/*      $OpenBSD: st.c,v 1.191 2024/09/04 07:54:53 mglocker Exp $       */
/*      $NetBSD: st.c,v 1.71 1997/02/21 23:03:49 thorpej Exp $  */

/*
 * Copyright (c) 1994 Charles Hannum.  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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Charles Hannum.
 * 4. 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 ``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 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.
 */

/*
 * Originally written by Julian Elischer (julian@tfs.com)
 * for TRW Financial Systems for use under the MACH(2.5) operating system.
 *
 * TRW Financial Systems, in accordance with their agreement with Carnegie
 * Mellon University, makes this software available to CMU to distribute
 * or use in any manner that they see fit as long as this message is kept with
 * the software. For this reason TFS also grants any other persons or
 * organisations permission to use or modify this software.
 *
 * TFS supplies this software to be publicly redistributed
 * on the understanding that TFS is not responsible for the correct
 * functioning of this software in any circumstances.
 *
 * Ported to run under 386BSD by Julian Elischer (julian@tfs.com) Sept 1992
 * major changes by Julian Elischer (julian@jules.dialix.oz.au) May 1993
 */

/*
 * To do:
 * work out some better way of guessing what a good timeout is going
 * to be depending on whether we expect to retension or not.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/timeout.h>
#include <sys/fcntl.h>
#include <sys/errno.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/pool.h>
#include <sys/buf.h>
#include <sys/mtio.h>
#include <sys/device.h>
#include <sys/disk.h>
#include <sys/conf.h>
#include <sys/vnode.h>

#include <scsi/scsi_all.h>
#include <scsi/scsi_debug.h>
#include <scsi/scsi_tape.h>
#include <scsi/scsiconf.h>

/* Defines for device specific stuff */
#define DEF_FIXED_BSIZE  512

#define STMODE(z)       ( minor(z)       & 0x03)
#define STUNIT(z)       ((minor(z) >> 4)       )

#define STMINOR(unit, mode)     (((unit) << 4) + (mode))
#define MAXSTMODES      16      /* Old max retained so minor's don't change. */

#define ST_IO_TIME      (3 * 60 * 1000)         /* 3 minutes */
#define ST_CTL_TIME     (30 * 1000)             /* 30 seconds */
#define ST_SPC_TIME     (4 * 60 * 60 * 1000)    /* 4 hours */

/*
 * Maximum density code allowed in SCSI spec (SSC2R08f, Section 8.3).
 */
#define SCSI_MAX_DENSITY_CODE           0xff

/*
 * Define various devices that we know mis-behave in some way,
 * and note how they are bad, so we can correct for them
 */
struct mode {
        int blksize;
        u_int8_t density;
};

struct quirkdata {
        u_int quirks;
#define ST_Q_SENSE_HELP         0x0001  /* must do READ for good MODE SENSE */
#define ST_Q_IGNORE_LOADS       0x0002
#define ST_Q_UNIMODAL           0x0004  /* unimode drive rejects mode select */
        struct mode mode;
};

struct st_quirk_inquiry_pattern {
        struct scsi_inquiry_pattern pattern;
        struct quirkdata quirkdata;
};

const struct st_quirk_inquiry_pattern st_quirk_patterns[] = {
        {{T_SEQUENTIAL, T_REMOV,
                 "        ", "                ", "    "}, {0,
                                                           {512, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "TANDBERG", " TDC 3800       ", ""},     {0,
                                                           {512, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "ARCHIVE ", "VIPER 2525 25462", ""},     {ST_Q_SENSE_HELP,
                                                           {0, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "SANKYO  ", "CP525           ", ""},     {0,
                                                           {512, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "ANRITSU ", "DMT780          ", ""},     {0,
                                                           {512, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "ARCHIVE ", "VIPER 150  21531", ""},     {ST_Q_SENSE_HELP,
                                                           {0, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "WANGTEK ", "5099ES SCSI",      ""},     {0,
                                                           {512, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "WANGTEK ", "5150ES SCSI",      ""},     {0,
                                                           {512, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "HP      ", "T4000s          ", ""},     {ST_Q_UNIMODAL,
                                                           {0, QIC_3095}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "WANGTEK ", "5150ES SCSI FA15", "01 A"}, {ST_Q_IGNORE_LOADS,
                                                           {0, 0}}},
        {{T_SEQUENTIAL, T_REMOV,
                 "TEAC    ", "MT-2ST/N50      ", ""},     {ST_Q_IGNORE_LOADS,
                                                           {0, 0}}},
};

#define NOEJECT 0
#define EJECT 1

#define NOREWIND 0
#define DOREWIND 1

struct st_softc {
        struct device sc_dev;
        struct disk sc_dk;

        int flags;
#define ST_INFO_VALID           0x00000001
#define ST_WRITTEN              0x00000004
#define ST_FIXEDBLOCKS          0x00000008
#define ST_AT_FILEMARK          0x00000010
#define ST_EIO_PENDING          0x00000020
#define ST_EOM_PENDING          0x00000040
#define ST_EOD_DETECTED         0x00000080
#define ST_FM_WRITTEN           0x00000100
#define ST_BLANK_READ           0x00000200
#define ST_2FM_AT_EOD           0x00000400
#define ST_MOUNTED              0x00000800
#define ST_DONTBUFFER           0x00001000
#define ST_DYING                0x00004000
#define ST_BOD_DETECTED         0x00008000
#define ST_MODE_DENSITY         0x00010000
#define ST_MODE_BLKSIZE         0x00040000

        u_int quirks;           /* quirks for the open mode           */
        int blksize;            /* blksize we are using               */
        u_int8_t density;       /* present density                    */
        short mt_resid;         /* last (short) resid                 */
        short mt_erreg;         /* last error (sense key) seen        */

        struct scsi_link *sc_link;      /* our link to the adapter etc.       */

        int blkmin;             /* min blk size                       */
        int blkmax;             /* max blk size                       */

        u_int32_t media_blksize;        /* 0 if not ST_FIXEDBLOCKS            */
        u_int32_t media_density;        /* this is what it said when asked    */
        int media_fileno;               /* relative to BOT. -1 means unknown. */
        int media_blkno;                /* relative to BOF. -1 means unknown. */
        int media_eom;                  /* relative to BOT. -1 means unknown. */

        struct mode mode;
        struct bufq sc_bufq;
        struct scsi_xshandler sc_xsh;
};


int     stmatch(struct device *, void *, void *);
void    stattach(struct device *, struct device *, void *);
int     stactivate(struct device *, int);
int     stdetach(struct device *, int);
void    stminphys(struct buf *);
void    ststart(struct scsi_xfer *);

int     st_mount_tape(struct st_softc *, int);
void    st_unmount(struct st_softc *, int, int);
int     st_decide_mode(struct st_softc *, int);
void    st_buf_done(struct scsi_xfer *);
int     st_read(struct st_softc *, char *, int, int);
int     st_read_block_limits(struct st_softc *, int);
int     st_mode_sense(struct st_softc *, int);
int     st_mode_select(struct st_softc *, int);
int     st_space(struct st_softc *, int, u_int, int);
int     st_write_filemarks(struct st_softc *, int, int);
int     st_check_eod(struct st_softc *, int, int *, int);
int     st_load(struct st_softc *, u_int, int);
int     st_rewind(struct st_softc *, u_int, int);
int     st_interpret_sense(struct scsi_xfer *);
int     st_touch_tape(struct st_softc *);
int     st_erase(struct st_softc *, int, int);

const struct cfattach st_ca = {
        sizeof(struct st_softc), stmatch, stattach,
        stdetach, stactivate
};

struct cfdriver st_cd = {
        NULL, "st", DV_TAPE
};

#define ST_PER_ACTION   (ST_AT_FILEMARK | ST_EIO_PENDING | ST_EOM_PENDING | \
                         ST_BLANK_READ)

#define stlookup(unit) (struct st_softc *)device_lookup(&st_cd, (unit))

const struct scsi_inquiry_pattern st_patterns[] = {
        {T_SEQUENTIAL, T_REMOV,
         "",         "",                 ""},
};

int
stmatch(struct device *parent, void *match, void *aux)
{
        struct scsi_attach_args *sa = aux;
        struct scsi_inquiry_data *inq = &sa->sa_sc_link->inqdata;
        int priority;

