* mkdir */
	{ &vop_rmdir_desc, kernfs_rmdir },		/* rmdir */
	{ &vop_symlink_desc, kernfs_symlink },		/* symlink */
	{ &vop_readdir_desc, kernfs_readdir },		/* readdir */
	{ &vop_readlink_desc, kernfs_readlink },	/* readlink */
	{ &vop_abortop_desc, kernfs_abortop },		/* abortop */
	{ &vop_inactive_desc, kernfs_inactive },	/* inactive */
	{ &vop_reclaim_desc, kernfs_reclaim },		/* reclaim */
	{ &vop_lock_desc, kernfs_lock },		/* lock */
	{ &vop_unlock_desc, kernfs_unlock },		/* unlock */
	{ &vop_bmap_desc, kernfs_bmap },		/* bmap */
	{ &vop_strategy_desc, kernfs_strategy },	/* strategy */
	{ &vop_print_desc, kernfs_print },		/* print */
	{ &vop_islocked_desc, kernfs_islocked },	/* islocked */
	{ &vop_pathconf_desc, kernfs_pathconf },	/* pathconf */
	{ &vop_advlock_desc, kernfs_advlock },		/* advlock */
	{ &vop_bwrite_desc, kernfs_bwrite },		/* bwrite */
	{ &vop_putpages_desc, kernfs_putpages },	/* putpages */
	{ NULL, NULL }
};
const struct vnodeopv_desc kernfs_vnodeop_opv_desc =
	{ &kernfs_vnodeop_p, kernfs_vnodeop_entries };

static inline int
kernfs_fileop_compare(struct kernfs_fileop *a, struct kernfs_fileop *b)
{
	if (a->kf_type < b->kf_type)
		return -1;
	if (a->kf_type > b->kf_type)
		return 1;
	if (a->kf_fileop < b->kf_fileop)
		return -1;
	if (a->kf_fileop > b->kf_fileop)
		return 1;
	return (0);
}

SPLAY_HEAD(kfsfileoptree, kernfs_fileop) kfsfileoptree =
	SPLAY_INITIALIZER(kfsfileoptree);
SPLAY_PROTOTYPE(kfsfileoptree, kernfs_fileop, kf_node, kernfs_fileop_compare);
SPLAY_GENERATE(kfsfileoptree, kernfs_fileop, kf_node, kernfs_fileop_compare);

kfstype
kernfs_alloctype(int nkf, const struct kernfs_fileop *kf)
{
	static u_char nextfreetype = KFSlasttype;
	struct kernfs_fileop *dkf, *fkf, skf;
	int i;

	/* XXX need to keep track of dkf's memory if we support
           deallocating types */
	dkf = malloc(sizeof(kernfs_default_fileops), M_TEMP, M_WAITOK);
	memcpy(dkf, kernfs_default_fileops, sizeof(kernfs_default_fileops));

	for (i = 0; i < sizeof(kernfs_default_fileops) /
		     sizeof(kernfs_default_fileops[0]); i++) {
		dkf[i].kf_type = nextfreetype;
		SPLAY_INSERT(kfsfileoptree, &kfsfileoptree, &dkf[i]);
	}

	for (i = 0; i < nkf; i++) {
		skf.kf_type = nextfreetype;
		skf.kf_fileop = kf[i].kf_fileop;
		if ((fkf = SPLAY_FIND(kfsfileoptree, &kfsfileoptree, &skf)))
			fkf->kf_vop = kf[i].kf_vop;
	}

	return nextfreetype++;
}

int
kernfs_try_fileop(kfstype type, kfsfileop fileop, void *v, int error)
{
	struct kernfs_fileop *kf, skf;

	skf.kf_type = type;
	skf.kf_fileop = fileop;
	if ((kf = SPLAY_FIND(kfsfileoptree, &kfsfileoptree, &skf)))
		if (kf->kf_vop)
			return kf->kf_vop(v);
	return error;
}

int
kernfs_try_xread(kfstype type, const struct kernfs_node *kfs, char **bfp,
    size_t len, int error)
{
	struct kernfs_fileop *kf, skf;

