3124 Remove any existing references to utmp, use utmpx instead

[unleashed.git] / usr / src / cmd / utmpd / utmpd.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*      Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
/*        All Rights Reserved   */

/*
 * Portions of such source code were derived from Berkeley 4.3 BSD
 * under license from the Regents of the University of California.
 */

/*
 * utmpd        - utmp daemon
 *
 *              This program receives requests from  pututxline(3)
 *              via a named pipe to watch the process to make sure it cleans up
 *              its utmpx entry on termination.
 *              The program keeps a list of procs
 *              and uses poll() on their /proc files to detect termination.
 *              Also the  program periodically scans the /etc/utmpx file for
 *              processes that aren't in the table so they can be watched.
 *
 *              If utmpd doesn't hear back over the pipe from pututline(3) that
 *              the process has removed its entry it cleans the entry when the
 *              the process terminates.
 *              The AT&T Copyright above is there since we borrowed the pipe
 *              mechanism from init(1m).
 */


#include        <sys/types.h>
#include        <signal.h>
#include        <stdio.h>
#include        <stdio_ext.h>
#include        <unistd.h>
#include        <utmpx.h>
#include        <errno.h>
#include        <termio.h>
#include        <sys/termios.h>
#include        <sys/tty.h>
#include        <ctype.h>
#include        <sys/stat.h>
#include        <sys/statvfs.h>
#include        <fcntl.h>
#include        <time.h>
#include        <sys/stropts.h>
#include        <wait.h>
#include        <syslog.h>
#include        <stdlib.h>
#include        <string.h>
#include        <poll.h>
#include        <deflt.h>
#include        <procfs.h>
#include        <sys/resource.h>

#define dprintf(x)      if (Debug) (void) printf x

/*
 * Memory allocation keyed off MAX_FDS
 */
#define MAX_FDS         4064    /* Maximum # file descriptors */
#define EXTRA_MARGIN    32      /* Allocate this many more FDS over Max_Fds */
/*
 * MAX_POLLNV & RESETS - paranoia to cover an error case that might not exist
 */
#define MAX_POLL_ERRS   1024    /* Count of bad errors */
#define MAX_RESETS      1024    /* Maximum times to reload tables */
#define POLL_TIMEOUT    300     /* Default Timeout for poll() in seconds */
#define CLEANIT         1       /* Used by rem_pid() */
#define DONT_CLEAN      0       /* Used by rem_pid() */
#define UTMP_DEFAULT    "/etc/default/utmpd"
#define WARN_TIME       3600    /* seconds between utmp checks */
#define WTMPX_UFREQ     60      /* seconds between updating WTMPX's atime */


/*
 * The pidrec structure describes the data shipped down the pipe to
 * us from the pututxline() library in
 * lib/libc/port/gen/getutx.c
 */

/*
 * pd_type's
 */
#define ADDPID  1
#define REMPID  2

struct  pidrec {
        int     pd_type;                /* Command type */
        pid_t   pd_pid;                 /* pid to add or remove */
};


/*
 * Since this program uses poll(2) and poll takes an array of file descriptors
 * as an argument we maintain our data in tables.
 * One table is the file descriptor array for poll, another parallel
 * array is a table which contains the process ID of the corresponding
 * open fd.  These tables are kept sorted by process ID for quick lookups.
 */

struct  pidentry {
        pid_t   pl_pid;                 /* pid to watch for */
        int     pl_status;              /* Exit status of proc */
};

static struct pidentry *pidtable = NULL;

static pollfd_t *fdtable = NULL;

static int      pidcnt = 0;             /* Number of procs being watched */
static char     *prog_name;             /* To save the invocation name away */
static char     *UTMPPIPE_DIR = "/var/run";
static char     *UTMPPIPE = "/var/run/utmppipe";
static int      Pfd = -1;               /* File descriptor of named pipe */
static int      Poll_timeout = POLL_TIMEOUT;
static int      WTMPXfd = -1;           /* File descriptor of WTMPX_FILE */
static int      WTMPX_ufreq = WTMPX_UFREQ;
static int      Debug = 0;              /* Set by command line argument */
static int      Max_fds         = MAX_FDS;

