cgroups: fix a race between cgroup_clone and umount

[linux-2.6/mini2440.git] / drivers / scsi / sr.c

/*
 *  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 <drew@colorado.edu>
 *
 *      Modified by Eric Youngdale ericy@andante.org to
 *      add scatter-gather, multiple outstanding request, and other
 *      enhancements.
 *
 *      Modified by Eric Youngdale eric@andante.org to support loadable
 *      low-level scsi drivers.
 *
 *      Modified by Thomas Quinot thomas@melchior.cuivre.fdn.fr to
 *      provide auto-eject.
 *
 *      Modified by Gerd Knorr <kraxel@cs.tu-berlin.de> to support the
 *      generic cdrom interface
 *
 *      Modified by Jens Axboe <axboe@suse.de> - Uniform sr_packet()
 *      interface, capabilities probe additions, ioctl cleanups, etc.
 *
 *      Modified by Richard Gooch <rgooch@atnf.csiro.au> to support devfs
 *
 *      Modified by Jens Axboe <axboe@suse.de> - support DVD-RAM
 *      transparently and lose the GHOST hack
 *
 *      Modified by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *      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 <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 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 int sr_media_change(struct cdrom_device_info *, int);
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,
        .media_changed          = sr_media_change,
        .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);
}

/* identical to scsi_test_unit_ready except that it doesn't
 * eat the NOT_READY returns for removable media */
int sr_test_unit_ready(struct scsi_device *sdev, struct scsi_sense_hdr *sshdr)
{
        int retries = MAX_RETRIES;
        int the_result;
        u8 cmd[] = {TEST_UNIT_READY, 0, 0, 0, 0, 0 };

        /* issue TEST_UNIT_READY until the initial startup UNIT_ATTENTION
         * conditions are gone, or a timeout happens
         */
        do {
                the_result = scsi_execute_req(sdev, cmd, DMA_NONE, NULL,
                                              0, sshdr, SR_TIMEOUT,
                                              retries--, NULL);
                if (scsi_sense_valid(sshdr) &&
                    sshdr->sense_key == UNIT_ATTENTION)
                        sdev->changed = 1;

        } while (retries > 0 &&
                 (!scsi_status_is_good(the_result) ||
                  (scsi_sense_valid(sshdr) &&
                   sshdr->sense_key == UNIT_ATTENTION)));
        return the_result;
}

/*
 * This function checks to see if the media has been changed in the
 * CDROM drive.  It is possible that we have already sensed a change,
 * or the drive may have sensed one and not yet reported it.  We must
 * be ready for either case. This function always reports the current
 * value of the changed bit.  If flag is 0, then the changed bit is reset.
 * This function could be done as an ioctl, but we would need to have
 * an inode for that to work, and we do not always have one.
 */

static int sr_media_change(struct cdrom_device_info *cdi, int slot)
{
        struct scsi_cd *cd = cdi->handle;
        int retval;
        struct scsi_sense_hdr *sshdr;

        if (CDSL_CURRENT != slot) {
                /* no changer support */
                return -EINVAL;
        }

        sshdr =  kzalloc(sizeof(*sshdr), GFP_KERNEL);
        retval = sr_test_unit_ready(cd->device, sshdr);
        if (retval || (scsi_sense_valid(sshdr) &&
                       /* 0x3a is medium not present */
                       sshdr->asc == 0x3a)) {
                /* Media not present or unable to test, unit probably not
                 * ready. This usually means there is no disc in the drive.
                 * Mark as changed, and we will figure it out later once
                 * the drive is available again.
                 */
                cd->device->changed = 1;
                /* This will force a flush, if called from check_disk_change */
                retval = 1;
                goto out;
        };

        retval = cd->device->changed;
        cd->device->changed = 0;
        /* If the disk changed, the capacity will now be different,
         * so we force a re-read of this information */
        if (retval) {
                /* check multisession offset etc */
                sr_cd_check(cdi);
                get_sectorsize(cd);
        }

out:
        /* Notify userspace, that media has changed. */
        if (retval != cd->previous_state)
                sdev_evt_send_simple(cd->device, SDEV_EVT_MEDIA_CHANGE,
                                     GFP_KERNEL);
        cd->previous_state = retval;
        kfree(sshdr);

        return retval;
}
 
/*
 * 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 - SCpnt->request->sector) << 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:

                        /*
                         * An error occured, but it recovered.  Inform the
                         * user, but make sure that it's not treated as a
                         * hard error.
                         */
                        scsi_print_sense("sr", SCpnt);
                        SCpnt->result = 0;
                        SCpnt->sense_buffer[0] = 0x0;
                        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 %ld sectors\n",
                                        rq->nr_sectors));
                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)rq->sector % (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/%ld 512 byte blocks.\n",
                                cd->cdi.name,
                                (rq_data_dir(rq) == WRITE) ?
                                        "writing" : "reading",
                                this_count, rq->nr_sectors));

        SCpnt->cmnd[1] = 0;
        block = (unsigned int)rq->sector / (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 = scsi_cd_get(bdev->bd_disk);
        int ret = -ENXIO;

        if (cd) {
                ret = cdrom_open(&cd->cdi, bdev, mode);
                if (ret)
                        scsi_cd_put(cd);
        }
        return ret;
}

static int sr_block_release(struct gendisk *disk, fmode_t mode)
{
        struct scsi_cd *cd = scsi_cd(disk);
        cdrom_release(&cd->cdi, mode);
        scsi_cd_put(cd);
        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;

        /*
         * 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:
                return scsi_ioctl(sdev, cmd, argp);
        }

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

        /*
         * 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)
                return ret;
        return scsi_ioctl(sdev, cmd, argp);
}

static int sr_block_media_changed(struct gendisk *disk)
{
        struct scsi_cd *cd = scsi_cd(disk);
        return cdrom_media_changed(&cd->cdi);
}

static struct block_device_operations sr_bdops =
{
        .owner          = THIS_MODULE,
        .open           = sr_block_open,
        .release        = sr_block_release,
        .locked_ioctl   = sr_block_ioctl,
        .media_changed  = sr_block_media_changed,
        /* 
         * No compat_ioctl for now because sr_block_ioctl never
         * seems to pass arbitary 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;

        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->previous_state = 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 {
#if 0
                if (cdrom_get_last_written(&cd->cdi,
                                           &cd->capacity))
#endif
                        cd->capacity = 1 + ((buffer[0] << 24) |
                                                    (buffer[1] << 16) |
                                                    (buffer[2] << 8) |
                                                    buffer[3]);
                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_hardsect_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 */
        sr_test_unit_ready(cd->device, &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)
{
        if (cgc->timeout <= 0)
                cgc->timeout = IOCTL_TIMEOUT;

        sr_do_ioctl(cdi->handle, cgc);

        return cgc->stat;
}

/**
 *      sr_kref_release - Called to free the scsi_cd structure
 *      @kref: pointer to embedded kref
 *
 *      sr_ref_mutex must be held entering this routine.  Because it is
 *      called on last put, you should always use the scsi_cd_get()
 *      scsi_cd_put() helpers which manipulate the semaphore directly
 *      and never do a direct kref_put().
 **/
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);

        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");