        (void)scsi_inqmatch(inq, st_patterns, nitems(st_patterns),
            sizeof(st_patterns[0]), &priority);
        return priority;
}

/*
 * The routine called by the low level scsi routine when it discovers
 * a device suitable for this driver.
 */
void
stattach(struct device *parent, struct device *self, void *aux)
{
        const struct st_quirk_inquiry_pattern *finger;
        struct st_softc *st = (void *)self;
        struct scsi_attach_args *sa = aux;
        struct scsi_link *link = sa->sa_sc_link;
        int priority;

        SC_DEBUG(link, SDEV_DB2, ("stattach:\n"));

        /*
         * Store information needed to contact our base driver
         */
        st->sc_link = link;
        link->interpret_sense = st_interpret_sense;
        link->device_softc = st;

        /* Get any quirks and mode information. */
        finger = (const struct st_quirk_inquiry_pattern *)scsi_inqmatch(
            &link->inqdata,
            st_quirk_patterns,
            nitems(st_quirk_patterns),
            sizeof(st_quirk_patterns[0]), &priority);
        if (finger != NULL) {
                st->quirks = finger->quirkdata.quirks;
                st->mode = finger->quirkdata.mode;
                CLR(st->flags, ST_MODE_BLKSIZE | ST_MODE_DENSITY);
                if (st->mode.blksize != 0)
                        SET(st->flags, ST_MODE_BLKSIZE);
                if (st->mode.density != 0)
                        SET(st->flags, ST_MODE_DENSITY);
        }
        printf("\n");

        scsi_xsh_set(&st->sc_xsh, link, ststart);

        st->sc_dk.dk_name = st->sc_dev.dv_xname;

        /* Set up the buf queue for this device. */
        bufq_init(&st->sc_bufq, BUFQ_FIFO);

        /* Start up with media position unknown. */
        st->media_fileno = -1;
        st->media_blkno = -1;
        st->media_eom = -1;

        /*
         * Reset the media loaded flag, sometimes the data
         * acquired at boot time is not quite accurate.  This
         * will be checked again at the first open.
         */
        CLR(link->flags, SDEV_MEDIA_LOADED);

        st->sc_dk.dk_flags = DKF_NOLABELREAD;
        disk_attach(&st->sc_dev, &st->sc_dk);
}

int
stactivate(struct device *self, int act)
{
        struct st_softc *st = (struct st_softc *)self;

        switch (act) {
        case DVACT_DEACTIVATE:
                SET(st->flags, ST_DYING);
                scsi_xsh_del(&st->sc_xsh);
                break;
        }

        return 0;
}

int
stdetach(struct device *self, int flags)
{
        struct st_softc *st = (struct st_softc *)self;
        int cmaj, mn;

        bufq_drain(&st->sc_bufq);

        /* Locate the lowest minor number to be detached. */
        mn = STMINOR(self->dv_unit, 0);

        for (cmaj = 0; cmaj < nchrdev; cmaj++)
                if (cdevsw[cmaj].d_open == stopen)
                        vdevgone(cmaj, mn, mn + MAXSTMODES - 1, VCHR);

        bufq_destroy(&st->sc_bufq);

        disk_detach(&st->sc_dk);

        return 0;
}

/*
 * open the device.
 */
int
stopen(dev_t dev, int flags, int fmt, struct proc *p)
{
        struct scsi_link *link;
        struct st_softc *st;
        int error = 0;

        st = stlookup(STUNIT(dev));
        if (st == NULL)
                return ENXIO;
        if (ISSET(st->flags, ST_DYING)) {
                device_unref(&st->sc_dev);
                return ENXIO;
        }
        link = st->sc_link;

        if ((error = disk_lock(&st->sc_dk)) != 0) {
                device_unref(&st->sc_dev);
                return error;
        }

        if (ISSET(flags, FWRITE) && ISSET(link->flags, SDEV_READONLY)) {
                error = EACCES;
                goto done;
        }

        SC_DEBUG(link, SDEV_DB1, ("open: dev=0x%x (unit %d (of %d))\n", dev,
            STUNIT(dev), st_cd.cd_ndevs));

        /*
         * Tape is an exclusive media. Only one open at a time.
         */
        if (ISSET(link->flags, SDEV_OPEN)) {
                SC_DEBUG(link, SDEV_DB4, ("already open\n"));
                error = EBUSY;
                goto done;
        }

        /* Use st_interpret_sense() now. */
        SET(link->flags, SDEV_OPEN);

        /*
         * Check the unit status. This clears any outstanding errors and
         * will ensure that media is present.
         */
        error = scsi_test_unit_ready(link, TEST_READY_RETRIES,
            SCSI_SILENT | SCSI_IGNORE_MEDIA_CHANGE |
            SCSI_IGNORE_ILLEGAL_REQUEST);

        /*
         * Terminate any existing mount session if there is no media.
         */
        if (!ISSET(link->flags, SDEV_MEDIA_LOADED))
                st_unmount(st, NOEJECT, DOREWIND);

        if (error != 0) {
                CLR(link->flags, SDEV_OPEN);
                goto done;
        }

        error = st_mount_tape(st, flags);
        if (error != 0) {
                CLR(link->flags, SDEV_OPEN);
                goto done;
        }

        /*
         * Make sure that a tape opened in write-only mode will have
         * file marks written on it when closed, even if not written to.
         * This is for SUN compatibility
         */
        if ((flags & O_ACCMODE) == FWRITE)
                SET(st->flags, ST_WRITTEN);

done:
        SC_DEBUG(link, SDEV_DB2, ("open complete\n"));
        disk_unlock(&st->sc_dk);
        device_unref(&st->sc_dev);
        return error;
}

/*
 * close the device.. only called if we are the LAST
 * occurrence of an open device
 */
int
stclose(dev_t dev, int flags, int mode, struct proc *p)
{
        struct scsi_link *link;
        struct st_softc *st;
        int error = 0;

        st = stlookup(STUNIT(dev));
        if (st == NULL)
                return ENXIO;
        if (ISSET(st->flags, ST_DYING)) {
                error = ENXIO;
                goto done;
        }
        link = st->sc_link;

        disk_lock_nointr(&st->sc_dk);

        SC_DEBUG(link, SDEV_DB1, ("closing\n"));

        if (ISSET(st->flags, ST_WRITTEN) && !ISSET(st->flags, ST_FM_WRITTEN))
                st_write_filemarks(st, 1, 0);

        switch (STMODE(dev)) {
        case 0:         /* /dev/rstN */
                st_unmount(st, NOEJECT, DOREWIND);
                break;
        case 1:         /* /dev/nrstN */
                st_unmount(st, NOEJECT, NOREWIND);
                break;
        case 2:         /* /dev/erstN */
                st_unmount(st, EJECT, DOREWIND);
                break;
        case 3:         /* /dev/enrstN */
                st_unmount(st, EJECT, NOREWIND);
                break;
        }
        CLR(link->flags, SDEV_OPEN);
        scsi_xsh_del(&st->sc_xsh);

        disk_unlock(&st->sc_dk);

done:
        device_unref(&st->sc_dev);
        return error;
}

/*
 * Start a new mount session if needed.
 */
int
st_mount_tape(struct st_softc *st, int flags)
{
        struct scsi_link *link = st->sc_link;
        int error = 0;

        if (ISSET(st->flags, ST_MOUNTED))
                return 0;

        SC_DEBUG(link, SDEV_DB1, ("mounting\n"));

        /*
         * Assume the media is new and give it a chance to
         * to do a 'load' instruction.
         */
        if ((error = st_load(st, LD_LOAD, 0)) != 0)
                goto done;

        /*
         * Throw another dummy instruction to catch
         * 'Unit attention' errors. Some drives appear to give
         * these after doing a Load instruction.
         * (notably some DAT drives)
         */
        /* XXX */
        scsi_test_unit_ready(link, TEST_READY_RETRIES, SCSI_SILENT);

        /*
         * Some devices can't tell you much until they have been
         * asked to look at the media. This quirk does this.
         */
        if (ISSET(st->quirks, ST_Q_SENSE_HELP))
                if ((error = st_touch_tape(st)) != 0)
                        return error;
        /*
         * Load the physical device parameters
         * loads: blkmin, blkmax
         */
        if (!ISSET(link->flags, SDEV_ATAPI) &&
            (error = st_read_block_limits(st, 0)) != 0)
                goto done;

