sr.c

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/*
 *  sr.c Copyright (C) 1992 David Giller
 *           Copyright (C) 1993, 1994, 1995, 1999 Eric Youngdale
 *
 *  adapted from:
 *      sd.c Copyright (C) 1992 Drew Eckhardt
 *      Linux scsi disk driver by
 *              Drew Eckhardt <[email protected]>
 *
 *  Modified by Eric Youngdale [email protected] to
 *  add scatter-gather, multiple outstanding request, and other
 *  enhancements.
 *
 *      Modified by Eric Youngdale [email protected] to support loadable
 *      low-level scsi drivers.
 *
 *      Modified by Thomas Quinot [email protected] to
 *      provide auto-eject.
 *
 *      Modified by Gerd Knorr <[email protected]> to support the
 *      generic cdrom interface
 *
 *      Modified by Jens Axboe <[email protected]> - Uniform sr_packet()
 *      interface, capabilities probe additions, ioctl cleanups, etc.
 *
 *  Modified by Richard Gooch <[email protected]> to support devfs
 *
 *  Modified by Jens Axboe <[email protected]> - support DVD-RAM
 *  transparently and lose the GHOST hack
 *
 *  Modified by Arnaldo Carvalho de Melo <[email protected]>
 *  check resource allocation in sr_init and some cleanups
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/bio.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/cdrom.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/blkdev.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <asm/uaccess.h>

#include <scsi/scsi.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_driver.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_ioctl.h>    /* For the door lock/unlock commands */

#include "scsi_logging.h"
#include "sr.h"


MODULE_DESCRIPTION("SCSI cdrom (sr) driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(SCSI_CDROM_MAJOR);
MODULE_ALIAS_SCSI_DEVICE(TYPE_ROM);
MODULE_ALIAS_SCSI_DEVICE(TYPE_WORM);

#define SR_DISKS    256

#define SR_CAPABILITIES \
    (CDC_CLOSE_TRAY|CDC_OPEN_TRAY|CDC_LOCK|CDC_SELECT_SPEED| \
     CDC_SELECT_DISC|CDC_MULTI_SESSION|CDC_MCN|CDC_MEDIA_CHANGED| \
     CDC_PLAY_AUDIO|CDC_RESET|CDC_DRIVE_STATUS| \
     CDC_CD_R|CDC_CD_RW|CDC_DVD|CDC_DVD_R|CDC_DVD_RAM|CDC_GENERIC_PACKET| \
     CDC_MRW|CDC_MRW_W|CDC_RAM)

static DEFINE_MUTEX(sr_mutex);
static int sr_probe(struct device *);
static int sr_remove(struct device *);
static int sr_done(struct scsi_cmnd *);

static struct scsi_driver sr_template = {
    .owner          = THIS_MODULE,
    .gendrv = {
        .name       = "sr",
        .probe      = sr_probe,
        .remove     = sr_remove,
    },
    .done           = sr_done,
};

static unsigned long sr_index_bits[SR_DISKS / BITS_PER_LONG];
static DEFINE_SPINLOCK(sr_index_lock);

/* This semaphore is used to mediate the 0->1 reference get in the
 * face of object destruction (i.e. we can't allow a get on an
 * object after last put) */
static DEFINE_MUTEX(sr_ref_mutex);

static int sr_open(struct cdrom_device_info *, int);
static void sr_release(struct cdrom_device_info *);

static void get_sectorsize(struct scsi_cd *);
static void get_capabilities(struct scsi_cd *);

static unsigned int sr_check_events(struct cdrom_device_info *cdi,
                    unsigned int clearing, int slot);
static int sr_packet(struct cdrom_device_info *, struct packet_command *);

static struct cdrom_device_ops sr_dops = {
    .open           = sr_open,
    .release        = sr_release,
    .drive_status       = sr_drive_status,
    .check_events       = sr_check_events,
    .tray_move      = sr_tray_move,
    .lock_door      = sr_lock_door,
    .select_speed       = sr_select_speed,
    .get_last_session   = sr_get_last_session,
    .get_mcn        = sr_get_mcn,
    .reset          = sr_reset,
    .audio_ioctl        = sr_audio_ioctl,
    .capability     = SR_CAPABILITIES,
    .generic_packet     = sr_packet,
};

static void sr_kref_release(struct kref *kref);

static inline struct scsi_cd *scsi_cd(struct gendisk *disk)
{
    return container_of(disk->private_data, struct scsi_cd, driver);
}

