vserver 1.9.3

[linux-2.6.git] / drivers / scsi / sd.c

/*
 *      sd.c Copyright (C) 1992 Drew Eckhardt
 *           Copyright (C) 1993, 1994, 1995, 1999 Eric Youngdale
 *
 *      Linux scsi disk driver
 *              Initial versions: Drew Eckhardt
 *              Subsequent revisions: Eric Youngdale
 *      Modification history:
 *       - Drew Eckhardt <drew@colorado.edu> original
 *       - Eric Youngdale <eric@andante.org> add scatter-gather, multiple 
 *         outstanding request, and other enhancements.
 *         Support loadable low-level scsi drivers.
 *       - Jirka Hanika <geo@ff.cuni.cz> support more scsi disks using 
 *         eight major numbers.
 *       - Richard Gooch <rgooch@atnf.csiro.au> support devfs.
 *       - Torben Mathiasen <tmm@image.dk> Resource allocation fixes in 
 *         sd_init and cleanups.
 *       - Alex Davis <letmein@erols.com> Fix problem where partition info
 *         not being read in sd_open. Fix problem where removable media 
 *         could be ejected after sd_open.
 *       - Douglas Gilbert <dgilbert@interlog.com> cleanup for lk 2.5.x
 *       - Badari Pulavarty <pbadari@us.ibm.com>, Matthew Wilcox 
 *         <willy@debian.org>, Kurt Garloff <garloff@suse.de>: 
 *         Support 32k/1M disks.
 *
 *      Logging policy (needs CONFIG_SCSI_LOGGING defined):
 *       - setting up transfer: SCSI_LOG_HLQUEUE levels 1 and 2
 *       - end of transfer (bh + scsi_lib): SCSI_LOG_HLCOMPLETE level 1
 *       - entering sd_ioctl: SCSI_LOG_IOCTL level 1
 *       - entering other commands: SCSI_LOG_HLQUEUE level 3
 *      Note: when the logging level is set by the user, it must be greater
 *      than the level indicated above to trigger output.       
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/bio.h>
#include <linux/genhd.h>
#include <linux/hdreg.h>
#include <linux/errno.h>
#include <linux/idr.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/blkdev.h>
#include <linux/blkpg.h>
#include <linux/kref.h>
#include <asm/uaccess.h>

#include <scsi/scsi.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_driver.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_ioctl.h>
#include <scsi/scsi_request.h>
#include <scsi/scsicam.h>

#include "scsi_logging.h"

/*
 * More than enough for everybody ;)  The huge number of majors
 * is a leftover from 16bit dev_t days, we don't really need that
 * much numberspace.
 */
#define SD_MAJORS       16

/*
 * This is limited by the naming scheme enforced in sd_probe,
 * add another character to it if you really need more disks.
 */
#define SD_MAX_DISKS    (((26 * 26) + 26 + 1) * 26)

/*
 * Time out in seconds for disks and Magneto-opticals (which are slower).
 */
#define SD_TIMEOUT              (30 * HZ)
#define SD_MOD_TIMEOUT          (75 * HZ)

/*
 * Number of allowed retries
 */
#define SD_MAX_RETRIES          5

static void scsi_disk_release(struct kref *kref);

struct scsi_disk {
        struct scsi_driver *driver;     /* always &sd_template */
        struct scsi_device *device;
        struct kref     kref;
        struct gendisk  *disk;
        unsigned int    openers;        /* protected by BKL for now, yuck */
        sector_t        capacity;       /* size in 512-byte sectors */
        u32             index;
        u8              media_present;
        u8              write_prot;
        unsigned        WCE : 1;        /* state of disk WCE bit */
        unsigned        RCD : 1;        /* state of disk RCD bit, unused */
};

static DEFINE_IDR(sd_index_idr);
static spinlock_t sd_index_lock = SPIN_LOCK_UNLOCKED;

/* 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 DECLARE_MUTEX(sd_ref_sem);

static int sd_revalidate_disk(struct gendisk *disk);
static void sd_rw_intr(struct scsi_cmnd * SCpnt);

static int sd_probe(struct device *);
static int sd_remove(struct device *);
static void sd_shutdown(struct device *dev);
static void sd_rescan(struct device *);
static int sd_init_command(struct scsi_cmnd *);
static int sd_issue_flush(struct device *, sector_t *);
static void sd_read_capacity(struct scsi_disk *sdkp, char *diskname,
                 struct scsi_request *SRpnt, unsigned char *buffer);

static struct scsi_driver sd_template = {
        .owner                  = THIS_MODULE,
        .gendrv = {
                .name           = "sd",
                .probe          = sd_probe,
                .remove         = sd_remove,
                .shutdown       = sd_shutdown,
        },
        .rescan                 = sd_rescan,
        .init_command           = sd_init_command,
        .issue_flush            = sd_issue_flush,
};

/*
 * Device no to disk mapping:
 * 
 *       major         disc2     disc  p1
 *   |............|.............|....|....| <- dev_t
 *    31        20 19          8 7  4 3  0
 * 
 * Inside a major, we have 16k disks, however mapped non-
 * contiguously. The first 16 disks are for major0, the next
 * ones with major1, ... Disk 256 is for major0 again, disk 272 
 * for major1, ... 
 * As we stay compatible with our numbering scheme, we can reuse 
 * the well-know SCSI majors 8, 65--71, 136--143.
 */
static int sd_major(int major_idx)
{
        switch (major_idx) {
        case 0:
                return SCSI_DISK0_MAJOR;
        case 1 ... 7:
                return SCSI_DISK1_MAJOR + major_idx - 1;
        case 8 ... 15:
                return SCSI_DISK8_MAJOR + major_idx - 8;
        default:
                BUG();
                return 0;       /* shut up gcc */
        }
}

#define to_scsi_disk(obj) container_of(obj,struct scsi_disk,kref)

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

static struct scsi_disk *scsi_disk_get(struct gendisk *disk)
{
        struct scsi_disk *sdkp = NULL;

        down(&sd_ref_sem);
        if (disk->private_data == NULL)
                goto out;
        sdkp = scsi_disk(disk);
        kref_get(&sdkp->kref);
        if (scsi_device_get(sdkp->device))
                goto out_put;
        up(&sd_ref_sem);
        return sdkp;

 out_put:
        kref_put(&sdkp->kref, scsi_disk_release);
        sdkp = NULL;
 out:
        up(&sd_ref_sem);
        return sdkp;
}

static void scsi_disk_put(struct scsi_disk *sdkp)
{
        down(&sd_ref_sem);
        scsi_device_put(sdkp->device);
        kref_put(&sdkp->kref, scsi_disk_release);
        up(&sd_ref_sem);
}

