/*
 *  History:
 *  Started: Aug 9 by Lawrence Foard (entropy@world.std.com),
 *           to allow user process control of SCSI devices.
 *  Development Sponsored by Killy Corp. NY NY
 *
 * Original driver (sg.c):
 *        Copyright (C) 1992 Lawrence Foard
 * Version 2 and 3 extensions to driver:
 *        Copyright (C) 1998 - 2005 Douglas Gilbert
 *
 *  Modified  19-JAN-1998  Richard Gooch <rgooch@atnf.csiro.au>  Devfs support
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 */

static int sg_version_num = 30534;      /* 2 digits for each component */
#define SG_VERSION_STR "3.5.34"

/*
 *  D. P. Gilbert (dgilbert@interlog.com, dougg@triode.net.au), notes:
 *      - scsi logging is available via SCSI_LOG_TIMEOUT macros. First
 *        the kernel/module needs to be built with CONFIG_SCSI_LOGGING
 *        (otherwise the macros compile to empty statements).
 *
 */
#include <linux/module.h>

#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/aio.h>
#include <linux/errno.h>
#include <linux/mtio.h>
#include <linux/ioctl.h>
#include <linux/slab.h>
#include <linux/fcntl.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/moduleparam.h>
#include <linux/cdev.h>
#include <linux/idr.h>
#include <linux/seq_file.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/blktrace_api.h>
#include <linux/mutex.h>
#include <linux/ratelimit.h>

#include "scsi.h"
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_driver.h>
#include <scsi/scsi_ioctl.h>
#include <scsi/sg.h>

#include "scsi_logging.h"

#ifdef CONFIG_SCSI_PROC_FS
#include <linux/proc_fs.h>
static char *sg_version_date = "20061027";

static int sg_proc_init(void);
static void sg_proc_cleanup(void);
#endif

#define SG_ALLOW_DIO_DEF 0

#define SG_MAX_DEVS 32768

/*
 * Suppose you want to calculate the formula muldiv(x,m,d)=int(x * m / d)
 * Then when using 32 bit integers x * m may overflow during the calculation.
 * Replacing muldiv(x) by muldiv(x)=((x % d) * m) / d + int(x / d) * m
 * calculates the same, but prevents the overflow when both m and d
 * are "small" numbers (like HZ and USER_HZ).
 * Of course an overflow is inavoidable if the result of muldiv doesn't fit
 * in 32 bits.
 */
#define MULDIV(X,MUL,DIV) ((((X % DIV) * MUL) / DIV) + ((X / DIV) * MUL))

#define SG_DEFAULT_TIMEOUT MULDIV(SG_DEFAULT_TIMEOUT_USER, HZ, USER_HZ)

int sg_big_buff = SG_DEF_RESERVED_SIZE;
/* N.B. This variable is readable and writeable via
   /proc/scsi/sg/def_reserved_size . Each time sg_open() is called a buffer
   of this size (or less if there is not enough memory) will be reserved
   for use by this file descriptor. [Deprecated usage: this variable is also
   readable via /proc/sys/kernel/sg-big-buff if the sg driver is built into
   the kernel (i.e. it is not a module).] */
static int def_reserved_size = -1;      /* picks up init parameter */
static int sg_allow_dio = SG_ALLOW_DIO_DEF;

static int scatter_elem_sz = SG_SCATTER_SZ;
static int scatter_elem_sz_prev = SG_SCATTER_SZ;

#define SG_SECTOR_SZ 512

static int sg_add(struct device *, struct class_interface *);
static void sg_remove(struct device *, struct class_interface *);

static DEFINE_SPINLOCK(sg_open_exclusive_lock);

static DEFINE_IDR(sg_index_idr);
static DEFINE_RWLOCK(sg_index_lock);    /* Also used to lock
                                                           file descriptor list for device */

static struct class_interface sg_interface = {
        .add_dev        = sg_add,
        .remove_dev     = sg_remove,
};

typedef struct sg_scatter_hold { /* holding area for scsi scatter gather info */
        unsigned short k_use_sg; /* Count of kernel scatter-gather pieces */
        unsigned sglist_len; /* size of malloc'd scatter-gather list ++ */
        unsigned bufflen;       /* Size of (aggregate) data buffer */
        struct page **pages;
        int page_order;
        char dio_in_use;        /* 0->indirect IO (or mmap), 1->dio */
        unsigned char cmd_opcode; /* first byte of command */
} Sg_scatter_hold;

struct sg_device;               /* forward declarations */
struct sg_fd;

typedef struct sg_request {     /* SG_MAX_QUEUE requests outstanding per file */
        struct sg_request *nextrp;      /* NULL -> tail request (slist) */
        struct sg_fd *parentfp; /* NULL -> not in use */
        Sg_scatter_hold data;   /* hold buffer, perhaps scatter list */
        sg_io_hdr_t header;     /* scsi command+info, see <scsi/sg.h> */
        unsigned char sense_b[SCSI_SENSE_BUFFERSIZE];
        char res_used;          /* 1 -> using reserve buffer, 0 -> not ... */
        char orphan;            /* 1 -> drop on sight, 0 -> normal */
        char sg_io_owned;       /* 1 -> packet belongs to SG_IO */
        /* done protected by rq_list_lock */
        char done;              /* 0->before bh, 1->before read, 2->read */
        struct request *rq;
        struct bio *bio;
        struct execute_work ew;
} Sg_request;

typedef struct sg_fd {          /* holds the state of a file descriptor */
        /* sfd_siblings is protected by sg_index_lock */
        struct list_head sfd_siblings;
        struct sg_device *parentdp;     /* owning device */
        wait_queue_head_t read_wait;    /* queue read until command done */
        rwlock_t rq_list_lock;  /* protect access to list in req_arr */
        int timeout;            /* defaults to SG_DEFAULT_TIMEOUT      */
        int timeout_user;       /* defaults to SG_DEFAULT_TIMEOUT_USER */
        Sg_scatter_hold reserve;        /* buffer held for this file descriptor */
        unsigned save_scat_len; /* original length of trunc. scat. element */
        Sg_request *headrp;     /* head of request slist, NULL->empty */
        struct fasync_struct *async_qp; /* used by asynchronous notification */
        Sg_request req_arr[SG_MAX_QUEUE];       /* used as singly-linked list */
        char low_dma;           /* as in parent but possibly overridden to 1 */
        char force_packid;      /* 1 -> pack_id input to read(), 0 -> ignored */
        char cmd_q;             /* 1 -> allow command queuing, 0 -> don't */
        char next_cmd_len;      /* 0 -> automatic (def), >0 -> use on next write() */
        char keep_orphan;       /* 0 -> drop orphan (def), 1 -> keep for read() */
        char mmap_called;       /* 0 -> mmap() never called on this fd */
        struct kref f_ref;
        struct execute_work ew;
} Sg_fd;

typedef struct sg_device { /* holds the state of each scsi generic device */
        struct scsi_device *device;
        wait_queue_head_t o_excl_wait;  /* queue open() when O_EXCL in use */
        int sg_tablesize;       /* adapter's max scatter-gather table size */
        u32 index;              /* device index number */
        /* sfds is protected by sg_index_lock */
        struct list_head sfds;
        volatile char detached; /* 0->attached, 1->detached pending removal */
        /* exclude protected by sg_open_exclusive_lock */
        char exclude;           /* opened for exclusive access */
        char sgdebug;           /* 0->off, 1->sense, 9->dump dev, 10-> all devs */
        struct gendisk *disk;
        struct cdev * cdev;     /* char_dev [sysfs: /sys/cdev/major/sg<n>] */
        struct kref d_ref;
} Sg_device;

/* tasklet or soft irq callback */
static void sg_rq_end_io(struct request *rq, int uptodate);
static int sg_start_req(Sg_request *srp, unsigned char *cmd);
static int sg_finish_rem_req(Sg_request * srp);
static int sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size);
static ssize_t sg_new_read(Sg_fd * sfp, char __user *buf, size_t count,
                           Sg_request * srp);
static ssize_t sg_new_write(Sg_fd *sfp, struct file *file,
                        const char __user *buf, size_t count, int blocking,
                        int read_only, int sg_io_owned, Sg_request **o_srp);
static int sg_common_write(Sg_fd * sfp, Sg_request * srp,
                           unsigned char *cmnd, int timeout, int blocking);
static int sg_read_oxfer(Sg_request * srp, char __user *outp, int num_read_xfer);
static void sg_remove_scat(Sg_scatter_hold * schp);
static void sg_build_reserve(Sg_fd * sfp, int req_size);
static void sg_link_reserve(Sg_fd * sfp, Sg_request * srp, int size);
static void sg_unlink_reserve(Sg_fd * sfp, Sg_request * srp);
static Sg_fd *sg_add_sfp(Sg_device * sdp, int dev);
static void sg_remove_sfp(struct kref *);
static Sg_request *sg_get_rq_mark(Sg_fd * sfp, int pack_id);
static Sg_request *sg_add_request(Sg_fd * sfp);
static int sg_remove_request(Sg_fd * sfp, Sg_request * srp);
static int sg_res_in_use(Sg_fd * sfp);
static Sg_device *sg_get_dev(int dev);
static void sg_put_dev(Sg_device *sdp);

