NetBSD/lib/libkvm/kvm_proc.c

/*	$NetBSD: kvm_proc.c,v 1.31 1999/07/02 15:28:50 simonb Exp $	*/

/*-
 * Copyright (c) 1998 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Charles M. Hannum.
 *
 * 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 the NetBSD
 *        Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation 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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*-
 * Copyright (c) 1989, 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software developed by the Computer Systems
 * Engineering group at Lawrence Berkeley Laboratory under DARPA contract
 * BG 91-66 and contributed to Berkeley.
 *
 * 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 the University of
 *	California, Berkeley and its contributors.
 * 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.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)kvm_proc.c	8.3 (Berkeley) 9/23/93";
#else
__RCSID("$NetBSD: kvm_proc.c,v 1.31 1999/07/02 15:28:50 simonb Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

/*
 * Proc traversal interface for kvm.  ps and w are (probably) the exclusive
 * users of this code, so we've factored it out into a separate module.
 * Thus, we keep this grunge out of the other kvm applications (i.e.,
 * most other applications are interested only in open/close/read/nlist).
 */

#include <sys/param.h>
#include <sys/user.h>
#include <sys/proc.h>
#include <sys/exec.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/tty.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <nlist.h>
#include <kvm.h>

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

#include <uvm/uvm_extern.h>
#include <uvm/uvm_amap.h>

#include <sys/sysctl.h>

#include <limits.h>
#include <db.h>
#include <paths.h>

#include "kvm_private.h"

#define KREAD(kd, addr, obj) \
	(kvm_read(kd, addr, (void *)(obj), sizeof(*obj)) != sizeof(*obj))

char		*_kvm_uread __P((kvm_t *, const struct proc *, u_long, u_long *));
ssize_t		kvm_uread __P((kvm_t *, const struct proc *, u_long, char *,
		    size_t));

static char	**kvm_argv __P((kvm_t *, const struct proc *, u_long, int,
		    int));
static int	kvm_deadprocs __P((kvm_t *, int, int, u_long, u_long, u_long,
		    int));
static char	**kvm_doargv __P((kvm_t *, const struct kinfo_proc *, int,
		    void (*)(struct ps_strings *, u_long *, int *)));
static int	kvm_proclist __P((kvm_t *, int, int, struct proc *,
		    struct kinfo_proc *, int));
static int	proc_verify __P((kvm_t *, u_long, const struct proc *));
static void	ps_str_a __P((struct ps_strings *, u_long *, int *));
static void	ps_str_e __P((struct ps_strings *, u_long *, int *));

char *
_kvm_uread(kd, p, va, cnt)
	kvm_t *kd;
	const struct proc *p;
	u_long va;
	u_long *cnt;
{
	int true = 1;
	u_long addr, head;
	u_long offset;
	struct vm_map_entry vme;
	struct vm_amap amap;
	struct vm_anon *anonp, anon;
	struct vm_page pg;
	u_long slot;

	if (kd->swapspc == 0) {
		kd->swapspc = (char *)_kvm_malloc(kd, (size_t)kd->nbpg);
		if (kd->swapspc == 0)
			return (0);
	}

	/*
	 * Look through the address map for the memory object
	 * that corresponds to the given virtual address.
	 * The header just has the entire valid range.
	 */
	head = (u_long)&p->p_vmspace->vm_map.header;
	addr = head;
	while (true) {
		if (KREAD(kd, addr, &vme))
			return (0);

		if (va >= vme.start && va < vme.end &&
		    vme.aref.ar_amap != NULL)
			break;

		addr = (u_long)vme.next;
		if (addr == head)
			return (0);

	}

	/*
	 * we found the map entry, now to find the object...
	 */
	if (vme.aref.ar_amap == NULL)
		return NULL;

	addr = (u_long)vme.aref.ar_amap;
	if (KREAD(kd, addr, &amap))
		return NULL;

	offset = va - vme.start;
	slot = offset / kd->nbpg + vme.aref.ar_pageoff;
	/* sanity-check slot number */
	if (slot  > amap.am_nslot)
		return NULL;

	addr = (u_long)amap.am_anon + (offset / kd->nbpg) * sizeof(anonp);
	if (KREAD(kd, addr, &anonp))
		return NULL;

	addr = (u_long)anonp;
	if (KREAD(kd, addr, &anon))
		return NULL;

	addr = (u_long)anon.u.an_page;
	if (addr) {
		if (KREAD(kd, addr, &pg))
			return NULL;

		if (pread(kd->pmfd, (void *)kd->swapspc, (size_t)kd->nbpg,
		    (off_t)pg.phys_addr) != kd->nbpg)
			return NULL;
	}
	else {
		if (pread(kd->swfd, (void *)kd->swapspc, (size_t)kd->nbpg,
		    (off_t)(anon.an_swslot * kd->nbpg)) != kd->nbpg)
			return NULL;
	}