/**
 *      sd_init_command - build a scsi (read or write) command from
 *      information in the request structure.
 *      @SCpnt: pointer to mid-level's per scsi command structure that
 *      contains request and into which the scsi command is written
 *
 *      Returns 1 if successful and 0 if error (or cannot be done now).
 **/
static int sd_init_command(struct scsi_cmnd * SCpnt)
{
        unsigned int this_count, timeout;
        struct gendisk *disk;
        sector_t block;
        struct scsi_device *sdp = SCpnt->device;

        timeout = sdp->timeout;

        /*
         * these are already setup, just copy cdb basically
         */
        if (SCpnt->request->flags & REQ_BLOCK_PC) {
                struct request *rq = SCpnt->request;

                if (sizeof(rq->cmd) > sizeof(SCpnt->cmnd))
                        return 0;

                memcpy(SCpnt->cmnd, rq->cmd, sizeof(SCpnt->cmnd));
                if (rq_data_dir(rq) == WRITE)
                        SCpnt->sc_data_direction = DMA_TO_DEVICE;
                else if (rq->data_len)
                        SCpnt->sc_data_direction = DMA_FROM_DEVICE;
                else
                        SCpnt->sc_data_direction = DMA_NONE;

                this_count = rq->data_len;
                if (rq->timeout)
                        timeout = rq->timeout;

                SCpnt->transfersize = rq->data_len;
                goto queue;
        }

        /*
         * we only do REQ_CMD and REQ_BLOCK_PC
         */
        if (!(SCpnt->request->flags & REQ_CMD))
                return 0;

        disk = SCpnt->request->rq_disk;
        block = SCpnt->request->sector;
        this_count = SCpnt->request_bufflen >> 9;

        SCSI_LOG_HLQUEUE(1, printk("sd_init_command: disk=%s, block=%llu, "
                            "count=%d\n", disk->disk_name, (unsigned long long)block, this_count));

        if (!sdp || !scsi_device_online(sdp) ||
            block + SCpnt->request->nr_sectors > get_capacity(disk)) {
                SCSI_LOG_HLQUEUE(2, printk("Finishing %ld sectors\n", 
                                 SCpnt->request->nr_sectors));
                SCSI_LOG_HLQUEUE(2, printk("Retry with 0x%p\n", SCpnt));
                return 0;
        }

        if (sdp->changed) {
                /*
                 * quietly refuse to do anything to a changed disc until 
                 * the changed bit has been reset
                 */
                /* printk("SCSI disk has been changed. Prohibiting further I/O.\n"); */
                return 0;
        }
        SCSI_LOG_HLQUEUE(2, printk("%s : block=%llu\n",
                                   disk->disk_name, (unsigned long long)block));

        /*
         * If we have a 1K hardware sectorsize, prevent access to single
         * 512 byte sectors.  In theory we could handle this - in fact
         * the scsi cdrom driver must be able to handle this because
         * we typically use 1K blocksizes, and cdroms typically have
         * 2K hardware sectorsizes.  Of course, things are simpler
         * with the cdrom, since it is read-only.  For performance
         * reasons, the filesystems should be able to handle this
         * and not force the scsi disk driver to use bounce buffers
         * for this.
         */
        if (sdp->sector_size == 1024) {
                if ((block & 1) || (SCpnt->request->nr_sectors & 1)) {
                        printk(KERN_ERR "sd: Bad block number requested");
                        return 0;
                } else {
                        block = block >> 1;
                        this_count = this_count >> 1;
                }
        }
        if (sdp->sector_size == 2048) {
                if ((block & 3) || (SCpnt->request->nr_sectors & 3)) {
                        printk(KERN_ERR "sd: Bad block number requested");
                        return 0;
                } else {
                        block = block >> 2;
                        this_count = this_count >> 2;
                }
        }
        if (sdp->sector_size == 4096) {
                if ((block & 7) || (SCpnt->request->nr_sectors & 7)) {
                        printk(KERN_ERR "sd: Bad block number requested");
                        return 0;
                } else {
                        block = block >> 3;
                        this_count = this_count >> 3;
                }
        }
        if (rq_data_dir(SCpnt->request) == WRITE) {
                if (!sdp->writeable) {
                        return 0;
                }
                SCpnt->cmnd[0] = WRITE_6;
                SCpnt->sc_data_direction = DMA_TO_DEVICE;
        } else if (rq_data_dir(SCpnt->request) == READ) {
                SCpnt->cmnd[0] = READ_6;
                SCpnt->sc_data_direction = DMA_FROM_DEVICE;
        } else {
                printk(KERN_ERR "sd: Unknown command %lx\n", 
                       SCpnt->request->flags);
/* overkill     panic("Unknown sd command %lx\n", SCpnt->request->flags); */
                return 0;
        }

        SCSI_LOG_HLQUEUE(2, printk("%s : %s %d/%ld 512 byte blocks.\n", 
                disk->disk_name, (rq_data_dir(SCpnt->request) == WRITE) ? 
                "writing" : "reading", this_count, SCpnt->request->nr_sectors));

        SCpnt->cmnd[1] = 0;
        
        if (block > 0xffffffff) {
                SCpnt->cmnd[0] += READ_16 - READ_6;
                SCpnt->cmnd[2] = sizeof(block) > 4 ? (unsigned char) (block >> 56) & 0xff : 0;
                SCpnt->cmnd[3] = sizeof(block) > 4 ? (unsigned char) (block >> 48) & 0xff : 0;
                SCpnt->cmnd[4] = sizeof(block) > 4 ? (unsigned char) (block >> 40) & 0xff : 0;
                SCpnt->cmnd[5] = sizeof(block) > 4 ? (unsigned char) (block >> 32) & 0xff : 0;
                SCpnt->cmnd[6] = (unsigned char) (block >> 24) & 0xff;
                SCpnt->cmnd[7] = (unsigned char) (block >> 16) & 0xff;
                SCpnt->cmnd[8] = (unsigned char) (block >> 8) & 0xff;
                SCpnt->cmnd[9] = (unsigned char) block & 0xff;
                SCpnt->cmnd[10] = (unsigned char) (this_count >> 24) & 0xff;
                SCpnt->cmnd[11] = (unsigned char) (this_count >> 16) & 0xff;
                SCpnt->cmnd[12] = (unsigned char) (this_count >> 8) & 0xff;
                SCpnt->cmnd[13] = (unsigned char) this_count & 0xff;
                SCpnt->cmnd[14] = SCpnt->cmnd[15] = 0;
        } else if ((this_count > 0xff) || (block > 0x1fffff) ||
                   SCpnt->device->use_10_for_rw) {
                if (this_count > 0xffff)
                        this_count = 0xffff;

                SCpnt->cmnd[0] += READ_10 - READ_6;
                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;
        } else {
                if (this_count > 0xff)
                        this_count = 0xff;

