disk caches and bioctl hacking

[David Gwynne]

this code lets userland check and change the caches on disks using
the new ioctl i just put into the tree.

id be extremely happy if someone would take the functionality here
and fit it into bioctl.

/*
 * Copyright (c) 2010 David Gwynne <d...@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/dkio.h>

__dead void usage(void);

__dead void
usage(void)
{
        extern char *__progname;

        fprintf(stderr, "usage: %s [-rRwW] disk\n", __progname);

        exit(1);
}

int
main(int argc, char *argv[])
{
        struct dk_cache dkc;
        int fd;
        char *disk = NULL;
        long cmd = 0;
        int rdcache = -1, wrcache = -1;
        int set = 0;

        int ch;

        while ((ch = getopt(argc, argv, "rRwW")) != -1) {
                switch (ch) {
                case 'r':
                        rdcache = 0;
                        break;
                case 'R':
                        rdcache = 1;
                        break;
                case 'w':
                        wrcache = 0;
                        break;
                case 'W':
                        wrcache = 1;
                        break;
                default:
                        usage();
                        /* NOTREACHED */
                }
        }
        argc -= optind;
        argv += optind;

        if (argc != 1)
                usage();
        disk = argv[0];

        fd = open(disk, O_RDONLY);
        if (fd == -1)
                err(1, "open: %s", disk);

        if (ioctl(fd, DIOCGCACHE, &dkc) == -1)
                err(1, "ioctl DIOCGCACHE");

        if (wrcache != -1) {
                dkc.wrcache = wrcache;
                set = 1;
        }
        if (rdcache != -1) {
                dkc.rdcache = rdcache;
                set = 1;
        }

        if (set) {
                if (ioctl(fd, DIOCSCACHE, &dkc) == -1)
                        err(1, "ioctl DIOCSCACHE");
        }

        printf("%s: write cache: %s, read cache: %s\n", disk,
            dkc.wrcache ? "enabled" : "disabled",
            dkc.rdcache ? "enabled" : "disabled");

        return (0);
}