	skf.kf_type = type;
	skf.kf_fileop = KERNFS_XREAD;
	if ((kf = SPLAY_FIND(kfsfileoptree, &kfsfileoptree, &skf)))
		if (kf->kf_xread)
			return kf->kf_xread(kfs, bfp, len);
	return error;
}

int
kernfs_try_xwrite(kfstype type, const struct kernfs_node *kfs, char *bf,
    size_t len, int error)
{
	struct kernfs_fileop *kf, skf;

	skf.kf_type = type;
	skf.kf_fileop = KERNFS_XWRITE;
	if ((kf = SPLAY_FIND(kfsfileoptree, &kfsfileoptree, &skf)))
		if (kf->kf_xwrite)
			return kf->kf_xwrite(kfs, bf, len);
	return error;
}

int
kernfs_addentry(kernfs_parentdir_t *pkt, kernfs_entry_t *dkt)
{
	struct kernfs_subdir *ks, *parent;

	if (pkt == NULL) {
		SIMPLEQ_INSERT_TAIL(&dyn_kern_targets, dkt, dkt_queue);
		nkern_targets++;
		if (dkt->dkt_kt.kt_vtype == VDIR)
			nkern_dirs++;
	} else {
		parent = (struct kernfs_subdir *)pkt->kt_data;
		SIMPLEQ_INSERT_TAIL(&parent->ks_entries, dkt, dkt_queue);
		parent->ks_nentries++;
		if (dkt->dkt_kt.kt_vtype == VDIR)
			parent->ks_dirs++;
	}
	if (dkt->dkt_kt.kt_vtype == VDIR && dkt->dkt_kt.kt_data == NULL) {
		ks = malloc(sizeof(struct kernfs_subdir),
		    M_TEMP, M_WAITOK);
		SIMPLEQ_INIT(&ks->ks_entries);
		ks->ks_nentries = 2; /* . and .. */
		ks->ks_dirs = 2;
		ks->ks_parent = pkt ? pkt : &kern_targets[0];
		dkt->dkt_kt.kt_data = ks;
	}
	return 0;
}

static int
kernfs_xread(struct kernfs_node *kfs, int off, char **bufp, size_t len, size_t *wrlen)
{
	const struct kern_target *kt;
	int err;

	kt = kfs->kfs_kt;

	switch (kfs->kfs_type) {
	case KFStime: {
		struct timeval tv;

		microtime(&tv);
		snprintf(*bufp, len, "%lld %ld\n", (long long)tv.tv_sec,
		    (long)tv.tv_usec);
		break;
	}

	case KFSint: {
		int *ip = kt->kt_data;

		snprintf(*bufp, len, "%d\n", *ip);
		break;
	}

	case KFSstring: {
		char *cp = kt->kt_data;

		*bufp = cp;
		break;
	}

	case KFSmsgbuf: {
		long n;

		/*
		 * deal with cases where the message buffer has
		 * become corrupted.
		 */
		if (!msgbufenabled || msgbufp->msg_magic != MSG_MAGIC) {
			msgbufenabled = 0;
			return (ENXIO);
		}

		/*
		 * Note that reads of /kern/msgbuf won't necessarily yield
		 * consistent results, if the message buffer is modified
		 * while the read is in progress.  The worst that can happen
		 * is that incorrect data will be read.  There's no way
		 * that this can crash the system unless the values in the
		 * message buffer header are corrupted, but that'll cause
		 * the system to die anyway.
		 */
		if (off >= msgbufp->msg_bufs) {
			*wrlen = 0;
			return (0);
		}
		n = msgbufp->msg_bufx + off;
		if (n >= msgbufp->msg_bufs)
			n -= msgbufp->msg_bufs;
		len = min(msgbufp->msg_bufs - n, msgbufp->msg_bufs - off);
		*bufp = msgbufp->msg_bufc + n;
		*wrlen = len;
		return (0);
	}

	case KFShostname: {
		char *cp = hostname;
		size_t xlen = hostnamelen;

		if (xlen >= (len - 2))
			return (EINVAL);

		memcpy(*bufp, cp, xlen);
		(*bufp)[xlen] = '\n';
		(*bufp)[xlen+1] = '\0';
		break;
	}