        /*
         * Load the media dependent parameters
         * includes: media_blksize,media_density
         * As we have a tape in, it should be reflected here.
         * If not you may need the "quirk" above.
         */
        if ((error = st_mode_sense(st, 0)) != 0)
                goto done;

        /*
         * If we have gained a permanent density from somewhere,
         * then use it in preference to the one supplied by
         * default by the driver.
         */
        if (ISSET(st->flags, ST_MODE_DENSITY))
                st->density = st->mode.density;
        else
                st->density = st->media_density;
        /*
         * If we have gained a permanent blocksize
         * then use it in preference to the one supplied by
         * default by the driver.
         */
        CLR(st->flags, ST_FIXEDBLOCKS);
        if (ISSET(st->flags, ST_MODE_BLKSIZE)) {
                st->blksize = st->mode.blksize;
                if (st->blksize)
                        SET(st->flags, ST_FIXEDBLOCKS);
        } else {
                if ((error = st_decide_mode(st, 0)) != 0)
                        goto done;
        }
        if ((error = st_mode_select(st, 0)) != 0) {
                printf("%s: cannot set selected mode\n", st->sc_dev.dv_xname);
                goto done;
        }
        scsi_prevent(link, PR_PREVENT,
            SCSI_IGNORE_ILLEGAL_REQUEST | SCSI_IGNORE_NOT_READY);
        SET(st->flags, ST_MOUNTED);
        SET(link->flags, SDEV_MEDIA_LOADED);    /* move earlier? */
        st->media_fileno = 0;
        st->media_blkno = 0;
        st->media_eom = -1;

done:
        return error;
}

/*
 * End the present mount session.
 * Rewind, and optionally eject the tape.
 * Reset various flags to indicate that all new
 * operations require another mount operation
 */
void
st_unmount(struct st_softc *st, int eject, int rewind)
{
        struct scsi_link *link = st->sc_link;
        int nmarks;

        if (eject == NOEJECT && rewind == NOREWIND) {
                if (ISSET(link->flags, SDEV_MEDIA_LOADED))
                        return;
        }

        st->media_fileno = -1;
        st->media_blkno = -1;

        if (!ISSET(st->flags, ST_MOUNTED))
                return;
        SC_DEBUG(link, SDEV_DB1, ("unmounting\n"));
        st_check_eod(st, 0, &nmarks, SCSI_IGNORE_NOT_READY);
        if (rewind == DOREWIND)
                st_rewind(st, 0, SCSI_IGNORE_NOT_READY);
        scsi_prevent(link, PR_ALLOW,
            SCSI_IGNORE_ILLEGAL_REQUEST | SCSI_IGNORE_NOT_READY);
        if (eject == EJECT)
                st_load(st, LD_UNLOAD, SCSI_IGNORE_NOT_READY);
        CLR(st->flags, ST_MOUNTED);
        CLR(link->flags, SDEV_MEDIA_LOADED);
}

/*
 * Given all we know about the device, media, mode, 'quirks' and
 * initial operation, make a decision as to how we should be set
 * to run (regarding blocking and EOD marks)
 */
int
st_decide_mode(struct st_softc *st, int first_read)
{
        struct scsi_link *link = st->sc_link;

        SC_DEBUG(link, SDEV_DB2, ("starting block mode decision\n"));

        /* ATAPI tapes are always fixed blocksize. */
        if (ISSET(link->flags, SDEV_ATAPI)) {
                SET(st->flags, ST_FIXEDBLOCKS);
                if (st->media_blksize > 0)
                        st->blksize = st->media_blksize;
                else
                        st->blksize = DEF_FIXED_BSIZE;
                goto done;
        }

        /*
         * If the drive can only handle fixed-length blocks and only at
         * one size, perhaps we should just do that.
         */
        if (st->blkmin && (st->blkmin == st->blkmax)) {
                SET(st->flags, ST_FIXEDBLOCKS);
                st->blksize = st->blkmin;
                SC_DEBUG(link, SDEV_DB3,
                    ("blkmin == blkmax of %d\n", st->blkmin));
                goto done;
        }
        /*
         * If the tape density mandates (or even suggests) use of fixed
         * or variable-length blocks, comply.
         */
        switch (st->density) {
        case HALFINCH_800:
        case HALFINCH_1600:
        case HALFINCH_6250:
        case DDS:
                CLR(st->flags, ST_FIXEDBLOCKS);
                st->blksize = 0;
                SC_DEBUG(link, SDEV_DB3, ("density specified variable\n"));
                goto done;
        case QIC_11:
        case QIC_24:
        case QIC_120:
        case QIC_150:
        case QIC_525:
        case QIC_1320:
                SET(st->flags, ST_FIXEDBLOCKS);
                if (st->media_blksize > 0)
                        st->blksize = st->media_blksize;
                else
                        st->blksize = DEF_FIXED_BSIZE;
                SC_DEBUG(link, SDEV_DB3, ("density specified fixed\n"));
                goto done;
        }
        /*
         * If we're about to read the tape, perhaps we should choose
         * fixed or variable-length blocks and block size according to
         * what the drive found on the tape.
         */
        if (first_read) {
                if (st->media_blksize > 0)
                        SET(st->flags, ST_FIXEDBLOCKS);
                else
                        CLR(st->flags, ST_FIXEDBLOCKS);
                st->blksize = st->media_blksize;
                SC_DEBUG(link, SDEV_DB3,
                    ("Used media_blksize of %d\n", st->media_blksize));
                goto done;
        }
        /*
         * We're getting no hints from any direction.  Choose variable-
         * length blocks arbitrarily.
         */
        CLR(st->flags, ST_FIXEDBLOCKS);
        st->blksize = 0;
        SC_DEBUG(link, SDEV_DB3,
            ("Give up and default to variable mode\n"));

done:
        /*
         * Decide whether or not to write two file marks to signify end-
         * of-data.  Make the decision as a function of density.  If
         * the decision is not to use a second file mark, the SCSI BLANK
         * CHECK condition code will be recognized as end-of-data when
         * first read.
         * (I think this should be a by-product of fixed/variable..julian)
         */
        switch (st->density) {
/*      case 8 mm:   What is the SCSI density code for 8 mm, anyway? */
        case QIC_11:
        case QIC_24:
        case QIC_120:
        case QIC_150:
        case QIC_525:
        case QIC_1320:
                CLR(st->flags, ST_2FM_AT_EOD);
                break;
        default:
                SET(st->flags, ST_2FM_AT_EOD);
        }
        return 0;
}

/*
 * Actually translate the requested transfer into
 * one the physical driver can understand
 * The transfer is described by a buf and will include
 * only one physical transfer.
 */
void
ststrategy(struct buf *bp)
{
        struct scsi_link *link;
        struct st_softc *st;
        int s;

        st = stlookup(STUNIT(bp->b_dev));
        if (st == NULL) {
                bp->b_error = ENXIO;
                goto bad;
        }
        if (ISSET(st->flags, ST_DYING)) {
                bp->b_error = ENXIO;
                goto bad;
        }
        link = st->sc_link;

        SC_DEBUG(link, SDEV_DB2, ("ststrategy: %ld bytes @ blk %lld\n",
            bp->b_bcount, (long long)bp->b_blkno));

        /*
         * If it's a null transfer, return immediately.
         */
        if (bp->b_bcount == 0)
                goto done;
        /*
         * Odd sized request on fixed drives are verboten
         */
        if (ISSET(st->flags, ST_FIXEDBLOCKS)) {
                if (bp->b_bcount % st->blksize) {
                        printf("%s: bad request, must be multiple of %d\n",
                            st->sc_dev.dv_xname, st->blksize);
                        bp->b_error = EIO;
                        goto bad;
                }
        }
        /*
         * as are out-of-range requests on variable drives.
         */
        else if (bp->b_bcount < st->blkmin ||
            (st->blkmax && bp->b_bcount > st->blkmax)) {
                printf("%s: bad request, must be between %d and %d\n",
                    st->sc_dev.dv_xname, st->blkmin, st->blkmax);
                bp->b_error = EIO;
                goto bad;
        }

