More minor IPI work.

[dragonfly/vkernel-mp.git] / lib / libkvm / kvm_proc.c

/*-
 * 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.
 *
 * $FreeBSD: src/lib/libkvm/kvm_proc.c,v 1.25.2.3 2002/08/24 07:27:46 kris Exp $
 * $DragonFly: src/lib/libkvm/kvm_proc.c,v 1.15 2007/05/09 04:33:50 dillon Exp $
 *
 * @(#)kvm_proc.c       8.3 (Berkeley) 9/23/93
 */

/*
 * 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/user.h>   /* MUST BE FIRST */
#include <sys/conf.h>
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/exec.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/tty.h>
#include <sys/file.h>
#include <sys/jail.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <nlist.h>
#include <kvm.h>

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

#include <sys/sysctl.h>

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

#include "kvm_private.h"

#if used
static char *
kvm_readswap(kvm_t *kd, const struct proc *p, u_long va, u_long *cnt)
{
#if defined(__FreeBSD__) || defined(__DragonFly__)
        /* XXX Stubbed out, our vm system is differnet */
        _kvm_err(kd, kd->program, "kvm_readswap not implemented");
        return(0);
#endif
}
#endif

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


static struct kinfo_proc *
kinfo_resize_proc(kvm_t *kd, struct kinfo_proc *bp)
{
        if (bp < kd->procend)
                return bp;

        size_t pos = bp - kd->procend;
        size_t size = kd->procend - kd->procbase;

        if (size == 0)
                size = 8;
        else
                size *= 2;
        kd->procbase = _kvm_realloc(kd, kd->procbase, sizeof(*bp) * size);
        if (kd->procbase == NULL)
                return NULL;
        kd->procend = kd->procbase + size;
        bp = kd->procbase + pos;
        return bp;
}

/*
 * note: this function is also used by /usr/src/sys/kern/kern_kinfo.c as
 * compiled by userland.
 */
dev_t
dev2udev(cdev_t dev)
{
        if (dev == NULL)
                return NOUDEV;
        if ((dev->si_umajor & 0xffffff00) ||
            (dev->si_uminor & 0x0000ff00)) {
                return NOUDEV;
        }
        return((dev->si_umajor << 8) | dev->si_uminor);
}


/*
 * Read proc's from memory file into buffer bp, which has space to hold
 * at most maxcnt procs.
 */
static int
kvm_proclist(kvm_t *kd, int what, int arg, struct proc *p,
             struct kinfo_proc *bp)
{
        struct pgrp pgrp;
        struct pgrp tpgrp;
        struct session sess;
        struct tty tty;
        struct proc proc;
        struct ucred ucred;
        struct thread thread;
        struct proc pproc;
        struct cdev cdev;
        struct vmspace vmspace;
        struct prison prison;
        struct lwp lwp;
        uintptr_t lwppos;

        for (; 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_ucred, &ucred)) {
                        _kvm_err(kd, kd->program, "can't read ucred at %p",
                                 proc.p_ucred);
                        return (-1);
                }
                proc.p_ucred = &ucred;

                switch(what & ~KERN_PROC_FLAGMASK) {

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

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

                case KERN_PROC_RUID:
                        if (ucred.cr_ruid != (uid_t)arg)
                                continue;
                        break;
                }

                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);
                }
                proc.p_pgrp = &pgrp;
                if (proc.p_pptr) {
                  if (KREAD(kd, (u_long)proc.p_pptr, &pproc)) {
                        _kvm_err(kd, kd->program, "can't read pproc at %x",
                                 proc.p_pptr);
                        return (-1);
                  }
                  proc.p_pptr = &pproc;
                }
                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);
                }
                pgrp.pg_session = &sess;

                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);
                        }
                        sess.s_ttyp = &tty;
                        if (tty.t_dev && tty.t_dev != NULL) {
                                if (KREAD(kd, (u_long)tty.t_dev, &cdev))
                                        tty.t_dev = NULL;
                                else
                                        tty.t_dev = &cdev;
                        }
                        if (tty.t_pgrp != NULL) {
                                if (KREAD(kd, (u_long)tty.t_pgrp, &tpgrp)) {
                                        _kvm_err(kd, kd->program,
                                                 "can't read tpgrp at %x",
                                                tty.t_pgrp);
                                        return (-1);
                                }
                                tty.t_pgrp = &tpgrp;
                        }
                }