#define SZ_SG_HEADER sizeof(struct sg_header)
#define SZ_SG_IO_HDR sizeof(sg_io_hdr_t)
#define SZ_SG_IOVEC sizeof(sg_iovec_t)
#define SZ_SG_REQ_INFO sizeof(sg_req_info_t)

static int sg_allow_access(struct file *filp, unsigned char *cmd)
{
        struct sg_fd *sfp = filp->private_data;

        if (sfp->parentdp->device->type == TYPE_SCANNER)
                return 0;

        return blk_verify_command(cmd, filp->f_mode & FMODE_WRITE);
}

static int get_exclude(Sg_device *sdp)
{
        unsigned long flags;
        int ret;

        spin_lock_irqsave(&sg_open_exclusive_lock, flags);
        ret = sdp->exclude;
        spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
        return ret;
}

static int set_exclude(Sg_device *sdp, char val)
{
        unsigned long flags;

        spin_lock_irqsave(&sg_open_exclusive_lock, flags);
        sdp->exclude = val;
        spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
        return val;
}

static int sfds_list_empty(Sg_device *sdp)
{
        unsigned long flags;
        int ret;

        read_lock_irqsave(&sg_index_lock, flags);
        ret = list_empty(&sdp->sfds);
        read_unlock_irqrestore(&sg_index_lock, flags);
        return ret;
}

static int
sg_open(struct inode *inode, struct file *filp)
{
        int dev = iminor(inode);
        int flags = filp->f_flags;
        struct request_queue *q;
        Sg_device *sdp;
        Sg_fd *sfp;
        int res;
        int retval;

        nonseekable_open(inode, filp);
        SCSI_LOG_TIMEOUT(3, printk("sg_open: dev=%d, flags=0x%x\n", dev, flags));
        sdp = sg_get_dev(dev);
        if (IS_ERR(sdp)) {
                retval = PTR_ERR(sdp);
                sdp = NULL;
                goto sg_put;
        }

        /* This driver's module count bumped by fops_get in <linux/fs.h> */
        /* Prevent the device driver from vanishing while we sleep */
        retval = scsi_device_get(sdp->device);
        if (retval)
                goto sg_put;

        retval = scsi_autopm_get_device(sdp->device);
        if (retval)
                goto sdp_put;

        if (!((flags & O_NONBLOCK) ||
              scsi_block_when_processing_errors(sdp->device))) {
                retval = -ENXIO;
                /* we are in error recovery for this device */
                goto error_out;
        }

        if (flags & O_EXCL) {
                if (O_RDONLY == (flags & O_ACCMODE)) {
                        retval = -EPERM; /* Can't lock it with read only access */
                        goto error_out;
                }
                if (!sfds_list_empty(sdp) && (flags & O_NONBLOCK)) {
                        retval = -EBUSY;
                        goto error_out;
                }
                res = wait_event_interruptible(sdp->o_excl_wait,
                                           ((!sfds_list_empty(sdp) || get_exclude(sdp)) ? 0 : set_exclude(sdp, 1)));
                if (res) {
                        retval = res;   /* -ERESTARTSYS because signal hit process */
                        goto error_out;
                }
        } else if (get_exclude(sdp)) {  /* some other fd has an exclusive lock on dev */
                if (flags & O_NONBLOCK) {
                        retval = -EBUSY;
                        goto error_out;
                }
                res = wait_event_interruptible(sdp->o_excl_wait, !get_exclude(sdp));
                if (res) {
                        retval = res;   /* -ERESTARTSYS because signal hit process */
                        goto error_out;
                }
        }
        if (sdp->detached) {
                retval = -ENODEV;
                goto error_out;
        }
        if (sfds_list_empty(sdp)) {     /* no existing opens on this device */
                sdp->sgdebug = 0;
                q = sdp->device->request_queue;
                sdp->sg_tablesize = queue_max_segments(q);
        }
        if ((sfp = sg_add_sfp(sdp, dev)))
                filp->private_data = sfp;
        else {
                if (flags & O_EXCL) {
                        set_exclude(sdp, 0);    /* undo if error */
                        wake_up_interruptible(&sdp->o_excl_wait);
                }
                retval = -ENOMEM;
                goto error_out;
        }
        retval = 0;
error_out:
        if (retval) {
                scsi_autopm_put_device(sdp->device);
sdp_put:
                scsi_device_put(sdp->device);
        }
sg_put:
        if (sdp)
                sg_put_dev(sdp);
        return retval;
}

/* Following function was formerly called 'sg_close' */
static int
sg_release(struct inode *inode, struct file *filp)
{
        Sg_device *sdp;
        Sg_fd *sfp;

        if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
                return -ENXIO;
        SCSI_LOG_TIMEOUT(3, printk("sg_release: %s\n", sdp->disk->disk_name));

        set_exclude(sdp, 0);
        wake_up_interruptible(&sdp->o_excl_wait);

        scsi_autopm_put_device(sdp->device);
        kref_put(&sfp->f_ref, sg_remove_sfp);
        return 0;
}

static ssize_t
sg_read(struct file *filp, char __user *buf, size_t count, loff_t * ppos)
{
        Sg_device *sdp;
        Sg_fd *sfp;
        Sg_request *srp;
        int req_pack_id = -1;
        sg_io_hdr_t *hp;
        struct sg_header *old_hdr = NULL;
        int retval = 0;

        if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
                return -ENXIO;
        SCSI_LOG_TIMEOUT(3, printk("sg_read: %s, count=%d\n",
                                   sdp->disk->disk_name, (int) count));

        if (!access_ok(VERIFY_WRITE, buf, count))
                return -EFAULT;
        if (sfp->force_packid && (count >= SZ_SG_HEADER)) {
                old_hdr = kmalloc(SZ_SG_HEADER, GFP_KERNEL);
                if (!old_hdr)
                        return -ENOMEM;
                if (__copy_from_user(old_hdr, buf, SZ_SG_HEADER)) {
                        retval = -EFAULT;
                        goto free_old_hdr;
                }
                if (old_hdr->reply_len < 0) {
                        if (count >= SZ_SG_IO_HDR) {
                                sg_io_hdr_t *new_hdr;
                                new_hdr = kmalloc(SZ_SG_IO_HDR, GFP_KERNEL);
                                if (!new_hdr) {
                                        retval = -ENOMEM;
                                        goto free_old_hdr;
                                }
                                retval =__copy_from_user
                                    (new_hdr, buf, SZ_SG_IO_HDR);
                                req_pack_id = new_hdr->pack_id;
                                kfree(new_hdr);
                                if (retval) {
                                        retval = -EFAULT;
                                        goto free_old_hdr;
                                }
                        }
                } else
                        req_pack_id = old_hdr->pack_id;
        }
        srp = sg_get_rq_mark(sfp, req_pack_id);
        if (!srp) {             /* now wait on packet to arrive */
                if (sdp->detached) {
                        retval = -ENODEV;
                        goto free_old_hdr;
                }
                if (filp->f_flags & O_NONBLOCK) {
                        retval = -EAGAIN;
                        goto free_old_hdr;
                }
                retval = wait_event_interruptible(sfp->read_wait,
                        (sdp->detached ||
                        (srp = sg_get_rq_mark(sfp, req_pack_id))));
                if (sdp->detached) {
                        retval = -ENODEV;
                        goto free_old_hdr;
                }
                if (retval) {
                        /* -ERESTARTSYS as signal hit process */
                        goto free_old_hdr;
                }
        }
        if (srp->header.interface_id != '\0') {
                retval = sg_new_read(sfp, buf, count, srp);
                goto free_old_hdr;
        }

        hp = &srp->header;
        if (old_hdr == NULL) {
                old_hdr = kmalloc(SZ_SG_HEADER, GFP_KERNEL);
                if (! old_hdr) {
                        retval = -ENOMEM;
                        goto free_old_hdr;
                }
        }
        memset(old_hdr, 0, SZ_SG_HEADER);
        old_hdr->reply_len = (int) hp->timeout;
        old_hdr->pack_len = old_hdr->reply_len; /* old, strange behaviour */
        old_hdr->pack_id = hp->pack_id;
        old_hdr->twelve_byte =
            ((srp->data.cmd_opcode >= 0xc0) && (12 == hp->cmd_len)) ? 1 : 0;
        old_hdr->target_status = hp->masked_status;
        old_hdr->host_status = hp->host_status;
        old_hdr->driver_status = hp->driver_status;
        if ((CHECK_CONDITION & hp->masked_status) ||
            (DRIVER_SENSE & hp->driver_status))
                memcpy(old_hdr->sense_buffer, srp->sense_b,
                       sizeof (old_hdr->sense_buffer));
        switch (hp->host_status) {
        /* This setup of 'result' is for backward compatibility and is best
           ignored by the user who should use target, host + driver status */
        case DID_OK:
        case DID_PASSTHROUGH:
        case DID_SOFT_ERROR:
                old_hdr->result = 0;
                break;
        case DID_NO_CONNECT:
        case DID_BUS_BUSY:
        case DID_TIME_OUT:
                old_hdr->result = EBUSY;
                break;
        case DID_BAD_TARGET:
        case DID_ABORT:
        case DID_PARITY:
        case DID_RESET:
        case DID_BAD_INTR:
                old_hdr->result = EIO;
                break;
        case DID_ERROR:
                old_hdr->result = (srp->sense_b[0] == 0 && 
                                  hp->masked_status == GOOD) ? 0 : EIO;
                break;
        default:
                old_hdr->result = EIO;
                break;
        }