        /*
         * Place it in the queue of activities for this tape
         * at the end (a bit silly because we only have on user..
         * (but it could fork()))
         */
        bufq_queue(&st->sc_bufq, bp);

        /*
         * Tell the device to get going on the transfer if it's
         * not doing anything, otherwise just wait for completion
         * (All a bit silly if we're only allowing 1 open but..)
         */
        scsi_xsh_add(&st->sc_xsh);

        device_unref(&st->sc_dev);
        return;
bad:
        SET(bp->b_flags, B_ERROR);
done:
        /* Set b_resid to indicate no xfer was done. */
        bp->b_resid = bp->b_bcount;
        s = splbio();
        biodone(bp);
        splx(s);
        if (st)
                device_unref(&st->sc_dev);
}

void
ststart(struct scsi_xfer *xs)
{
        struct scsi_link *link = xs->sc_link;
        struct st_softc *st = link->device_softc;
        struct buf *bp;
        struct scsi_rw_tape *cmd;
        int s;

        SC_DEBUG(link, SDEV_DB2, ("ststart\n"));

        if (ISSET(st->flags, ST_DYING)) {
                scsi_xs_put(xs);
                return;
        }

        /*
         * if the device has been unmounted by the user
         * then throw away all requests until done
         */
        if (!ISSET(st->flags, ST_MOUNTED) ||
            !ISSET(link->flags, SDEV_MEDIA_LOADED)) {
                /* make sure that one implies the other.. */
                CLR(link->flags, SDEV_MEDIA_LOADED);
                bufq_drain(&st->sc_bufq);
                scsi_xs_put(xs);
                return;
        }

        for (;;) {
                bp = bufq_dequeue(&st->sc_bufq);
                if (bp == NULL) {
                        scsi_xs_put(xs);
                        return;
                }

                /*
                 * Only FIXEDBLOCK devices have pending I/O or space
                 * operations.
                 */
                if (ISSET(st->flags, ST_FIXEDBLOCKS)) {
                        /*
                         * If we are at a filemark but have not reported it yet
                         * then we should report it now
                         */
                        if (ISSET(st->flags, ST_AT_FILEMARK)) {
                                if ((bp->b_flags & B_READ) == B_WRITE) {
                                        /*
                                         * Handling of ST_AT_FILEMARK in
                                         * st_space will fill in the right file
                                         * mark count.
                                         * Back up over filemark
                                         */
                                        if (st_space(st, 0, SP_FILEMARKS, 0)) {
                                                SET(bp->b_flags, B_ERROR);
                                                bp->b_resid = bp->b_bcount;
                                                bp->b_error = EIO;
                                                s = splbio();
                                                biodone(bp);
                                                splx(s);
                                                continue;
                                        }
                                } else {
                                        bp->b_resid = bp->b_bcount;
                                        bp->b_error = 0;
                                        CLR(bp->b_flags, B_ERROR);
                                        CLR(st->flags, ST_AT_FILEMARK);
                                        s = splbio();
                                        biodone(bp);
                                        splx(s);
                                        continue;       /* seek more work */
                                }
                        }
                }

                /*
                 * If we are at EIO or EOM but have not reported it
                 * yet then we should report it now.
                 */
                if (ISSET(st->flags, ST_EOM_PENDING | ST_EIO_PENDING)) {
                        bp->b_resid = bp->b_bcount;
                        if (ISSET(st->flags, ST_EIO_PENDING)) {
                                bp->b_error = EIO;
                                SET(bp->b_flags, B_ERROR);
                        }
                        CLR(st->flags, ST_EOM_PENDING | ST_EIO_PENDING);
                        s = splbio();
                        biodone(bp);
                        splx(s);
                        continue;       /* seek more work */
                }
                break;
        }

        /*
         *  Fill out the scsi command
         */
        cmd = (struct scsi_rw_tape *)&xs->cmd;
        bzero(cmd, sizeof(*cmd));
        if ((bp->b_flags & B_READ) == B_WRITE) {
                cmd->opcode = WRITE;
                CLR(st->flags, ST_FM_WRITTEN);
                SET(st->flags, ST_WRITTEN);
                SET(xs->flags, SCSI_DATA_OUT);
        } else {
                cmd->opcode = READ;
                SET(xs->flags, SCSI_DATA_IN);
        }

        /*
         * Handle "fixed-block-mode" tape drives by using the
         * block count instead of the length.
         */
        if (ISSET(st->flags, ST_FIXEDBLOCKS)) {
                SET(cmd->byte2, SRW_FIXED);
                _lto3b(bp->b_bcount / st->blksize, cmd->len);
        } else
                _lto3b(bp->b_bcount, cmd->len);

        if (st->media_blkno != -1) {
                /* Update block count now, errors will set it to -1. */
                if (ISSET(st->flags, ST_FIXEDBLOCKS))
                        st->media_blkno += _3btol(cmd->len);
                else if (_3btol(cmd->len) != 0)
                        st->media_blkno++;
        }

        xs->cmdlen = sizeof(*cmd);
        xs->timeout = ST_IO_TIME;
        xs->data = bp->b_data;
        xs->datalen = bp->b_bcount;
        xs->done = st_buf_done;
        xs->cookie = bp;
        xs->bp = bp;

        /* Instrumentation. */
        disk_busy(&st->sc_dk);

        /*
         * go ask the adapter to do all this for us
         */
        scsi_xs_exec(xs);

        /*
         * should we try do more work now?
         */
        if (bufq_peek(&st->sc_bufq))
                scsi_xsh_add(&st->sc_xsh);
}

void
st_buf_done(struct scsi_xfer *xs)
{
        struct st_softc *st = xs->sc_link->device_softc;
        struct buf *bp = xs->cookie;
        int error, s;

        switch (xs->error) {
        case XS_NOERROR:
                bp->b_error = 0;
                CLR(bp->b_flags, B_ERROR);
                bp->b_resid = xs->resid;
                break;

        case XS_SENSE:
        case XS_SHORTSENSE:
                SC_DEBUG_SENSE(xs);
                error = st_interpret_sense(xs);
                if (error == 0) {
                        bp->b_error = 0;
                        CLR(bp->b_flags, B_ERROR);
                        bp->b_resid = xs->resid;
                        break;
                }
                if (error != ERESTART)
                        xs->retries = 0;
                goto retry;

        case XS_BUSY:
                if (xs->retries) {
                        if (scsi_delay(xs, 1) != ERESTART)
                                xs->retries = 0;
                }
                goto retry;

        case XS_TIMEOUT:
 retry:
                if (xs->retries--) {
                        scsi_xs_exec(xs);
                        return;
                }
                /* FALLTHROUGH */

        default:
                bp->b_error = EIO;
                SET(bp->b_flags, B_ERROR);
                bp->b_resid = bp->b_bcount;
                break;
        }

        disk_unbusy(&st->sc_dk, bp->b_bcount - xs->resid, bp->b_blkno,
                bp->b_flags & B_READ);

        s = splbio();
        biodone(bp);
        splx(s);
        scsi_xs_put(xs);
}

void
stminphys(struct buf *bp)
{
        struct scsi_link        *link;
        struct st_softc         *sc;

        sc = stlookup(STUNIT(bp->b_dev));
        if (sc == NULL)
                return;
        link = sc->sc_link;

        if (link->bus->sb_adapter->dev_minphys != NULL)
                (*link->bus->sb_adapter->dev_minphys)(bp, link);
        else
                minphys(bp);

        device_unref(&sc->sc_dev);
}

int
stread(dev_t dev, struct uio *uio, int iomode)
{
        return physio(ststrategy, dev, B_READ, stminphys, uio);
}

int
stwrite(dev_t dev, struct uio *uio, int iomode)
{
        return physio(ststrategy, dev, B_WRITE, stminphys, uio);
}

/*
 * Perform special action on behalf of the user;
 * knows about the internals of this device
 */
int
stioctl(dev_t dev, u_long cmd, caddr_t arg, int flag, struct proc *p)
{
        int error = 0;
        int nmarks;
        int flags = 0;
        struct st_softc *st;
        int hold_blksize;
        u_int8_t hold_density;
        struct mtop *mt = (struct mtop *) arg;
        int number;