	case KFSavenrun:
		averunnable.fscale = FSCALE;
		snprintf(*bufp, len, "%d %d %d %ld\n",
		    averunnable.ldavg[0], averunnable.ldavg[1],
		    averunnable.ldavg[2], averunnable.fscale);
		break;

	default:
		err = kernfs_try_xread(kfs->kfs_type, kfs, bufp, len,
		    EOPNOTSUPP);
		if (err)
			return err;
	}

	len = strlen(*bufp);
	if (len <= off)
		*wrlen = 0;
	else {
		*bufp += off;
		*wrlen = len - off;
	}
	return (0);
}

static int
kernfs_xwrite(const struct kernfs_node *kfs, char *bf, size_t len)
{

	switch (kfs->kfs_type) {
	case KFShostname:
		if (bf[len-1] == '\n')
			--len;
		memcpy(hostname, bf, len);
		hostname[len] = '\0';
		hostnamelen = (size_t) len;
		return (0);

	default:
		return kernfs_try_xwrite(kfs->kfs_type, kfs, bf, len, EIO);
	}
}


/*
 * vp is the current namei directory
 * ndp is the name to locate in that directory...
 */
int
kernfs_lookup(void *v)
{
	struct vop_lookup_v2_args /* {
		struct vnode * a_dvp;
		struct vnode ** a_vpp;
		struct componentname * a_cnp;
	} */ *ap = v;
	struct componentname *cnp = ap->a_cnp;
	struct vnode **vpp = ap->a_vpp;
	struct vnode *dvp = ap->a_dvp;
	const char *pname = cnp->cn_nameptr;
	const struct kernfs_node *kfs;
	const struct kern_target *kt;
	const struct dyn_kern_target *dkt;
	const struct kernfs_subdir *ks;
	int error, i;

	*vpp = NULLVP;

	if (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)
		return (EROFS);

	if (cnp->cn_namelen == 1 && *pname == '.') {
		*vpp = dvp;
		vref(dvp);
		return (0);
	}

	kfs = VTOKERN(dvp);
	switch (kfs->kfs_type) {
	case KFSkern:
		/*
		 * Shouldn't get here with .. in the root node.
		 */
		if (cnp->cn_flags & ISDOTDOT)
			return (EIO);

		for (i = 0; i < static_nkern_targets; i++) {
			kt = &kern_targets[i];
			if (cnp->cn_namelen == kt->kt_namlen &&
			    memcmp(kt->kt_name, pname, cnp->cn_namelen) == 0)
				goto found;
		}
		SIMPLEQ_FOREACH(dkt, &dyn_kern_targets, dkt_queue) {
			if (cnp->cn_namelen == dkt->dkt_kt.kt_namlen &&
			    memcmp(dkt->dkt_kt.kt_name, pname, cnp->cn_namelen) == 0) {
				kt = &dkt->dkt_kt;
				goto found;
			}
		}
		break;

	found:
		error = vcache_get(dvp->v_mount, &kt, sizeof(kt), vpp);
		return error;

	case KFSsubdir:
		ks = (struct kernfs_subdir *)kfs->kfs_kt->kt_data;
		if (cnp->cn_flags & ISDOTDOT) {
			kt = ks->ks_parent;
			goto found;
		}

		SIMPLEQ_FOREACH(dkt, &ks->ks_entries, dkt_queue) {
			if (cnp->cn_namelen == dkt->dkt_kt.kt_namlen &&
			    memcmp(dkt->dkt_kt.kt_name, pname, cnp->cn_namelen) == 0) {
				kt = &dkt->dkt_kt;
				goto found;
			}
		}
		break;

	default:
		return (ENOTDIR);
	}

	return (cnp->cn_nameiop == LOOKUP ? ENOENT : EROFS);
}

int
kernfs_open(void *v)
{
	struct vop_open_args /* {
		struct vnode *a_vp;
		int a_mode;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);

	return kernfs_try_fileop(kfs->kfs_type, KERNFS_FILEOP_OPEN, v, 0);
}

int
kernfs_close(void *v)
{
	struct vop_close_args /* {
		struct vnode *a_vp;
		int a_fflag;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);