/*
 * This program has three main components plus utilities and debug routines
 *      Receiver - receives the process ID or process for us to watch.
 *                 (Uses a named pipe to get messages)
 *      Watcher  - Use poll(2) to watch for processes to die so they
 *                 can be cleaned up (get marked as DEAD_PROCESS)
 *      Scanner  - periodically scans the utmpx file for stale entries
 *                 or live entries that we don't know about.
 */

static int wait_for_pids();     /* Watcher - uses poll */
static void scan_utmps();       /* Scanner, reads utmpx file */
static void drain_pipe();       /* Receiver - reads mesgs over UTMPPIPE */
static void setup_pipe();       /* For setting up receiver */

static void add_pid();          /* Adds a process to the table */
static void rem_pid();          /* Removes a process from the table */
static int find_pid();          /* Finds a process in the table */
static int proc_to_fd();        /* Takes a pid and returns an fd for its proc */
static void load_tables();      /* Loads up the tables the first time around */
static int pidcmp();            /* For sorting pids */

static void clean_entry();      /* Removes entry from our table and calls ... */
static void clean_utmpx_ent();  /* Cleans a utmpx entry */

static void fatal() __NORETURN; /* Prints error message and calls exit */
static void nonfatal();         /* Prints error message */
static void print_tables();     /* Prints out internal tables for Debug */
static int proc_is_alive(pid_t pid);    /* Check if a process is alive */
static void warn_utmp(void);

/*
 * main()  - Main does basic setup and calls wait_for_pids() to do the work
 */

int
main(argc, argv)
        char **argv;
{
        char *defp;
        struct rlimit rlim;
        int i;
        time_t curtime, now;

        prog_name = argv[0];                    /* Save invocation name */

        if (getuid() != 0)  {
                (void) fprintf(stderr,
                        "You must be root to run this program\n");
                fatal("You must be root to run this program");
        }

        if (argc > 1) {
                if ((argc == 2 && (int)strlen(argv[1]) >= 2) &&
                    (argv[1][0] == '-' && argv[1][1] == 'd')) {
                        Debug = 1;
                } else {
                        (void) fprintf(stderr,
                                "%s: Wrong number of arguments\n", prog_name);
                        (void) fprintf(stderr,
                                "Usage: %s [-debug]\n", prog_name);
                        exit(2);
                }
        }

        /*
         * Read defaults file for poll timeout
         */
        if (defopen(UTMP_DEFAULT) == 0) {
                if ((defp = defread("SCAN_PERIOD=")) != NULL) {
                        Poll_timeout = atol(defp);
                        dprintf(("Poll timeout set to %d\n", Poll_timeout));
                }

                if ((defp = defread("WTMPX_UPDATE_FREQ=")) != NULL) {
                        WTMPX_ufreq = atol(defp);
                        dprintf(("WTMPX update frequency set to %d\n",
                            WTMPX_ufreq));
                }

                /*
                 * Paranoia - if polling on large number of FDs is expensive /
                 * buggy the number can be set lower in the field.
                 */
                if ((defp = defread("MAX_FDS=")) != NULL) {
                        Max_fds = atol(defp);
                        dprintf(("Max_fds set to %d\n", Max_fds));
                }
                (void) defopen((char *)NULL);
        }

        if (Debug == 0) {
                /*
                 * Daemonize ourselves
                 */
                if (fork()) {
                        exit(0);
                }
                (void) close(0);
                (void) close(1);
                (void) close(2);
                /*
                 * We open these to avoid accidentally writing to a proc file
                 */
                (void) open("/dev/null", O_RDONLY);
                (void) open("/dev/null", O_WRONLY);
                (void) open("/dev/null", O_WRONLY);
                (void) setsid();                /* release process from tty */
        }

        openlog(prog_name, LOG_PID, LOG_DAEMON);        /* For error messages */
        warn_utmp();    /* check to see if utmp came back by accident */

        /*
         * Allocate the pidtable and fdtable.  An earlier version did
         * this as we go, but this is simpler.
         */
        if ((pidtable = malloc(Max_fds * sizeof (struct pidentry))) == NULL)
                fatal("Malloc failed");
        if ((fdtable = malloc(Max_fds * sizeof (pollfd_t))) == NULL)
                fatal("Malloc failed");

        /*
         * Up the limit on FDs
         */
        if (getrlimit(RLIMIT_NOFILE, &rlim) == 0) {
                rlim.rlim_cur = Max_fds + EXTRA_MARGIN + 1;
                rlim.rlim_max = Max_fds + EXTRA_MARGIN + 1;
                if (setrlimit(RLIMIT_NOFILE, &rlim) != 0) {
                        fatal("Out of File Descriptors");
                }
        } else
                fatal("getrlimit returned failure");