        /*
         * Find the device that the user is talking about
         */
        st = stlookup(STUNIT(dev));
        if (st == NULL)
                return ENXIO;

        if (ISSET(st->flags, ST_DYING)) {
                error = ENXIO;
                goto done;
        }

        hold_blksize = st->blksize;
        hold_density = st->density;

        switch (cmd) {

        case MTIOCGET: {
                struct mtget *g = (struct mtget *) arg;

                /*
                 * (to get the current state of READONLY)
                 */
                error = st_mode_sense(st, SCSI_SILENT);
                if (error != 0)
                        break;

                SC_DEBUG(st->sc_link, SDEV_DB1, ("[ioctl: get status]\n"));
                bzero(g, sizeof(struct mtget));
                g->mt_type = 0x7;       /* Ultrix compat *//*? */
                g->mt_blksiz = st->blksize;
                g->mt_density = st->density;
                g->mt_mblksiz = st->mode.blksize;
                g->mt_mdensity = st->mode.density;
                if (ISSET(st->sc_link->flags, SDEV_READONLY))
                        SET(g->mt_dsreg, MT_DS_RDONLY);
                if (ISSET(st->flags, ST_MOUNTED))
                        SET(g->mt_dsreg, MT_DS_MOUNTED);
                g->mt_resid = st->mt_resid;
                g->mt_erreg = st->mt_erreg;
                g->mt_fileno = st->media_fileno;
                g->mt_blkno = st->media_blkno;
                /*
                 * clear latched errors.
                 */
                st->mt_resid = 0;
                st->mt_erreg = 0;
                break;
        }
        case MTIOCTOP: {

                SC_DEBUG(st->sc_link, SDEV_DB1,
                    ("[ioctl: op=0x%x count=0x%x]\n", mt->mt_op, mt->mt_count));

                number = mt->mt_count;
                switch (mt->mt_op) {
                case MTWEOF:    /* write an end-of-file record */
                        error = st_write_filemarks(st, number, flags);
                        break;
                case MTBSF:     /* backward space file */
                        number = -number;
                case MTFSF:     /* forward space file */
                        error = st_check_eod(st, 0, &nmarks, flags);
                        if (error == 0)
                                error = st_space(st, number - nmarks,
                                    SP_FILEMARKS, flags);
                        break;
                case MTBSR:     /* backward space record */
                        number = -number;
                case MTFSR:     /* forward space record */
                        error = st_check_eod(st, 1, &nmarks, flags);
                        if (error == 0)
                                error = st_space(st, number, SP_BLKS, flags);
                        break;
                case MTREW:     /* rewind */
                        error = st_rewind(st, 0, flags);
                        break;
                case MTOFFL:    /* rewind and put the drive offline */
                        st_unmount(st, EJECT, DOREWIND);
                        break;
                case MTNOP:     /* no operation, sets status only */
                        break;
                case MTRETEN:   /* retension the tape */
                        error = st_load(st, LD_RETENSION, flags);
                        if (error == 0)
                                error = st_load(st, LD_LOAD, flags);
                        break;
                case MTEOM:     /* forward space to end of media */
                        error = st_check_eod(st, 0, &nmarks, flags);
                        if (error == 0)
                                error = st_space(st, 1, SP_EOM, flags);
                        break;
                case MTCACHE:   /* enable controller cache */
                        CLR(st->flags, ST_DONTBUFFER);
                        goto try_new_value;
                case MTNOCACHE: /* disable controller cache */
                        SET(st->flags, ST_DONTBUFFER);
                        goto try_new_value;
                case MTERASE:   /* erase volume */
                        error = st_erase(st, number, flags);
                        break;
                case MTSETBSIZ: /* Set block size for device and mode. */
                        if (number == 0) {
                                CLR(st->flags, ST_FIXEDBLOCKS);
                        } else {
                                if ((st->blkmin || st->blkmax) &&
                                    (number < st->blkmin ||
                                    number > st->blkmax)) {
                                        error = EINVAL;
                                        break;
                                }
                                SET(st->flags, ST_FIXEDBLOCKS);
                        }
                        st->blksize = number;
                        goto try_new_value;

                case MTSETDNSTY:        /* Set density for device and mode. */
                        if (number < 0 || number > SCSI_MAX_DENSITY_CODE) {
                                error = EINVAL;
                                break;
                        }
                        st->density = number;
                        goto try_new_value;

                default:
                        error = EINVAL;
                }
                break;
        }
        case MTIOCIEOT:
        case MTIOCEEOT:
                break;

#if 0
        case MTIOCRDSPOS:
                error = st_rdpos(st, 0, (u_int32_t *) arg);
                break;

        case MTIOCRDHPOS:
                error = st_rdpos(st, 1, (u_int32_t *) arg);
                break;

        case MTIOCSLOCATE:
                error = st_setpos(st, 0, (u_int32_t *) arg);
                break;

        case MTIOCHLOCATE:
                error = st_setpos(st, 1, (u_int32_t *) arg);
                break;
#endif /* 0 */

        default:
                error = scsi_do_ioctl(st->sc_link, cmd, arg, flag);
                break;
        }
        goto done;

try_new_value:
        /*
         * Check that the mode being asked for is agreeable to the
         * drive. If not, put it back the way it was.
         */
        if ((error = st_mode_select(st, 0)) != 0) {/* put it back as it was */
                printf("%s: cannot set selected mode\n", st->sc_dev.dv_xname);
                st->density = hold_density;
                st->blksize = hold_blksize;
                if (st->blksize)
                        SET(st->flags, ST_FIXEDBLOCKS);
                else
                        CLR(st->flags, ST_FIXEDBLOCKS);
                goto done;
        }
        /*
         * As the drive liked it, if we are setting a new default,
         * set it into the structures as such.
         */
        switch (mt->mt_op) {
        case MTSETBSIZ:
                st->mode.blksize = st->blksize;
                SET(st->flags, ST_MODE_BLKSIZE);
                break;
        case MTSETDNSTY:
                st->mode.density = st->density;
                SET(st->flags, ST_MODE_DENSITY);
                break;
        }

done:
        device_unref(&st->sc_dev);
        return error;
}

/*
 * Do a synchronous read.
 */
int
st_read(struct st_softc *st, char *buf, int size, int flags)
{
        struct scsi_rw_tape *cmd;
        struct scsi_xfer *xs;
        int error;

        if (size == 0)
                return 0;

        xs = scsi_xs_get(st->sc_link, flags | SCSI_DATA_IN);
        if (xs == NULL)
                return ENOMEM;
        xs->cmdlen = sizeof(*cmd);
        xs->data = buf;
        xs->datalen = size;
        xs->retries = 0;
        xs->timeout = ST_IO_TIME;

        cmd = (struct scsi_rw_tape *)&xs->cmd;
        cmd->opcode = READ;
        if (ISSET(st->flags, ST_FIXEDBLOCKS)) {
                SET(cmd->byte2, SRW_FIXED);
                _lto3b(size / (st->blksize ? st->blksize : DEF_FIXED_BSIZE),
                    cmd->len);
        } else
                _lto3b(size, cmd->len);

        error = scsi_xs_sync(xs);
        scsi_xs_put(xs);

        return error;
}

/*
 * Ask the drive what its min and max blk sizes are.
 */
int
st_read_block_limits(struct st_softc *st, int flags)
{
        struct scsi_block_limits_data *block_limits = NULL;
        struct scsi_block_limits *cmd;
        struct scsi_link *link = st->sc_link;
        struct scsi_xfer *xs;
        int error = 0;

        if (ISSET(link->flags, SDEV_MEDIA_LOADED))
                return 0;

        block_limits = dma_alloc(sizeof(*block_limits), PR_NOWAIT);
        if (block_limits == NULL)
                return ENOMEM;

        xs = scsi_xs_get(link, flags | SCSI_DATA_IN);
        if (xs == NULL) {
                error = ENOMEM;
                goto done;
        }

        xs->cmdlen = sizeof(*cmd);
        xs->data = (void *)block_limits;
        xs->datalen = sizeof(*block_limits);
        xs->timeout = ST_CTL_TIME;

        cmd = (struct scsi_block_limits *)&xs->cmd;
        cmd->opcode = READ_BLOCK_LIMITS;

        error = scsi_xs_sync(xs);
        scsi_xs_put(xs);

        if (error == 0) {
                st->blkmin = _2btol(block_limits->min_length);
                st->blkmax = _3btol(block_limits->max_length);
                SC_DEBUG(link, SDEV_DB3,
                    ("(%d <= blksize <= %d)\n", st->blkmin, st->blkmax));
        }

done:
        if (block_limits)
                dma_free(block_limits, sizeof(*block_limits));
        return error;
}