/*
 * The get and put routines for the struct scsi_cd.  Note this entity
 * has a scsi_device pointer and owns a reference to this.
 */
static inline struct scsi_cd *scsi_cd_get(struct gendisk *disk)
{
    struct scsi_cd *cd = NULL;

    mutex_lock(&sr_ref_mutex);
    if (disk->private_data == NULL)
        goto out;
    cd = scsi_cd(disk);
    kref_get(&cd->kref);
    if (scsi_device_get(cd->device))
        goto out_put;
    goto out;

 out_put:
    kref_put(&cd->kref, sr_kref_release);
    cd = NULL;
 out:
    mutex_unlock(&sr_ref_mutex);
    return cd;
}

static void scsi_cd_put(struct scsi_cd *cd)
{
    struct scsi_device *sdev = cd->device;

    mutex_lock(&sr_ref_mutex);
    kref_put(&cd->kref, sr_kref_release);
    scsi_device_put(sdev);
    mutex_unlock(&sr_ref_mutex);
}

static unsigned int sr_get_events(struct scsi_device *sdev)
{
    u8 buf[8];
    u8 cmd[] = { GET_EVENT_STATUS_NOTIFICATION,
             1,         /* polled */
             0, 0,      /* reserved */
             1 << 4,        /* notification class: media */
             0, 0,      /* reserved */
             0, sizeof(buf),    /* allocation length */
             0,         /* control */
    };
    struct event_header *eh = (void *)buf;
    struct media_event_desc *med = (void *)(buf + 4);
    struct scsi_sense_hdr sshdr;
    int result;

    result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buf, sizeof(buf),
                  &sshdr, SR_TIMEOUT, MAX_RETRIES, NULL);
    if (scsi_sense_valid(&sshdr) && sshdr.sense_key == UNIT_ATTENTION)
        return DISK_EVENT_MEDIA_CHANGE;

    if (result || be16_to_cpu(eh->data_len) < sizeof(*med))
        return 0;

    if (eh->nea || eh->notification_class != 0x4)
        return 0;

    if (med->media_event_code == 1)
        return DISK_EVENT_EJECT_REQUEST;
    else if (med->media_event_code == 2)
        return DISK_EVENT_MEDIA_CHANGE;
    return 0;
}

/*
 * This function checks to see if the media has been changed or eject
 * button has been pressed.  It is possible that we have already
 * sensed a change, or the drive may have sensed one and not yet
 * reported it.  The past events are accumulated in sdev->changed and
 * returned together with the current state.
 */
static unsigned int sr_check_events(struct cdrom_device_info *cdi,
                    unsigned int clearing, int slot)
{
    struct scsi_cd *cd = cdi->handle;
    bool last_present;
    struct scsi_sense_hdr sshdr;
    unsigned int events;
    int ret;

    /* no changer support */
    if (CDSL_CURRENT != slot)
        return 0;

    events = sr_get_events(cd->device);
    cd->get_event_changed |= events & DISK_EVENT_MEDIA_CHANGE;

    /*
     * If earlier GET_EVENT_STATUS_NOTIFICATION and TUR did not agree
     * for several times in a row.  We rely on TUR only for this likely
     * broken device, to prevent generating incorrect media changed
     * events for every open().
     */
    if (cd->ignore_get_event) {
        events &= ~DISK_EVENT_MEDIA_CHANGE;
        goto do_tur;
    }

    /*
     * GET_EVENT_STATUS_NOTIFICATION is enough unless MEDIA_CHANGE
     * is being cleared.  Note that there are devices which hang
     * if asked to execute TUR repeatedly.
     */
    if (cd->device->changed) {
        events |= DISK_EVENT_MEDIA_CHANGE;
        cd->device->changed = 0;
        cd->tur_changed = true;
    }

    if (!(clearing & DISK_EVENT_MEDIA_CHANGE))
        return events;
do_tur:
    /* let's see whether the media is there with TUR */
    last_present = cd->media_present;
    ret = scsi_test_unit_ready(cd->device, SR_TIMEOUT, MAX_RETRIES, &sshdr);