        /* Now copy the result back to the user buffer.  */
        if (count >= SZ_SG_HEADER) {
                if (__copy_to_user(buf, old_hdr, SZ_SG_HEADER)) {
                        retval = -EFAULT;
                        goto free_old_hdr;
                }
                buf += SZ_SG_HEADER;
                if (count > old_hdr->reply_len)
                        count = old_hdr->reply_len;
                if (count > SZ_SG_HEADER) {
                        if (sg_read_oxfer(srp, buf, count - SZ_SG_HEADER)) {
                                retval = -EFAULT;
                                goto free_old_hdr;
                        }
                }
        } else
                count = (old_hdr->result == 0) ? 0 : -EIO;
        sg_finish_rem_req(srp);
        retval = count;
free_old_hdr:
        kfree(old_hdr);
        return retval;
}

static ssize_t
sg_new_read(Sg_fd * sfp, char __user *buf, size_t count, Sg_request * srp)
{
        sg_io_hdr_t *hp = &srp->header;
        int err = 0;
        int len;

        if (count < SZ_SG_IO_HDR) {
                err = -EINVAL;
                goto err_out;
        }
        hp->sb_len_wr = 0;
        if ((hp->mx_sb_len > 0) && hp->sbp) {
                if ((CHECK_CONDITION & hp->masked_status) ||
                    (DRIVER_SENSE & hp->driver_status)) {
                        int sb_len = SCSI_SENSE_BUFFERSIZE;
                        sb_len = (hp->mx_sb_len > sb_len) ? sb_len : hp->mx_sb_len;
                        len = 8 + (int) srp->sense_b[7];        /* Additional sense length field */
                        len = (len > sb_len) ? sb_len : len;
                        if (copy_to_user(hp->sbp, srp->sense_b, len)) {
                                err = -EFAULT;
                                goto err_out;
                        }
                        hp->sb_len_wr = len;
                }
        }
        if (hp->masked_status || hp->host_status || hp->driver_status)
                hp->info |= SG_INFO_CHECK;
        if (copy_to_user(buf, hp, SZ_SG_IO_HDR)) {
                err = -EFAULT;
                goto err_out;
        }
err_out:
        err = sg_finish_rem_req(srp);
        return (0 == err) ? count : err;
}

static ssize_t
sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
{
        int mxsize, cmd_size, k;
        int input_size, blocking;
        unsigned char opcode;
        Sg_device *sdp;
        Sg_fd *sfp;
        Sg_request *srp;
        struct sg_header old_hdr;
        sg_io_hdr_t *hp;
        unsigned char cmnd[MAX_COMMAND_SIZE];

        if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
                return -ENXIO;
        SCSI_LOG_TIMEOUT(3, printk("sg_write: %s, count=%d\n",
                                   sdp->disk->disk_name, (int) count));
        if (sdp->detached)
                return -ENODEV;
        if (!((filp->f_flags & O_NONBLOCK) ||
              scsi_block_when_processing_errors(sdp->device)))
                return -ENXIO;

        if (!access_ok(VERIFY_READ, buf, count))
                return -EFAULT; /* protects following copy_from_user()s + get_user()s */
        if (count < SZ_SG_HEADER)
                return -EIO;
        if (__copy_from_user(&old_hdr, buf, SZ_SG_HEADER))
                return -EFAULT;
        blocking = !(filp->f_flags & O_NONBLOCK);
        if (old_hdr.reply_len < 0)
                return sg_new_write(sfp, filp, buf, count,
                                    blocking, 0, 0, NULL);
        if (count < (SZ_SG_HEADER + 6))
                return -EIO;    /* The minimum scsi command length is 6 bytes. */

        if (!(srp = sg_add_request(sfp))) {
                SCSI_LOG_TIMEOUT(1, printk("sg_write: queue full\n"));
                return -EDOM;
        }
        buf += SZ_SG_HEADER;
        __get_user(opcode, buf);
        if (sfp->next_cmd_len > 0) {
                if (sfp->next_cmd_len > MAX_COMMAND_SIZE) {
                        SCSI_LOG_TIMEOUT(1, printk("sg_write: command length too long\n"));
                        sfp->next_cmd_len = 0;
                        sg_remove_request(sfp, srp);
                        return -EIO;
                }
                cmd_size = sfp->next_cmd_len;
                sfp->next_cmd_len = 0;  /* reset so only this write() effected */
        } else {
                cmd_size = COMMAND_SIZE(opcode);        /* based on SCSI command group */
                if ((opcode >= 0xc0) && old_hdr.twelve_byte)
                        cmd_size = 12;
        }
        SCSI_LOG_TIMEOUT(4, printk(
                "sg_write:   scsi opcode=0x%02x, cmd_size=%d\n", (int) opcode, cmd_size));
/* Determine buffer size.  */
        input_size = count - cmd_size;
        mxsize = (input_size > old_hdr.reply_len) ? input_size : old_hdr.reply_len;
        mxsize -= SZ_SG_HEADER;
        input_size -= SZ_SG_HEADER;
        if (input_size < 0) {
                sg_remove_request(sfp, srp);
                return -EIO;    /* User did not pass enough bytes for this command. */
        }
        hp = &srp->header;
        hp->interface_id = '\0';        /* indicator of old interface tunnelled */
        hp->cmd_len = (unsigned char) cmd_size;
        hp->iovec_count = 0;
        hp->mx_sb_len = 0;
        if (input_size > 0)
                hp->dxfer_direction = (old_hdr.reply_len > SZ_SG_HEADER) ?
                    SG_DXFER_TO_FROM_DEV : SG_DXFER_TO_DEV;
        else
                hp->dxfer_direction = (mxsize > 0) ? SG_DXFER_FROM_DEV : SG_DXFER_NONE;
        hp->dxfer_len = mxsize;
        if (hp->dxfer_direction == SG_DXFER_TO_DEV)
                hp->dxferp = (char __user *)buf + cmd_size;
        else
                hp->dxferp = NULL;
        hp->sbp = NULL;
        hp->timeout = old_hdr.reply_len;        /* structure abuse ... */
        hp->flags = input_size; /* structure abuse ... */
        hp->pack_id = old_hdr.pack_id;
        hp->usr_ptr = NULL;
        if (__copy_from_user(cmnd, buf, cmd_size))
                return -EFAULT;
        /*
         * SG_DXFER_TO_FROM_DEV is functionally equivalent to SG_DXFER_FROM_DEV,
         * but is is possible that the app intended SG_DXFER_TO_DEV, because there
         * is a non-zero input_size, so emit a warning.
         */
        if (hp->dxfer_direction == SG_DXFER_TO_FROM_DEV) {
                static char cmd[TASK_COMM_LEN];
                if (strcmp(current->comm, cmd)) {
                        printk_ratelimited(KERN_WARNING
                                           "sg_write: data in/out %d/%d bytes "
                                           "for SCSI command 0x%x-- guessing "
                                           "data in;\n   program %s not setting "
                                           "count and/or reply_len properly\n",
                                           old_hdr.reply_len - (int)SZ_SG_HEADER,
                                           input_size, (unsigned int) cmnd[0],
                                           current->comm);
                        strcpy(cmd, current->comm);
                }
        }
        k = sg_common_write(sfp, srp, cmnd, sfp->timeout, blocking);
        return (k < 0) ? k : count;
}

static ssize_t
sg_new_write(Sg_fd *sfp, struct file *file, const char __user *buf,
                 size_t count, int blocking, int read_only, int sg_io_owned,
                 Sg_request **o_srp)
{
        int k;
        Sg_request *srp;
        sg_io_hdr_t *hp;
        unsigned char cmnd[MAX_COMMAND_SIZE];
        int timeout;
        unsigned long ul_timeout;

        if (count < SZ_SG_IO_HDR)
                return -EINVAL;
        if (!access_ok(VERIFY_READ, buf, count))
                return -EFAULT; /* protects following copy_from_user()s + get_user()s */