                if (KREAD(kd, (u_long)proc.p_vmspace, &vmspace)) {
                        _kvm_err(kd, kd->program, "can't read vmspace at %p",
                                 proc.p_vmspace);
                        return (-1);
                }
                proc.p_vmspace = &vmspace;

                if (ucred.cr_prison != NULL) {
                        if (KREAD(kd, (u_long)ucred.cr_prison, &prison)) {
                                _kvm_err(kd, kd->program, "can't read prison at %p",
                                         ucred.cr_prison);
                                return (-1);
                        }
                        ucred.cr_prison = &prison;
                }

                switch (what & ~KERN_PROC_FLAGMASK) {

                case KERN_PROC_PGRP:
                        if (proc.p_pgrp->pg_id != (pid_t)arg)
                                continue;
                        break;

                case KERN_PROC_TTY:
                        if ((proc.p_flag & P_CONTROLT) == 0 ||
                            dev2udev(proc.p_pgrp->pg_session->s_ttyp->t_dev)
                                        != (dev_t)arg)
                                continue;
                        break;
                }

                if ((bp = kinfo_resize_proc(kd, bp)) == NULL)
                        return (-1);
                fill_kinfo_proc(&proc, bp);
                bp->kp_paddr = (uintptr_t)p;

                lwppos = (uintptr_t)proc.p_lwps.lh_first;
                if (lwppos == 0)
                        bp++;           /* Just export the proc then */
                while (lwppos != 0) {
                        if (KREAD(kd, lwppos, &lwp)) {
                                _kvm_err(kd, kd->program, "can't read lwp at %p",
                                    lwppos);
                                return (-1);
                        }
                        if (p != lwp.lwp_proc) {
                                _kvm_err(kd, kd->program, "lwp has wrong parent");
                                return (-1);
                        }
                        lwp.lwp_proc = &proc;
                        if (KREAD(kd, (u_long)lwp.lwp_thread, &thread)) {
                                _kvm_err(kd, kd->program, "can't read thread at %x",
                                    lwp.lwp_thread);
                                return (-1);
                        }
                        lwp.lwp_thread = &thread;

                        if ((bp = kinfo_resize_proc(kd, bp)) == NULL)
                                return (-1);
                        fill_kinfo_proc(&proc, bp);
                        fill_kinfo_lwp(&lwp, &bp->kp_lwp);
                        bp->kp_paddr = (uintptr_t)p;
                        bp++;
                        if ((what & KERN_PROC_FLAG_LWP) == 0)
                                break;

                        lwppos = (uintptr_t)lwp.lwp_list.le_next;
                }
        }
        return (0);
}

/*
 * Build proc info array by reading in proc list from a crash dump.
 * We reallocate kd->procbase as necessary.
 */
static int
kvm_deadprocs(kvm_t *kd, int what, int arg, u_long a_allproc,
              u_long a_zombproc)
{
        struct kinfo_proc *bp = kd->procbase;
        int acnt, 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);
        if (acnt < 0)
                return (acnt);

        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);
        if (zcnt < 0)
                zcnt = 0;

        return (acnt + zcnt);
}

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

        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, op == KERN_PROC_ALL ? 3 : 4, NULL, &size, NULL, 0);
                if (st == -1) {
                        _kvm_syserr(kd, kd->program, "kvm_getprocs");
                        return (0);
                }
                do {
                        size += size / 10;
                        kd->procbase = (struct kinfo_proc *)
                            _kvm_realloc(kd, kd->procbase, size);
                        if (kd->procbase == 0)
                                return (0);
                        st = sysctl(mib, op == KERN_PROC_ALL ? 3 : 4,
                            kd->procbase, &size, NULL, 0);
                } while (st == -1 && errno == ENOMEM);
                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[4], *p;

                nl[0].n_name = "_nprocs";
                nl[1].n_name = "_allproc";
                nl[2].n_name = "_zombproc";
                nl[3].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);
                }
                nprocs = kvm_deadprocs(kd, op, arg, nl[1].n_value,
                                      nl[2].n_value);
#ifdef notdef
                size = nprocs * sizeof(struct kinfo_proc);
                (void)realloc(kd->procbase, size);
#endif
        }
        *cnt = nprocs;
        return (kd->procbase);
}

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

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

        if (np == 0) {
                free(p);
                _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 pid.
 * 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(kvm_t *kd, pid_t pid, u_long addr, int narg, int maxcnt)
{
        char *np, *cp, *ep, *ap;
        u_long oaddr = -1;
        int len, cc;
        char **argv;