/*
 * Get the scsi driver to send a full inquiry to the
 * device and use the results to fill out the global
 * parameter structure.
 *
 * called from:
 * attach
 * open
 * ioctl (to reset original blksize)
 */
int
st_mode_sense(struct st_softc *st, int flags)
{
        union scsi_mode_sense_buf *data = NULL;
        struct scsi_link *link = st->sc_link;
        u_int64_t block_count;
        u_int32_t density, block_size;
        u_char *page0 = NULL;
        u_int8_t dev_spec;
        int error = 0, big;

        data = dma_alloc(sizeof(*data), PR_NOWAIT);
        if (data == NULL)
                return ENOMEM;

        /*
         * Ask for page 0 (vendor specific) mode sense data.
         */
        density = 0;
        block_count = 0;
        block_size = 0;
        error = scsi_do_mode_sense(link, 0, data, (void **)&page0, 1,
            flags | SCSI_SILENT, &big);
        if (error != 0)
                goto done;
        scsi_parse_blkdesc(link, data, big, &density, &block_count,
            &block_size);

        /* It is valid for no page0 to be available. */

        if (big)
                dev_spec = data->hdr_big.dev_spec;
        else
                dev_spec = data->hdr.dev_spec;

        if (ISSET(dev_spec, SMH_DSP_WRITE_PROT))
                SET(link->flags, SDEV_READONLY);
        else
                CLR(link->flags, SDEV_READONLY);

        st->media_blksize = block_size;
        st->media_density = density;

        SC_DEBUG(link, SDEV_DB3,
            ("density code 0x%x, %d-byte blocks, write-%s, %sbuffered\n",
            st->media_density, st->media_blksize,
            ISSET(link->flags, SDEV_READONLY) ? "protected" : "enabled",
            ISSET(dev_spec, SMH_DSP_BUFF_MODE) ? "" : "un"));

        SET(link->flags, SDEV_MEDIA_LOADED);

 done:
        if (data)
                dma_free(data, sizeof(*data));
        return error;
}

/*
 * Send a filled out parameter structure to the drive to
 * set it into the desire mode etc.
 */
int
st_mode_select(struct st_softc *st, int flags)
{
        union scsi_mode_sense_buf *inbuf = NULL, *outbuf = NULL;
        struct scsi_blk_desc general;
        struct scsi_link *link = st->sc_link;
        u_int8_t *page0 = NULL;
        int error = 0, big, page0_size;

        inbuf = dma_alloc(sizeof(*inbuf), PR_NOWAIT);
        if (inbuf == NULL) {
                error = ENOMEM;
                goto done;
        }
        outbuf = dma_alloc(sizeof(*outbuf), PR_NOWAIT | PR_ZERO);
        if (outbuf == NULL) {
                error = ENOMEM;
                goto done;
        }

        /*
         * This quirk deals with drives that have only one valid mode and think
         * this gives them license to reject all mode selects, even if the
         * selected mode is the one that is supported.
         */
        if (ISSET(st->quirks, ST_Q_UNIMODAL)) {
                SC_DEBUG(link, SDEV_DB3,
                    ("not setting density 0x%x blksize 0x%x\n",
                    st->density, st->blksize));
                error = 0;
                goto done;
        }

        if (ISSET(link->flags, SDEV_ATAPI)) {
                error = 0;
                goto done;
        }

        bzero(&general, sizeof(general));

        general.density = st->density;
        if (ISSET(st->flags, ST_FIXEDBLOCKS))
                _lto3b(st->blksize, general.blklen);

        /*
         * Ask for page 0 (vendor specific) mode sense data.
         *
         * page0 == NULL is a valid situation.
         */
        error = scsi_do_mode_sense(link, 0, inbuf, (void **)&page0, 1,
            flags | SCSI_SILENT, &big);
        if (error != 0)
                goto done;

        if (page0 == NULL) {
                page0_size = 0;
        } else if (big == 0) {
                page0_size = inbuf->hdr.data_length +
                    sizeof(inbuf->hdr.data_length) - sizeof(inbuf->hdr) -
                    inbuf->hdr.blk_desc_len;
                memcpy(&outbuf->buf[sizeof(outbuf->hdr)+ sizeof(general)],
                    page0, page0_size);
        } else {
                page0_size = _2btol(inbuf->hdr_big.data_length) +
                    sizeof(inbuf->hdr_big.data_length) -
                    sizeof(inbuf->hdr_big) -
                    _2btol(inbuf->hdr_big.blk_desc_len);
                memcpy(&outbuf->buf[sizeof(outbuf->hdr_big) + sizeof(general)],
                    page0, page0_size);
        }

        /*
         * Set up for a mode select.
         */
        if (big == 0) {
                outbuf->hdr.data_length = sizeof(outbuf->hdr) +
                    sizeof(general) + page0_size -
                    sizeof(outbuf->hdr.data_length);
                if (!ISSET(st->flags, ST_DONTBUFFER))
                        outbuf->hdr.dev_spec = SMH_DSP_BUFF_MODE_ON;
                outbuf->hdr.blk_desc_len = sizeof(general);
                memcpy(&outbuf->buf[sizeof(outbuf->hdr)],
                    &general, sizeof(general));
                error = scsi_mode_select(st->sc_link, 0, &outbuf->hdr,
                    flags, ST_CTL_TIME);
                goto done;
        }

        /* MODE SENSE (10) header was returned, so use MODE SELECT (10). */
        _lto2b((sizeof(outbuf->hdr_big) + sizeof(general) + page0_size -
            sizeof(outbuf->hdr_big.data_length)), outbuf->hdr_big.data_length);
        if (!ISSET(st->flags, ST_DONTBUFFER))
                outbuf->hdr_big.dev_spec = SMH_DSP_BUFF_MODE_ON;
        _lto2b(sizeof(general), outbuf->hdr_big.blk_desc_len);
        memcpy(&outbuf->buf[sizeof(outbuf->hdr_big)], &general,
            sizeof(general));

        error = scsi_mode_select_big(st->sc_link, 0, &outbuf->hdr_big,
            flags, ST_CTL_TIME);
done:
        if (inbuf)
                dma_free(inbuf, sizeof(*inbuf));
        if (outbuf)
                dma_free(outbuf, sizeof(*outbuf));
        return error;
}

/*
 * issue an erase command
 */
int
st_erase(struct st_softc *st, int full, int flags)
{
        struct scsi_erase *cmd;
        struct scsi_xfer *xs;
        int error;

        xs = scsi_xs_get(st->sc_link, flags);
        if (xs == NULL)
                return ENOMEM;
        xs->cmdlen = sizeof(*cmd);

        /*
         * Full erase means set LONG bit in erase command, which asks
         * the drive to erase the entire unit.  Without this bit, we're
         * asking the drive to write an erase gap.
         */
        cmd = (struct scsi_erase *)&xs->cmd;
        cmd->opcode = ERASE;
        if (full) {
                cmd->byte2 = SE_IMMED|SE_LONG;
                xs->timeout = ST_SPC_TIME;
        } else {
                cmd->byte2 = SE_IMMED;
                xs->timeout = ST_IO_TIME;
        }