        sfp->cmd_q = 1; /* when sg_io_hdr seen, set command queuing on */
        if (!(srp = sg_add_request(sfp))) {
                SCSI_LOG_TIMEOUT(1, printk("sg_new_write: queue full\n"));
                return -EDOM;
        }
        srp->sg_io_owned = sg_io_owned;
        hp = &srp->header;
        if (__copy_from_user(hp, buf, SZ_SG_IO_HDR)) {
                sg_remove_request(sfp, srp);
                return -EFAULT;
        }
        if (hp->interface_id != 'S') {
                sg_remove_request(sfp, srp);
                return -ENOSYS;
        }
        if (hp->flags & SG_FLAG_MMAP_IO) {
                if (hp->dxfer_len > sfp->reserve.bufflen) {
                        sg_remove_request(sfp, srp);
                        return -ENOMEM; /* MMAP_IO size must fit in reserve buffer */
                }
                if (hp->flags & SG_FLAG_DIRECT_IO) {
                        sg_remove_request(sfp, srp);
                        return -EINVAL; /* either MMAP_IO or DIRECT_IO (not both) */
                }
                if (sg_res_in_use(sfp)) {
                        sg_remove_request(sfp, srp);
                        return -EBUSY;  /* reserve buffer already being used */
                }
        }
        ul_timeout = msecs_to_jiffies(srp->header.timeout);
        timeout = (ul_timeout < INT_MAX) ? ul_timeout : INT_MAX;
        if ((!hp->cmdp) || (hp->cmd_len < 6) || (hp->cmd_len > sizeof (cmnd))) {
                sg_remove_request(sfp, srp);
                return -EMSGSIZE;
        }
        if (!access_ok(VERIFY_READ, hp->cmdp, hp->cmd_len)) {
                sg_remove_request(sfp, srp);
                return -EFAULT; /* protects following copy_from_user()s + get_user()s */
        }
        if (__copy_from_user(cmnd, hp->cmdp, hp->cmd_len)) {
                sg_remove_request(sfp, srp);
                return -EFAULT;
        }
        if (read_only && sg_allow_access(file, cmnd)) {
                sg_remove_request(sfp, srp);
                return -EPERM;
        }
        k = sg_common_write(sfp, srp, cmnd, timeout, blocking);
        if (k < 0)
                return k;
        if (o_srp)
                *o_srp = srp;
        return count;
}

static int
sg_common_write(Sg_fd * sfp, Sg_request * srp,
                unsigned char *cmnd, int timeout, int blocking)
{
        int k, data_dir;
        Sg_device *sdp = sfp->parentdp;
        sg_io_hdr_t *hp = &srp->header;

        srp->data.cmd_opcode = cmnd[0]; /* hold opcode of command */
        hp->status = 0;
        hp->masked_status = 0;
        hp->msg_status = 0;
        hp->info = 0;
        hp->host_status = 0;
        hp->driver_status = 0;
        hp->resid = 0;
        SCSI_LOG_TIMEOUT(4, printk("sg_common_write:  scsi opcode=0x%02x, cmd_size=%d\n",
                          (int) cmnd[0], (int) hp->cmd_len));

        k = sg_start_req(srp, cmnd);
        if (k) {
                SCSI_LOG_TIMEOUT(1, printk("sg_common_write: start_req err=%d\n", k));
                sg_finish_rem_req(srp);
                return k;       /* probably out of space --> ENOMEM */
        }
        if (sdp->detached) {
                if (srp->bio)
                        blk_end_request_all(srp->rq, -EIO);
                sg_finish_rem_req(srp);
                return -ENODEV;
        }

        switch (hp->dxfer_direction) {
        case SG_DXFER_TO_FROM_DEV:
        case SG_DXFER_FROM_DEV:
                data_dir = DMA_FROM_DEVICE;
                break;
        case SG_DXFER_TO_DEV:
                data_dir = DMA_TO_DEVICE;
                break;
        case SG_DXFER_UNKNOWN:
                data_dir = DMA_BIDIRECTIONAL;
                break;
        default:
                data_dir = DMA_NONE;
                break;
        }
        hp->duration = jiffies_to_msecs(jiffies);

        srp->rq->timeout = timeout;
        kref_get(&sfp->f_ref); /* sg_rq_end_io() does kref_put(). */
        blk_execute_rq_nowait(sdp->device->request_queue, sdp->disk,
                              srp->rq, 1, sg_rq_end_io);
        return 0;
}

static int srp_done(Sg_fd *sfp, Sg_request *srp)
{
        unsigned long flags;
        int ret;

        read_lock_irqsave(&sfp->rq_list_lock, flags);
        ret = srp->done;
        read_unlock_irqrestore(&sfp->rq_list_lock, flags);
        return ret;
}

static long
sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
{
        void __user *p = (void __user *)arg;
        int __user *ip = p;
        int result, val, read_only;
        Sg_device *sdp;
        Sg_fd *sfp;
        Sg_request *srp;
        unsigned long iflags;

        if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
                return -ENXIO;

        SCSI_LOG_TIMEOUT(3, printk("sg_ioctl: %s, cmd=0x%x\n",
                                   sdp->disk->disk_name, (int) cmd_in));
        read_only = (O_RDWR != (filp->f_flags & O_ACCMODE));

        switch (cmd_in) {
        case SG_IO:
                if (sdp->detached)
                        return -ENODEV;
                if (!scsi_block_when_processing_errors(sdp->device))
                        return -ENXIO;
                if (!access_ok(VERIFY_WRITE, p, SZ_SG_IO_HDR))
                        return -EFAULT;
                result = sg_new_write(sfp, filp, p, SZ_SG_IO_HDR,
                                 1, read_only, 1, &srp);
                if (result < 0)
                        return result;
                result = wait_event_interruptible(sfp->read_wait,
                        (srp_done(sfp, srp) || sdp->detached));
                if (sdp->detached)
                        return -ENODEV;
                write_lock_irq(&sfp->rq_list_lock);
                if (srp->done) {
                        srp->done = 2;
                        write_unlock_irq(&sfp->rq_list_lock);
                        result = sg_new_read(sfp, p, SZ_SG_IO_HDR, srp);
                        return (result < 0) ? result : 0;
                }
                srp->orphan = 1;
                write_unlock_irq(&sfp->rq_list_lock);
                return result;  /* -ERESTARTSYS because signal hit process */
        case SG_SET_TIMEOUT:
                result = get_user(val, ip);
                if (result)
                        return result;
                if (val < 0)
                        return -EIO;
                if (val >= MULDIV (INT_MAX, USER_HZ, HZ))
                    val = MULDIV (INT_MAX, USER_HZ, HZ);
                sfp->timeout_user = val;
                sfp->timeout = MULDIV (val, HZ, USER_HZ);

                return 0;
        case SG_GET_TIMEOUT:    /* N.B. User receives timeout as return value */
                                /* strange ..., for backward compatibility */
                return sfp->timeout_user;
        case SG_SET_FORCE_LOW_DMA:
                result = get_user(val, ip);
                if (result)
                        return result;
                if (val) {
                        sfp->low_dma = 1;
                        if ((0 == sfp->low_dma) && (0 == sg_res_in_use(sfp))) {
                                val = (int) sfp->reserve.bufflen;
                                sg_remove_scat(&sfp->reserve);
                                sg_build_reserve(sfp, val);
                        }
                } else {
                        if (sdp->detached)
                                return -ENODEV;
                        sfp->low_dma = sdp->device->host->unchecked_isa_dma;
                }
                return 0;
        case SG_GET_LOW_DMA:
                return put_user((int) sfp->low_dma, ip);
        case SG_GET_SCSI_ID:
                if (!access_ok(VERIFY_WRITE, p, sizeof (sg_scsi_id_t)))
                        return -EFAULT;
                else {
                        sg_scsi_id_t __user *sg_idp = p;

                        if (sdp->detached)
                                return -ENODEV;
                        __put_user((int) sdp->device->host->host_no,
                                   &sg_idp->host_no);
                        __put_user((int) sdp->device->channel,
                                   &sg_idp->channel);
                        __put_user((int) sdp->device->id, &sg_idp->scsi_id);
                        __put_user((int) sdp->device->lun, &sg_idp->lun);
                        __put_user((int) sdp->device->type, &sg_idp->scsi_type);
                        __put_user((short) sdp->device->host->cmd_per_lun,
                                   &sg_idp->h_cmd_per_lun);
                        __put_user((short) sdp->device->queue_depth,
                                   &sg_idp->d_queue_depth);
                        __put_user(0, &sg_idp->unused[0]);
                        __put_user(0, &sg_idp->unused[1]);
                        return 0;
                }
        case SG_SET_FORCE_PACK_ID:
                result = get_user(val, ip);
                if (result)
                        return result;
                sfp->force_packid = val ? 1 : 0;
                return 0;
        case SG_GET_PACK_ID:
                if (!access_ok(VERIFY_WRITE, ip, sizeof (int)))
                        return -EFAULT;
                read_lock_irqsave(&sfp->rq_list_lock, iflags);
                for (srp = sfp->headrp; srp; srp = srp->nextrp) {
                        if ((1 == srp->done) && (!srp->sg_io_owned)) {
                                read_unlock_irqrestore(&sfp->rq_list_lock,
                                                       iflags);
                                __put_user(srp->header.pack_id, ip);
                                return 0;
                        }
                }
                read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
                __put_user(-1, ip);
                return 0;
        case SG_GET_NUM_WAITING:
                read_lock_irqsave(&sfp->rq_list_lock, iflags);
                for (val = 0, srp = sfp->headrp; srp; srp = srp->nextrp) {
                        if ((1 == srp->done) && (!srp->sg_io_owned))
                                ++val;
                }
                read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
                return put_user(val, ip);
        case SG_GET_SG_TABLESIZE:
                return put_user(sdp->sg_tablesize, ip);
        case SG_SET_RESERVED_SIZE:
                result = get_user(val, ip);
                if (result)
                        return result;
                if (val < 0)
                        return -EINVAL;
                val = min_t(int, val,
                            queue_max_sectors(sdp->device->request_queue) * 512);
                if (val != sfp->reserve.bufflen) {
                        if (sg_res_in_use(sfp) || sfp->mmap_called)
                                return -EBUSY;
                        sg_remove_scat(&sfp->reserve);
                        sg_build_reserve(sfp, val);
                }
                return 0;
        case SG_GET_RESERVED_SIZE:
                val = min_t(int, sfp->reserve.bufflen,
                            queue_max_sectors(sdp->device->request_queue) * 512);
                return put_user(val, ip);
        case SG_SET_COMMAND_Q:
                result = get_user(val, ip);
                if (result)
                        return result;
                sfp->cmd_q = val ? 1 : 0;
                return 0;
        case SG_GET_COMMAND_Q:
                return put_user((int) sfp->cmd_q, ip);
        case SG_SET_KEEP_ORPHAN:
                result = get_user(val, ip);
                if (result)
                        return result;
                sfp->keep_orphan = val;
                return 0;
        case SG_GET_KEEP_ORPHAN:
                return put_user((int) sfp->keep_orphan, ip);
        case SG_NEXT_CMD_LEN:
                result = get_user(val, ip);
                if (result)
                        return result;
                sfp->next_cmd_len = (val > 0) ? val : 0;
                return 0;
        case SG_GET_VERSION_NUM:
                return put_user(sg_version_num, ip);
        case SG_GET_ACCESS_COUNT:
                /* faked - we don't have a real access count anymore */
                val = (sdp->device ? 1 : 0);
                return put_user(val, ip);
        case SG_GET_REQUEST_TABLE:
                if (!access_ok(VERIFY_WRITE, p, SZ_SG_REQ_INFO * SG_MAX_QUEUE))
                        return -EFAULT;
                else {
                        sg_req_info_t *rinfo;
                        unsigned int ms;