                SCpnt->cmnd[1] |= (unsigned char) ((block >> 16) & 0x1f);
                SCpnt->cmnd[2] = (unsigned char) ((block >> 8) & 0xff);
                SCpnt->cmnd[3] = (unsigned char) block & 0xff;
                SCpnt->cmnd[4] = (unsigned char) this_count;
                SCpnt->cmnd[5] = 0;
        }
        SCpnt->request_bufflen = SCpnt->bufflen =
                        this_count * sdp->sector_size;

        /*
         * 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 = sdp->sector_size;
        SCpnt->underflow = this_count << 9;

queue:
        SCpnt->allowed = SD_MAX_RETRIES;
        SCpnt->timeout_per_command = timeout;

        /*
         * This is the completion routine we use.  This is matched in terms
         * of capability to this function.
         */
        SCpnt->done = sd_rw_intr;

        /*
         * This indicates that the command is ready from our end to be
         * queued.
         */
        return 1;
}

/**
 *      sd_open - open a scsi disk device
 *      @inode: only i_rdev member may be used
 *      @filp: only f_mode and f_flags may be used
 *
 *      Returns 0 if successful. Returns a negated errno value in case 
 *      of error.
 *
 *      Note: This can be called from a user context (e.g. fsck(1) )
 *      or from within the kernel (e.g. as a result of a mount(1) ).
 *      In the latter case @inode and @filp carry an abridged amount
 *      of information as noted above.
 **/
static int sd_open(struct inode *inode, struct file *filp)
{
        struct gendisk *disk = inode->i_bdev->bd_disk;
        struct scsi_disk *sdkp;
        struct scsi_device *sdev;
        int retval;

        if (!(sdkp = scsi_disk_get(disk)))
                return -ENXIO;


        SCSI_LOG_HLQUEUE(3, printk("sd_open: disk=%s\n", disk->disk_name));

        sdev = sdkp->device;

        /*
         * 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;

        if (sdev->removable || sdkp->write_prot)
                check_disk_change(inode->i_bdev);

        /*
         * If the drive is empty, just let the open fail.
         */
        retval = -ENOMEDIUM;
        if (sdev->removable && !sdkp->media_present &&
            !(filp->f_flags & O_NDELAY))
                goto error_out;

        /*
         * If the device has the write protect tab set, have the open fail
         * if the user expects to be able to write to the thing.
         */
        retval = -EROFS;
        if (sdkp->write_prot && (filp->f_mode & FMODE_WRITE))
                goto error_out;

        /*
         * It is possible that the disk changing stuff resulted in
         * the device being taken offline.  If this is the case,
         * report this to the user, and don't pretend that the
         * open actually succeeded.
         */
        retval = -ENXIO;
        if (!scsi_device_online(sdev))
                goto error_out;

        if (!sdkp->openers++ && sdev->removable) {
                if (scsi_block_when_processing_errors(sdev))
                        scsi_set_medium_removal(sdev, SCSI_REMOVAL_PREVENT);
        }

        return 0;

error_out:
        scsi_disk_put(sdkp);
        return retval;  
}

/**
 *      sd_release - invoked when the (last) close(2) is called on this
 *      scsi disk.
 *      @inode: only i_rdev member may be used
 *      @filp: only f_mode and f_flags may be used
 *
 *      Returns 0. 
 *
 *      Note: may block (uninterruptible) if error recovery is underway
 *      on this disk.
 **/
static int sd_release(struct inode *inode, struct file *filp)
{
        struct gendisk *disk = inode->i_bdev->bd_disk;
        struct scsi_disk *sdkp = scsi_disk(disk);
        struct scsi_device *sdev = sdkp->device;

        SCSI_LOG_HLQUEUE(3, printk("sd_release: disk=%s\n", disk->disk_name));

        if (!--sdkp->openers && sdev->removable) {
                if (scsi_block_when_processing_errors(sdev))
                        scsi_set_medium_removal(sdev, SCSI_REMOVAL_ALLOW);
        }

        /*
         * XXX and what if there are packets in flight and this close()
         * XXX is followed by a "rmmod sd_mod"?
         */
        scsi_disk_put(sdkp);
        return 0;
}

static int sd_hdio_getgeo(struct block_device *bdev, struct hd_geometry __user *loc)
{
        struct scsi_disk *sdkp = scsi_disk(bdev->bd_disk);
        struct scsi_device *sdp = sdkp->device;
        struct Scsi_Host *host = sdp->host;
        int diskinfo[4];

        /* default to most commonly used values */
        diskinfo[0] = 0x40;     /* 1 << 6 */
        diskinfo[1] = 0x20;     /* 1 << 5 */
        diskinfo[2] = sdkp->capacity >> 11;
        
        /* override with calculated, extended default, or driver values */
        if (host->hostt->bios_param)
                host->hostt->bios_param(sdp, bdev, sdkp->capacity, diskinfo);
        else
                scsicam_bios_param(bdev, sdkp->capacity, diskinfo);

        if (put_user(diskinfo[0], &loc->heads))
                return -EFAULT;
        if (put_user(diskinfo[1], &loc->sectors))
                return -EFAULT;
        if (put_user(diskinfo[2], &loc->cylinders))
                return -EFAULT;
        if (put_user((unsigned)get_start_sect(bdev),
                     (unsigned long __user *)&loc->start))
                return -EFAULT;
        return 0;
}

/**
 *      sd_ioctl - process an ioctl
 *      @inode: only i_rdev/i_bdev members may be used
 *      @filp: only f_mode and f_flags may be used
 *      @cmd: ioctl command number
 *      @arg: this is third argument given to ioctl(2) system call.
 *      Often contains a pointer.
 *
 *      Returns 0 if successful (some ioctls return postive numbers on
 *      success as well). Returns a negated errno value in case of error.
 *
 *      Note: most ioctls are forward onto the block subsystem or further
 *      down in the scsi subsytem.
 **/
static int sd_ioctl(struct inode * inode, struct file * filp, 
                    unsigned int cmd, unsigned long arg)
{
        struct block_device *bdev = inode->i_bdev;
        struct gendisk *disk = bdev->bd_disk;
        struct scsi_device *sdp = scsi_disk(disk)->device;
        void __user *p = (void __user *)arg;
        int error;
    
        SCSI_LOG_IOCTL(1, printk("sd_ioctl: disk=%s, cmd=0x%x\n",
                                                disk->disk_name, cmd));

        /*
         * If we are in the middle of error recovery, don't let anyone
         * else try and use this device.  Also, if error recovery fails, it
         * may try and take the device offline, in which case all further
         * access to the device is prohibited.
         */
        if (!scsi_block_when_processing_errors(sdp))
                return -ENODEV;

        if (cmd == HDIO_GETGEO) {
                if (!arg)
                        return -EINVAL;
                return sd_hdio_getgeo(bdev, p);
        }

