Prepare to support polling(4) on multiple cpus:

[dragonfly/port-amd64.git] / lib / libdevstat / devstat.c

/*
 * Copyright (c) 1997, 1998 Kenneth D. Merry.
 * All rights reserved.
 *
 * 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. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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/libdevstat/devstat.c,v 1.6 1999/08/28 00:04:26 peter Exp $
 * $DragonFly: src/lib/libdevstat/devstat.c,v 1.5 2005/01/08 19:19:26 joerg Exp $
 */

#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/errno.h>

#include <ctype.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "devstat.h"

char devstat_errbuf[DEVSTAT_ERRBUF_SIZE];

/*
 * Table to match descriptive strings with device types.  These are in
 * order from most common to least common to speed search time.
 */
struct devstat_match_table match_table[] = {
        {"da",          DEVSTAT_TYPE_DIRECT,    DEVSTAT_MATCH_TYPE},
        {"cd",          DEVSTAT_TYPE_CDROM,     DEVSTAT_MATCH_TYPE},
        {"scsi",        DEVSTAT_TYPE_IF_SCSI,   DEVSTAT_MATCH_IF},
        {"ide",         DEVSTAT_TYPE_IF_IDE,    DEVSTAT_MATCH_IF},
        {"other",       DEVSTAT_TYPE_IF_OTHER,  DEVSTAT_MATCH_IF},
        {"worm",        DEVSTAT_TYPE_WORM,      DEVSTAT_MATCH_TYPE},
        {"sa",          DEVSTAT_TYPE_SEQUENTIAL,DEVSTAT_MATCH_TYPE},
        {"pass",        DEVSTAT_TYPE_PASS,      DEVSTAT_MATCH_PASS},
        {"optical",     DEVSTAT_TYPE_OPTICAL,   DEVSTAT_MATCH_TYPE},
        {"array",       DEVSTAT_TYPE_STORARRAY, DEVSTAT_MATCH_TYPE},
        {"changer",     DEVSTAT_TYPE_CHANGER,   DEVSTAT_MATCH_TYPE},
        {"scanner",     DEVSTAT_TYPE_SCANNER,   DEVSTAT_MATCH_TYPE},
        {"printer",     DEVSTAT_TYPE_PRINTER,   DEVSTAT_MATCH_TYPE},
        {"floppy",      DEVSTAT_TYPE_FLOPPY,    DEVSTAT_MATCH_TYPE},
        {"proc",        DEVSTAT_TYPE_PROCESSOR, DEVSTAT_MATCH_TYPE},
        {"comm",        DEVSTAT_TYPE_COMM,      DEVSTAT_MATCH_TYPE},
        {"enclosure",   DEVSTAT_TYPE_ENCLOSURE, DEVSTAT_MATCH_TYPE},
        {NULL,          0,                      0}
};

/*
 * Local function declarations.
 */
static int compare_select(const void *arg1, const void *arg2);

int
getnumdevs(void)
{
        size_t numdevsize;
        int numdevs;
        char *func_name = "getnumdevs";

        numdevsize = sizeof(int);

        /*
         * Find out how many devices we have in the system.
         */
        if (sysctlbyname("kern.devstat.numdevs", &numdevs,
                         &numdevsize, NULL, 0) == -1) {
                sprintf(devstat_errbuf, "%s: error getting number of devices\n"
                        "%s: %s", func_name, func_name, strerror(errno));
                return(-1);
        } else
                return(numdevs);
}

/*
 * This is an easy way to get the generation number, but the generation is
 * supplied in a more atmoic manner by the kern.devstat.all sysctl.
 * Because this generation sysctl is separate from the statistics sysctl,
 * the device list and the generation could change between the time that
 * this function is called and the device list is retreived.
 */
long
getgeneration(void)
{
        size_t gensize;
        long generation;
        char *func_name = "getgeneration";

        gensize = sizeof(long);

        /*
         * Get the current generation number.
         */
        if (sysctlbyname("kern.devstat.generation", &generation, 
                         &gensize, NULL, 0) == -1) {
                sprintf(devstat_errbuf,"%s: error getting devstat generation\n"
                        "%s: %s", func_name, func_name, strerror(errno));
                return(-1);
        } else
                return(generation);
}

/*
 * Get the current devstat version.  The return value of this function
 * should be compared with DEVSTAT_VERSION, which is defined in
 * sys/devicestat.h.  This will enable userland programs to determine
 * whether they are out of sync with the kernel.
 */
int
getversion(void)
{
        size_t versize;
        int version;
        char *func_name = "getversion";

        versize = sizeof(int);

        /*
         * Get the current devstat version.
         */
        if (sysctlbyname("kern.devstat.version", &version, &versize,
                         NULL, 0) == -1) {
                sprintf(devstat_errbuf, "%s: error getting devstat version\n"
                        "%s: %s", func_name, func_name, strerror(errno));
                return(-1);
        } else
                return(version);
}