    /*
     * Media is considered to be present if TUR succeeds or fails with
     * sense data indicating something other than media-not-present
     * (ASC 0x3a).
     */
    cd->media_present = scsi_status_is_good(ret) ||
        (scsi_sense_valid(&sshdr) && sshdr.asc != 0x3a);

    if (last_present != cd->media_present)
        cd->device->changed = 1;

    if (cd->device->changed) {
        events |= DISK_EVENT_MEDIA_CHANGE;
        cd->device->changed = 0;
        cd->tur_changed = true;
    }

    if (cd->ignore_get_event)
        return events;

    /* check whether GET_EVENT is reporting spurious MEDIA_CHANGE */
    if (!cd->tur_changed) {
        if (cd->get_event_changed) {
            if (cd->tur_mismatch++ > 8) {
                sdev_printk(KERN_WARNING, cd->device,
                        "GET_EVENT and TUR disagree continuously, suppress GET_EVENT events\n");
                cd->ignore_get_event = true;
            }
        } else {
            cd->tur_mismatch = 0;
        }
    }
    cd->tur_changed = false;
    cd->get_event_changed = false;

    return events;
}

/*
 * sr_done is the interrupt routine for the device driver.
 *
 * It will be notified on the end of a SCSI read / write, and will take one
 * of several actions based on success or failure.
 */
static int sr_done(struct scsi_cmnd *SCpnt)
{
    int result = SCpnt->result;
    int this_count = scsi_bufflen(SCpnt);
    int good_bytes = (result == 0 ? this_count : 0);
    int block_sectors = 0;
    long error_sector;
    struct scsi_cd *cd = scsi_cd(SCpnt->request->rq_disk);

#ifdef DEBUG
    printk("sr.c done: %x\n", result);
#endif

    /*
     * Handle MEDIUM ERRORs or VOLUME OVERFLOWs that indicate partial
     * success.  Since this is a relatively rare error condition, no
     * care is taken to avoid unnecessary additional work such as
     * memcpy's that could be avoided.
     */
    if (driver_byte(result) != 0 &&     /* An error occurred */
        (SCpnt->sense_buffer[0] & 0x7f) == 0x70) { /* Sense current */
        switch (SCpnt->sense_buffer[2]) {
        case MEDIUM_ERROR:
        case VOLUME_OVERFLOW:
        case ILLEGAL_REQUEST:
            if (!(SCpnt->sense_buffer[0] & 0x90))
                break;
            error_sector = (SCpnt->sense_buffer[3] << 24) |
                (SCpnt->sense_buffer[4] << 16) |
                (SCpnt->sense_buffer[5] << 8) |
                SCpnt->sense_buffer[6];
            if (SCpnt->request->bio != NULL)
                block_sectors =
                    bio_sectors(SCpnt->request->bio);
            if (block_sectors < 4)
                block_sectors = 4;
            if (cd->device->sector_size == 2048)
                error_sector <<= 2;
            error_sector &= ~(block_sectors - 1);
            good_bytes = (error_sector -
                      blk_rq_pos(SCpnt->request)) << 9;
            if (good_bytes < 0 || good_bytes >= this_count)
                good_bytes = 0;
            /*
             * The SCSI specification allows for the value
             * returned by READ CAPACITY to be up to 75 2K
             * sectors past the last readable block.
             * Therefore, if we hit a medium error within the
             * last 75 2K sectors, we decrease the saved size
             * value.
             */
            if (error_sector < get_capacity(cd->disk) &&
                cd->capacity - error_sector < 4 * 75)
                set_capacity(cd->disk, error_sector);
            break;

        case RECOVERED_ERROR:
            good_bytes = this_count;
            break;

        default:
            break;
        }
    }

    return good_bytes;
}

static int sr_prep_fn(struct request_queue *q, struct request *rq)
{
    int block = 0, this_count, s_size;
    struct scsi_cd *cd;
    struct scsi_cmnd *SCpnt;
    struct scsi_device *sdp = q->queuedata;
    int ret;

    if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
        ret = scsi_setup_blk_pc_cmnd(sdp, rq);
        goto out;
    } else if (rq->cmd_type != REQ_TYPE_FS) {
        ret = BLKPREP_KILL;
        goto out;
    }
    ret = scsi_setup_fs_cmnd(sdp, rq);
    if (ret != BLKPREP_OK)
        goto out;
    SCpnt = rq->special;
    cd = scsi_cd(rq->rq_disk);