	/* Found the page. */
	offset %= kd->nbpg;
	*cnt = kd->nbpg - offset;
	return (&kd->swapspc[(size_t)offset]);
}

/*
 * Read proc's from memory file into buffer bp, which has space to hold
 * at most maxcnt procs.
 */
static int
kvm_proclist(kd, what, arg, p, bp, maxcnt)
	kvm_t *kd;
	int what, arg;
	struct proc *p;
	struct kinfo_proc *bp;
	int maxcnt;
{
	int cnt = 0;
	struct eproc eproc;
	struct pgrp pgrp;
	struct session sess;
	struct tty tty;
	struct proc proc;

	for (; cnt < maxcnt && p != NULL; p = proc.p_list.le_next) {
		if (KREAD(kd, (u_long)p, &proc)) {
			_kvm_err(kd, kd->program, "can't read proc at %x", p);
			return (-1);
		}
		if (KREAD(kd, (u_long)proc.p_cred, &eproc.e_pcred) == 0)
			if (KREAD(kd, (u_long)eproc.e_pcred.pc_ucred,
			    &eproc.e_ucred)) {
				_kvm_err(kd, kd->program,
				    "can't read proc credentials at %x", p);
				return -1;
			}

		switch(what) {

		case KERN_PROC_PID:
			if (proc.p_pid != (pid_t)arg)
				continue;
			break;

		case KERN_PROC_UID:
			if (eproc.e_ucred.cr_uid != (uid_t)arg)
				continue;
			break;

		case KERN_PROC_RUID:
			if (eproc.e_pcred.p_ruid != (uid_t)arg)
				continue;
			break;
		}
		/*
		 * We're going to add another proc to the set.  If this
		 * will overflow the buffer, assume the reason is because
		 * nprocs (or the proc list) is corrupt and declare an error.
		 */
		if (cnt >= maxcnt) {
			_kvm_err(kd, kd->program, "nprocs corrupt");
			return (-1);
		}
		/*
		 * gather eproc
		 */
		eproc.e_paddr = p;
		if (KREAD(kd, (u_long)proc.p_pgrp, &pgrp)) {
			_kvm_err(kd, kd->program, "can't read pgrp at %x",
				 proc.p_pgrp);
			return (-1);
		}
		eproc.e_sess = pgrp.pg_session;
		eproc.e_pgid = pgrp.pg_id;
		eproc.e_jobc = pgrp.pg_jobc;
		if (KREAD(kd, (u_long)pgrp.pg_session, &sess)) {
			_kvm_err(kd, kd->program, "can't read session at %x",
				pgrp.pg_session);
			return (-1);
		}
		if ((proc.p_flag & P_CONTROLT) && sess.s_ttyp != NULL) {
			if (KREAD(kd, (u_long)sess.s_ttyp, &tty)) {
				_kvm_err(kd, kd->program,
					 "can't read tty at %x", sess.s_ttyp);
				return (-1);
			}
			eproc.e_tdev = tty.t_dev;
			eproc.e_tsess = tty.t_session;
			if (tty.t_pgrp != NULL) {
				if (KREAD(kd, (u_long)tty.t_pgrp, &pgrp)) {
					_kvm_err(kd, kd->program,
						 "can't read tpgrp at &x",
						tty.t_pgrp);
					return (-1);
				}
				eproc.e_tpgid = pgrp.pg_id;
			} else
				eproc.e_tpgid = -1;
		} else
			eproc.e_tdev = NODEV;
		eproc.e_flag = sess.s_ttyvp ? EPROC_CTTY : 0;
		if (sess.s_leader == p)
			eproc.e_flag |= EPROC_SLEADER;
		if (proc.p_wmesg)
			(void)kvm_read(kd, (u_long)proc.p_wmesg,
			    eproc.e_wmesg, WMESGLEN);