	return kernfs_try_fileop(kfs->kfs_type, KERNFS_FILEOP_CLOSE, v, 0);
}

int
kernfs_access(void *v)
{
	struct vop_access_args /* {
		struct vnode *a_vp;
		int a_mode;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct vattr va;
	int error;

	if ((error = VOP_GETATTR(ap->a_vp, &va, ap->a_cred)) != 0)
		return (error);

	return kauth_authorize_vnode(ap->a_cred,
	    KAUTH_ACCESS_ACTION(ap->a_mode, ap->a_vp->v_type, va.va_mode),
	    ap->a_vp, NULL, genfs_can_access(va.va_type, va.va_mode,
	    va.va_uid, va.va_gid, ap->a_mode, ap->a_cred));
}

static int
kernfs_default_fileop_getattr(void *v)
{
	struct vop_getattr_args /* {
		struct vnode *a_vp;
		struct vattr *a_vap;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct vattr *vap = ap->a_vap;

	vap->va_nlink = 1;
	vap->va_bytes = vap->va_size = 0;

	return 0;
}

int
kernfs_getattr(void *v)
{
	struct vop_getattr_args /* {
		struct vnode *a_vp;
		struct vattr *a_vap;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);
	struct kernfs_subdir *ks;
	struct vattr *vap = ap->a_vap;
	int error = 0;
	char strbuf[KSTRING], *bf;
	size_t nread, total;

	vattr_null(vap);
	vap->va_type = ap->a_vp->v_type;
	vap->va_uid = 0;
	vap->va_gid = 0;
	vap->va_mode = kfs->kfs_mode;
	vap->va_fileid = kfs->kfs_fileno;
	vap->va_flags = 0;
	vap->va_size = 0;
	vap->va_blocksize = DEV_BSIZE;
	/* Make all times be current TOD, except for the "boottime" node. */
	if (kfs->kfs_kt->kt_namlen == 8 &&
	    !memcmp(kfs->kfs_kt->kt_name, "boottime", 8)) {
		vap->va_ctime = boottime;
	} else {
		getnanotime(&vap->va_ctime);
	}
	vap->va_atime = vap->va_mtime = vap->va_ctime;
	vap->va_gen = 0;
	vap->va_flags = 0;
	vap->va_rdev = 0;
	vap->va_bytes = 0;

	switch (kfs->kfs_type) {
	case KFSkern:
		vap->va_nlink = nkern_dirs;
		vap->va_bytes = vap->va_size = DEV_BSIZE;
		break;

	case KFSdevice:
		vap->va_nlink = 1;
		vap->va_rdev = ap->a_vp->v_rdev;
		break;

	case KFSroot:
		vap->va_nlink = 1;
		vap->va_bytes = vap->va_size = DEV_BSIZE;
		break;

	case KFSsubdir:
		ks = (struct kernfs_subdir *)kfs->kfs_kt->kt_data;
		vap->va_nlink = ks->ks_dirs;
		vap->va_bytes = vap->va_size = DEV_BSIZE;
		break;

	case KFSnull:
	case KFStime:
	case KFSint:
	case KFSstring:
	case KFShostname:
	case KFSavenrun:
	case KFSmsgbuf:
		vap->va_nlink = 1;
		total = 0;
		do {
			bf = strbuf;
			error = kernfs_xread(kfs, total, &bf,
			    sizeof(strbuf), &nread);
			total += nread;
		} while (error == 0 && nread != 0);
		vap->va_bytes = vap->va_size = total;
		break;

	default:
		error = kernfs_try_fileop(kfs->kfs_type,
		    KERNFS_FILEOP_GETATTR, v, EINVAL);
		break;
	}

	return (error);
}

/*ARGSUSED*/
int
kernfs_setattr(void *v)
{

	/*
	 * Silently ignore attribute changes.
	 * This allows for open with truncate to have no
	 * effect until some data is written.  I want to
	 * do it this way because all writes are atomic.
	 */
	return (0);
}

int
kernfs_default_xread(void *v)
{
	struct vop_read_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int  a_ioflag;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct uio *uio = ap->a_uio;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);
	char strbuf[KSTRING], *bf;
	int off;
	size_t len;
	int error;