    /* from here on until we're complete, any goto out
     * is used for a killable error condition */
    ret = BLKPREP_KILL;

    SCSI_LOG_HLQUEUE(1, printk("Doing sr request, dev = %s, block = %d\n",
                cd->disk->disk_name, block));

    if (!cd->device || !scsi_device_online(cd->device)) {
        SCSI_LOG_HLQUEUE(2, printk("Finishing %u sectors\n",
                       blk_rq_sectors(rq)));
        SCSI_LOG_HLQUEUE(2, printk("Retry with 0x%p\n", SCpnt));
        goto out;
    }

    if (cd->device->changed) {
        /*
         * quietly refuse to do anything to a changed disc until the
         * changed bit has been reset
         */
        goto out;
    }

    /*
     * we do lazy blocksize switching (when reading XA sectors,
     * see CDROMREADMODE2 ioctl) 
     */
    s_size = cd->device->sector_size;
    if (s_size > 2048) {
        if (!in_interrupt())
            sr_set_blocklength(cd, 2048);
        else
            printk("sr: can't switch blocksize: in interrupt\n");
    }

    if (s_size != 512 && s_size != 1024 && s_size != 2048) {
        scmd_printk(KERN_ERR, SCpnt, "bad sector size %d\n", s_size);
        goto out;
    }

    if (rq_data_dir(rq) == WRITE) {
        if (!cd->device->writeable)
            goto out;
        SCpnt->cmnd[0] = WRITE_10;
        SCpnt->sc_data_direction = DMA_TO_DEVICE;
        cd->cdi.media_written = 1;
    } else if (rq_data_dir(rq) == READ) {
        SCpnt->cmnd[0] = READ_10;
        SCpnt->sc_data_direction = DMA_FROM_DEVICE;
    } else {
        blk_dump_rq_flags(rq, "Unknown sr command");
        goto out;
    }

    {
        struct scatterlist *sg;
        int i, size = 0, sg_count = scsi_sg_count(SCpnt);

        scsi_for_each_sg(SCpnt, sg, sg_count, i)
            size += sg->length;

        if (size != scsi_bufflen(SCpnt)) {
            scmd_printk(KERN_ERR, SCpnt,
                "mismatch count %d, bytes %d\n",
                size, scsi_bufflen(SCpnt));
            if (scsi_bufflen(SCpnt) > size)
                SCpnt->sdb.length = size;
        }
    }

    /*
     * request doesn't start on hw block boundary, add scatter pads
     */
    if (((unsigned int)blk_rq_pos(rq) % (s_size >> 9)) ||
        (scsi_bufflen(SCpnt) % s_size)) {
        scmd_printk(KERN_NOTICE, SCpnt, "unaligned transfer\n");
        goto out;
    }

    this_count = (scsi_bufflen(SCpnt) >> 9) / (s_size >> 9);


    SCSI_LOG_HLQUEUE(2, printk("%s : %s %d/%u 512 byte blocks.\n",
                cd->cdi.name,
                (rq_data_dir(rq) == WRITE) ?
                    "writing" : "reading",
                this_count, blk_rq_sectors(rq)));

    SCpnt->cmnd[1] = 0;
    block = (unsigned int)blk_rq_pos(rq) / (s_size >> 9);

    if (this_count > 0xffff) {
        this_count = 0xffff;
        SCpnt->sdb.length = this_count * s_size;
    }

    SCpnt->cmnd[2] = (unsigned char) (block >> 24) & 0xff;
    SCpnt->cmnd[3] = (unsigned char) (block >> 16) & 0xff;
    SCpnt->cmnd[4] = (unsigned char) (block >> 8) & 0xff;
    SCpnt->cmnd[5] = (unsigned char) block & 0xff;
    SCpnt->cmnd[6] = SCpnt->cmnd[9] = 0;
    SCpnt->cmnd[7] = (unsigned char) (this_count >> 8) & 0xff;
    SCpnt->cmnd[8] = (unsigned char) this_count & 0xff;