        /*
         * Check that there aren't an unreasonable number of agruments,
         * and that the address is in user space.
         */
        if (narg > 512 || 
            addr < VM_MIN_USER_ADDRESS || addr >= VM_MAX_USER_ADDRESS) {
                return (0);
        }

        /*
         * kd->argv : work space for fetching the strings from the target 
         *            process's space, and is converted for returning to caller
         */
        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);
        }
        /*
         * kd->argspc : returned to user, this is where the kd->argv
         *              arrays are left pointing to the collected strings.
         */
        if (kd->argspc == 0) {
                kd->argspc = (char *)_kvm_malloc(kd, PAGE_SIZE);
                if (kd->argspc == 0)
                        return (0);
                kd->arglen = PAGE_SIZE;
        }
        /*
         * kd->argbuf : used to pull in pages from the target process.
         *              the strings are copied out of here.
         */
        if (kd->argbuf == 0) {
                kd->argbuf = (char *)_kvm_malloc(kd, PAGE_SIZE);
                if (kd->argbuf == 0)
                        return (0);
        }

        /* Pull in the target process'es argv vector */
        cc = sizeof(char *) * narg;
        if (kvm_uread(kd, pid, addr, (char *)kd->argv, cc) != cc)
                return (0);
        /*
         * ap : saved start address of string we're working on in kd->argspc
         * np : pointer to next place to write in kd->argspc
         * len: length of data in kd->argspc
         * argv: pointer to the argv vector that we are hunting around the
         *       target process space for, and converting to addresses in
         *       our address space (kd->argspc).
         */
        ap = np = kd->argspc;
        argv = kd->argv;
        len = 0;
        /*
         * Loop over pages, filling in the argument vector.
         * Note that the argv strings could be pointing *anywhere* in
         * the user address space and are no longer contiguous.
         * Note that *argv is modified when we are going to fetch a string
         * that crosses a page boundary.  We copy the next part of the string
         * into to "np" and eventually convert the pointer.
         */
        while (argv < kd->argv + narg && *argv != 0) {

                /* get the address that the current argv string is on */
                addr = (u_long)*argv & ~(PAGE_SIZE - 1);

                /* is it the same page as the last one? */
                if (addr != oaddr) {
                        if (kvm_uread(kd, pid, addr, kd->argbuf, PAGE_SIZE) !=
                            PAGE_SIZE)
                                return (0);
                        oaddr = addr;
                }

                /* offset within the page... kd->argbuf */
                addr = (u_long)*argv & (PAGE_SIZE - 1);

                /* cp = start of string, cc = count of chars in this chunk */
                cp = kd->argbuf + addr;
                cc = PAGE_SIZE - addr;

                /* dont get more than asked for by user process */
                if (maxcnt > 0 && cc > maxcnt - len)
                        cc = maxcnt - len;

                /* pointer to end of string if we found it in this page */
                ep = memchr(cp, '\0', cc);
                if (ep != 0)
                        cc = ep - cp + 1;
                /*
                 * at this point, cc is the count of the chars that we are
                 * going to retrieve this time. we may or may not have found
                 * the end of it.  (ep points to the null if the end is known)
                 */

                /* will we exceed the malloc/realloced buffer? */
                if (len + cc > kd->arglen) {
                        int off;
                        char **pp;
                        char *op = kd->argspc;

                        kd->arglen *= 2;
                        kd->argspc = (char *)_kvm_realloc(kd, kd->argspc,
                                                          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;
                }
                /* np = where to put the next part of the string in kd->argspc*/
                /* np is kinda redundant.. could use "kd->argspc + len" */
                memcpy(np, cp, cc);
                np += cc;       /* inc counters */
                len += cc;

                /*
                 * if end of string found, set the *argv pointer to the
                 * saved beginning of string, and advance. argv points to
                 * somewhere in kd->argv..  This is initially relative
                 * to the target process, but when we close it off, we set
                 * it to point in our address space.
                 */
                if (ep != 0) {
                        *argv++ = ap;
                        ap = np;
                } else {
                        /* update the address relative to the target process */
                        *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(struct ps_strings *p, u_long *addr, int *n)
{
        *addr = (u_long)p->ps_argvstr;
        *n = p->ps_nargvstr;
}

static void
ps_str_e(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(kvm_t *kd, const struct kinfo_proc *p)
{
        struct kinfo_proc kp;
        int mib[4];
        size_t len;
        int error;