        /*
         * Send SCSI addressing ioctls directly to mid level, send other
         * ioctls to block level and then onto mid level if they can't be
         * resolved.
         */
        switch (cmd) {
                case SCSI_IOCTL_GET_IDLUN:
                case SCSI_IOCTL_GET_BUS_NUMBER:
                        return scsi_ioctl(sdp, cmd, p);
                default:
                        error = scsi_cmd_ioctl(filp, disk, cmd, p);
                        if (error != -ENOTTY)
                                return error;
        }
        return scsi_ioctl(sdp, cmd, p);
}

static void set_media_not_present(struct scsi_disk *sdkp)
{
        sdkp->media_present = 0;
        sdkp->capacity = 0;
        sdkp->device->changed = 1;
}

/**
 *      sd_media_changed - check if our medium changed
 *      @disk: kernel device descriptor 
 *
 *      Returns 0 if not applicable or no change; 1 if change
 *
 *      Note: this function is invoked from the block subsystem.
 **/
static int sd_media_changed(struct gendisk *disk)
{
        struct scsi_disk *sdkp = scsi_disk(disk);
        struct scsi_device *sdp = sdkp->device;
        int retval;

        SCSI_LOG_HLQUEUE(3, printk("sd_media_changed: disk=%s\n",
                                                disk->disk_name));

        if (!sdp->removable)
                return 0;

        /*
         * If the device is offline, don't send any commands - just pretend as
         * if the command failed.  If the device ever comes back online, we
         * can deal with it then.  It is only because of unrecoverable errors
         * that we would ever take a device offline in the first place.
         */
        if (!scsi_device_online(sdp))
                goto not_present;

        /*
         * Using TEST_UNIT_READY enables differentiation between drive with
         * no cartridge loaded - NOT READY, drive with changed cartridge -
         * UNIT ATTENTION, or with same cartridge - GOOD STATUS.
         *
         * Drives that auto spin down. eg iomega jaz 1G, will be started
         * by sd_spinup_disk() from sd_revalidate_disk(), which happens whenever
         * sd_revalidate() is called.
         */
        retval = -ENODEV;
        if (scsi_block_when_processing_errors(sdp))
                retval = scsi_test_unit_ready(sdp, SD_TIMEOUT, SD_MAX_RETRIES);

        /*
         * 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.
         */
        if (retval)
                 goto not_present;

        /*
         * For removable scsi disk we have to recognise the presence
         * of a disk in the drive. This is kept in the struct scsi_disk
         * struct and tested at open !  Daniel Roche (dan@lectra.fr)
         */
        sdkp->media_present = 1;

        retval = sdp->changed;
        sdp->changed = 0;

        return retval;

not_present:
        set_media_not_present(sdkp);
        return 1;
}

static int sd_sync_cache(struct scsi_device *sdp)
{
        struct scsi_request *sreq;
        int retries, res;

        if (!scsi_device_online(sdp))
                return -ENODEV;

        sreq = scsi_allocate_request(sdp, GFP_KERNEL);
        if (!sreq) {
                printk("FAILED\n  No memory for request\n");
                return -ENOMEM;
        }

        sreq->sr_data_direction = DMA_NONE;
        for (retries = 3; retries > 0; --retries) {
                unsigned char cmd[10] = { 0 };

                cmd[0] = SYNCHRONIZE_CACHE;
                /*
                 * Leave the rest of the command zero to indicate
                 * flush everything.
                 */
                scsi_wait_req(sreq, cmd, NULL, 0, SD_TIMEOUT, SD_MAX_RETRIES);
                if (sreq->sr_result == 0)
                        break;
        }

        res = sreq->sr_result;
        if (res) {
                printk(KERN_WARNING "FAILED\n  status = %x, message = %02x, "
                                    "host = %d, driver = %02x\n  ",
                                    status_byte(res), msg_byte(res),
                                    host_byte(res), driver_byte(res));
                        if (driver_byte(res) & DRIVER_SENSE)
                                scsi_print_req_sense("sd", sreq);
        }

        scsi_release_request(sreq);
        return res;
}

static int sd_issue_flush(struct device *dev, sector_t *error_sector)
{
        struct scsi_device *sdp = to_scsi_device(dev);
        struct scsi_disk *sdkp = dev_get_drvdata(dev);

        if (!sdkp)
               return -ENODEV;

        if (!sdkp->WCE)
                return 0;

        return sd_sync_cache(sdp);
}

static void sd_rescan(struct device *dev)
{
        struct scsi_disk *sdkp = dev_get_drvdata(dev);
        sd_revalidate_disk(sdkp->disk);
}

static struct block_device_operations sd_fops = {
        .owner                  = THIS_MODULE,
        .open                   = sd_open,
        .release                = sd_release,
        .ioctl                  = sd_ioctl,
        .media_changed          = sd_media_changed,
        .revalidate_disk        = sd_revalidate_disk,
};

/**
 *      sd_rw_intr - bottom half handler: called when the lower level
 *      driver has completed (successfully or otherwise) a scsi command.
 *      @SCpnt: mid-level's per command structure.
 *
 *      Note: potentially run from within an ISR. Must not block.
 **/
static void sd_rw_intr(struct scsi_cmnd * SCpnt)
{
        int result = SCpnt->result;
        int this_count = SCpnt->bufflen;
        int good_bytes = (result == 0 ? this_count : 0);
        sector_t block_sectors = 1;
        sector_t error_sector;
#ifdef CONFIG_SCSI_LOGGING
        SCSI_LOG_HLCOMPLETE(1, printk("sd_rw_intr: %s: res=0x%x\n", 
                                SCpnt->request->rq_disk->disk_name, result));
        if (0 != result) {
                SCSI_LOG_HLCOMPLETE(1, printk("sd_rw_intr: sb[0,2,asc,ascq]"
                                "=%x,%x,%x,%x\n", SCpnt->sense_buffer[0],
                        SCpnt->sense_buffer[2], SCpnt->sense_buffer[12],
                        SCpnt->sense_buffer[13]));
        }
#endif
        /*
           Handle MEDIUM ERRORs 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.
         */

        /* An error occurred */
        if (driver_byte(result) != 0 &&         /* An error occurred */
            (SCpnt->sense_buffer[0] & 0x7f) == 0x70) { /* Sense current */
                switch (SCpnt->sense_buffer[2]) {
                case MEDIUM_ERROR:
                        if (!(SCpnt->sense_buffer[0] & 0x80))
                                break;
                        if (!blk_fs_request(SCpnt->request))
                                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);
                        switch (SCpnt->device->sector_size) {
                        case 1024:
                                error_sector <<= 1;
                                if (block_sectors < 2)
                                        block_sectors = 2;
                                break;
                        case 2048:
                                error_sector <<= 2;
                                if (block_sectors < 4)
                                        block_sectors = 4;
                                break;
                        case 4096:
                                error_sector <<=3;
                                if (block_sectors < 8)
                                        block_sectors = 8;
                                break;
                        case 256:
                                error_sector >>= 1;
                                break;
                        default:
                                break;
                        }