    /*
     * We shouldn't disconnect in the middle of a sector, so with a dumb
     * host adapter, it's safe to assume that we can at least transfer
     * this many bytes between each connect / disconnect.
     */
    SCpnt->transfersize = cd->device->sector_size;
    SCpnt->underflow = this_count << 9;
    SCpnt->allowed = MAX_RETRIES;

    /*
     * This indicates that the command is ready from our end to be
     * queued.
     */
    ret = BLKPREP_OK;
 out:
    return scsi_prep_return(q, rq, ret);
}

static int sr_block_open(struct block_device *bdev, fmode_t mode)
{
    struct scsi_cd *cd;
    int ret = -ENXIO;

    mutex_lock(&sr_mutex);
    cd = scsi_cd_get(bdev->bd_disk);
    if (cd) {
        ret = cdrom_open(&cd->cdi, bdev, mode);
        if (ret)
            scsi_cd_put(cd);
    }
    mutex_unlock(&sr_mutex);
    return ret;
}

static int sr_block_release(struct gendisk *disk, fmode_t mode)
{
    struct scsi_cd *cd = scsi_cd(disk);
    mutex_lock(&sr_mutex);
    cdrom_release(&cd->cdi, mode);
    scsi_cd_put(cd);
    mutex_unlock(&sr_mutex);
    return 0;
}

static int sr_block_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
              unsigned long arg)
{
    struct scsi_cd *cd = scsi_cd(bdev->bd_disk);
    struct scsi_device *sdev = cd->device;
    void __user *argp = (void __user *)arg;
    int ret;

    mutex_lock(&sr_mutex);

    /*
     * Send SCSI addressing ioctls directly to mid level, send other
     * ioctls to cdrom/block level.
     */
    switch (cmd) {
    case SCSI_IOCTL_GET_IDLUN:
    case SCSI_IOCTL_GET_BUS_NUMBER:
        ret = scsi_ioctl(sdev, cmd, argp);
        goto out;
    }

    ret = cdrom_ioctl(&cd->cdi, bdev, mode, cmd, arg);
    if (ret != -ENOSYS)
        goto out;

    /*
     * ENODEV means that we didn't recognise the ioctl, or that we
     * cannot execute it in the current device state.  In either
     * case fall through to scsi_ioctl, which will return ENDOEV again
     * if it doesn't recognise the ioctl
     */
    ret = scsi_nonblockable_ioctl(sdev, cmd, argp,
                    (mode & FMODE_NDELAY) != 0);
    if (ret != -ENODEV)
        goto out;
    ret = scsi_ioctl(sdev, cmd, argp);

out:
    mutex_unlock(&sr_mutex);
    return ret;
}

static unsigned int sr_block_check_events(struct gendisk *disk,
                      unsigned int clearing)
{
    struct scsi_cd *cd = scsi_cd(disk);
    return cdrom_check_events(&cd->cdi, clearing);
}

static int sr_block_revalidate_disk(struct gendisk *disk)
{
    struct scsi_cd *cd = scsi_cd(disk);
    struct scsi_sense_hdr sshdr;

    /* if the unit is not ready, nothing more to do */
    if (scsi_test_unit_ready(cd->device, SR_TIMEOUT, MAX_RETRIES, &sshdr))
        return 0;

    sr_cd_check(&cd->cdi);
    get_sectorsize(cd);
    return 0;
}

static const struct block_device_operations sr_bdops =
{
    .owner      = THIS_MODULE,
    .open       = sr_block_open,
    .release    = sr_block_release,
    .ioctl      = sr_block_ioctl,
    .check_events   = sr_block_check_events,
    .revalidate_disk = sr_block_revalidate_disk,
    /* 
     * No compat_ioctl for now because sr_block_ioctl never
     * seems to pass arbitrary ioctls down to host drivers.
     */
};

static int sr_open(struct cdrom_device_info *cdi, int purpose)
{
    struct scsi_cd *cd = cdi->handle;
    struct scsi_device *sdev = cd->device;
    int retval;