/*
 * Check the devstat version we know about against the devstat version the
 * kernel knows about.  If they don't match, print an error into the
 * devstat error buffer, and return -1.  If they match, return 0.
 */
int
checkversion(void)
{
        int retval = 0;
        int errlen = 0;
        char *func_name = "checkversion";
        int version;

        version = getversion();

        if (version != DEVSTAT_VERSION) {
                int buflen = 0;
                char tmpstr[256];

                /*
                 * This is really pretty silly, but basically the idea is
                 * that if getversion() returns an error (i.e. -1), then it
                 * has printed an error message in the buffer.  Therefore,
                 * we need to add a \n to the end of that message before we
                 * print our own message in the buffer.
                 */
                if (version == -1) {
                        buflen = strlen(devstat_errbuf);
                        errlen = snprintf(tmpstr, sizeof(tmpstr), "\n");
                        strncat(devstat_errbuf, tmpstr,
                                DEVSTAT_ERRBUF_SIZE - buflen - 1);
                        buflen += errlen;
                }

                errlen = snprintf(tmpstr, sizeof(tmpstr),
                                  "%s: userland devstat version %d is not "
                                  "the same as the kernel\n%s: devstat "
                                  "version %d\n", func_name, DEVSTAT_VERSION,
                                  func_name, version);

                if (version == -1) {
                        strncat(devstat_errbuf, tmpstr,
                                DEVSTAT_ERRBUF_SIZE - buflen - 1);
                        buflen += errlen;
                } else {
                        strncpy(devstat_errbuf, tmpstr, DEVSTAT_ERRBUF_SIZE);
                        devstat_errbuf[DEVSTAT_ERRBUF_SIZE - 1] = '\0';
                }

                if (version < DEVSTAT_VERSION)
                        snprintf(tmpstr, sizeof(tmpstr),
                                 "%s: libdevstat newer than kernel\n",
                                 func_name);
                else
                        snprintf(tmpstr, sizeof(tmpstr),
                                 "%s: kernel newer than libdevstat\n",
                                 func_name);

                strncat(devstat_errbuf, tmpstr,
                        DEVSTAT_ERRBUF_SIZE - buflen - 1);

                retval = -1;
        }

        return(retval);
}

/*
 * Get the current list of devices and statistics, and the current
 * generation number.
 * 
 * Return values:
 * -1  -- error
 *  0  -- device list is unchanged
 *  1  -- device list has changed
 */
int
getdevs(struct statinfo *stats)
{
        int error;
        size_t dssize;
        int oldnumdevs;
        long oldgeneration;
        int retval = 0;
        struct devinfo *dinfo;
        char *func_name = "getdevs";

        dinfo = stats->dinfo;

        if (dinfo == NULL) {
                sprintf(devstat_errbuf, "%s: stats->dinfo was NULL", func_name);
                return(-1);
        }

        oldnumdevs = dinfo->numdevs;
        oldgeneration = dinfo->generation;

        /*
         * If this is our first time through, mem_ptr will be null.  
         */
        if (dinfo->mem_ptr == NULL) {
                /*
                 * Get the number of devices.  If it's negative, it's an
                 * error.  Don't bother setting the error string, since
                 * getnumdevs() has already done that for us.
                 */
                if ((dinfo->numdevs = getnumdevs()) < 0)
                        return(-1);

                /*
                 * The kern.devstat.all sysctl returns the current generation
                 * number, as well as all the devices.  So we need four
                 * bytes more.
                 */
                dssize =(dinfo->numdevs * sizeof(struct devstat)) +sizeof(long);
                dinfo->mem_ptr = (u_int8_t *)malloc(dssize);
        } else
                dssize =(dinfo->numdevs * sizeof(struct devstat)) +sizeof(long);

        /* Get the current time when we get the stats */
        gettimeofday(&stats->busy_time, NULL);

        /*
         * Request all of the devices.  We only really allow for one
         * ENOMEM failure.  It would, of course, be possible to just go in
         * a loop and keep reallocing the device structure until we don't
         * get ENOMEM back.  I'm not sure it's worth it, though.  If
         * devices are being added to the system that quickly, maybe the
         * user can just wait until all devices are added.
         */
        if ((error = sysctlbyname("kern.devstat.all", dinfo->mem_ptr, 
             &dssize, NULL, 0)) == -1) {
                /*
                 * If we get ENOMEM back, that means that there are 
                 * more devices now, so we need to allocate more 
                 * space for the device array.
                 */
                if (errno == ENOMEM) {
                        /*
                         * No need to set the error string here, getnumdevs()
                         * will do that if it fails.
                         */
                        if ((dinfo->numdevs = getnumdevs()) < 0)
                                return(-1);