        (void) enable_extended_FILE_stdio(-1, -1);

        if ((WTMPXfd = open(WTMPX_FILE, O_RDONLY)) < 0)
                nonfatal("WARNING: unable to open " WTMPX_FILE "for update.");

        /*
         * Loop here scanning the utmpx file and waiting for processes
         * to terminate.  Most of the activity is directed out of wait_for_pids.
         * If wait_for_pids fails we reload the table and try again.
         */

        curtime = time(NULL);
        dprintf(("utmp warning timer set to %d seconds\n", WARN_TIME));

        for (i = 0; i < MAX_RESETS; i++) {
                load_tables();
                while (wait_for_pids() == 1) {
                        now = time(NULL);
                        if ((now - curtime) >= WARN_TIME) {
                                dprintf(("utmp warning timer expired\n"));
                                warn_utmp();
                                curtime = now;
                        }
                }
        }

        (void) close(WTMPXfd);

        /*
         * We only get here if we had a bunch of resets - so give up
         */
        fatal("Too many resets, giving up");
        return (1);
}

/*
 * load_tables()        - Designed to be called repeatedly if we need to
 *                        restart things.  Zeros the pidcount, and loads
 *                        the tables by scanning utmpx
 */

static void
load_tables()
{
        int i;

        dprintf(("Load tables\n"));

        /*
         * Close any open files.
         */
        for (i = 0; i < pidcnt; i++)
                (void) close(fdtable[i].fd);

        pidcnt = 0;
        Pfd = -1;
        setup_pipe();           /* Setup the pipe to receive messages */
        scan_utmps();           /* Read in USER procs entries to watch */
}


/*
 *                      *** The Watcher ***
 *
 * Wait_for_pids        - wait for the termination of a process in the table.
 *                        Returns 1 on normal exist, 0 on failure.
 */

static int
wait_for_pids()
{
        register struct pollfd *pfd;
        register int i;
        pid_t pid;
        int ret_val;
        int timeout;
        static time_t last_timeout  = 0;
        static int bad_error  = 0;      /* Count of POLL errors */

        /*
         * First time through we initialize last_timeout to now.
         */
        if (last_timeout == 0)
                last_timeout = time(NULL);

        /*
         * Recalculate timeout - checking to see if time expired.
         */

        if ((timeout = Poll_timeout - (time(NULL) - last_timeout)) <= 0) {
                timeout = Poll_timeout;
                last_timeout = time(NULL);
                scan_utmps();
        }

        fdtable[0].events = POLLRDNORM;

        for (i = 0; i < (timeout / WTMPX_ufreq); i++) {

                /*
                 * Loop here while getting EAGAIN
                 */

                while ((ret_val = poll(fdtable, pidcnt, WTMPX_ufreq*1000)) < 0)
                        if (errno == EAGAIN)
                                (void) sleep(2);
                        else
                                fatal("poll");
                /*
                 * The results of pread(2) are discarded; we only want
                 * to update the access time of WTMPX_FILE.
                 * Periodically touching WTMPX helps determine when the
                 * OS became unavailable when the OS boots again .
                 * See PSARC 2004/462 for more information.
                 */

                (void) pread(WTMPXfd, (void *)&pid, sizeof (pid), 0);

                if (ret_val)            /* file descriptor(s) need attention */
                        break;
        }

        /*
         * If ret_val == 0 the poll timed out - reset last_time and
         * call scan_utmps
         */
        if (ret_val == 0) {
                last_timeout = time(NULL);
                scan_utmps();
                return (1);
        }

        /*
         * Check the pipe file descriptor
         */
        if (fdtable[0].revents & POLLRDNORM) {
                drain_pipe();
                fdtable[0].revents = 0;
                ret_val--;
        }

        (void) sleep(5);        /* Give parents time to cleanup children */

        /*
         * We got here because the status of one of the pids that
         * we are polling on has changed, so search the table looking
         * for the entry.
         *
         * The table is scanned backwards so that entries can be removed
         * while we go since the table is compacted from high down to low
         */
        for (i = pidcnt - 1; i > 0; i--) {
                /*
                 * Break out of the loop if we've processed all the entries.
                 */
                if (ret_val == 0)
                        break;

                pfd = &fdtable[i];

                if (pfd->fd < 0) {
                        rem_pid((pid_t)0, i, DONT_CLEAN);
                        continue;
                }
                /*
                 * POLLHUP      - Process terminated
                 */
                if (pfd->revents & POLLHUP) {
                        psinfo_t psinfo;