    /*
     * If the device is in error recovery, wait until it is done.
     * If the device is offline, then disallow any access to it.
     */
    retval = -ENXIO;
    if (!scsi_block_when_processing_errors(sdev))
        goto error_out;

    return 0;

error_out:
    return retval;  
}

static void sr_release(struct cdrom_device_info *cdi)
{
    struct scsi_cd *cd = cdi->handle;

    if (cd->device->sector_size > 2048)
        sr_set_blocklength(cd, 2048);

}

static int sr_probe(struct device *dev)
{
    struct scsi_device *sdev = to_scsi_device(dev);
    struct gendisk *disk;
    struct scsi_cd *cd;
    int minor, error;

    error = -ENODEV;
    if (sdev->type != TYPE_ROM && sdev->type != TYPE_WORM)
        goto fail;

    error = -ENOMEM;
    cd = kzalloc(sizeof(*cd), GFP_KERNEL);
    if (!cd)
        goto fail;

    kref_init(&cd->kref);

    disk = alloc_disk(1);
    if (!disk)
        goto fail_free;

    spin_lock(&sr_index_lock);
    minor = find_first_zero_bit(sr_index_bits, SR_DISKS);
    if (minor == SR_DISKS) {
        spin_unlock(&sr_index_lock);
        error = -EBUSY;
        goto fail_put;
    }
    __set_bit(minor, sr_index_bits);
    spin_unlock(&sr_index_lock);

    disk->major = SCSI_CDROM_MAJOR;
    disk->first_minor = minor;
    sprintf(disk->disk_name, "sr%d", minor);
    disk->fops = &sr_bdops;
    disk->flags = GENHD_FL_CD | GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE;
    disk->events = DISK_EVENT_MEDIA_CHANGE | DISK_EVENT_EJECT_REQUEST;

    blk_queue_rq_timeout(sdev->request_queue, SR_TIMEOUT);

    cd->device = sdev;
    cd->disk = disk;
    cd->driver = &sr_template;
    cd->disk = disk;
    cd->capacity = 0x1fffff;
    cd->device->changed = 1;    /* force recheck CD type */
    cd->media_present = 1;
    cd->use = 1;
    cd->readcd_known = 0;
    cd->readcd_cdda = 0;

    cd->cdi.ops = &sr_dops;
    cd->cdi.handle = cd;
    cd->cdi.mask = 0;
    cd->cdi.capacity = 1;
    sprintf(cd->cdi.name, "sr%d", minor);

    sdev->sector_size = 2048;   /* A guess, just in case */

    /* FIXME: need to handle a get_capabilities failure properly ?? */
    get_capabilities(cd);
    blk_queue_prep_rq(sdev->request_queue, sr_prep_fn);
    sr_vendor_init(cd);

    disk->driverfs_dev = &sdev->sdev_gendev;
    set_capacity(disk, cd->capacity);
    disk->private_data = &cd->driver;
    disk->queue = sdev->request_queue;
    cd->cdi.disk = disk;

    if (register_cdrom(&cd->cdi))
        goto fail_put;

    dev_set_drvdata(dev, cd);
    disk->flags |= GENHD_FL_REMOVABLE;
    add_disk(disk);

    sdev_printk(KERN_DEBUG, sdev,
            "Attached scsi CD-ROM %s\n", cd->cdi.name);
    return 0;

fail_put:
    put_disk(disk);
fail_free:
    kfree(cd);
fail:
    return error;
}


static void get_sectorsize(struct scsi_cd *cd)
{
    unsigned char cmd[10];
    unsigned char buffer[8];
    int the_result, retries = 3;
    int sector_size;
    struct request_queue *queue;

    do {
        cmd[0] = READ_CAPACITY;
        memset((void *) &cmd[1], 0, 9);
        memset(buffer, 0, sizeof(buffer));

        /* Do the command and wait.. */
        the_result = scsi_execute_req(cd->device, cmd, DMA_FROM_DEVICE,
                          buffer, sizeof(buffer), NULL,
                          SR_TIMEOUT, MAX_RETRIES, NULL);

        retries--;