                        dssize = (dinfo->numdevs * sizeof(struct devstat)) +
                                sizeof(long);
                        dinfo->mem_ptr = (u_int8_t *)realloc(dinfo->mem_ptr,
                                                             dssize);
                        if ((error = sysctlbyname("kern.devstat.all", 
                            dinfo->mem_ptr, &dssize, NULL, 0)) == -1) {
                                sprintf(devstat_errbuf,
                                        "%s: error getting device stats\n"
                                        "%s: %s", func_name, func_name,
                                        strerror(errno));
                                return(-1);
                        }
                } else {
                        sprintf(devstat_errbuf,
                                "%s: error getting device stats\n"
                                "%s: %s", func_name, func_name,
                                strerror(errno));
                        return(-1);
                }
        } 

        /*
         * The sysctl spits out the generation as the first four bytes,
         * then all of the device statistics structures.
         */
        dinfo->generation = *(long *)dinfo->mem_ptr;

        /*
         * If the generation has changed, and if the current number of
         * devices is not the same as the number of devices recorded in the
         * devinfo structure, it is likely that the device list has shrunk.
         * The reason that it is likely that the device list has shrunk in
         * this case is that if the device list has grown, the sysctl above
         * will return an ENOMEM error, and we will reset the number of
         * devices and reallocate the device array.  If the second sysctl
         * fails, we will return an error and therefore never get to this
         * point.  If the device list has shrunk, the sysctl will not
         * return an error since we have more space allocated than is
         * necessary.  So, in the shrinkage case, we catch it here and
         * reallocate the array so that we don't use any more space than is
         * necessary.
         */
        if (oldgeneration != dinfo->generation) {
                if (getnumdevs() != dinfo->numdevs) {
                        if ((dinfo->numdevs = getnumdevs()) < 0)
                                return(-1);
                        dssize = (dinfo->numdevs * sizeof(struct devstat)) +
                                sizeof(long);
                        dinfo->mem_ptr = (u_int8_t *)realloc(dinfo->mem_ptr,
                                                             dssize);
                }
                retval = 1;
        }

        dinfo->devices = (struct devstat *)(dinfo->mem_ptr + sizeof(long));

        return(retval);
}

/*
 * selectdevs():
 *
 * Devices are selected/deselected based upon the following criteria:
 * - devices specified by the user on the command line
 * - devices matching any device type expressions given on the command line
 * - devices with the highest I/O, if 'top' mode is enabled
 * - the first n unselected devices in the device list, if maxshowdevs
 *   devices haven't already been selected and if the user has not
 *   specified any devices on the command line and if we're in "add" mode.
 *
 * Input parameters:
 * - device selection list (dev_select)
 * - current number of devices selected (num_selected)
 * - total number of devices in the selection list (num_selections)
 * - devstat generation as of the last time selectdevs() was called
 *   (select_generation)
 * - current devstat generation (current_generation)
 * - current list of devices and statistics (devices)
 * - number of devices in the current device list (numdevs)
 * - compiled version of the command line device type arguments (matches)
 *   - This is optional.  If the number of devices is 0, this will be ignored.
 *   - The matching code pays attention to the current selection mode.  So
 *     if you pass in a matching expression, it will be evaluated based
 *     upon the selection mode that is passed in.  See below for details.
 * - number of device type matching expressions (num_matches)
 *   - Set to 0 to disable the matching code.
 * - list of devices specified on the command line by the user (dev_selections)
 * - number of devices selected on the command line by the user
 *   (num_dev_selections)
 * - Our selection mode.  There are four different selection modes:
 *      - add mode.  (DS_SELECT_ADD) Any devices matching devices explicitly
 *        selected by the user or devices matching a pattern given by the
 *        user will be selected in addition to devices that are already
 *        selected.  Additional devices will be selected, up to maxshowdevs
 *        number of devices. 
 *      - only mode. (DS_SELECT_ONLY)  Only devices matching devices
 *        explicitly given by the user or devices matching a pattern
 *        given by the user will be selected.  No other devices will be
 *        selected.
 *      - addonly mode.  (DS_SELECT_ADDONLY)  This is similar to add and
 *        only.  Basically, this will not de-select any devices that are
 *        current selected, as only mode would, but it will also not
 *        gratuitously select up to maxshowdevs devices as add mode would.
 *      - remove mode.  (DS_SELECT_REMOVE)  Any devices matching devices
 *        explicitly selected by the user or devices matching a pattern
 *        given by the user will be de-selected.
 * - maximum number of devices we can select (maxshowdevs)
 * - flag indicating whether or not we're in 'top' mode (perf_select)
 *
 * Output data:
 * - the device selection list may be modified and passed back out
 * - the number of devices selected and the total number of items in the
 *   device selection list may be changed
 * - the selection generation may be changed to match the current generation
 * 
 * Return values:
 * -1  -- error
 *  0  -- selected devices are unchanged
 *  1  -- selected devices changed
 */
int
selectdevs(struct device_selection **dev_select, int *num_selected,
           int *num_selections, long *select_generation, 
           long current_generation, struct devstat *devices, int numdevs,
           struct devstat_match *matches, int num_matches,
           char **dev_selections, int num_dev_selections,
           devstat_select_mode select_mode, int maxshowdevs, int perf_select)
{
        int i, j, k;
        int init_selections = 0, init_selected_var = 0;
        struct device_selection *old_dev_select = NULL;
        int old_num_selections = 0, old_num_selected;
        int selection_number = 0;
        int changed = 0, found = 0;