                        rinfo = kmalloc(SZ_SG_REQ_INFO * SG_MAX_QUEUE,
                                                                GFP_KERNEL);
                        if (!rinfo)
                                return -ENOMEM;
                        read_lock_irqsave(&sfp->rq_list_lock, iflags);
                        for (srp = sfp->headrp, val = 0; val < SG_MAX_QUEUE;

                             ++val, srp = srp ? srp->nextrp : srp) {
                                memset(&rinfo[val], 0, SZ_SG_REQ_INFO);
                                if (srp) {
                                        rinfo[val].req_state = srp->done + 1;
                                        rinfo[val].problem =
                                            srp->header.masked_status & 
                                            srp->header.host_status & 
                                            srp->header.driver_status;
                                        if (srp->done)
                                                rinfo[val].duration =
                                                        srp->header.duration;
                                        else {
                                                ms = jiffies_to_msecs(jiffies);
                                                rinfo[val].duration =
                                                    (ms > srp->header.duration) ?
                                                    (ms - srp->header.duration) : 0;
                                        }
                                        rinfo[val].orphan = srp->orphan;
                                        rinfo[val].sg_io_owned =
                                                        srp->sg_io_owned;
                                        rinfo[val].pack_id =
                                                        srp->header.pack_id;
                                        rinfo[val].usr_ptr =
                                                        srp->header.usr_ptr;
                                }
                        }
                        read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
                        result = __copy_to_user(p, rinfo, 
                                                SZ_SG_REQ_INFO * SG_MAX_QUEUE);
                        result = result ? -EFAULT : 0;
                        kfree(rinfo);
                        return result;
                }
        case SG_EMULATED_HOST:
                if (sdp->detached)
                        return -ENODEV;
                return put_user(sdp->device->host->hostt->emulated, ip);
        case SG_SCSI_RESET:
                if (sdp->detached)
                        return -ENODEV;
                if (filp->f_flags & O_NONBLOCK) {
                        if (scsi_host_in_recovery(sdp->device->host))
                                return -EBUSY;
                } else if (!scsi_block_when_processing_errors(sdp->device))
                        return -EBUSY;
                result = get_user(val, ip);
                if (result)
                        return result;
                if (SG_SCSI_RESET_NOTHING == val)
                        return 0;
                switch (val) {
                case SG_SCSI_RESET_DEVICE:
                        val = SCSI_TRY_RESET_DEVICE;
                        break;
                case SG_SCSI_RESET_TARGET:
                        val = SCSI_TRY_RESET_TARGET;
                        break;
                case SG_SCSI_RESET_BUS:
                        val = SCSI_TRY_RESET_BUS;
                        break;
                case SG_SCSI_RESET_HOST:
                        val = SCSI_TRY_RESET_HOST;
                        break;
                default:
                        return -EINVAL;
                }
                if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
                        return -EACCES;
                return (scsi_reset_provider(sdp->device, val) ==
                        SUCCESS) ? 0 : -EIO;
        case SCSI_IOCTL_SEND_COMMAND:
                if (sdp->detached)
                        return -ENODEV;
                if (read_only) {
                        unsigned char opcode = WRITE_6;
                        Scsi_Ioctl_Command __user *siocp = p;

                        if (copy_from_user(&opcode, siocp->data, 1))
                                return -EFAULT;
                        if (sg_allow_access(filp, &opcode))
                                return -EPERM;
                }
                return sg_scsi_ioctl(sdp->device->request_queue, NULL, filp->f_mode, p);
        case SG_SET_DEBUG:
                result = get_user(val, ip);
                if (result)
                        return result;
                sdp->sgdebug = (char) val;
                return 0;
        case SCSI_IOCTL_GET_IDLUN:
        case SCSI_IOCTL_GET_BUS_NUMBER:
        case SCSI_IOCTL_PROBE_HOST:
        case SG_GET_TRANSFORM:
                if (sdp->detached)
                        return -ENODEV;
                return scsi_ioctl(sdp->device, cmd_in, p);
        case BLKSECTGET:
                return put_user(queue_max_sectors(sdp->device->request_queue) * 512,
                                ip);
        case BLKTRACESETUP:
                return blk_trace_setup(sdp->device->request_queue,
                                       sdp->disk->disk_name,
                                       MKDEV(SCSI_GENERIC_MAJOR, sdp->index),
                                       NULL,
                                       (char *)arg);
        case BLKTRACESTART:
                return blk_trace_startstop(sdp->device->request_queue, 1);
        case BLKTRACESTOP:
                return blk_trace_startstop(sdp->device->request_queue, 0);
        case BLKTRACETEARDOWN:
                return blk_trace_remove(sdp->device->request_queue);
        default:
                if (read_only)
                        return -EPERM;  /* don't know so take safe approach */
                return scsi_ioctl(sdp->device, cmd_in, p);
        }
}

#ifdef CONFIG_COMPAT
static long sg_compat_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
{
        Sg_device *sdp;
        Sg_fd *sfp;
        struct scsi_device *sdev;

        if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
                return -ENXIO;

        sdev = sdp->device;
        if (sdev->host->hostt->compat_ioctl) { 
                int ret;

                ret = sdev->host->hostt->compat_ioctl(sdev, cmd_in, (void __user *)arg);

                return ret;
        }
        
        return -ENOIOCTLCMD;
}
#endif

static unsigned int
sg_poll(struct file *filp, poll_table * wait)
{
        unsigned int res = 0;
        Sg_device *sdp;
        Sg_fd *sfp;
        Sg_request *srp;
        int count = 0;
        unsigned long iflags;

        sfp = filp->private_data;
        if (!sfp)
                return POLLERR;
        sdp = sfp->parentdp;
        if (!sdp)
                return POLLERR;
        poll_wait(filp, &sfp->read_wait, wait);
        read_lock_irqsave(&sfp->rq_list_lock, iflags);
        for (srp = sfp->headrp; srp; srp = srp->nextrp) {
                /* if any read waiting, flag it */
                if ((0 == res) && (1 == srp->done) && (!srp->sg_io_owned))
                        res = POLLIN | POLLRDNORM;
                ++count;
        }
        read_unlock_irqrestore(&sfp->rq_list_lock, iflags);

        if (sdp->detached)
                res |= POLLHUP;
        else if (!sfp->cmd_q) {
                if (0 == count)
                        res |= POLLOUT | POLLWRNORM;
        } else if (count < SG_MAX_QUEUE)
                res |= POLLOUT | POLLWRNORM;
        SCSI_LOG_TIMEOUT(3, printk("sg_poll: %s, res=0x%x\n",
                                   sdp->disk->disk_name, (int) res));
        return res;
}

static int
sg_fasync(int fd, struct file *filp, int mode)
{
        Sg_device *sdp;
        Sg_fd *sfp;

        if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
                return -ENXIO;
        SCSI_LOG_TIMEOUT(3, printk("sg_fasync: %s, mode=%d\n",
                                   sdp->disk->disk_name, mode));

        return fasync_helper(fd, filp, mode, &sfp->async_qp);
}

static int
sg_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        Sg_fd *sfp;
        unsigned long offset, len, sa;
        Sg_scatter_hold *rsv_schp;
        int k, length;