                        if (pread(pfd->fd, &psinfo, sizeof (psinfo), (off_t)0)
                            != sizeof (psinfo)) {
                                dprintf(("! %d: terminated, status 0x%.4x\n", \
                                    (int)pidtable[i].pl_pid, psinfo.pr_wstat));
                                pidtable[i].pl_status = psinfo.pr_wstat;

                        } else {
                                dprintf(("! %d: terminated\n", \
                                    (int)pidtable[i].pl_pid));
                                pidtable[i].pl_status = 0;
                        }
                        /*
                         * PID gets removed when terminated only
                         */
                        rem_pid((pid_t)0, i, CLEANIT);
                        ret_val--;
                        continue;
                }
                /*
                 * POLLNVAL and POLLERR
                 *      These error's shouldn't occurr but until their fixed
                 *      we perform some simple error recovery.
                 */
                if (pfd->revents & (POLLNVAL|POLLERR)) {
                        dprintf(("Poll Err = %d pid = %d i = %d\n", \
                            pfd->revents, (int)pidtable[i].pl_pid, i));

                        pid = pidtable[i].pl_pid; /* Save pid for below */
                        /*
                         * If its POLLNVAL we just remove the process for
                         * now, it will get picked up in the next scan.
                         * POLLERR pids get re-added after being deleted.
                         */
                        if (pfd->revents & POLLNVAL) {
                                rem_pid((pid_t)0, i, DONT_CLEAN);
                        } else {                        /* Else... POLLERR */
                                rem_pid((pid_t)0, i, DONT_CLEAN);
                                add_pid(pid);
                        }

                        if (bad_error++ > MAX_POLL_ERRS) {
                                bad_error = 0;
                                return (0);     /* 0 Indicates severe error */
                        }
                        ret_val--;
                        continue;
                }

                /*
                 * No more bits should be set in revents but check anyway
                 */
                if (pfd->revents != 0) {
                        dprintf(("%d: unknown err %d\n", \
                            (int)pidtable[i].pl_pid, pfd->revents));

                        rem_pid((pid_t)0, i, DONT_CLEAN);
                        ret_val--;

                        if (bad_error++ > MAX_POLL_ERRS) {
                                bad_error = 0;
                                return (0);     /* 0 Indicates severe error */
                        }
                        return (1);
                }
        }
        return (1);                     /* 1 Indicates Everything okay */
}

/*
 *              *** The Scanner ***
 *
 * scan_utmps()         - Scan the utmpx file.
 *                        For each USER_PROCESS check
 *                        if its alive or dead.  If alive and its not in
 *                        our table to be watched, put it there.  If its
 *                        dead, remove it from our table and clean it up.
 */

static void
scan_utmps()
{
        struct  utmpx   *utmpx;
        int     i;

        dprintf(("Scan utmps\n"));
        /*
         * Scan utmpx.
         */
        setutxent();
        while ((utmpx = getutxent()) != NULL) {
                if (utmpx->ut_type == USER_PROCESS) {
                        /*
                         * Is the process alive?
                         */
                        if (proc_is_alive(utmpx->ut_pid)) {
                                /*
                                 * Yes, the process is alive, so add it if we
                                 * don't have it in our table.
                                 */
                                if (find_pid(utmpx->ut_pid, &i) == 0)
                                        add_pid(utmpx->ut_pid); /* No, add it */
                        } else {
                                /*
                                 * No, the process is dead, so remove it if its
                                 * in our table, otherwise just clean it.
                                 */
                                if (find_pid(utmpx->ut_pid, &i) == 1)
                                        rem_pid(utmpx->ut_pid, i, CLEANIT);
                                else
                                        clean_utmpx_ent(utmpx);
                        }
                }
        }
        /*
         * Close it to flush the buffer.
         */
        endutxent();
}