        if ((dev_select == NULL) || (devices == NULL) || (numdevs <= 0))
                return(-1);

        /*
         * We always want to make sure that we have as many dev_select
         * entries as there are devices. 
         */
        /*
         * In this case, we haven't selected devices before.
         */
        if (*dev_select == NULL) {
                *dev_select = (struct device_selection *)malloc(numdevs *
                        sizeof(struct device_selection));
                *select_generation = current_generation;
                init_selections = 1;
                changed = 1;
        /*
         * In this case, we have selected devices before, but the device
         * list has changed since we last selected devices, so we need to
         * either enlarge or reduce the size of the device selection list.
         */
        } else if (*num_selections != numdevs) {
                *dev_select = (struct device_selection *)realloc(*dev_select,
                        numdevs * sizeof(struct device_selection));
                *select_generation = current_generation;
                init_selections = 1;
        /*
         * In this case, we've selected devices before, and the selection
         * list is the same size as it was the last time, but the device
         * list has changed.
         */
        } else if (*select_generation < current_generation) {
                *select_generation = current_generation;
                init_selections = 1;
        }

        /*
         * If we're in "only" mode, we want to clear out the selected
         * variable since we're going to select exactly what the user wants
         * this time through.
         */
        if (select_mode == DS_SELECT_ONLY)
                init_selected_var = 1;

        /*
         * In all cases, we want to back up the number of selected devices.
         * It is a quick and accurate way to determine whether the selected
         * devices have changed.
         */
        old_num_selected = *num_selected;

        /*
         * We want to make a backup of the current selection list if 
         * the list of devices has changed, or if we're in performance 
         * selection mode.  In both cases, we don't want to make a backup
         * if we already know for sure that the list will be different.
         * This is certainly the case if this is our first time through the
         * selection code.
         */
        if (((init_selected_var != 0) || (init_selections != 0)
         || (perf_select != 0)) && (changed == 0)){
                old_dev_select = (struct device_selection *)malloc(
                    *num_selections * sizeof(struct device_selection));
                old_num_selections = *num_selections;
                bcopy(*dev_select, old_dev_select, 
                    sizeof(struct device_selection) * *num_selections);
        }

        if (init_selections != 0) {
                bzero(*dev_select, sizeof(struct device_selection) * numdevs);

                for (i = 0; i < numdevs; i++) {
                        (*dev_select)[i].device_number = 
                                devices[i].device_number;
                        strncpy((*dev_select)[i].device_name,
                                devices[i].device_name,
                                DEVSTAT_NAME_LEN);
                        (*dev_select)[i].device_name[DEVSTAT_NAME_LEN - 1]='\0';
                        (*dev_select)[i].unit_number = devices[i].unit_number;
                        (*dev_select)[i].position = i;
                }
                *num_selections = numdevs;
        } else if (init_selected_var != 0) {
                for (i = 0; i < numdevs; i++) 
                        (*dev_select)[i].selected = 0;
        }

        /* we haven't gotten around to selecting anything yet.. */
        if ((select_mode == DS_SELECT_ONLY) || (init_selections != 0)
         || (init_selected_var != 0))
                *num_selected = 0;

        /*
         * Look through any devices the user specified on the command line
         * and see if they match known devices.  If so, select them.
         */
        for (i = 0; (i < *num_selections) && (num_dev_selections > 0); i++) {
                char tmpstr[80];