		(void)kvm_read(kd, (u_long)proc.p_vmspace,
		    (void *)&eproc.e_vm, sizeof(eproc.e_vm));

		eproc.e_xsize = eproc.e_xrssize = 0;
		eproc.e_xccount = eproc.e_xswrss = 0;

		switch (what) {

		case KERN_PROC_PGRP:
			if (eproc.e_pgid != (pid_t)arg)
				continue;
			break;

		case KERN_PROC_TTY:
			if ((proc.p_flag & P_CONTROLT) == 0 ||
			     eproc.e_tdev != (dev_t)arg)
				continue;
			break;
		}
		memcpy(&bp->kp_proc, &proc, sizeof(proc));
		memcpy(&bp->kp_eproc, &eproc, sizeof(eproc));
		++bp;
		++cnt;
	}
	return (cnt);
}

/*
 * Build proc info array by reading in proc list from a crash dump.
 * Return number of procs read.  maxcnt is the max we will read.
 */
static int
kvm_deadprocs(kd, what, arg, a_allproc, a_deadproc, a_zombproc, maxcnt)
	kvm_t *kd;
	int what, arg;
	u_long a_allproc;
	u_long a_deadproc;
	u_long a_zombproc;
	int maxcnt;
{
	struct kinfo_proc *bp = kd->procbase;
	int acnt, dcnt, zcnt;
	struct proc *p;

	if (KREAD(kd, a_allproc, &p)) {
		_kvm_err(kd, kd->program, "cannot read allproc");
		return (-1);
	}
	acnt = kvm_proclist(kd, what, arg, p, bp, maxcnt);
	if (acnt < 0)
		return (acnt);

	if (KREAD(kd, a_deadproc, &p)) {
		_kvm_err(kd, kd->program, "cannot read deadproc");
		return (-1);
	}

	dcnt = kvm_proclist(kd, what, arg, p, bp, maxcnt - acnt);
	if (dcnt < 0)
		dcnt = 0;

	if (KREAD(kd, a_zombproc, &p)) {
		_kvm_err(kd, kd->program, "cannot read zombproc");
		return (-1);
	}
	zcnt = kvm_proclist(kd, what, arg, p, bp + acnt,
	    maxcnt - (acnt + dcnt));
	if (zcnt < 0)
		zcnt = 0;

	return (acnt + zcnt);
}

struct kinfo_proc *
kvm_getprocs(kd, op, arg, cnt)
	kvm_t *kd;
	int op, arg;
	int *cnt;
{
	size_t size;
	int mib[4], st, nprocs;

	if (kd->procbase != 0) {
		free((void *)kd->procbase);
		/*
		 * Clear this pointer in case this call fails.  Otherwise,
		 * kvm_close() will free it again.
		 */
		kd->procbase = 0;
	}
	if (ISALIVE(kd)) {
		size = 0;
		mib[0] = CTL_KERN;
		mib[1] = KERN_PROC;
		mib[2] = op;
		mib[3] = arg;
		st = sysctl(mib, 4, NULL, &size, NULL, 0);
		if (st == -1) {
			_kvm_syserr(kd, kd->program, "kvm_getprocs");
			return (0);
		}
		kd->procbase = (struct kinfo_proc *)_kvm_malloc(kd, size);
		if (kd->procbase == 0)
			return (0);
		st = sysctl(mib, 4, kd->procbase, &size, NULL, 0);
		if (st == -1) {
			_kvm_syserr(kd, kd->program, "kvm_getprocs");
			return (0);
		}
		if (size % sizeof(struct kinfo_proc) != 0) {
			_kvm_err(kd, kd->program,
				"proc size mismatch (%d total, %d chunks)",
				size, sizeof(struct kinfo_proc));
			return (0);
		}
		nprocs = size / sizeof(struct kinfo_proc);
	} else {
		struct nlist nl[5], *p;

		nl[0].n_name = "_nprocs";
		nl[1].n_name = "_allproc";
		nl[2].n_name = "_deadproc";
		nl[3].n_name = "_zombproc";
		nl[4].n_name = 0;