        /*
         * XXX We always do this asynchronously, for now.  How long should
         * we wait if we want to (eventually) to it synchronously?
         */
        error = scsi_xs_sync(xs);
        scsi_xs_put(xs);

        return error;
}

/*
 * skip N blocks/filemarks/seq filemarks/eom
 */
int
st_space(struct st_softc *st, int number, u_int what, int flags)
{
        struct scsi_space *cmd;
        struct scsi_xfer *xs;
        int error;

        switch (what) {
        case SP_BLKS:
                if (ISSET(st->flags, ST_PER_ACTION)) {
                        if (number > 0) {
                                CLR(st->flags, ST_PER_ACTION);
                                return EIO;
                        } else if (number < 0) {
                                if (ISSET(st->flags, ST_AT_FILEMARK)) {
                                        /*
                                         * Handling of ST_AT_FILEMARK
                                         * in st_space will fill in the
                                         * right file mark count.
                                         */
                                        error = st_space(st, 0, SP_FILEMARKS,
                                            flags);
                                        if (error != 0)
                                                return error;
                                }
                                if (ISSET(st->flags, ST_BLANK_READ)) {
                                        CLR(st->flags, ST_BLANK_READ);
                                        return EIO;
                                }
                                CLR(st->flags, ST_EIO_PENDING | ST_EOM_PENDING);
                        }
                }
                break;
        case SP_FILEMARKS:
                if (ISSET(st->flags,  ST_EIO_PENDING)) {
                        if (number > 0) {
                                /* pretend we just discovered the error */
                                CLR(st->flags, ST_EIO_PENDING);
                                return EIO;
                        } else if (number < 0) {
                                /* back away from the error */
                                CLR(st->flags, ST_EIO_PENDING);
                        }
                }
                if (ISSET(st->flags, ST_AT_FILEMARK)) {
                        CLR(st->flags, ST_AT_FILEMARK);
                        number--;
                }
                if (ISSET(st->flags, ST_BLANK_READ) && (number < 0)) {
                        /* back away from unwritten tape */
                        CLR(st->flags, ST_BLANK_READ);
                        number++;       /* XXX dubious */
                }
                break;
        case SP_EOM:
                if (ISSET(st->flags, ST_EOM_PENDING)) {
                        /* We are already there. */
                        CLR(st->flags, ST_EOM_PENDING);
                        return 0;
                }
                if (ISSET(st->flags, ST_EIO_PENDING)) {
                        /* pretend we just discovered the error */
                        CLR(st->flags, ST_EIO_PENDING);
                        return EIO;
                }
                if (ISSET(st->flags, ST_AT_FILEMARK))
                        CLR(st->flags, ST_AT_FILEMARK);
                break;
        }
        if (number == 0)
                return 0;

        xs = scsi_xs_get(st->sc_link, flags);
        if (xs == NULL)
                return ENOMEM;

        cmd = (struct scsi_space *)&xs->cmd;
        cmd->opcode = SPACE;
        cmd->byte2 = what;
        _lto3b(number, cmd->number);
        xs->cmdlen = sizeof(*cmd);
        xs->timeout = ST_SPC_TIME;

        CLR(st->flags, ST_EOD_DETECTED);

        error = scsi_xs_sync(xs);
        scsi_xs_put(xs);

        if (error != 0) {
                st->media_fileno = -1;
                st->media_blkno = -1;
        } else {
                switch (what) {
                case SP_BLKS:
                        if (st->media_blkno != -1) {
                                st->media_blkno += number;
                                if (st->media_blkno < 0)
                                        st->media_blkno = -1;
                        }
                        break;
                case SP_FILEMARKS:
                        if (st->media_fileno != -1) {
                                if (!ISSET(st->flags, ST_EOD_DETECTED))
                                        st->media_fileno += number;
                                if (st->media_fileno > st->media_eom)
                                        st->media_eom = st->media_fileno;
                                st->media_blkno = 0;
                        }
                        break;
                case SP_EOM:
                        if (st->media_eom != -1) {
                                st->media_fileno = st->media_eom;
                                st->media_blkno = 0;
                        } else {
                                st->media_fileno = -1;
                                st->media_blkno = -1;
                        }
                        break;
                default:
                        st->media_fileno = -1;
                        st->media_blkno = -1;
                        break;
                }
        }

        return error;
}

/*
 * write N filemarks
 */
int
st_write_filemarks(struct st_softc *st, int number, int flags)
{
        struct scsi_write_filemarks *cmd;
        struct scsi_xfer *xs;
        int error;

        if (number < 0)
                return EINVAL;

        xs = scsi_xs_get(st->sc_link, flags);
        if (xs == NULL)
                return ENOMEM;

        xs->cmdlen = sizeof(*cmd);
        xs->timeout = ST_IO_TIME * 4;

        switch (number) {
        case 0:         /* really a command to sync the drive's buffers */
                break;
        case 1:
                if (ISSET(st->flags, ST_FM_WRITTEN))    /* already have one down */
                        CLR(st->flags, ST_WRITTEN);
                else
                        SET(st->flags, ST_FM_WRITTEN);
                CLR(st->flags, ST_PER_ACTION);
                break;
        default:
                CLR(st->flags, ST_PER_ACTION | ST_WRITTEN);
                break;
        }

        cmd = (struct scsi_write_filemarks *)&xs->cmd;
        cmd->opcode = WRITE_FILEMARKS;
        _lto3b(number, cmd->number);

        error = scsi_xs_sync(xs);
        scsi_xs_put(xs);

        if (error != 0) {
                st->media_fileno = -1;
                st->media_blkno = -1;
                st->media_eom = -1;
        } else if (st->media_fileno != -1) {
                st->media_fileno += number;
                st->media_eom = st->media_fileno;
                st->media_blkno = 0;
        }

        return error;
}

/*
 * Make sure the right number of file marks is on tape if the
 * tape has been written.  If the position argument is true,
 * leave the tape positioned where it was originally.
 *
 * nmarks returns the number of marks to skip (or, if position
 * true, which were skipped) to get back original position.
 */
int
st_check_eod(struct st_softc *st, int position, int *nmarks, int flags)
{
        int error;

        switch (st->flags & (ST_WRITTEN | ST_FM_WRITTEN | ST_2FM_AT_EOD)) {
        default:
                *nmarks = 0;
                return 0;
        case ST_WRITTEN:
        case ST_WRITTEN | ST_FM_WRITTEN | ST_2FM_AT_EOD:
                *nmarks = 1;
                break;
        case ST_WRITTEN | ST_2FM_AT_EOD:
                *nmarks = 2;
        }
        error = st_write_filemarks(st, *nmarks, flags);
        if (error == 0 && position != 0)
                error = st_space(st, -*nmarks, SP_FILEMARKS, flags);
        return error;
}

/*
 * load/unload/retension
 */
int
st_load(struct st_softc *st, u_int type, int flags)
{
        struct scsi_load *cmd;
        struct scsi_xfer *xs;
        int error, nmarks;

        st->media_fileno = -1;
        st->media_blkno = -1;
        st->media_eom = -1;

        if (type != LD_LOAD) {
                error = st_check_eod(st, 0, &nmarks, flags);
                if (error != 0)
                        return error;
        }

        if (ISSET(st->quirks, ST_Q_IGNORE_LOADS)) {
                if (type == LD_LOAD) {
                        /*
                         * If we ignore loads, at least we should try a rewind.
                         */
                        return st_rewind(st, 0, flags);
                }
                return 0;
        }


        xs = scsi_xs_get(st->sc_link, flags);
        if (xs == NULL)
                return ENOMEM;
        xs->cmdlen = sizeof(*cmd);
        xs->timeout = ST_SPC_TIME;

        cmd = (struct scsi_load *)&xs->cmd;
        cmd->opcode = LOAD;
        cmd->how = type;

        error = scsi_xs_sync(xs);
        scsi_xs_put(xs);

        return error;
}

/*
 *  Rewind the device
 */
int
st_rewind(struct st_softc *st, u_int immediate, int flags)
{
        struct scsi_rewind *cmd;
        struct scsi_xfer *xs;
        int error, nmarks;

        error = st_check_eod(st, 0, &nmarks, flags);
        if (error != 0)
                return error;
        CLR(st->flags, ST_PER_ACTION);

        xs = scsi_xs_get(st->sc_link, flags);
        if (xs == NULL)
                return ENOMEM;
        xs->cmdlen = sizeof(*cmd);
        xs->timeout = immediate ? ST_CTL_TIME : ST_SPC_TIME;

        cmd = (struct scsi_rewind *)&xs->cmd;
        cmd->opcode = REWIND;
        cmd->byte2 = immediate;

        error = scsi_xs_sync(xs);
        scsi_xs_put(xs);

        if (error == 0) {
                st->media_fileno = 0;
                st->media_blkno = 0;
        }