	if (ap->a_vp->v_type == VDIR)
		return EISDIR;

	off = (int)uio->uio_offset;
	/* Don't allow negative offsets */
	if (off < 0)
		return EINVAL;

	bf = strbuf;
	if ((error = kernfs_xread(kfs, off, &bf, sizeof(strbuf), &len)) == 0)
		error = uiomove(bf, len, uio);
	return (error);
}

int
kernfs_read(void *v)
{
	struct vop_read_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int  a_ioflag;
		struct ucred *a_cred;
	} */ *ap = v;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);

	if (kfs->kfs_type < KFSlasttype) {
		/* use default function */
		return kernfs_default_xread(v);
	}
	return kernfs_try_fileop(kfs->kfs_type, KERNFS_FILEOP_READ, v,
	   EOPNOTSUPP);
}

static int
kernfs_default_xwrite(void *v)
{
	struct vop_write_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int  a_ioflag;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);
	struct uio *uio = ap->a_uio;
	int error;
	size_t xlen;
	char strbuf[KSTRING];

	if (uio->uio_offset != 0)
		return (EINVAL);

	xlen = min(uio->uio_resid, KSTRING-1);
	if ((error = uiomove(strbuf, xlen, uio)) != 0)
		return (error);

	if (uio->uio_resid != 0)
		return (EIO);

	strbuf[xlen] = '\0';
	xlen = strlen(strbuf);
	return (kernfs_xwrite(kfs, strbuf, xlen));
}

int
kernfs_write(void *v)
{
	struct vop_write_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int  a_ioflag;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);

	if (kfs->kfs_type < KFSlasttype) {
		/* use default function */
		return kernfs_default_xwrite(v);
	}
	return kernfs_try_fileop(kfs->kfs_type, KERNFS_FILEOP_WRITE, v,
	    EOPNOTSUPP);
}

int
kernfs_ioctl(void *v)
{
	struct vop_ioctl_args /* {
		const struct vnodeop_desc *a_desc;
		struct vnode *a_vp;
		u_long a_command;
		void *a_data;
		int a_fflag;
		kauth_cred_t a_cred;
	} */ *ap = v;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);

	return kernfs_try_fileop(kfs->kfs_type, KERNFS_FILEOP_IOCTL, v,
	    EPASSTHROUGH);
}

static int
kernfs_setdirentfileno_kt(struct dirent *d, const struct kern_target *kt,
    struct vop_readdir_args *ap)
{
	struct kernfs_node *kfs;
	struct vnode *vp;
	int error;

	if ((error = vcache_get(ap->a_vp->v_mount, &kt, sizeof(kt), &vp)) != 0)
		return error;
	kfs = VTOKERN(vp);
	d->d_fileno = kfs->kfs_fileno;
	vrele(vp);
	return 0;
}

static int
kernfs_setdirentfileno(struct dirent *d, off_t entry,
    struct kernfs_node *thisdir_kfs, const struct kern_target *parent_kt,
    const struct kern_target *kt, struct vop_readdir_args *ap)
{
	const struct kern_target *ikt;
	int error;

	switch (entry) {
	case 0:
		d->d_fileno = thisdir_kfs->kfs_fileno;
		return 0;
	case 1:
		ikt = parent_kt;
		break;
	default:
		ikt = kt;
		break;
	}
	if (ikt != thisdir_kfs->kfs_kt) {
		if ((error = kernfs_setdirentfileno_kt(d, ikt, ap)) != 0)
			return error;
	} else
		d->d_fileno = thisdir_kfs->kfs_fileno;
	return 0;
}

int
kernfs_readdir(void *v)
{
	struct vop_readdir_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		kauth_cred_t a_cred;
		int *a_eofflag;
		off_t **a_cookies;
		int a_*ncookies;
	} */ *ap = v;
	struct uio *uio = ap->a_uio;
	struct dirent d;
	struct kernfs_node *kfs = VTOKERN(ap->a_vp);
	const struct kern_target *kt;
	const struct dyn_kern_target *dkt = NULL;
	const struct kernfs_subdir *ks;
	off_t i, j;
	int error;
	off_t *cookies = NULL;
	int ncookies = 0, n;