        if ((NULL == vma) || (!(sfp = (Sg_fd *) vma->vm_private_data)))
                return VM_FAULT_SIGBUS;
        rsv_schp = &sfp->reserve;
        offset = vmf->pgoff << PAGE_SHIFT;
        if (offset >= rsv_schp->bufflen)
                return VM_FAULT_SIGBUS;
        SCSI_LOG_TIMEOUT(3, printk("sg_vma_fault: offset=%lu, scatg=%d\n",
                                   offset, rsv_schp->k_use_sg));
        sa = vma->vm_start;
        length = 1 << (PAGE_SHIFT + rsv_schp->page_order);
        for (k = 0; k < rsv_schp->k_use_sg && sa < vma->vm_end; k++) {
                len = vma->vm_end - sa;
                len = (len < length) ? len : length;
                if (offset < len) {
                        struct page *page = nth_page(rsv_schp->pages[k],
                                                     offset >> PAGE_SHIFT);
                        get_page(page); /* increment page count */
                        vmf->page = page;
                        return 0; /* success */
                }
                sa += len;
                offset -= len;
        }

        return VM_FAULT_SIGBUS;
}

static const struct vm_operations_struct sg_mmap_vm_ops = {
        .fault = sg_vma_fault,
};

static int
sg_mmap(struct file *filp, struct vm_area_struct *vma)
{
        Sg_fd *sfp;
        unsigned long req_sz, len, sa;
        Sg_scatter_hold *rsv_schp;
        int k, length;

        if ((!filp) || (!vma) || (!(sfp = (Sg_fd *) filp->private_data)))
                return -ENXIO;
        req_sz = vma->vm_end - vma->vm_start;
        SCSI_LOG_TIMEOUT(3, printk("sg_mmap starting, vm_start=%p, len=%d\n",
                                   (void *) vma->vm_start, (int) req_sz));
        if (vma->vm_pgoff)
                return -EINVAL; /* want no offset */
        rsv_schp = &sfp->reserve;
        if (req_sz > rsv_schp->bufflen)
                return -ENOMEM; /* cannot map more than reserved buffer */

        sa = vma->vm_start;
        length = 1 << (PAGE_SHIFT + rsv_schp->page_order);
        for (k = 0; k < rsv_schp->k_use_sg && sa < vma->vm_end; k++) {
                len = vma->vm_end - sa;
                len = (len < length) ? len : length;
                sa += len;
        }

        sfp->mmap_called = 1;
        vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
        vma->vm_private_data = sfp;
        vma->vm_ops = &sg_mmap_vm_ops;
        return 0;
}

static void sg_rq_end_io_usercontext(struct work_struct *work)
{
        struct sg_request *srp = container_of(work, struct sg_request, ew.work);
        struct sg_fd *sfp = srp->parentfp;

        sg_finish_rem_req(srp);
        kref_put(&sfp->f_ref, sg_remove_sfp);
}

/*
 * This function is a "bottom half" handler that is called by the mid
 * level when a command is completed (or has failed).
 */
static void sg_rq_end_io(struct request *rq, int uptodate)
{
        struct sg_request *srp = rq->end_io_data;
        Sg_device *sdp;
        Sg_fd *sfp;
        unsigned long iflags;
        unsigned int ms;
        char *sense;
        int result, resid, done = 1;

        if (WARN_ON(srp->done != 0))
                return;

        sfp = srp->parentfp;
        if (WARN_ON(sfp == NULL))
                return;

        sdp = sfp->parentdp;
        if (unlikely(sdp->detached))
                printk(KERN_INFO "sg_rq_end_io: device detached\n");

        sense = rq->sense;
        result = rq->errors;
        resid = rq->resid_len;

        SCSI_LOG_TIMEOUT(4, printk("sg_cmd_done: %s, pack_id=%d, res=0x%x\n",
                sdp->disk->disk_name, srp->header.pack_id, result));
        srp->header.resid = resid;
        ms = jiffies_to_msecs(jiffies);
        srp->header.duration = (ms > srp->header.duration) ?
                                (ms - srp->header.duration) : 0;
        if (0 != result) {
                struct scsi_sense_hdr sshdr;

                srp->header.status = 0xff & result;
                srp->header.masked_status = status_byte(result);
                srp->header.msg_status = msg_byte(result);
                srp->header.host_status = host_byte(result);
                srp->header.driver_status = driver_byte(result);
                if ((sdp->sgdebug > 0) &&
                    ((CHECK_CONDITION == srp->header.masked_status) ||
                     (COMMAND_TERMINATED == srp->header.masked_status)))
                        __scsi_print_sense("sg_cmd_done", sense,
                                           SCSI_SENSE_BUFFERSIZE);

                /* Following if statement is a patch supplied by Eric Youngdale */
                if (driver_byte(result) != 0
                    && scsi_normalize_sense(sense, SCSI_SENSE_BUFFERSIZE, &sshdr)
                    && !scsi_sense_is_deferred(&sshdr)
                    && sshdr.sense_key == UNIT_ATTENTION
                    && sdp->device->removable) {
                        /* Detected possible disc change. Set the bit - this */
                        /* may be used if there are filesystems using this device */
                        sdp->device->changed = 1;
                }
        }
        /* Rely on write phase to clean out srp status values, so no "else" */

        write_lock_irqsave(&sfp->rq_list_lock, iflags);
        if (unlikely(srp->orphan)) {
                if (sfp->keep_orphan)
                        srp->sg_io_owned = 0;
                else
                        done = 0;
        }
        srp->done = done;
        write_unlock_irqrestore(&sfp->rq_list_lock, iflags);

        if (likely(done)) {
                /* Now wake up any sg_read() that is waiting for this
                 * packet.
                 */
                wake_up_interruptible(&sfp->read_wait);
                kill_fasync(&sfp->async_qp, SIGPOLL, POLL_IN);
                kref_put(&sfp->f_ref, sg_remove_sfp);
        } else {
                INIT_WORK(&srp->ew.work, sg_rq_end_io_usercontext);
                schedule_work(&srp->ew.work);
        }
}

static const struct file_operations sg_fops = {
        .owner = THIS_MODULE,
        .read = sg_read,
        .write = sg_write,
        .poll = sg_poll,
        .unlocked_ioctl = sg_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl = sg_compat_ioctl,
#endif
        .open = sg_open,
        .mmap = sg_mmap,
        .release = sg_release,
        .fasync = sg_fasync,
        .llseek = no_llseek,
};

static struct class *sg_sysfs_class;

static int sg_sysfs_valid = 0;

static Sg_device *sg_alloc(struct gendisk *disk, struct scsi_device *scsidp)
{
        struct request_queue *q = scsidp->request_queue;
        Sg_device *sdp;
        unsigned long iflags;
        int error;
        u32 k;

        sdp = kzalloc(sizeof(Sg_device), GFP_KERNEL);
        if (!sdp) {
                printk(KERN_WARNING "kmalloc Sg_device failure\n");
                return ERR_PTR(-ENOMEM);
        }

        idr_preload(GFP_KERNEL);
        write_lock_irqsave(&sg_index_lock, iflags);

        error = idr_alloc(&sg_index_idr, sdp, 0, SG_MAX_DEVS, GFP_NOWAIT);
        if (error < 0) {
                if (error == -ENOSPC) {
                        sdev_printk(KERN_WARNING, scsidp,
                                    "Unable to attach sg device type=%d, minor number exceeds %d\n",
                                    scsidp->type, SG_MAX_DEVS - 1);
                        error = -ENODEV;
                } else {
                        printk(KERN_WARNING
                               "idr allocation Sg_device failure: %d\n", error);
                }
                goto out_unlock;
        }
        k = error;

        SCSI_LOG_TIMEOUT(3, printk("sg_alloc: dev=%d \n", k));
        sprintf(disk->disk_name, "sg%d", k);
        disk->first_minor = k;
        sdp->disk = disk;
        sdp->device = scsidp;
        INIT_LIST_HEAD(&sdp->sfds);
        init_waitqueue_head(&sdp->o_excl_wait);
        sdp->sg_tablesize = queue_max_segments(q);
        sdp->index = k;
        kref_init(&sdp->d_ref);
        error = 0;

out_unlock:
        write_unlock_irqrestore(&sg_index_lock, iflags);
        idr_preload_end();

        if (error) {
                kfree(sdp);
                return ERR_PTR(error);
        }
        return sdp;
}

static int
sg_add(struct device *cl_dev, struct class_interface *cl_intf)
{
        struct scsi_device *scsidp = to_scsi_device(cl_dev->parent);
        struct gendisk *disk;
        Sg_device *sdp = NULL;
        struct cdev * cdev = NULL;
        int error;
        unsigned long iflags;

        disk = alloc_disk(1);
        if (!disk) {
                printk(KERN_WARNING "alloc_disk failed\n");
                return -ENOMEM;
        }
        disk->major = SCSI_GENERIC_MAJOR;

        error = -ENOMEM;
        cdev = cdev_alloc();
        if (!cdev) {
                printk(KERN_WARNING "cdev_alloc failed\n");
                goto out;
        }
        cdev->owner = THIS_MODULE;
        cdev->ops = &sg_fops;

        sdp = sg_alloc(disk, scsidp);
        if (IS_ERR(sdp)) {
                printk(KERN_WARNING "sg_alloc failed\n");
                error = PTR_ERR(sdp);
                goto out;
        }