                snprintf(tmpstr, sizeof(tmpstr), "%s%d",
                        (*dev_select)[i].device_name,
                        (*dev_select)[i].unit_number);
                for (j = 0; j < num_dev_selections; j++) {
                        if (strcmp(tmpstr, dev_selections[j]) == 0) {
                                /*
                                 * Here we do different things based on the
                                 * mode we're in.  If we're in add or
                                 * addonly mode, we only select this device
                                 * if it hasn't already been selected.
                                 * Otherwise, we would be unnecessarily
                                 * changing the selection order and
                                 * incrementing the selection count.  If
                                 * we're in only mode, we unconditionally
                                 * select this device, since in only mode
                                 * any previous selections are erased and
                                 * manually specified devices are the first
                                 * ones to be selected.  If we're in remove
                                 * mode, we de-select the specified device and
                                 * decrement the selection count.
                                 */
                                switch(select_mode) {
                                case DS_SELECT_ADD:
                                case DS_SELECT_ADDONLY:
                                        if ((*dev_select)[i].selected)
                                                break;
                                        /* FALLTHROUGH */
                                case DS_SELECT_ONLY:
                                        (*dev_select)[i].selected =
                                                ++selection_number;
                                        (*num_selected)++;
                                        break;
                                case DS_SELECT_REMOVE:
                                        (*dev_select)[i].selected = 0;
                                        (*num_selected)--;
                                        /*
                                         * This isn't passed back out, we
                                         * just use it to keep track of
                                         * how many devices we've removed.
                                         */
                                        num_dev_selections--;
                                        break;
                                }
                                break;
                        }
                }
        }

        /*
         * Go through the user's device type expressions and select devices
         * accordingly.  We only do this if the number of devices already
         * selected is less than the maximum number we can show.
         */
        for (i = 0; (i < num_matches) && (*num_selected < maxshowdevs); i++) {
                /* We should probably indicate some error here */
                if ((matches[i].match_fields == DEVSTAT_MATCH_NONE)
                 || (matches[i].num_match_categories <= 0))
                        continue;

                for (j = 0; j < numdevs; j++) {
                        int num_match_categories;

                        num_match_categories = matches[i].num_match_categories;

                        /*
                         * Determine whether or not the current device
                         * matches the given matching expression.  This if
                         * statement consists of three components:
                         *   - the device type check
                         *   - the device interface check
                         *   - the passthrough check
                         * If a the matching test is successful, it 
                         * decrements the number of matching categories,
                         * and if we've reached the last element that
                         * needed to be matched, the if statement succeeds.
                         * 
                         */
                        if ((((matches[i].match_fields & DEVSTAT_MATCH_TYPE)!=0)
                          && ((devices[j].device_type & DEVSTAT_TYPE_MASK) ==
                                (matches[i].device_type & DEVSTAT_TYPE_MASK))
                          &&(((matches[i].match_fields & DEVSTAT_MATCH_PASS)!=0)
                           || (((matches[i].match_fields & 
                                DEVSTAT_MATCH_PASS) == 0)
                            && ((devices[j].device_type &
                                DEVSTAT_TYPE_PASS) == 0)))
                          && (--num_match_categories == 0)) 
                         || (((matches[i].match_fields & DEVSTAT_MATCH_IF) != 0)
                          && ((devices[j].device_type & DEVSTAT_TYPE_IF_MASK) ==
                                (matches[i].device_type & DEVSTAT_TYPE_IF_MASK))
                          &&(((matches[i].match_fields & DEVSTAT_MATCH_PASS)!=0)
                           || (((matches[i].match_fields &
                                DEVSTAT_MATCH_PASS) == 0)
                            && ((devices[j].device_type & 
                                DEVSTAT_TYPE_PASS) == 0)))
                          && (--num_match_categories == 0))
                         || (((matches[i].match_fields & DEVSTAT_MATCH_PASS)!=0)
                          && ((devices[j].device_type & DEVSTAT_TYPE_PASS) != 0)
                          && (--num_match_categories == 0))) {

                                /*
                                 * This is probably a non-optimal solution
                                 * to the problem that the devices in the
                                 * device list will not be in the same
                                 * order as the devices in the selection
                                 * array.
                                 */
                                for (k = 0; k < numdevs; k++) {
                                        if ((*dev_select)[k].position == j) {
                                                found = 1;
                                                break;
                                        }
                                }

                                /*
                                 * There shouldn't be a case where a device
                                 * in the device list is not in the
                                 * selection list...but it could happen.
                                 */
                                if (found != 1) {
                                        fprintf(stderr, "selectdevs: couldn't"
                                                " find %s%d in selection "
                                                "list\n",
                                                devices[j].device_name,
                                                devices[j].unit_number);
                                        break;
                                }

                                /*
                                 * We do different things based upon the
                                 * mode we're in.  If we're in add or only
                                 * mode, we go ahead and select this device
                                 * if it hasn't already been selected.  If
                                 * it has already been selected, we leave
                                 * it alone so we don't mess up the
                                 * selection ordering.  Manually specified
                                 * devices have already been selected, and
                                 * they have higher priority than pattern
                                 * matched devices.  If we're in remove
                                 * mode, we de-select the given device and
                                 * decrement the selected count.
                                 */
                                switch(select_mode) {
                                case DS_SELECT_ADD:
                                case DS_SELECT_ADDONLY:
                                case DS_SELECT_ONLY:
                                        if ((*dev_select)[k].selected != 0)
                                                break;
                                        (*dev_select)[k].selected =
                                                ++selection_number;
                                        (*num_selected)++;
                                        break;
                                case DS_SELECT_REMOVE:
                                        (*dev_select)[k].selected = 0;
                                        (*num_selected)--;
                                        break;
                                }
                        }
                }
        }