/*
 *                      *** Receiver Routines ***
 */

/*
 * setup_pipe   - Set up the pipe to read pids over
 */

static void
setup_pipe()
{

        struct statvfs statvfs_buf;
        /*
         * This code & comments swiped from init and left stock since it works
         */

        if (Pfd < 0) {
                if ((statvfs(UTMPPIPE_DIR, &statvfs_buf) == 0) &&
                    ((statvfs_buf.f_flag & ST_RDONLY) == 0)) {
                        (void) unlink(UTMPPIPE);
                        (void) mknod(UTMPPIPE, S_IFIFO | 0600, 0);
                }
                Pfd = open(UTMPPIPE, O_RDWR | O_NDELAY);
        }
        if (Pfd < 0)
                nonfatal(UTMPPIPE);
        /*
         * This code from init modified to be poll based instead of SIGPOLL,
         * signal based.
         */

        if (Pfd >= 0) {
                /*
                 * Read pipe in message discard mode.  When read reads a
                 * pidrec size record, the remainder of the message will
                 * be discarded.  Though there shouldn't be any it will
                 * help resynch if someone else wrote some garbage.
                 */
                (void) ioctl(Pfd, I_SRDOPT, RMSGD);
        }

        /*
         * My code.  We use slot 0 in the table to hold the fd of the pipe
         */
        add_pid(0);                     /* Proc 0 guaranteed to get slot 0 */
        fdtable[0].fd = Pfd;            /* Pfd could be -1, should be okay */
        fdtable[0].events = POLLRDNORM;
}

/*
 * drain_pipe()         - The receiver routine that reads the pipe
 */

static void
drain_pipe()
{
        struct pidrec prec;
        register struct pidrec *p = &prec;
        int bytes_read;
        int i;

        for (;;) {
                /*
                 * Important Note: Either read will really fail (in which case
                 * return is all we can do) or will get EAGAIN (Pfd was opened
                 * O_NDELAY), in which case we also want to return.
                 */

                if ((bytes_read = read(Pfd, p, sizeof (struct pidrec))) !=
                    sizeof (struct pidrec))  {
                        /*
                         * Something went wrong reading, so read until pipe
                         * is empty
                         */
                        if (bytes_read > 0)
                                while (read(Pfd, p, sizeof (struct pidrec)) > 0)
                                        ;
                        return;
                }

                dprintf(("drain_pipe: Recd command %d, pid %d\n",
                    p->pd_type, (int)p->pd_pid));
                switch (p->pd_type) {
                case ADDPID:
                        /*
                         * Check if we already have the process, adding it
                         * if we don't.
                         */
                        if (find_pid(p->pd_pid, &i) == 0)
                                add_pid(p->pd_pid);
                        break;

                case REMPID:
                        rem_pid(p->pd_pid, -1, DONT_CLEAN);
                        break;
                default:
                        nonfatal("Bad message on utmppipe\n");
                                break;
                }
        }
}


/*
 *              *** Utilities for add and removing entries in the tables ***
 */

/*
 * add_pid      - add a pid to the fd table and the pidtable.
 *                these tables are sorted tables for quick lookups.
 *
 */
static void
add_pid(pid)
        pid_t pid;
{
        int fd = 0;
        int i = 0, move_amt;
        int j;
        static int first_time = 1;

        /*
         * Check to see if the pid is already in our table, or being passed
         * pid zero.
         */
        if (pidcnt != 0 && (find_pid(pid, &j) == 1 || pid == 0))
                return;

        if (pidcnt >= Max_fds) {
                if (first_time == 1) {
                        /*
                         * Print this error only once
                         */
                        nonfatal("File Descriptor limit exceeded");
                        first_time = 0;
                }
                return;
        }
        /*
         * Open the /proc file checking if there's still a valid proc file.
         */
        if (pid != 0 && (fd = proc_to_fd(pid)) == -1) {
                /*
                 * No so the process died before we got to watch for him
                 */
                return;
        }

        /*
         * We only do this code if we're not putting in the first element
         * Which we know will be for proc zero which is used by setup_pipe
         * for its pipe fd.
         */
        if (pidcnt != 0) {
                for (i = 0; i < pidcnt; i++) {
                        if (pid <= pidtable[i].pl_pid)
                                break;
                }

                /*
                 * Handle the case where we're not sticking our entry on the
                 * the end, or overwriting an existing entry.
                 */
                if (i != pidcnt && pid != pidtable[i].pl_pid) {

                        move_amt = pidcnt - i;
                        /*
                         * Move table down
                         */
                        if (move_amt != 0) {
                                (void) memmove(&pidtable[i+1], &pidtable[i],
                                        move_amt * sizeof (struct pidentry));
                                (void) memmove(&fdtable[i+1], &fdtable[i],
                                        move_amt * sizeof (pollfd_t));
                        }
                }
        }