                        error_sector &= ~(block_sectors - 1);
                        good_bytes = (error_sector - SCpnt->request->sector) << 9;
                        if (good_bytes < 0 || good_bytes >= this_count)
                                good_bytes = 0;
                        break;

                case RECOVERED_ERROR: /* an error occurred, but it recovered */
                case NO_SENSE: /* LLDD got sense data */
                        /*
                         * Inform the user, but make sure that it's not treated
                         * as a hard error.
                         */
                        scsi_print_sense("sd", SCpnt);
                        SCpnt->result = 0;
                        SCpnt->sense_buffer[0] = 0x0;
                        good_bytes = this_count;
                        break;

                case ILLEGAL_REQUEST:
                        if (SCpnt->device->use_10_for_rw &&
                            (SCpnt->cmnd[0] == READ_10 ||
                             SCpnt->cmnd[0] == WRITE_10))
                                SCpnt->device->use_10_for_rw = 0;
                        if (SCpnt->device->use_10_for_ms &&
                            (SCpnt->cmnd[0] == MODE_SENSE_10 ||
                             SCpnt->cmnd[0] == MODE_SELECT_10))
                                SCpnt->device->use_10_for_ms = 0;
                        break;

                default:
                        break;
                }
        }
        /*
         * This calls the generic completion function, now that we know
         * how many actual sectors finished, and how many sectors we need
         * to say have failed.
         */
        scsi_io_completion(SCpnt, good_bytes, block_sectors << 9);
}

static int media_not_present(struct scsi_disk *sdkp, struct scsi_request *srp)
{
        if (!srp->sr_result)
                return 0;
        if (!(driver_byte(srp->sr_result) & DRIVER_SENSE))
                return 0;
        if (srp->sr_sense_buffer[2] != NOT_READY &&
            srp->sr_sense_buffer[2] != UNIT_ATTENTION)
                return 0;
        if (srp->sr_sense_buffer[12] != 0x3A) /* medium not present */
                return 0;

        set_media_not_present(sdkp);
        return 1;
}

/*
 * spinup disk - called only in sd_revalidate_disk()
 */
static void
sd_spinup_disk(struct scsi_disk *sdkp, char *diskname,
               struct scsi_request *SRpnt, unsigned char *buffer) {
        unsigned char cmd[10];
        unsigned long spintime_value = 0;
        int retries, spintime;
        unsigned int the_result;

        spintime = 0;

        /* Spin up drives, as required.  Only do this at boot time */
        /* Spinup needs to be done for module loads too. */
        do {
                retries = 0;

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

                        SRpnt->sr_cmd_len = 0;
                        SRpnt->sr_sense_buffer[0] = 0;
                        SRpnt->sr_sense_buffer[2] = 0;
                        SRpnt->sr_data_direction = DMA_NONE;

                        scsi_wait_req (SRpnt, (void *) cmd, (void *) buffer,
                                       0/*512*/, SD_TIMEOUT, SD_MAX_RETRIES);

                        the_result = SRpnt->sr_result;
                        retries++;
                } while (retries < 3 && 
                         (!scsi_status_is_good(the_result) ||
                          ((driver_byte(the_result) & DRIVER_SENSE) &&
                           SRpnt->sr_sense_buffer[2] == UNIT_ATTENTION)));

                /*
                 * If the drive has indicated to us that it doesn't have
                 * any media in it, don't bother with any of the rest of
                 * this crap.
                 */
                if (media_not_present(sdkp, SRpnt))
                        return;

                if ((driver_byte(the_result) & DRIVER_SENSE) == 0) {
                        /* no sense, TUR either succeeded or failed
                         * with a status error */
                        if(!spintime && !scsi_status_is_good(the_result))
                                printk(KERN_NOTICE "%s: Unit Not Ready, error = 0x%x\n", diskname, the_result);
                        break;
                }
                                        
                /*
                 * The device does not want the automatic start to be issued.
                 */
                if (sdkp->device->no_start_on_add) {
                        break;
                }

                /*
                 * If manual intervention is required, or this is an
                 * absent USB storage device, a spinup is meaningless.
                 */
                if (SRpnt->sr_sense_buffer[2] == NOT_READY &&
                    SRpnt->sr_sense_buffer[12] == 4 /* not ready */ &&
                    SRpnt->sr_sense_buffer[13] == 3) {
                        break;          /* manual intervention required */

                /*
                 * Issue command to spin up drive when not ready
                 */
                } else if (SRpnt->sr_sense_buffer[2] == NOT_READY) {
                        unsigned long time1;
                        if (!spintime) {
                                printk(KERN_NOTICE "%s: Spinning up disk...",
                                       diskname);
                                cmd[0] = START_STOP;
                                cmd[1] = 1;     /* Return immediately */
                                memset((void *) &cmd[2], 0, 8);
                                cmd[4] = 1;     /* Start spin cycle */
                                SRpnt->sr_cmd_len = 0;
                                SRpnt->sr_sense_buffer[0] = 0;
                                SRpnt->sr_sense_buffer[2] = 0;

                                SRpnt->sr_data_direction = DMA_NONE;
                                scsi_wait_req(SRpnt, (void *)cmd, 
                                              (void *) buffer, 0/*512*/, 
                                              SD_TIMEOUT, SD_MAX_RETRIES);
                                spintime_value = jiffies;
                        }
                        spintime = 1;
                        time1 = HZ;
                        /* Wait 1 second for next try */
                        do {
                                current->state = TASK_UNINTERRUPTIBLE;
                                time1 = schedule_timeout(time1);
                        } while(time1);
                        printk(".");
                } else {
                        /* we don't understand the sense code, so it's
                         * probably pointless to loop */
                        if(!spintime) {
                                printk(KERN_NOTICE "%s: Unit Not Ready, sense:\n", diskname);
                                scsi_print_req_sense("", SRpnt);
                        }
                        break;
                }
                                
        } while (spintime &&
                 time_after(spintime_value + 100 * HZ, jiffies));

        if (spintime) {
                if (scsi_status_is_good(the_result))
                        printk("ready\n");
                else
                        printk("not responding...\n");
        }
}

/*
 * read disk capacity
 */
static void
sd_read_capacity(struct scsi_disk *sdkp, char *diskname,
                 struct scsi_request *SRpnt, unsigned char *buffer) {
        unsigned char cmd[16];
        struct scsi_device *sdp = sdkp->device;
        int the_result, retries;
        int sector_size = 0;
        int longrc = 0;

repeat:
        retries = 3;
        do {
                if (longrc) {
                        memset((void *) cmd, 0, 16);
                        cmd[0] = SERVICE_ACTION_IN;
                        cmd[1] = SAI_READ_CAPACITY_16;
                        cmd[13] = 12;
                        memset((void *) buffer, 0, 12);
                } else {
                        cmd[0] = READ_CAPACITY;
                        memset((void *) &cmd[1], 0, 9);
                        memset((void *) buffer, 0, 8);
                }
                