        error = cdev_add(cdev, MKDEV(SCSI_GENERIC_MAJOR, sdp->index), 1);
        if (error)
                goto cdev_add_err;

        sdp->cdev = cdev;
        if (sg_sysfs_valid) {
                struct device *sg_class_member;

                sg_class_member = device_create(sg_sysfs_class, cl_dev->parent,
                                                MKDEV(SCSI_GENERIC_MAJOR,
                                                      sdp->index),
                                                sdp, "%s", disk->disk_name);
                if (IS_ERR(sg_class_member)) {
                        printk(KERN_ERR "sg_add: "
                               "device_create failed\n");
                        error = PTR_ERR(sg_class_member);
                        goto cdev_add_err;
                }
                error = sysfs_create_link(&scsidp->sdev_gendev.kobj,
                                          &sg_class_member->kobj, "generic");
                if (error)
                        printk(KERN_ERR "sg_add: unable to make symlink "
                                        "'generic' back to sg%d\n", sdp->index);
        } else
                printk(KERN_WARNING "sg_add: sg_sys Invalid\n");

        sdev_printk(KERN_NOTICE, scsidp,
                    "Attached scsi generic sg%d type %d\n", sdp->index,
                    scsidp->type);

        dev_set_drvdata(cl_dev, sdp);

        return 0;

cdev_add_err:
        write_lock_irqsave(&sg_index_lock, iflags);
        idr_remove(&sg_index_idr, sdp->index);
        write_unlock_irqrestore(&sg_index_lock, iflags);
        kfree(sdp);

out:
        put_disk(disk);
        if (cdev)
                cdev_del(cdev);
        return error;
}

static void sg_device_destroy(struct kref *kref)
{
        struct sg_device *sdp = container_of(kref, struct sg_device, d_ref);
        unsigned long flags;

        /* CAUTION!  Note that the device can still be found via idr_find()
         * even though the refcount is 0.  Therefore, do idr_remove() BEFORE
         * any other cleanup.
         */

        write_lock_irqsave(&sg_index_lock, flags);
        idr_remove(&sg_index_idr, sdp->index);
        write_unlock_irqrestore(&sg_index_lock, flags);

        SCSI_LOG_TIMEOUT(3,
                printk("sg_device_destroy: %s\n",
                        sdp->disk->disk_name));

        put_disk(sdp->disk);
        kfree(sdp);
}

static void sg_remove(struct device *cl_dev, struct class_interface *cl_intf)
{
        struct scsi_device *scsidp = to_scsi_device(cl_dev->parent);
        Sg_device *sdp = dev_get_drvdata(cl_dev);
        unsigned long iflags;
        Sg_fd *sfp;

        if (!sdp || sdp->detached)
                return;

        SCSI_LOG_TIMEOUT(3, printk("sg_remove: %s\n", sdp->disk->disk_name));

        /* Need a write lock to set sdp->detached. */
        write_lock_irqsave(&sg_index_lock, iflags);
        sdp->detached = 1;
        list_for_each_entry(sfp, &sdp->sfds, sfd_siblings) {
                wake_up_interruptible(&sfp->read_wait);
                kill_fasync(&sfp->async_qp, SIGPOLL, POLL_HUP);
        }
        write_unlock_irqrestore(&sg_index_lock, iflags);

        sysfs_remove_link(&scsidp->sdev_gendev.kobj, "generic");
        device_destroy(sg_sysfs_class, MKDEV(SCSI_GENERIC_MAJOR, sdp->index));
        cdev_del(sdp->cdev);
        sdp->cdev = NULL;

        sg_put_dev(sdp);
}

module_param_named(scatter_elem_sz, scatter_elem_sz, int, S_IRUGO | S_IWUSR);
module_param_named(def_reserved_size, def_reserved_size, int,
                   S_IRUGO | S_IWUSR);
module_param_named(allow_dio, sg_allow_dio, int, S_IRUGO | S_IWUSR);

MODULE_AUTHOR("Douglas Gilbert");
MODULE_DESCRIPTION("SCSI generic (sg) driver");
MODULE_LICENSE("GPL");
MODULE_VERSION(SG_VERSION_STR);
MODULE_ALIAS_CHARDEV_MAJOR(SCSI_GENERIC_MAJOR);

MODULE_PARM_DESC(scatter_elem_sz, "scatter gather element "
                "size (default: max(SG_SCATTER_SZ, PAGE_SIZE))");
MODULE_PARM_DESC(def_reserved_size, "size of buffer reserved for each fd");
MODULE_PARM_DESC(allow_dio, "allow direct I/O (default: 0 (disallow))");

static int __init
init_sg(void)
{
        int rc;

        if (scatter_elem_sz < PAGE_SIZE) {
                scatter_elem_sz = PAGE_SIZE;
                scatter_elem_sz_prev = scatter_elem_sz;
        }
        if (def_reserved_size >= 0)
                sg_big_buff = def_reserved_size;
        else
                def_reserved_size = sg_big_buff;

        rc = register_chrdev_region(MKDEV(SCSI_GENERIC_MAJOR, 0), 
                                    SG_MAX_DEVS, "sg");
        if (rc)
                return rc;
        sg_sysfs_class = class_create(THIS_MODULE, "scsi_generic");
        if ( IS_ERR(sg_sysfs_class) ) {
                rc = PTR_ERR(sg_sysfs_class);
                goto err_out;
        }
        sg_sysfs_valid = 1;
        rc = scsi_register_interface(&sg_interface);
        if (0 == rc) {
#ifdef CONFIG_SCSI_PROC_FS
                sg_proc_init();
#endif                          /* CONFIG_SCSI_PROC_FS */
                return 0;
        }
        class_destroy(sg_sysfs_class);
err_out:
        unregister_chrdev_region(MKDEV(SCSI_GENERIC_MAJOR, 0), SG_MAX_DEVS);
        return rc;
}

static void __exit
exit_sg(void)
{
#ifdef CONFIG_SCSI_PROC_FS
        sg_proc_cleanup();
#endif                          /* CONFIG_SCSI_PROC_FS */
        scsi_unregister_interface(&sg_interface);
        class_destroy(sg_sysfs_class);
        sg_sysfs_valid = 0;
        unregister_chrdev_region(MKDEV(SCSI_GENERIC_MAJOR, 0),
                                 SG_MAX_DEVS);
        idr_destroy(&sg_index_idr);
}

static int sg_start_req(Sg_request *srp, unsigned char *cmd)
{
        int res;
        struct request *rq;
        Sg_fd *sfp = srp->parentfp;
        sg_io_hdr_t *hp = &srp->header;
        int dxfer_len = (int) hp->dxfer_len;
        int dxfer_dir = hp->dxfer_direction;
        unsigned int iov_count = hp->iovec_count;
        Sg_scatter_hold *req_schp = &srp->data;
        Sg_scatter_hold *rsv_schp = &sfp->reserve;
        struct request_queue *q = sfp->parentdp->device->request_queue;
        struct rq_map_data *md, map_data;
        int rw = hp->dxfer_direction == SG_DXFER_TO_DEV ? WRITE : READ;

        SCSI_LOG_TIMEOUT(4, printk(KERN_INFO "sg_start_req: dxfer_len=%d\n",
                                   dxfer_len));

        rq = blk_get_request(q, rw, GFP_ATOMIC);
        if (!rq)
                return -ENOMEM;

        memcpy(rq->cmd, cmd, hp->cmd_len);

        rq->cmd_len = hp->cmd_len;
        rq->cmd_type = REQ_TYPE_BLOCK_PC;

        srp->rq = rq;
        rq->end_io_data = srp;
        rq->sense = srp->sense_b;
        rq->retries = SG_DEFAULT_RETRIES;

        if ((dxfer_len <= 0) || (dxfer_dir == SG_DXFER_NONE))
                return 0;

        if (sg_allow_dio && hp->flags & SG_FLAG_DIRECT_IO &&
            dxfer_dir != SG_DXFER_UNKNOWN && !iov_count &&
            !sfp->parentdp->device->host->unchecked_isa_dma &&
            blk_rq_aligned(q, (unsigned long)hp->dxferp, dxfer_len))
                md = NULL;
        else
                md = &map_data;

        if (md) {
                if (!sg_res_in_use(sfp) && dxfer_len <= rsv_schp->bufflen)
                        sg_link_reserve(sfp, srp, dxfer_len);
                else {
                        res = sg_build_indirect(req_schp, sfp, dxfer_len);
                        if (res)
                                return res;
                }

                md->pages = req_schp->pages;
                md->page_order = req_schp->page_order;
                md->nr_entries = req_schp->k_use_sg;
                md->offset = 0;
                md->null_mapped = hp->dxferp ? 0 : 1;
                if (dxfer_dir == SG_DXFER_TO_FROM_DEV)
                        md->from_user = 1;
                else
                        md->from_user = 0;
        }

        if (iov_count) {
                int len, size = sizeof(struct sg_iovec) * iov_count;
                struct iovec *iov;

                iov = memdup_user(hp->dxferp, size);
                if (IS_ERR(iov))
                        return PTR_ERR(iov);

                len = iov_length(iov, iov_count);
                if (hp->dxfer_len < len) {
                        iov_count = iov_shorten(iov, iov_count, hp->dxfer_len);
                        len = hp->dxfer_len;
                }

                res = blk_rq_map_user_iov(q, rq, md, (struct sg_iovec *)iov,
                                          iov_count,
                                          len, GFP_ATOMIC);
                kfree(iov);
        } else
                res = blk_rq_map_user(q, rq, md, hp->dxferp,
                                      hp->dxfer_len, GFP_ATOMIC);

        if (!res) {
                srp->bio = rq->bio;

                if (!md) {
                        req_schp->dio_in_use = 1;
                        hp->info |= SG_INFO_DIRECT_IO;
                }
        }
        return res;
}

static int sg_finish_rem_req(Sg_request * srp)
{
        int ret = 0;