        mib[0] = CTL_KERN;
        mib[1] = KERN_PROC;
        mib[2] = KERN_PROC_PID;
        mib[3] = p->kp_pid;

        len = sizeof(kp);
        error = sysctl(mib, 4, &kp, &len, NULL, 0);
        if (error)
                return (0);

        error = (p->kp_pid == kp.kp_pid &&
            (kp.kp_stat != SZOMB || p->kp_stat == SZOMB));
        return (error);
}

static char **
kvm_doargv(kvm_t *kd, const struct kinfo_proc *kp, int nchr,
           void (*info)(struct ps_strings *, u_long *, int *))
{
        char **ap;
        u_long addr;
        int cnt;
        static struct ps_strings arginfo;
        static u_long ps_strings;
        size_t len;

        if (ps_strings == NULL) {
                len = sizeof(ps_strings);
                if (sysctlbyname("kern.ps_strings", &ps_strings, &len, NULL,
                    0) == -1)
                        ps_strings = PS_STRINGS;
        }

        /*
         * Pointers are stored at the top of the user stack.
         */
        if (kp->kp_stat == SZOMB ||
            kvm_uread(kd, kp->kp_pid, ps_strings, (char *)&arginfo,
                      sizeof(arginfo)) != sizeof(arginfo))
                return (0);

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

/*
 * Get the command args.  This code is now machine independent.
 */
char **
kvm_getargv(kvm_t *kd, const struct kinfo_proc *kp, int nchr)
{
        int oid[4];
        int i;
        size_t bufsz;
        static unsigned long buflen;
        static char *buf, *p;
        static char **bufp;
        static int argc;

        if (!ISALIVE(kd)) {
                _kvm_err(kd, kd->program,
                    "cannot read user space from dead kernel");
                return (0);
        }

        if (!buflen) {
                bufsz = sizeof(buflen);
                i = sysctlbyname("kern.ps_arg_cache_limit", 
                    &buflen, &bufsz, NULL, 0);
                if (i == -1) {
                        buflen = 0;
                } else {
                        buf = malloc(buflen);
                        if (buf == NULL)
                                buflen = 0;
                        argc = 32;
                        bufp = malloc(sizeof(char *) * argc);
                }
        }
        if (buf != NULL) {
                oid[0] = CTL_KERN;
                oid[1] = KERN_PROC;
                oid[2] = KERN_PROC_ARGS;
                oid[3] = kp->kp_pid;
                bufsz = buflen;
                i = sysctl(oid, 4, buf, &bufsz, 0, 0);
                if (i == 0 && bufsz > 0) {
                        i = 0;
                        p = buf;
                        do {
                                bufp[i++] = p;
                                p += strlen(p) + 1;
                                if (i >= argc) {
                                        argc += argc;
                                        bufp = realloc(bufp,
                                            sizeof(char *) * argc);
                                }
                        } while (p < buf + bufsz);
                        bufp[i++] = 0;
                        return (bufp);
                }
        }
        if (kp->kp_flags & P_SYSTEM)
                return (NULL);
        return (kvm_doargv(kd, kp, nchr, ps_str_a));
}

char **
kvm_getenvv(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 pid.
 */
ssize_t
kvm_uread(kvm_t *kd, pid_t pid, u_long uva, char *buf, size_t len)
{
        char *cp;
        char procfile[MAXPATHLEN];
        ssize_t amount;
        int fd;

        if (!ISALIVE(kd)) {
                _kvm_err(kd, kd->program,
                    "cannot read user space from dead kernel");
                return (0);
        }

        sprintf(procfile, "/proc/%d/mem", pid);
        fd = open(procfile, O_RDONLY, 0);
        if (fd < 0) {
                _kvm_err(kd, kd->program, "cannot open %s", procfile);
                close(fd);
                return (0);
        }

        cp = buf;
        while (len > 0) {
                errno = 0;
                if (lseek(fd, (off_t)uva, 0) == -1 && errno != 0) {
                        _kvm_err(kd, kd->program, "invalid address (%x) in %s",
                            uva, procfile);
                        break;
                }
                amount = read(fd, cp, len);
                if (amount < 0) {
                        _kvm_syserr(kd, kd->program, "error reading %s",
                            procfile);
                        break;
                }
                if (amount == 0) {
                        _kvm_err(kd, kd->program, "EOF reading %s", procfile);
                        break;
                }
                cp += amount;
                uva += amount;
                len -= amount;
        }

        close(fd);
        return ((ssize_t)(cp - buf));
}