	if (uio->uio_resid < UIO_MX)
		return (EINVAL);
	if (uio->uio_offset < 0)
		return (EINVAL);

	error = 0;
	i = uio->uio_offset;
	memset(&d, 0, sizeof(d));
	d.d_reclen = UIO_MX;
	ncookies = uio->uio_resid / UIO_MX;

	switch (kfs->kfs_type) {
	case KFSkern:
		if (i >= nkern_targets)
			return (0);

		if (ap->a_ncookies) {
			ncookies = min(ncookies, (nkern_targets - i));
			cookies = malloc(ncookies * sizeof(off_t), M_TEMP,
			    M_WAITOK);
			*ap->a_cookies = cookies;
		}

		n = 0;
		for (; i < nkern_targets && uio->uio_resid >= UIO_MX; i++) {
			if (i < static_nkern_targets)
				kt = &kern_targets[i];
			else {
				if (dkt == NULL) {
					dkt = SIMPLEQ_FIRST(&dyn_kern_targets);
					for (j = static_nkern_targets; j < i &&
						     dkt != NULL; j++)
						dkt = SIMPLEQ_NEXT(dkt, dkt_queue);
					if (j != i)
						break;
				} else {
					dkt = SIMPLEQ_NEXT(dkt, dkt_queue);
				}
				if (dkt == NULL)
					break;
				kt = &dkt->dkt_kt;
			}
			if (kt->kt_tag == KFSdevice) {
				dev_t *dp = kt->kt_data;
				struct vnode *fvp;

				if (*dp == NODEV ||
				    !vfinddev(*dp, kt->kt_vtype, &fvp))
					continue;
				vrele(fvp);
			}
			if (kt->kt_tag == KFSmsgbuf) {
				if (!msgbufenabled
				    || msgbufp->msg_magic != MSG_MAGIC) {
					continue;
				}
			}
			d.d_namlen = kt->kt_namlen;
			if ((error = kernfs_setdirentfileno(&d, i, kfs,
			    &kern_targets[0], kt, ap)) != 0)
				break;
			memcpy(d.d_name, kt->kt_name, kt->kt_namlen + 1);
			d.d_type = kt->kt_type;
			if ((error = uiomove(&d, UIO_MX, uio)) != 0)
				break;
			if (cookies)
				*cookies++ = i + 1;
			n++;
		}
		ncookies = n;
		break;

	case KFSroot:
		if (i >= 2)
			return 0;

		if (ap->a_ncookies) {
			ncookies = min(ncookies, (2 - i));
			cookies = malloc(ncookies * sizeof(off_t), M_TEMP,
			    M_WAITOK);
			*ap->a_cookies = cookies;
		}

		n = 0;
		for (; i < 2 && uio->uio_resid >= UIO_MX; i++) {
			kt = &kern_targets[i];
			d.d_namlen = kt->kt_namlen;
			d.d_fileno = KERNFS_FILENO(kt, kt->kt_tag, 0);
			memcpy(d.d_name, kt->kt_name, kt->kt_namlen + 1);
			d.d_type = kt->kt_type;
			if ((error = uiomove(&d, UIO_MX, uio)) != 0)
				break;
			if (cookies)
				*cookies++ = i + 1;
			n++;
		}
		ncookies = n;
		break;

	case KFSsubdir:
		ks = (struct kernfs_subdir *)kfs->kfs_kt->kt_data;
		if (i >= ks->ks_nentries)
			return (0);

		if (ap->a_ncookies) {
			ncookies = min(ncookies, (ks->ks_nentries - i));
			cookies = malloc(ncookies * sizeof(off_t), M_TEMP,
			    M_WAITOK);
			*ap->a_cookies = cookies;
		}

		dkt = SIMPLEQ_FIRST(&ks->ks_entries);
		for (j = 0; j < i && dkt != NULL; j++)
			dkt = SIMPLEQ_NEXT(dkt, dkt_queue);
		n = 0;
		for (; i < ks->ks_nentries && uio->uio_resid >= UIO_MX; i++) {
			if (i < 2)
				kt = &subdir_targets[i];
			else {
				/* check if ks_nentries lied to us */
				if (dkt == NULL)
					break;
				kt = &dkt->dkt_kt;
				dkt = SIMPLEQ_NEXT(dkt, dkt_queue);
			}
			if (kt->kt_tag == KFSdevice) {
				dev_t *dp = kt->kt_data;
				struct vnode *fvp;