    } while (the_result && retries);


    if (the_result) {
        cd->capacity = 0x1fffff;
        sector_size = 2048; /* A guess, just in case */
    } else {
        long last_written;

        cd->capacity = 1 + ((buffer[0] << 24) | (buffer[1] << 16) |
                    (buffer[2] << 8) | buffer[3]);
        /*
         * READ_CAPACITY doesn't return the correct size on
         * certain UDF media.  If last_written is larger, use
         * it instead.
         *
         * http://bugzilla.kernel.org/show_bug.cgi?id=9668
         */
        if (!cdrom_get_last_written(&cd->cdi, &last_written))
            cd->capacity = max_t(long, cd->capacity, last_written);

        sector_size = (buffer[4] << 24) |
            (buffer[5] << 16) | (buffer[6] << 8) | buffer[7];
        switch (sector_size) {
            /*
             * HP 4020i CD-Recorder reports 2340 byte sectors
             * Philips CD-Writers report 2352 byte sectors
             *
             * Use 2k sectors for them..
             */
        case 0:
        case 2340:
        case 2352:
            sector_size = 2048;
            /* fall through */
        case 2048:
            cd->capacity *= 4;
            /* fall through */
        case 512:
            break;
        default:
            printk("%s: unsupported sector size %d.\n",
                   cd->cdi.name, sector_size);
            cd->capacity = 0;
        }

        cd->device->sector_size = sector_size;

        /*
         * Add this so that we have the ability to correctly gauge
         * what the device is capable of.
         */
        set_capacity(cd->disk, cd->capacity);
    }

    queue = cd->device->request_queue;
    blk_queue_logical_block_size(queue, sector_size);

    return;
}

static void get_capabilities(struct scsi_cd *cd)
{
    unsigned char *buffer;
    struct scsi_mode_data data;
    struct scsi_sense_hdr sshdr;
    int rc, n;

    static const char *loadmech[] =
    {
        "caddy",
        "tray",
        "pop-up",
        "",
        "changer",
        "cartridge changer",
        "",
        ""
    };


    /* allocate transfer buffer */
    buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
    if (!buffer) {
        printk(KERN_ERR "sr: out of memory.\n");
        return;
    }

    /* eat unit attentions */
    scsi_test_unit_ready(cd->device, SR_TIMEOUT, MAX_RETRIES, &sshdr);

    /* ask for mode page 0x2a */
    rc = scsi_mode_sense(cd->device, 0, 0x2a, buffer, 128,
                 SR_TIMEOUT, 3, &data, NULL);

    if (!scsi_status_is_good(rc)) {
        /* failed, drive doesn't have capabilities mode page */
        cd->cdi.speed = 1;
        cd->cdi.mask |= (CDC_CD_R | CDC_CD_RW | CDC_DVD_R |
                 CDC_DVD | CDC_DVD_RAM |
                 CDC_SELECT_DISC | CDC_SELECT_SPEED |
                 CDC_MRW | CDC_MRW_W | CDC_RAM);
        kfree(buffer);
        printk("%s: scsi-1 drive\n", cd->cdi.name);
        return;
    }