        /*
         * Here we implement "top" mode.  Devices are sorted in the
         * selection array based on two criteria:  whether or not they are
         * selected (not selection number, just the fact that they are
         * selected!) and the number of bytes in the "bytes" field of the
         * selection structure.  The bytes field generally must be kept up
         * by the user.  In the future, it may be maintained by library
         * functions, but for now the user has to do the work.
         *
         * At first glance, it may seem wrong that we don't go through and
         * select every device in the case where the user hasn't specified
         * any devices or patterns.  In fact, though, it won't make any
         * difference in the device sorting.  In that particular case (i.e.
         * when we're in "add" or "only" mode, and the user hasn't
         * specified anything) the first time through no devices will be
         * selected, so the only criterion used to sort them will be their
         * performance.  The second time through, and every time thereafter,
         * all devices will be selected, so again selection won't matter.
         */
        if (perf_select != 0) {

                /* Sort the device array by throughput  */
                qsort(*dev_select, *num_selections,
                      sizeof(struct device_selection),
                      compare_select);

                if (*num_selected == 0) {
                        /*
                         * Here we select every device in the array, if it
                         * isn't already selected.  Because the 'selected'
                         * variable in the selection array entries contains
                         * the selection order, the devstats routine can show
                         * the devices that were selected first.
                         */
                        for (i = 0; i < *num_selections; i++) {
                                if ((*dev_select)[i].selected == 0) {
                                        (*dev_select)[i].selected =
                                                ++selection_number;
                                        (*num_selected)++;
                                }
                        }
                } else {
                        selection_number = 0;
                        for (i = 0; i < *num_selections; i++) {
                                if ((*dev_select)[i].selected != 0) {
                                        (*dev_select)[i].selected =
                                                ++selection_number;
                                }
                        }
                }
        }

        /*
         * If we're in the "add" selection mode and if we haven't already
         * selected maxshowdevs number of devices, go through the array and
         * select any unselected devices.  If we're in "only" mode, we
         * obviously don't want to select anything other than what the user
         * specifies.  If we're in "remove" mode, it probably isn't a good
         * idea to go through and select any more devices, since we might
         * end up selecting something that the user wants removed.  Through
         * more complicated logic, we could actually figure this out, but
         * that would probably require combining this loop with the various
         * selections loops above.
         */
        if ((select_mode == DS_SELECT_ADD) && (*num_selected < maxshowdevs)) {
                for (i = 0; i < *num_selections; i++)
                        if ((*dev_select)[i].selected == 0) {
                                (*dev_select)[i].selected = ++selection_number;
                                (*num_selected)++;
                        }
        }

        /*
         * Look at the number of devices that have been selected.  If it
         * has changed, set the changed variable.  Otherwise, if we've
         * made a backup of the selection list, compare it to the current
         * selection list to see if the selected devices have changed.
         */
        if ((changed == 0) && (old_num_selected != *num_selected))
                changed = 1;
        else if ((changed == 0) && (old_dev_select != NULL)) {
                /*
                 * Now we go through the selection list and we look at
                 * it three different ways.
                 */
                for (i = 0; (i < *num_selections) && (changed == 0) && 
                     (i < old_num_selections); i++) {
                        /*
                         * If the device at index i in both the new and old
                         * selection arrays has the same device number and
                         * selection status, it hasn't changed.  We
                         * continue on to the next index.
                         */
                        if (((*dev_select)[i].device_number ==
                             old_dev_select[i].device_number)
                         && ((*dev_select)[i].selected == 
                             old_dev_select[i].selected))
                                continue;

                        /*
                         * Now, if we're still going through the if
                         * statement, the above test wasn't true.  So we
                         * check here to see if the device at index i in
                         * the current array is the same as the device at
                         * index i in the old array.  If it is, that means
                         * that its selection number has changed.  Set
                         * changed to 1 and exit the loop.
                         */
                        else if ((*dev_select)[i].device_number ==
                                  old_dev_select[i].device_number) {
                                changed = 1;
                                break;
                        }
                        /*
                         * If we get here, then the device at index i in
                         * the current array isn't the same device as the
                         * device at index i in the old array.
                         */
                        else {
                                int found = 0;