				if (*dp == NODEV ||
				    !vfinddev(*dp, kt->kt_vtype, &fvp))
					continue;
				vrele(fvp);
			}
			d.d_namlen = kt->kt_namlen;
			if ((error = kernfs_setdirentfileno(&d, i, kfs,
			    ks->ks_parent, kt, ap)) != 0)
				break;
			memcpy(d.d_name, kt->kt_name, kt->kt_namlen + 1);
			d.d_type = kt->kt_type;
			if ((error = uiomove(&d, UIO_MX, uio)) != 0)
				break;
			if (cookies)
				*cookies++ = i + 1;
			n++;
		}
		ncookies = n;
		break;

	default:
		error = ENOTDIR;
		break;
	}

	if (ap->a_ncookies) {
		if (error) {
			if (cookies)
				free(*ap->a_cookies, M_TEMP);
			*ap->a_ncookies = 0;
			*ap->a_cookies = NULL;
		} else
			*ap->a_ncookies = ncookies;
	}

	uio->uio_offset = i;
	return (error);
}

int
kernfs_inactive(void *v)
{
	struct vop_inactive_v2_args /* {
		struct vnode *a_vp;
		bool *a_recycle;
	} */ *ap = v;

	*ap->a_recycle = false;

	return (0);
}

int
kernfs_reclaim(void *v)
{
	struct vop_reclaim_args /* {
		struct vnode *a_vp;
	} */ *ap = v;
	struct vnode *vp = ap->a_vp;
	struct kernfs_node *kfs = VTOKERN(vp);

	vp->v_data = NULL;
	mutex_enter(&kfs_lock);
	TAILQ_REMOVE(&VFSTOKERNFS(vp->v_mount)->nodelist, kfs, kfs_list);
	mutex_exit(&kfs_lock);
	kmem_free(kfs, sizeof(struct kernfs_node));

	return 0;
}

/*
 * Return POSIX pathconf information applicable to special devices.
 */
int
kernfs_pathconf(void *v)
{
	struct vop_pathconf_args /* {
		struct vnode *a_vp;
		int a_name;
		register_t *a_retval;
	} */ *ap = v;

	switch (ap->a_name) {
	case _PC_LINK_MAX:
		*ap->a_retval = LINK_MAX;
		return (0);
	case _PC_MAX_CANON:
		*ap->a_retval = MAX_CANON;
		return (0);
	case _PC_MAX_INPUT:
		*ap->a_retval = MAX_INPUT;
		return (0);
	case _PC_PIPE_BUF:
		*ap->a_retval = PIPE_BUF;
		return (0);
	case _PC_CHOWN_RESTRICTED:
		*ap->a_retval = 1;
		return (0);
	case _PC_VDISABLE:
		*ap->a_retval = _POSIX_VDISABLE;
		return (0);
	case _PC_SYNC_IO:
		*ap->a_retval = 1;
		return (0);
	default:
		return (EINVAL);
	}
	/* NOTREACHED */
}

/*
 * Print out the contents of a /dev/fd vnode.
 */
/* ARGSUSED */
int
kernfs_print(void *v)
{

	printf("tag VT_KERNFS, kernfs vnode\n");
	return (0);
}

int
kernfs_link(void *v)
{
	struct vop_link_v2_args /* {
		struct vnode *a_dvp;
		struct vnode *a_vp;
		struct componentname *a_cnp;
	} */ *ap = v;

	VOP_ABORTOP(ap->a_dvp, ap->a_cnp);
	return (EROFS);
}

int
kernfs_symlink(void *v)
{
	struct vop_symlink_v3_args /* {
		struct vnode *a_dvp;
		struct vnode **a_vpp;
		struct componentname *a_cnp;
		struct vattr *a_vap;
		char *a_target;
	} */ *ap = v;

	VOP_ABORTOP(ap->a_dvp, ap->a_cnp);
	return (EROFS);
}