        return error;
}

/*
 * Look at the returned sense and act on the error to determine
 * the unix error number to pass back... (0 = report no error)
 *                            (-1 = continue processing)
 */
int
st_interpret_sense(struct scsi_xfer *xs)
{
        struct scsi_sense_data *sense = &xs->sense;
        struct scsi_link *link = xs->sc_link;
        struct scsi_space *space;
        struct st_softc *st = link->device_softc;
        u_int8_t serr = sense->error_code & SSD_ERRCODE;
        u_int8_t skey = sense->flags & SSD_KEY;
        int32_t resid, info, number;
        int datalen;

        if (!ISSET(link->flags, SDEV_OPEN) ||
            (serr != SSD_ERRCODE_CURRENT && serr != SSD_ERRCODE_DEFERRED))
                return scsi_interpret_sense(xs);

        info = (int32_t)_4btol(sense->info);

        switch (skey) {

        /*
         * We do custom processing in st for the unit becoming ready case.
         * in this case we do not allow xs->retries to be decremented
         * only on the "Unit Becoming Ready" case. This is because tape
         * drives report "Unit Becoming Ready" when loading media, etc.
         * and can take a long time.  Rather than having a massive timeout
         * for all operations (which would cause other problems) we allow
         * operations to wait (but be interruptible with Ctrl-C) forever
         * as long as the drive is reporting that it is becoming ready.
         * all other cases are handled as per the default.
         */

        case SKEY_NOT_READY:
                if (ISSET(xs->flags, SCSI_IGNORE_NOT_READY))
                        return 0;
                switch (ASC_ASCQ(sense)) {
                case SENSE_NOT_READY_BECOMING_READY:
                        SC_DEBUG(link, SDEV_DB1, ("not ready: busy (%#x)\n",
                            sense->add_sense_code_qual));
                        /* don't count this as a retry */
                        xs->retries++;
                        return scsi_delay(xs, 1);
                default:
                        return scsi_interpret_sense(xs);
                }
                break;
        case SKEY_BLANK_CHECK:
                if (sense->error_code & SSD_ERRCODE_VALID &&
                    xs->cmd.opcode == SPACE) {
                        switch (ASC_ASCQ(sense)) {
                        case SENSE_END_OF_DATA_DETECTED:
                                SET(st->flags, ST_EOD_DETECTED);
                                space = (struct scsi_space *)&xs->cmd;
                                number = _3btol(space->number);
                                st->media_fileno = number - info;
                                st->media_eom = st->media_fileno;
                                return 0;
                        case SENSE_BEGINNING_OF_MEDIUM_DETECTED:
                                /* Standard says: Position is undefined! */
                                SET(st->flags, ST_BOD_DETECTED);
                                st->media_fileno = -1;
                                st->media_blkno = -1;
                                return 0;
                        }
                }
                break;
        case SKEY_NO_SENSE:
        case SKEY_RECOVERED_ERROR:
        case SKEY_MEDIUM_ERROR:
        case SKEY_VOLUME_OVERFLOW:
                break;
        default:
                return scsi_interpret_sense(xs);
        }

        /*
         * 'resid' can be in units of st->blksize or bytes. xs->resid and
         * xs->datalen are always in units of bytes. So we need a variable
         * to store datalen in the same units as resid and to adjust
         * xs->resid to be in bytes.
         */
        if (ISSET(sense->error_code, SSD_ERRCODE_VALID)) {
                if (ISSET(st->flags, ST_FIXEDBLOCKS))
                        resid = info * st->blksize; /* XXXX overflow? */
                else
                        resid = info;
        } else {
                resid = xs->datalen;
        }

        if (resid < 0 || resid > xs->datalen)
                xs->resid = xs->datalen;
        else
                xs->resid = resid;

        datalen = xs->datalen;
        if (ISSET(st->flags, ST_FIXEDBLOCKS)) {
                resid /= st->blksize;
                datalen /= st->blksize;
        }

        if (ISSET(sense->flags, SSD_FILEMARK)) {
                if (st->media_fileno != -1) {
                        st->media_fileno++;
                        if (st->media_fileno > st->media_eom)
                                st->media_eom = st->media_fileno;
                        st->media_blkno = 0;
                }
                if (!ISSET(st->flags, ST_FIXEDBLOCKS))
                        return 0;
                SET(st->flags, ST_AT_FILEMARK);
        }

        if (ISSET(sense->flags, SSD_EOM)) {
                SET(st->flags, ST_EOM_PENDING);
                xs->resid = 0;
                if (ISSET(st->flags, ST_FIXEDBLOCKS))
                        return 0;
        }

        if (ISSET(sense->flags, SSD_ILI)) {
                if (!ISSET(st->flags, ST_FIXEDBLOCKS)) {
                        if (resid >= 0 && resid <= datalen)
                                return 0;
                        if (!ISSET(xs->flags, SCSI_SILENT))
                                printf( "%s: bad residual %d out of "
                                    "%d\n", st->sc_dev.dv_xname, resid,
                                    datalen);
                        return EIO;
                }

                /* Fixed size blocks. */
                if (ISSET(sense->error_code, SSD_ERRCODE_VALID))
                        if (!ISSET(xs->flags, SCSI_SILENT))
                                printf("%s: block wrong size, %d blocks "
                                    "residual\n", st->sc_dev.dv_xname, resid);
                SET(st->flags, ST_EIO_PENDING);
                /*
                 * This quirk code helps the drive read the first tape block,
                 * regardless of format.  That is required for these drives to
                 * return proper MODE SENSE information.
                 */
                if (ISSET(st->quirks, ST_Q_SENSE_HELP) &&
                    !ISSET(link->flags, SDEV_MEDIA_LOADED))
                        st->blksize -= 512;
        }

        if (ISSET(st->flags, ST_FIXEDBLOCKS) && xs->resid == xs->datalen) {
                if (ISSET(st->flags, ST_EIO_PENDING))
                        return EIO;
                if (ISSET(st->flags, ST_AT_FILEMARK))
                        return 0;
        }

        if (skey == SKEY_BLANK_CHECK) {
                /*
                 * This quirk code helps the drive read the first tape block,
                 * regardless of format.  That is required for these drives to
                 * return proper MODE SENSE information.
                 */
                if (ISSET(st->quirks, ST_Q_SENSE_HELP) &&
                    !ISSET(link->flags, SDEV_MEDIA_LOADED)) {
                        /* still starting */
                        st->blksize -= 512;
                } else if (!ISSET(st->flags, ST_2FM_AT_EOD | ST_BLANK_READ)) {
                        SET(st->flags, ST_BLANK_READ);
                        SET(st->flags, ST_EOM_PENDING);
                        xs->resid = xs->datalen;
                        return 0;
                }
        }

        return scsi_interpret_sense(xs);
}

/*
 * The quirk here is that the drive returns some value to st_mode_sense
 * incorrectly until the tape has actually passed by the head.
 *
 * The method is to set the drive to large fixed-block state (user-specified
 * density and 1024-byte blocks), then read and rewind to get it to sense the
 * tape.  If that doesn't work, try 512-byte fixed blocks.  If that doesn't
 * work, as a last resort, try variable- length blocks.  The result will be
 * the ability to do an accurate st_mode_sense.
 *
 * We know we can do a rewind because we just did a load, which implies rewind.
 * Rewind seems preferable to space backward if we have a virgin tape.
 *
 * The rest of the code for this quirk is in ILI processing and BLANK CHECK
 * error processing, both part of st_interpret_sense.
 */
int
st_touch_tape(struct st_softc *st)
{
        char *buf = NULL;
        int readsize, maxblksize = 1024;
        int error = 0;

        if ((error = st_mode_sense(st, 0)) != 0)
                goto done;
        buf = dma_alloc(maxblksize, PR_NOWAIT);
        if (buf == NULL) {
                error = ENOMEM;
                goto done;
        }

        st->blksize = 1024;
        do {
                switch (st->blksize) {
                case 512:
                case 1024:
                        readsize = st->blksize;
                        SET(st->flags, ST_FIXEDBLOCKS);
                        break;
                default:
                        readsize = 1;
                        CLR(st->flags, ST_FIXEDBLOCKS);
                }
                if ((error = st_mode_select(st, 0)) != 0)
                        goto done;
                st_read(st, buf, readsize, SCSI_SILENT);        /* XXX */
                if ((error = st_rewind(st, 0, 0)) != 0)
                        goto done;
        } while (readsize != 1 && readsize > st->blksize);
done:
        dma_free(buf, maxblksize);
        return error;
}