                                /*
                                 * Search through the old selection array
                                 * looking for a device with the same
                                 * device number as the device at index i
                                 * in the current array.  If the selection
                                 * status is the same, then we mark it as
                                 * found.  If the selection status isn't
                                 * the same, we break out of the loop.
                                 * Since found isn't set, changed will be
                                 * set to 1 below.
                                 */
                                for (j = 0; j < old_num_selections; j++) {
                                        if (((*dev_select)[i].device_number ==
                                              old_dev_select[j].device_number)
                                         && ((*dev_select)[i].selected ==
                                              old_dev_select[j].selected)){
                                                found = 1;
                                                break;
                                        }
                                        else if ((*dev_select)[i].device_number
                                            == old_dev_select[j].device_number)
                                                break;
                                }
                                if (found == 0)
                                        changed = 1;
                        }
                }
        }
        if (old_dev_select != NULL)
                free(old_dev_select);

        return(changed);
}

/*
 * Comparison routine for qsort() above.  Note that the comparison here is
 * backwards -- generally, it should return a value to indicate whether
 * arg1 is <, =, or > arg2.  Instead, it returns the opposite.  The reason
 * it returns the opposite is so that the selection array will be sorted in
 * order of decreasing performance.  We sort on two parameters.  The first
 * sort key is whether or not one or the other of the devices in question
 * has been selected.  If one of them has, and the other one has not, the
 * selected device is automatically more important than the unselected
 * device.  If neither device is selected, we judge the devices based upon
 * performance.
 */
static int
compare_select(const void *arg1, const void *arg2)
{
        if ((((struct device_selection *)arg1)->selected)
         && (((struct device_selection *)arg2)->selected == 0))
                return(-1);
        else if ((((struct device_selection *)arg1)->selected == 0)
              && (((struct device_selection *)arg2)->selected))
                return(1);
        else if (((struct device_selection *)arg2)->bytes <
                 ((struct device_selection *)arg1)->bytes)
                return(-1);
        else if (((struct device_selection *)arg2)->bytes >
                 ((struct device_selection *)arg1)->bytes)
                return(1);
        else
                return(0);
}

/*
 * Take a string with the general format "arg1,arg2,arg3", and build a
 * device matching expression from it.
 */
int
buildmatch(const char *match_str, struct devstat_match **matches,
           int *num_matches)
{
        char *tstr[5];
        char **tempstr;
        char *matchbuf_orig;    /* strdup of match_str */
        char *matchbuf;         /* allow strsep to clobber */
        int num_args;
        int i, j;
        int retval = -1;

        /* We can't do much without a string to parse */
        if (match_str == NULL) {
                sprintf(devstat_errbuf, "%s: no match expression", __func__);
                return(-1);
        }

        /*
         * Break the (comma delimited) input string out into separate strings.
         * strsep is destructive, so copy the string first.
         */
        matchbuf = matchbuf_orig = strdup(match_str);
        if (matchbuf == NULL) {
                sprintf(devstat_errbuf, "%s: out of memory", __func__);
                return(-1);
        }
        for (tempstr = tstr, num_args  = 0; 
             (*tempstr = strsep(&matchbuf, ",")) != NULL && (num_args < 5); 
             num_args++)
                if (**tempstr != '\0')
                        if (++tempstr >= &tstr[5])
                                break;

        /* The user gave us too many type arguments */
        if (num_args > 3) {
                sprintf(devstat_errbuf, "%s: too many type arguments",
                        __func__);
                goto cleanup;
        }

        /*
         * Since you can't realloc a pointer that hasn't been malloced
         * first, we malloc first and then realloc.
         */
        if (*num_matches == 0)
                *matches = (struct devstat_match *)malloc(
                           sizeof(struct devstat_match));
        else
                *matches = (struct devstat_match *)realloc(*matches,
                          sizeof(struct devstat_match) * (*num_matches + 1));
                          
        /* Make sure the current entry is clear */
        bzero(&matches[0][*num_matches], sizeof(struct devstat_match));

        /*
         * Step through the arguments the user gave us and build a device
         * matching expression from them.
         */
        for (i = 0; i < num_args; i++) {
                char *tempstr2, *tempstr3;

                /*
                 * Get rid of leading white space.
                 */
                tempstr2 = tstr[i];
                while (isspace(*tempstr2) && (*tempstr2 != '\0'))
                        tempstr2++;

                /*
                 * Get rid of trailing white space.
                 */
                tempstr3 = &tempstr2[strlen(tempstr2) - 1];

                while ((*tempstr3 != '\0') && (tempstr3 > tempstr2)
                    && (isspace(*tempstr3))) {
                        *tempstr3 = '\0';
                        tempstr3--;
                }