    n = data.header_length + data.block_descriptor_length;
    cd->cdi.speed = ((buffer[n + 8] << 8) + buffer[n + 9]) / 176;
    cd->readcd_known = 1;
    cd->readcd_cdda = buffer[n + 5] & 0x01;
    /* print some capability bits */
    printk("%s: scsi3-mmc drive: %dx/%dx %s%s%s%s%s%s\n", cd->cdi.name,
           ((buffer[n + 14] << 8) + buffer[n + 15]) / 176,
           cd->cdi.speed,
           buffer[n + 3] & 0x01 ? "writer " : "", /* CD Writer */
           buffer[n + 3] & 0x20 ? "dvd-ram " : "",
           buffer[n + 2] & 0x02 ? "cd/rw " : "", /* can read rewriteable */
           buffer[n + 4] & 0x20 ? "xa/form2 " : "", /* can read xa/from2 */
           buffer[n + 5] & 0x01 ? "cdda " : "", /* can read audio data */
           loadmech[buffer[n + 6] >> 5]);
    if ((buffer[n + 6] >> 5) == 0)
        /* caddy drives can't close tray... */
        cd->cdi.mask |= CDC_CLOSE_TRAY;
    if ((buffer[n + 2] & 0x8) == 0)
        /* not a DVD drive */
        cd->cdi.mask |= CDC_DVD;
    if ((buffer[n + 3] & 0x20) == 0) 
        /* can't write DVD-RAM media */
        cd->cdi.mask |= CDC_DVD_RAM;
    if ((buffer[n + 3] & 0x10) == 0)
        /* can't write DVD-R media */
        cd->cdi.mask |= CDC_DVD_R;
    if ((buffer[n + 3] & 0x2) == 0)
        /* can't write CD-RW media */
        cd->cdi.mask |= CDC_CD_RW;
    if ((buffer[n + 3] & 0x1) == 0)
        /* can't write CD-R media */
        cd->cdi.mask |= CDC_CD_R;
    if ((buffer[n + 6] & 0x8) == 0)
        /* can't eject */
        cd->cdi.mask |= CDC_OPEN_TRAY;

    if ((buffer[n + 6] >> 5) == mechtype_individual_changer ||
        (buffer[n + 6] >> 5) == mechtype_cartridge_changer)
        cd->cdi.capacity =
            cdrom_number_of_slots(&cd->cdi);
    if (cd->cdi.capacity <= 1)
        /* not a changer */
        cd->cdi.mask |= CDC_SELECT_DISC;
    /*else    I don't think it can close its tray
        cd->cdi.mask |= CDC_CLOSE_TRAY; */

    /*
     * if DVD-RAM, MRW-W or CD-RW, we are randomly writable
     */
    if ((cd->cdi.mask & (CDC_DVD_RAM | CDC_MRW_W | CDC_RAM | CDC_CD_RW)) !=
            (CDC_DVD_RAM | CDC_MRW_W | CDC_RAM | CDC_CD_RW)) {
        cd->device->writeable = 1;
    }

    kfree(buffer);
}

/*
 * sr_packet() is the entry point for the generic commands generated
 * by the Uniform CD-ROM layer. 
 */
static int sr_packet(struct cdrom_device_info *cdi,
        struct packet_command *cgc)
{
    struct scsi_cd *cd = cdi->handle;
    struct scsi_device *sdev = cd->device;

    if (cgc->cmd[0] == GPCMD_READ_DISC_INFO && sdev->no_read_disc_info)
        return -EDRIVE_CANT_DO_THIS;

    if (cgc->timeout <= 0)
        cgc->timeout = IOCTL_TIMEOUT;

    sr_do_ioctl(cd, cgc);

    return cgc->stat;
}

static void sr_kref_release(struct kref *kref)
{
    struct scsi_cd *cd = container_of(kref, struct scsi_cd, kref);
    struct gendisk *disk = cd->disk;

    spin_lock(&sr_index_lock);
    clear_bit(MINOR(disk_devt(disk)), sr_index_bits);
    spin_unlock(&sr_index_lock);

    unregister_cdrom(&cd->cdi);

    disk->private_data = NULL;

    put_disk(disk);

    kfree(cd);
}

static int sr_remove(struct device *dev)
{
    struct scsi_cd *cd = dev_get_drvdata(dev);

    blk_queue_prep_rq(cd->device->request_queue, scsi_prep_fn);
    del_gendisk(cd->disk);

    mutex_lock(&sr_ref_mutex);
    kref_put(&cd->kref, sr_kref_release);
    mutex_unlock(&sr_ref_mutex);

    return 0;
}

static int __init init_sr(void)
{
    int rc;

    rc = register_blkdev(SCSI_CDROM_MAJOR, "sr");
    if (rc)
        return rc;
    rc = scsi_register_driver(&sr_template.gendrv);
    if (rc)
        unregister_blkdev(SCSI_CDROM_MAJOR, "sr");

    return rc;
}

static void __exit exit_sr(void)
{
    scsi_unregister_driver(&sr_template.gendrv);
    unregister_blkdev(SCSI_CDROM_MAJOR, "sr");
}

module_init(init_sr);
module_exit(exit_sr);
MODULE_LICENSE("GPL");