		if (kvm_nlist(kd, nl) != 0) {
			for (p = nl; p->n_type != 0; ++p)
				;
			_kvm_err(kd, kd->program,
				 "%s: no such symbol", p->n_name);
			return (0);
		}
		if (KREAD(kd, nl[0].n_value, &nprocs)) {
			_kvm_err(kd, kd->program, "can't read nprocs");
			return (0);
		}
		size = nprocs * sizeof(struct kinfo_proc);
		kd->procbase = (struct kinfo_proc *)_kvm_malloc(kd, size);
		if (kd->procbase == 0)
			return (0);

		nprocs = kvm_deadprocs(kd, op, arg, nl[1].n_value,
		    nl[2].n_value, nl[3].n_value, nprocs);
#ifdef notdef
		size = nprocs * sizeof(struct kinfo_proc);
		(void)realloc(kd->procbase, size);
#endif
	}
	*cnt = nprocs;
	return (kd->procbase);
}

void
_kvm_freeprocs(kd)
	kvm_t *kd;
{
	if (kd->procbase) {
		free(kd->procbase);
		kd->procbase = 0;
	}
}

void *
_kvm_realloc(kd, p, n)
	kvm_t *kd;
	void *p;
	size_t n;
{
	void *np = (void *)realloc(p, n);

	if (np == 0)
		_kvm_err(kd, kd->program, "out of memory");
	return (np);
}

#ifndef MAX
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#endif

/*
 * Read in an argument vector from the user address space of process p.
 * addr if the user-space base address of narg null-terminated contiguous
 * strings.  This is used to read in both the command arguments and
 * environment strings.  Read at most maxcnt characters of strings.
 */
static char **
kvm_argv(kd, p, addr, narg, maxcnt)
	kvm_t *kd;
	const struct proc *p;
	u_long addr;
	int narg;
	int maxcnt;
{
	char *np, *cp, *ep, *ap;
	u_long oaddr = (u_long)~0L;
	u_long len;
	size_t cc;
	char **argv;

	/*
	 * Check that there aren't an unreasonable number of agruments,
	 * and that the address is in user space.
	 */
	if (narg > ARG_MAX || addr < kd->min_uva || addr >= kd->max_uva)
		return (0);

	if (kd->argv == 0) {
		/*
		 * Try to avoid reallocs.
		 */
		kd->argc = MAX(narg + 1, 32);
		kd->argv = (char **)_kvm_malloc(kd, kd->argc *
						sizeof(*kd->argv));
		if (kd->argv == 0)
			return (0);
	} else if (narg + 1 > kd->argc) {
		kd->argc = MAX(2 * kd->argc, narg + 1);
		kd->argv = (char **)_kvm_realloc(kd, kd->argv, kd->argc *
						sizeof(*kd->argv));
		if (kd->argv == 0)
			return (0);
	}
	if (kd->argspc == 0) {
		kd->argspc = (char *)_kvm_malloc(kd, (size_t)kd->nbpg);
		if (kd->argspc == 0)
			return (0);
		kd->arglen = kd->nbpg;
	}
	if (kd->argbuf == 0) {
		kd->argbuf = (char *)_kvm_malloc(kd, (size_t)kd->nbpg);
		if (kd->argbuf == 0)
			return (0);
	}
	cc = sizeof(char *) * narg;
	if (kvm_uread(kd, p, addr, (void *)kd->argv, cc) != cc)
		return (0);
	ap = np = kd->argspc;
	argv = kd->argv;
	len = 0;
	/*
	 * Loop over pages, filling in the argument vector.
	 */
	while (argv < kd->argv + narg && *argv != 0) {
		addr = (u_long)*argv & ~(kd->nbpg - 1);
		if (addr != oaddr) {
			if (kvm_uread(kd, p, addr, kd->argbuf,
			    (size_t)kd->nbpg) != kd->nbpg)
				return (0);
			oaddr = addr;
		}
		addr = (u_long)*argv & (kd->nbpg - 1);
		cp = kd->argbuf + (size_t)addr;
		cc = kd->nbpg - (size_t)addr;
		if (maxcnt > 0 && cc > (size_t)(maxcnt - len))
			cc = (size_t)(maxcnt - len);
		ep = memchr(cp, '\0', cc);
		if (ep != 0)
			cc = ep - cp + 1;
		if (len + cc > kd->arglen) {
			int off;
			char **pp;
			char *op = kd->argspc;