                SRpnt->sr_cmd_len = 0;
                SRpnt->sr_sense_buffer[0] = 0;
                SRpnt->sr_sense_buffer[2] = 0;
                SRpnt->sr_data_direction = DMA_FROM_DEVICE;

                scsi_wait_req(SRpnt, (void *) cmd, (void *) buffer,
                              longrc ? 12 : 8, SD_TIMEOUT, SD_MAX_RETRIES);

                if (media_not_present(sdkp, SRpnt))
                        return;

                the_result = SRpnt->sr_result;
                retries--;

        } while (the_result && retries);

        if (the_result && !longrc) {
                printk(KERN_NOTICE "%s : READ CAPACITY failed.\n"
                       "%s : status=%x, message=%02x, host=%d, driver=%02x \n",
                       diskname, diskname,
                       status_byte(the_result),
                       msg_byte(the_result),
                       host_byte(the_result),
                       driver_byte(the_result));

                if (driver_byte(the_result) & DRIVER_SENSE)
                        scsi_print_req_sense("sd", SRpnt);
                else
                        printk("%s : sense not available. \n", diskname);

                /* Set dirty bit for removable devices if not ready -
                 * sometimes drives will not report this properly. */
                if (sdp->removable &&
                    SRpnt->sr_sense_buffer[2] == NOT_READY)
                        sdp->changed = 1;

                /* Either no media are present but the drive didn't tell us,
                   or they are present but the read capacity command fails */
                /* sdkp->media_present = 0; -- not always correct */
                sdkp->capacity = 0x200000; /* 1 GB - random */

                return;
        } else if (the_result && longrc) {
                /* READ CAPACITY(16) has been failed */
                printk(KERN_NOTICE "%s : READ CAPACITY(16) failed.\n"
                       "%s : status=%x, message=%02x, host=%d, driver=%02x \n",
                       diskname, diskname,
                       status_byte(the_result),
                       msg_byte(the_result),
                       host_byte(the_result),
                       driver_byte(the_result));
                printk(KERN_NOTICE "%s : use 0xffffffff as device size\n",
                       diskname);
                
                sdkp->capacity = 1 + (sector_t) 0xffffffff;             
                goto got_data;
        }       
        
        if (!longrc) {
                sector_size = (buffer[4] << 24) |
                        (buffer[5] << 16) | (buffer[6] << 8) | buffer[7];
                if (buffer[0] == 0xff && buffer[1] == 0xff &&
                    buffer[2] == 0xff && buffer[3] == 0xff) {
                        if(sizeof(sdkp->capacity) > 4) {
                                printk(KERN_NOTICE "%s : very big device. try to use"
                                       " READ CAPACITY(16).\n", diskname);
                                longrc = 1;
                                goto repeat;
                        } else {
                                printk(KERN_ERR "%s: too big for kernel.  Assuming maximum 2Tb\n", diskname);
                        }
                }
                sdkp->capacity = 1 + (((sector_t)buffer[0] << 24) |
                        (buffer[1] << 16) |
                        (buffer[2] << 8) |
                        buffer[3]);                     
        } else {
                sdkp->capacity = 1 + (((u64)buffer[0] << 56) |
                        ((u64)buffer[1] << 48) |
                        ((u64)buffer[2] << 40) |
                        ((u64)buffer[3] << 32) |
                        ((sector_t)buffer[4] << 24) |
                        ((sector_t)buffer[5] << 16) |
                        ((sector_t)buffer[6] << 8)  |
                        (sector_t)buffer[7]);
                        
                sector_size = (buffer[8] << 24) |
                        (buffer[9] << 16) | (buffer[10] << 8) | buffer[11];
        }       

got_data:
        if (sector_size == 0) {
                sector_size = 512;
                printk(KERN_NOTICE "%s : sector size 0 reported, "
                       "assuming 512.\n", diskname);
        }

        if (sector_size != 512 &&
            sector_size != 1024 &&
            sector_size != 2048 &&
            sector_size != 4096 &&
            sector_size != 256) {
                printk(KERN_NOTICE "%s : unsupported sector size "
                       "%d.\n", diskname, sector_size);
                /*
                 * The user might want to re-format the drive with
                 * a supported sectorsize.  Once this happens, it
                 * would be relatively trivial to set the thing up.
                 * For this reason, we leave the thing in the table.
                 */
                sdkp->capacity = 0;
        }
        {
                /*
                 * The msdos fs needs to know the hardware sector size
                 * So I have created this table. See ll_rw_blk.c
                 * Jacques Gelinas (Jacques@solucorp.qc.ca)
                 */
                int hard_sector = sector_size;
                sector_t sz = sdkp->capacity * (hard_sector/256);
                request_queue_t *queue = sdp->request_queue;
                sector_t mb;

                blk_queue_hardsect_size(queue, hard_sector);
                /* avoid 64-bit division on 32-bit platforms */
                mb = sz >> 1;
                sector_div(sz, 1250);
                mb -= sz - 974;
                sector_div(mb, 1950);

                printk(KERN_NOTICE "SCSI device %s: "
                       "%llu %d-byte hdwr sectors (%llu MB)\n",
                       diskname, (unsigned long long)sdkp->capacity,
                       hard_sector, (unsigned long long)mb);
        }

        /* Rescale capacity to 512-byte units */
        if (sector_size == 4096)
                sdkp->capacity <<= 3;
        else if (sector_size == 2048)
                sdkp->capacity <<= 2;
        else if (sector_size == 1024)
                sdkp->capacity <<= 1;
        else if (sector_size == 256)
                sdkp->capacity >>= 1;

        sdkp->device->sector_size = sector_size;
}

/* called with buffer of length 512 */
static inline int
sd_do_mode_sense(struct scsi_request *SRpnt, int dbd, int modepage,
                 unsigned char *buffer, int len, struct scsi_mode_data *data)
{
        return __scsi_mode_sense(SRpnt, dbd, modepage, buffer, len,
                                 SD_TIMEOUT, SD_MAX_RETRIES, data);
}

/*
 * read write protect setting, if possible - called only in sd_revalidate_disk()
 * called with buffer of length 512
 */
static void
sd_read_write_protect_flag(struct scsi_disk *sdkp, char *diskname,
                   struct scsi_request *SRpnt, unsigned char *buffer) {
        int res;
        struct scsi_mode_data data;

        set_disk_ro(sdkp->disk, 0);
        if (sdkp->device->skip_ms_page_3f) {
                printk(KERN_NOTICE "%s: assuming Write Enabled\n", diskname);
                return;
        }

        if (sdkp->device->use_192_bytes_for_3f) {
                res = sd_do_mode_sense(SRpnt, 0, 0x3F, buffer, 192, &data);
        } else {
                /*
                 * First attempt: ask for all pages (0x3F), but only 4 bytes.
                 * We have to start carefully: some devices hang if we ask
                 * for more than is available.
                 */
                res = sd_do_mode_sense(SRpnt, 0, 0x3F, buffer, 4, &data);