        /*
         * Fill in the events field for poll and copy the entry into the array
         */
        fdtable[i].events = 0;
        fdtable[i].revents = 0;
        fdtable[i].fd = fd;

        /*
         * Likewise, setup pid field and pointer (index) to the fdtable entry
         */
        pidtable[i].pl_pid = pid;

        pidcnt++;                       /* Bump the pid count */
        dprintf(("  add_pid: pid = %d fd = %d index = %d pidcnt = %d\n",
                (int)pid, fd, i, pidcnt));
}


/*
 * rem_pid      - Remove an entry from the table and check to see if its
 *                not in the utmpx file.
 *                If i != -1 don't look up the pid, use i as index
 */

static void
rem_pid(pid, i, clean_it)
        pid_t pid;      /* Pid of process to clean or 0 if we don't know it */
        int i;          /* Index into table or -1 if we need to look it up */
        int clean_it;   /* Clean the entry, or just remove from table? */
{
        int move_amt;

        dprintf(("  rem_pid: pid = %d i = %d", (int)pid, i));

        /*
         * Don't allow slot 0 in the table to be removed - utmppipe fd
         */
        if ((i == -1 && pid == 0) || (i == 0))  {
                dprintf((" - attempted to remove proc 0\n"));
                return;
        }

        if (i != -1 || find_pid(pid, &i) == 1) {        /* Found the entry */
                (void) close(fdtable[i].fd);    /* We're done with the fd */

                dprintf((" fd = %d\n", fdtable[i].fd));

                if (clean_it == CLEANIT)
                        clean_entry(i);

                move_amt = (pidcnt - i) - 1;
                /*
                 * Remove entries from the tables.
                 */
                (void) memmove(&pidtable[i], &pidtable[i+1],
                        move_amt * sizeof (struct pidentry));

                (void) memmove(&fdtable[i], &fdtable[i+1],
                        move_amt * sizeof (pollfd_t));

                /*
                 * decrement the pid count - one less pid to worry about
                 */
                pidcnt--;
        }
        if (i == -1)
                dprintf((" - entry not found \n"));
}


/*
 * find_pid     - Returns an index into the pidtable of the specifed pid,
 *                else -1 if not found
 */

static int
find_pid(pid, i)
        pid_t pid;
        int *i;
{
        struct pidentry pe;
        struct pidentry *p;

        pe.pl_pid = pid;
        p = bsearch(&pe, pidtable, pidcnt, sizeof (struct pidentry), pidcmp);

        if (p == NULL)
                return (0);
        else {
                *i = p - (struct pidentry *)pidtable;
                return (1);
        }
}


/*
 * Pidcmp - Used by besearch for sorting and finding  process IDs.
 */

static int
pidcmp(a, b)
        struct pidentry *a, *b;
{
        if (b == NULL || a == NULL)
                return (0);
        return (a->pl_pid - b->pl_pid);
}


/*
 * proc_to_fd   - Take a process ID and return an open file descriptor to the
 *                /proc file for the specified process.
 */
static int
proc_to_fd(pid)
        pid_t pid;
{
        char procname[64];
        int fd, dfd;

        (void) sprintf(procname, "/proc/%d/psinfo", (int)pid);

        if ((fd = open(procname, O_RDONLY)) >= 0) {
                /*
                 * dup the fd above the low order values to assure
                 * stdio works for other fds - paranoia.
                 */
                if (fd < EXTRA_MARGIN) {
                        dfd = fcntl(fd, F_DUPFD, EXTRA_MARGIN);
                        if (dfd > 0) {
                                (void) close(fd);
                                fd = dfd;
                        }
                }
                /*
                 * More paranoia - set the close on exec flag
                 */
                (void) fcntl(fd, F_SETFD, 1);
                return (fd);
        }
        if (errno == ENOENT)
                return (-1);

        if (errno == EMFILE) {
                /*
                 * This is fatal, since libc won't be able to allocate
                 * any fds for the pututxline() routines
                 */
                fatal("Out of file descriptors");
        }
        fatal(procname);                /* Only get here on error */
        return (-1);
}