			kd->arglen *= 2;
			kd->argspc = (char *)_kvm_realloc(kd, kd->argspc,
			    (size_t)kd->arglen);
			if (kd->argspc == 0)
				return (0);
			/*
			 * Adjust argv pointers in case realloc moved
			 * the string space.
			 */
			off = kd->argspc - op;
			for (pp = kd->argv; pp < argv; pp++)
				*pp += off;
			ap += off;
			np += off;
		}
		memcpy(np, cp, cc);
		np += cc;
		len += cc;
		if (ep != 0) {
			*argv++ = ap;
			ap = np;
		} else
			*argv += cc;
		if (maxcnt > 0 && len >= maxcnt) {
			/*
			 * We're stopping prematurely.  Terminate the
			 * current string.
			 */
			if (ep == 0) {
				*np = '\0';
				*argv++ = ap;
			}
			break;
		}
	}
	/* Make sure argv is terminated. */
	*argv = 0;
	return (kd->argv);
}

static void
ps_str_a(p, addr, n)
	struct ps_strings *p;
	u_long *addr;
	int *n;
{
	*addr = (u_long)p->ps_argvstr;
	*n = p->ps_nargvstr;
}

static void
ps_str_e(p, addr, n)
	struct ps_strings *p;
	u_long *addr;
	int *n;
{
	*addr = (u_long)p->ps_envstr;
	*n = p->ps_nenvstr;
}

/*
 * Determine if the proc indicated by p is still active.
 * This test is not 100% foolproof in theory, but chances of
 * being wrong are very low.
 */
static int
proc_verify(kd, kernp, p)
	kvm_t *kd;
	u_long kernp;
	const struct proc *p;
{
	struct proc kernproc;

	/*
	 * Just read in the whole proc.  It's not that big relative
	 * to the cost of the read system call.
	 */
	if (kvm_read(kd, kernp, (void *)&kernproc, sizeof(kernproc)) !=
	    sizeof(kernproc))
		return (0);
	return (p->p_pid == kernproc.p_pid &&
		(kernproc.p_stat != SZOMB || p->p_stat == SZOMB));
}

static char **
kvm_doargv(kd, kp, nchr, info)
	kvm_t *kd;
	const struct kinfo_proc *kp;
	int nchr;
	void (*info)(struct ps_strings *, u_long *, int *);
{
	const struct proc *p = &kp->kp_proc;
	char **ap;
	u_long addr;
	int cnt;
	struct ps_strings arginfo;

	/*
	 * Pointers are stored at the top of the user stack.
	 */
	if (p->p_stat == SZOMB)
		return (0);
	cnt = kvm_uread(kd, p, kd->usrstack - sizeof(arginfo),
	    (void *)&arginfo, sizeof(arginfo));
	if (cnt != sizeof(arginfo))
		return (0);

	(*info)(&arginfo, &addr, &cnt);
	if (cnt == 0)
		return (0);
	ap = kvm_argv(kd, p, addr, cnt, nchr);
	/*
	 * For live kernels, make sure this process didn't go away.
	 */
	if (ap != 0 && ISALIVE(kd) &&
	    !proc_verify(kd, (u_long)kp->kp_eproc.e_paddr, p))
		ap = 0;
	return (ap);
}

/*
 * Get the command args.  This code is now machine independent.
 */
char **
kvm_getargv(kd, kp, nchr)
	kvm_t *kd;
	const struct kinfo_proc *kp;
	int nchr;
{
	return (kvm_doargv(kd, kp, nchr, ps_str_a));
}

char **
kvm_getenvv(kd, kp, nchr)
	kvm_t *kd;
	const struct kinfo_proc *kp;
	int nchr;
{
	return (kvm_doargv(kd, kp, nchr, ps_str_e));
}

/*
 * Read from user space.  The user context is given by p.
 */
ssize_t
kvm_uread(kd, p, uva, buf, len)
	kvm_t *kd;
	const struct proc *p;
	u_long uva;
	char *buf;
	size_t len;
{
	char *cp;

	cp = buf;
	while (len > 0) {
		size_t cc;
		char *dp;
		u_long cnt;

		dp = _kvm_uread(kd, p, uva, &cnt);
		if (dp == 0) {
			_kvm_err(kd, 0, "invalid address (%x)", uva);
			return (0);
		}
		cc = (size_t)MIN(cnt, len);
		memcpy(cp, dp, cc);
		cp += cc;
		uva += cc;
		len -= cc;
	}
	return (ssize_t)(cp - buf);
}