                /*
                 * Go through the match table comparing the user's
                 * arguments to known device types, interfaces, etc.  
                 */
                for (j = 0; match_table[j].match_str != NULL; j++) {
                        /*
                         * We do case-insensitive matching, in case someone
                         * wants to enter "SCSI" instead of "scsi" or
                         * something like that.  Only compare as many 
                         * characters as are in the string in the match 
                         * table.  This should help if someone tries to use 
                         * a super-long match expression.  
                         */
                        if (strncasecmp(tempstr2, match_table[j].match_str,
                            strlen(match_table[j].match_str)) == 0) {
                                /*
                                 * Make sure the user hasn't specified two
                                 * items of the same type, like "da" and
                                 * "cd".  One device cannot be both.
                                 */
                                if (((*matches)[*num_matches].match_fields &
                                    match_table[j].match_field) != 0) {
                                        sprintf(devstat_errbuf,
                                                "%s: cannot have more than "
                                                "one match item in a single "
                                                "category", __func__);
                                        goto cleanup;
                                }
                                /*
                                 * If we've gotten this far, we have a
                                 * winner.  Set the appropriate fields in
                                 * the match entry.
                                 */
                                (*matches)[*num_matches].match_fields |=
                                        match_table[j].match_field;
                                (*matches)[*num_matches].device_type |=
                                        match_table[j].type;
                                (*matches)[*num_matches].num_match_categories++;
                                break;
                        }
                }
                /*
                 * We should have found a match in the above for loop.  If
                 * not, that means the user entered an invalid device type
                 * or interface.
                 */
                if ((*matches)[*num_matches].num_match_categories != (i + 1)) {
                        snprintf(devstat_errbuf, sizeof(devstat_errbuf),
                                "%s: unknown match item \"%s\"", __func__,
                                tstr[i]);
                        goto cleanup;
                }
        }

        (*num_matches)++;
        retval = 0;
cleanup:
        free(matchbuf_orig);
        return(retval);
}

/*
 * Compute a number of device statistics.  Only one field is mandatory, and
 * that is "current".  Everything else is optional.  The caller passes in
 * pointers to variables to hold the various statistics he desires.  If he
 * doesn't want a particular staistic, he should pass in a NULL pointer.
 * Return values:
 * 0   -- success
 * -1  -- failure
 */
int
compute_stats(struct devstat *current, struct devstat *previous,
              long double etime, u_int64_t *total_bytes,
              u_int64_t *total_transfers, u_int64_t *total_blocks,
              long double *kb_per_transfer, long double *transfers_per_second,
              long double *mb_per_second, long double *blocks_per_second,
              long double *ms_per_transaction)
{
        u_int64_t totalbytes, totaltransfers, totalblocks;

        /*
         * current is the only mandatory field.
         */
        if (current == NULL) {
                sprintf(devstat_errbuf, "%s: current stats structure was NULL",
                        __func__);
                return(-1);
        }

        totalbytes = (current->bytes_written + current->bytes_read) -
                     ((previous) ? (previous->bytes_written +
                                    previous->bytes_read) : 0);

        if (total_bytes)
                *total_bytes = totalbytes;

        totaltransfers = (current->num_reads +
                          current->num_writes +
                          current->num_other) -
                         ((previous) ?
                          (previous->num_reads +
                           previous->num_writes +
                           previous->num_other) : 0);
        if (total_transfers)
                *total_transfers = totaltransfers;

        if (transfers_per_second) {
                if (etime > 0.0) {
                        *transfers_per_second = totaltransfers;
                        *transfers_per_second /= etime;
                } else
                        *transfers_per_second = 0.0;
        }

        if (kb_per_transfer) {
                *kb_per_transfer = totalbytes;
                *kb_per_transfer /= 1024;
                if (totaltransfers > 0)
                        *kb_per_transfer /= totaltransfers;
                else
                        *kb_per_transfer = 0.0;
        }

        if (mb_per_second) {
                *mb_per_second = totalbytes;
                *mb_per_second /= 1024 * 1024;
                if (etime > 0.0)
                        *mb_per_second /= etime;
                else
                        *mb_per_second = 0.0;
        }

        totalblocks = totalbytes;
        if (current->block_size > 0)
                totalblocks /= current->block_size;
        else
                totalblocks /= 512;

        if (total_blocks)
                *total_blocks = totalblocks;

        if (blocks_per_second) {
                *blocks_per_second = totalblocks;
                if (etime > 0.0)
                        *blocks_per_second /= etime;
                else
                        *blocks_per_second = 0.0;
        }

        if (ms_per_transaction) {
                if (totaltransfers > 0) {
                        *ms_per_transaction = etime;
                        *ms_per_transaction /= totaltransfers;
                        *ms_per_transaction *= 1000;
                } else
                        *ms_per_transaction = 0.0;
        }

        return(0);
}

long double
compute_etime(struct timeval cur_time, struct timeval prev_time)
{
        struct timeval busy_time;
        u_int64_t busy_usec;
        long double etime;

        timersub(&cur_time, &prev_time, &busy_time);

        busy_usec = busy_time.tv_sec;  
        busy_usec *= 1000000;          
        busy_usec += busy_time.tv_usec;
        etime = busy_usec;
        etime /= 1000000;

        return(etime);
}