/*
 *              *** Utmpx Cleaning Utilities ***
 */

/*
 * Clean_entry  - Cleans the specified entry - where i is an index
 *                into the pid_table.
 */
static void
clean_entry(i)
        int i;
{
        struct utmpx *u;

        if (pidcnt == 0)
                return;

        dprintf(("    Cleaning %d\n", (int)pidtable[i].pl_pid));

        /*
         * Double check if the process is dead.
         */
        if (proc_is_alive(pidtable[i].pl_pid)) {
                dprintf(("      Bad attempt to clean %d\n", \
                        (int)pidtable[i].pl_pid));
                return;
        }

        /*
         * Find the entry that corresponds to this pid.
         * Do nothing if entry not found in utmpx file.
         */
        setutxent();
        while ((u = getutxent()) != NULL) {
                if (u->ut_pid == pidtable[i].pl_pid) {
                        if (u->ut_type == USER_PROCESS) {
                                clean_utmpx_ent(u);
                        }
                }
        }
        endutxent();
}


/*
 * clean_utmpx_ent      - Clean a utmpx entry
 */

static void
clean_utmpx_ent(u)
        struct utmpx *u;
{
        dprintf(("      clean_utmpx_ent: %d\n", (int)u->ut_pid));
        u->ut_type = DEAD_PROCESS;
        (void) time(&u->ut_xtime);
        (void) pututxline(u);
        updwtmpx(WTMPX_FILE, u);
        /*
         * XXX update wtmp for ! nonuserx entries?
         */
}

/*
 *              *** Error Handling and Debugging Routines ***
 */

/*
 * fatal - Catastrophic failure
 */

static void
fatal(char *str)
{
        int oerrno = errno;

        syslog(LOG_ALERT, "%s", str);
        if (Debug == 1) {
                if ((errno = oerrno) != 0)
                        perror(prog_name);
                dprintf(("%s\n", str));
        }
        exit(1);
}

/*
 * nonfatal - Non-Catastrophic failure - print message and errno
 */

static void
nonfatal(char *str)
{
        syslog(LOG_WARNING, "%s", str);

        if (Debug == 1) {
                if (errno != 0)
                        perror(prog_name);
                dprintf(("%c%s\n", 7, str));
                print_tables();
                (void) sleep(5);        /* Time to read debug messages */
        }
}

/*
 * print_tables - Print internal tables - for debugging
 */

static void
print_tables()
{
        int i;

        if (Debug == 0)
                return;

        dprintf(("pidtable: "));
        for (i = 0; i < pidcnt; i++)
                dprintf(("%d: %d  ", i, (int)pidtable[i].pl_pid));
        dprintf(("\n"));
        dprintf(("fdtable:  "));
        for (i = 0; i < pidcnt; i++)
                dprintf(("%d: %d  ", i, fdtable[i].fd));
        dprintf(("\n"));
}

/*
 * proc_is_alive        - Check to see if a process is alive AND its
 *                        not a zombie.  Returns 1 if process is alive
 *                        and zero if it is dead or a zombie.
 */

static int
proc_is_alive(pid)
        pid_t pid;
{
        char psinfoname[64];
        int fd;
        psinfo_t psinfo;

        if (kill(pid, 0) != 0)
                return (0);             /* Kill failed - no process */

        /*
         * The process exists, so check if it's a zombie.
         */
        (void) sprintf(psinfoname, "/proc/%d/psinfo", (int)pid);

        if ((fd = open(psinfoname, O_RDONLY)) < 0 ||
            read(fd, &psinfo, sizeof (psinfo)) != sizeof (psinfo)) {
                /*
                 * We either couldn't open the proc, or we did but the
                 * read of the psinfo file failed, so pid is nonexistent.
                 */
                psinfo.pr_nlwp = 0;
        }
        if (fd >= 0)
                (void) close(fd);

        /* if pr_nlwp == 0, process is a zombie */
        return (psinfo.pr_nlwp != 0);
}

/*
 * warn_utmp -  /var/adm/utmp has been deprecated. It should no longer
 *              be used.  Applications that try to directly manipulate
 *              it may cause problems. Since the file is no longer
 *              shipped, if it appears on a system it's because an
 *              old application created it.  We'll have utmpd
 *              complain about it periodically.
 */

static void
warn_utmp()
{
        struct stat s;

        if (lstat(UTMP_FILE, &s) == 0 &&
            s.st_size % sizeof (struct utmp) == 0) {
                nonfatal("WARNING: /var/adm/utmp exists!\nSee "
                    "utmp(4) for more information");
        }
}