                /*
                 * Second attempt: ask for page 0 When only page 0 is
                 * implemented, a request for page 3F may return Sense Key
                 * 5: Illegal Request, Sense Code 24: Invalid field in
                 * CDB.
                 */
                if (!scsi_status_is_good(res))
                        res = sd_do_mode_sense(SRpnt, 0, 0, buffer, 4, &data);

                /*
                 * Third attempt: ask 255 bytes, as we did earlier.
                 */
                if (!scsi_status_is_good(res))
                        res = sd_do_mode_sense(SRpnt, 0, 0x3F, buffer, 255,
                                               &data);
        }

        if (!scsi_status_is_good(res)) {
                printk(KERN_WARNING
                       "%s: test WP failed, assume Write Enabled\n", diskname);
        } else {
                sdkp->write_prot = ((data.device_specific & 0x80) != 0);
                set_disk_ro(sdkp->disk, sdkp->write_prot);
                printk(KERN_NOTICE "%s: Write Protect is %s\n", diskname,
                       sdkp->write_prot ? "on" : "off");
                printk(KERN_DEBUG "%s: Mode Sense: %02x %02x %02x %02x\n",
                       diskname, buffer[0], buffer[1], buffer[2], buffer[3]);
        }
}

/*
 * sd_read_cache_type - called only from sd_revalidate_disk()
 * called with buffer of length 512
 */
static void
sd_read_cache_type(struct scsi_disk *sdkp, char *diskname,
                   struct scsi_request *SRpnt, unsigned char *buffer) {
        int len = 0, res;

        const int dbd = 0;         /* DBD */
        const int modepage = 0x08; /* current values, cache page */
        struct scsi_mode_data data;

        if (sdkp->device->skip_ms_page_8)
                goto defaults;

        /* cautiously ask */
        res = sd_do_mode_sense(SRpnt, dbd, modepage, buffer, 4, &data);

        if (!scsi_status_is_good(res))
                goto bad_sense;

        /* that went OK, now ask for the proper length */
        len = data.length;

        /*
         * We're only interested in the first three bytes, actually.
         * But the data cache page is defined for the first 20.
         */
        if (len < 3)
                goto bad_sense;
        if (len > 20)
                len = 20;

        /* Take headers and block descriptors into account */
        len += data.header_length + data.block_descriptor_length;

        /* Get the data */
        res = sd_do_mode_sense(SRpnt, dbd, modepage, buffer, len, &data);

        if (scsi_status_is_good(res)) {
                const char *types[] = {
                        "write through", "none", "write back",
                        "write back, no read (daft)"
                };
                int ct = 0;
                int offset = data.header_length +
                        data.block_descriptor_length + 2;

                sdkp->WCE = ((buffer[offset] & 0x04) != 0);
                sdkp->RCD = ((buffer[offset] & 0x01) != 0);

                ct =  sdkp->RCD + 2*sdkp->WCE;

                printk(KERN_NOTICE "SCSI device %s: drive cache: %s\n",
                       diskname, types[ct]);

                return;
        }

bad_sense:
        if ((SRpnt->sr_sense_buffer[0] & 0x70) == 0x70
             && (SRpnt->sr_sense_buffer[2] & 0x0f) == ILLEGAL_REQUEST
             /* ASC 0x24 ASCQ 0x00: Invalid field in CDB */
             && SRpnt->sr_sense_buffer[12] == 0x24
             && SRpnt->sr_sense_buffer[13] == 0x00) {
                printk(KERN_NOTICE "%s: cache data unavailable\n",
                       diskname);
        } else {
                printk(KERN_ERR "%s: asking for cache data failed\n",
                       diskname);
        }

defaults:
        printk(KERN_ERR "%s: assuming drive cache: write through\n",
               diskname);
        sdkp->WCE = 0;
        sdkp->RCD = 0;
}

/**
 *      sd_revalidate_disk - called the first time a new disk is seen,
 *      performs disk spin up, read_capacity, etc.
 *      @disk: struct gendisk we care about
 **/
static int sd_revalidate_disk(struct gendisk *disk)
{
        struct scsi_disk *sdkp = scsi_disk(disk);
        struct scsi_device *sdp = sdkp->device;
        struct scsi_request *sreq;
        unsigned char *buffer;

        SCSI_LOG_HLQUEUE(3, printk("sd_revalidate_disk: disk=%s\n", disk->disk_name));

        /*
         * If the device is offline, don't try and read capacity or any
         * of the other niceties.
         */
        if (!scsi_device_online(sdp))
                goto out;

        sreq = scsi_allocate_request(sdp, GFP_KERNEL);
        if (!sreq) {
                printk(KERN_WARNING "(sd_revalidate_disk:) Request allocation "
                       "failure.\n");
                goto out;
        }

        buffer = kmalloc(512, GFP_KERNEL | __GFP_DMA);
        if (!buffer) {
                printk(KERN_WARNING "(sd_revalidate_disk:) Memory allocation "
                       "failure.\n");
                goto out_release_request;
        }

        /* defaults, until the device tells us otherwise */
        sdp->sector_size = 512;
        sdkp->capacity = 0;
        sdkp->media_present = 1;
        sdkp->write_prot = 0;
        sdkp->WCE = 0;
        sdkp->RCD = 0;

        sd_spinup_disk(sdkp, disk->disk_name, sreq, buffer);

        /*
         * Without media there is no reason to ask; moreover, some devices
         * react badly if we do.
         */
        if (sdkp->media_present) {
                sd_read_capacity(sdkp, disk->disk_name, sreq, buffer);
                if (sdp->removable)
                        sd_read_write_protect_flag(sdkp, disk->disk_name,
                                        sreq, buffer);
                sd_read_cache_type(sdkp, disk->disk_name, sreq, buffer);
        }
                
        set_capacity(disk, sdkp->capacity);
        kfree(buffer);

 out_release_request: 
        scsi_release_request(sreq);
 out:
        return 0;
}

/**
 *      sd_probe - called during driver initialization and whenever a
 *      new scsi device is attached to the system. It is called once
 *      for each scsi device (not just disks) present.
 *      @dev: pointer to device object
 *
 *      Returns 0 if successful (or not interested in this scsi device 
 *      (e.g. scanner)); 1 when there is an error.
 *
 *      Note: this function is invoked from the scsi mid-level.
 *      This function sets up the mapping between a given 
 *      <host,channel,id,lun> (found in sdp) and new device name 
 *      (e.g. /dev/sda). More precisely it is the block device major 
 *      and minor number that is chosen here.
 *
 *      Assume sd_attach is not re-entrant (for time being)
 *      Also think about sd_attach() and sd_remove() running coincidentally.
 **/
static int sd_probe(struct device *dev)
{
        struct scsi_device *sdp = to_scsi_device(dev);
        struct scsi_disk *sdkp;
        struct gendisk *gd;
        u32 index;
        int error;

        error = -ENODEV;
        if ((sdp->type != TYPE_DISK) && (sdp->type != TYPE_MOD))
                goto out;

        SCSI_LOG_HLQUEUE(3, printk("sd_attach: scsi device: <%d,%d,%d,%d>\n", 
                         sdp->host->host_no, sdp->channel, sdp->id, sdp->lun));

        error = -ENOMEM;
        sdkp = kmalloc(sizeof(*sdkp), GFP_KERNEL);
        if (!sdkp)
                goto out;

        memset (sdkp, 0, sizeof(*sdkp));
        kref_init(&sdkp->kref);

        gd = alloc_disk(16);
        if (!gd)
                goto out_free;

        if (!idr_pre_get(&sd_index_idr, GFP_KERNEL))
                goto out_put;

        spin_lock(&sd_index_lock);
        error = idr_get_new(&sd_index_idr, NULL, &index);
        spin_unlock(&sd_index_lock);

        if (index >= SD_MAX_DISKS)
                error = -EBUSY;
        if (error)
                goto out_put;

        sdkp->device = sdp;
        sdkp->driver = &sd_template;
        sdkp->disk = gd;
        sdkp->index = index;
        sdkp->openers = 0;

        if (!sdp->timeout) {
                if (sdp->type == TYPE_DISK)
                        sdp->timeout = SD_TIMEOUT;
                else
                        sdp->timeout = SD_MOD_TIMEOUT;
        }

        gd->major = sd_major((index & 0xf0) >> 4);
        gd->first_minor = ((index & 0xf) << 4) | (index & 0xfff00);
        gd->minors = 16;
        gd->fops = &sd_fops;

        if (index < 26) {
                sprintf(gd->disk_name, "sd%c", 'a' + index % 26);
        } else if (index < (26 + 1) * 26) {
                sprintf(gd->disk_name, "sd%c%c",
                        'a' + index / 26 - 1,'a' + index % 26);
        } else {
                const unsigned int m1 = (index / 26 - 1) / 26 - 1;
                const unsigned int m2 = (index / 26 - 1) % 26;
                const unsigned int m3 =  index % 26;
                sprintf(gd->disk_name, "sd%c%c%c",
                        'a' + m1, 'a' + m2, 'a' + m3);
        }

        strcpy(gd->devfs_name, sdp->devfs_name);

        gd->private_data = &sdkp->driver;

        sd_revalidate_disk(gd);

        gd->driverfs_dev = &sdp->sdev_gendev;
        gd->flags = GENHD_FL_DRIVERFS;
        if (sdp->removable)
                gd->flags |= GENHD_FL_REMOVABLE;
        gd->queue = sdkp->device->request_queue;

        dev_set_drvdata(dev, sdkp);
        add_disk(gd);

        printk(KERN_NOTICE "Attached scsi %sdisk %s at scsi%d, channel %d, "
               "id %d, lun %d\n", sdp->removable ? "removable " : "",
               gd->disk_name, sdp->host->host_no, sdp->channel,
               sdp->id, sdp->lun);

        return 0;

out_put:
        put_disk(gd);
out_free:
        kfree(sdkp);
out:
        return error;
}

/**
 *      sd_remove - called whenever a scsi disk (previously recognized by
 *      sd_probe) is detached from the system. It is called (potentially
 *      multiple times) during sd module unload.
 *      @sdp: pointer to mid level scsi device object
 *
 *      Note: this function is invoked from the scsi mid-level.
 *      This function potentially frees up a device name (e.g. /dev/sdc)
 *      that could be re-used by a subsequent sd_probe().
 *      This function is not called when the built-in sd driver is "exit-ed".
 **/
static int sd_remove(struct device *dev)
{
        struct scsi_disk *sdkp = dev_get_drvdata(dev);

        del_gendisk(sdkp->disk);
        sd_shutdown(dev);
        down(&sd_ref_sem);
        kref_put(&sdkp->kref, scsi_disk_release);
        up(&sd_ref_sem);

        return 0;
}

/**
 *      scsi_disk_release - Called to free the scsi_disk structure
 *      @kref: pointer to embedded kref
 *
 *      sd_ref_sem must be held entering this routine.  Because it is
 *      called on last put, you should always use the scsi_disk_get()
 *      scsi_disk_put() helpers which manipulate the semaphore directly
 *      and never do a direct kref_put().
 **/
static void scsi_disk_release(struct kref *kref)
{
        struct scsi_disk *sdkp = to_scsi_disk(kref);
        struct gendisk *disk = sdkp->disk;
        
        spin_lock(&sd_index_lock);
        idr_remove(&sd_index_idr, sdkp->index);
        spin_unlock(&sd_index_lock);

        disk->private_data = NULL;

        put_disk(disk);

        kfree(sdkp);
}

/*
 * Send a SYNCHRONIZE CACHE instruction down to the device through
 * the normal SCSI command structure.  Wait for the command to
 * complete.
 */
static void sd_shutdown(struct device *dev)
{
        struct scsi_device *sdp = to_scsi_device(dev);
        struct scsi_disk *sdkp = dev_get_drvdata(dev);

        if (!sdkp)
                return;         /* this can happen */

        if (!sdkp->WCE)
                return;

        printk(KERN_NOTICE "Synchronizing SCSI cache for disk %s: \n",
                        sdkp->disk->disk_name);
        sd_sync_cache(sdp);
}       

/**
 *      init_sd - entry point for this driver (both when built in or when
 *      a module).
 *
 *      Note: this function registers this driver with the scsi mid-level.
 **/
static int __init init_sd(void)
{
        int majors = 0, i;

        SCSI_LOG_HLQUEUE(3, printk("init_sd: sd driver entry point\n"));

        for (i = 0; i < SD_MAJORS; i++)
                if (register_blkdev(sd_major(i), "sd") == 0)
                        majors++;

        if (!majors)
                return -ENODEV;

        return scsi_register_driver(&sd_template.gendrv);
}

/**
 *      exit_sd - exit point for this driver (when it is a module).
 *
 *      Note: this function unregisters this driver from the scsi mid-level.
 **/
static void __exit exit_sd(void)
{
        int i;

        SCSI_LOG_HLQUEUE(3, printk("exit_sd: exiting sd driver\n"));

        scsi_unregister_driver(&sd_template.gendrv);
        for (i = 0; i < SD_MAJORS; i++)
                unregister_blkdev(sd_major(i), "sd");
}

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Eric Youngdale");
MODULE_DESCRIPTION("SCSI disk (sd) driver");

module_init(init_sd);
module_exit(exit_sd);