        Sg_fd *sfp = srp->parentfp;
        Sg_scatter_hold *req_schp = &srp->data;

        SCSI_LOG_TIMEOUT(4, printk("sg_finish_rem_req: res_used=%d\n", (int) srp->res_used));
        if (srp->rq) {
                if (srp->bio)
                        ret = blk_rq_unmap_user(srp->bio);

                blk_put_request(srp->rq);
        }

        if (srp->res_used)
                sg_unlink_reserve(sfp, srp);
        else
                sg_remove_scat(req_schp);

        sg_remove_request(sfp, srp);

        return ret;
}

static int
sg_build_sgat(Sg_scatter_hold * schp, const Sg_fd * sfp, int tablesize)
{
        int sg_bufflen = tablesize * sizeof(struct page *);
        gfp_t gfp_flags = GFP_ATOMIC | __GFP_NOWARN;

        schp->pages = kzalloc(sg_bufflen, gfp_flags);
        if (!schp->pages)
                return -ENOMEM;
        schp->sglist_len = sg_bufflen;
        return tablesize;       /* number of scat_gath elements allocated */
}

static int
sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
{
        int ret_sz = 0, i, k, rem_sz, num, mx_sc_elems;
        int sg_tablesize = sfp->parentdp->sg_tablesize;
        int blk_size = buff_size, order;
        gfp_t gfp_mask = GFP_ATOMIC | __GFP_COMP | __GFP_NOWARN;

        if (blk_size < 0)
                return -EFAULT;
        if (0 == blk_size)
                ++blk_size;     /* don't know why */
        /* round request up to next highest SG_SECTOR_SZ byte boundary */
        blk_size = ALIGN(blk_size, SG_SECTOR_SZ);
        SCSI_LOG_TIMEOUT(4, printk("sg_build_indirect: buff_size=%d, blk_size=%d\n",
                                   buff_size, blk_size));

        /* N.B. ret_sz carried into this block ... */
        mx_sc_elems = sg_build_sgat(schp, sfp, sg_tablesize);
        if (mx_sc_elems < 0)
                return mx_sc_elems;     /* most likely -ENOMEM */

        num = scatter_elem_sz;
        if (unlikely(num != scatter_elem_sz_prev)) {
                if (num < PAGE_SIZE) {
                        scatter_elem_sz = PAGE_SIZE;
                        scatter_elem_sz_prev = PAGE_SIZE;
                } else
                        scatter_elem_sz_prev = num;
        }

        if (sfp->low_dma)
                gfp_mask |= GFP_DMA;

        if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
                gfp_mask |= __GFP_ZERO;

        order = get_order(num);
retry:
        ret_sz = 1 << (PAGE_SHIFT + order);

        for (k = 0, rem_sz = blk_size; rem_sz > 0 && k < mx_sc_elems;
             k++, rem_sz -= ret_sz) {

                num = (rem_sz > scatter_elem_sz_prev) ?
                        scatter_elem_sz_prev : rem_sz;

                schp->pages[k] = alloc_pages(gfp_mask, order);
                if (!schp->pages[k])
                        goto out;

                if (num == scatter_elem_sz_prev) {
                        if (unlikely(ret_sz > scatter_elem_sz_prev)) {
                                scatter_elem_sz = ret_sz;
                                scatter_elem_sz_prev = ret_sz;
                        }
                }

                SCSI_LOG_TIMEOUT(5, printk("sg_build_indirect: k=%d, num=%d, "
                                 "ret_sz=%d\n", k, num, ret_sz));
        }               /* end of for loop */

        schp->page_order = order;
        schp->k_use_sg = k;
        SCSI_LOG_TIMEOUT(5, printk("sg_build_indirect: k_use_sg=%d, "
                         "rem_sz=%d\n", k, rem_sz));

        schp->bufflen = blk_size;
        if (rem_sz > 0) /* must have failed */
                return -ENOMEM;
        return 0;
out:
        for (i = 0; i < k; i++)
                __free_pages(schp->pages[i], order);

        if (--order >= 0)
                goto retry;

        return -ENOMEM;
}

static void
sg_remove_scat(Sg_scatter_hold * schp)
{
        SCSI_LOG_TIMEOUT(4, printk("sg_remove_scat: k_use_sg=%d\n", schp->k_use_sg));
        if (schp->pages && schp->sglist_len > 0) {
                if (!schp->dio_in_use) {
                        int k;

                        for (k = 0; k < schp->k_use_sg && schp->pages[k]; k++) {
                                SCSI_LOG_TIMEOUT(5, printk(
                                    "sg_remove_scat: k=%d, pg=0x%p\n",
                                    k, schp->pages[k]));
                                __free_pages(schp->pages[k], schp->page_order);
                        }

                        kfree(schp->pages);
                }
        }
        memset(schp, 0, sizeof (*schp));
}

static int
sg_read_oxfer(Sg_request * srp, char __user *outp, int num_read_xfer)
{
        Sg_scatter_hold *schp = &srp->data;
        int k, num;

        SCSI_LOG_TIMEOUT(4, printk("sg_read_oxfer: num_read_xfer=%d\n",
                                   num_read_xfer));
        if ((!outp) || (num_read_xfer <= 0))
                return 0;

        num = 1 << (PAGE_SHIFT + schp->page_order);
        for (k = 0; k < schp->k_use_sg && schp->pages[k]; k++) {
                if (num > num_read_xfer) {
                        if (__copy_to_user(outp, page_address(schp->pages[k]),
                                           num_read_xfer))
                                return -EFAULT;
                        break;
                } else {
                        if (__copy_to_user(outp, page_address(schp->pages[k]),
                                           num))
                                return -EFAULT;
                        num_read_xfer -= num;
                        if (num_read_xfer <= 0)
                                break;
                        outp += num;
                }
        }

        return 0;
}

static void
sg_build_reserve(Sg_fd * sfp, int req_size)
{
        Sg_scatter_hold *schp = &sfp->reserve;

        SCSI_LOG_TIMEOUT(4, printk("sg_build_reserve: req_size=%d\n", req_size));
        do {
                if (req_size < PAGE_SIZE)
                        req_size = PAGE_SIZE;
                if (0 == sg_build_indirect(schp, sfp, req_size))
                        return;
                else
                        sg_remove_scat(schp);
                req_size >>= 1; /* divide by 2 */
        } while (req_size > (PAGE_SIZE / 2));
}

static void
sg_link_reserve(Sg_fd * sfp, Sg_request * srp, int size)
{
        Sg_scatter_hold *req_schp = &srp->data;
        Sg_scatter_hold *rsv_schp = &sfp->reserve;
        int k, num, rem;

        srp->res_used = 1;
        SCSI_LOG_TIMEOUT(4, printk("sg_link_reserve: size=%d\n", size));
        rem = size;

        num = 1 << (PAGE_SHIFT + rsv_schp->page_order);
        for (k = 0; k < rsv_schp->k_use_sg; k++) {
                if (rem <= num) {
                        req_schp->k_use_sg = k + 1;
                        req_schp->sglist_len = rsv_schp->sglist_len;
                        req_schp->pages = rsv_schp->pages;

                        req_schp->bufflen = size;
                        req_schp->page_order = rsv_schp->page_order;
                        break;
                } else
                        rem -= num;
        }

        if (k >= rsv_schp->k_use_sg)
                SCSI_LOG_TIMEOUT(1, printk("sg_link_reserve: BAD size\n"));
}

static void
sg_unlink_reserve(Sg_fd * sfp, Sg_request * srp)
{
        Sg_scatter_hold *req_schp = &srp->data;

        SCSI_LOG_TIMEOUT(4, printk("sg_unlink_reserve: req->k_use_sg=%d\n",
                                   (int) req_schp->k_use_sg));
        req_schp->k_use_sg = 0;
        req_schp->bufflen = 0;
        req_schp->pages = NULL;
        req_schp->page_order = 0;
        req_schp->sglist_len = 0;
        sfp->save_scat_len = 0;
        srp->res_used = 0;
}

static Sg_request *
sg_get_rq_mark(Sg_fd * sfp, int pack_id)
{
        Sg_request *resp;
        unsigned long iflags;

        write_lock_irqsave(&sfp->rq_list_lock, iflags);
        for (resp = sfp->headrp; resp; resp = resp->nextrp) {
                /* look for requests that are ready + not SG_IO owned */
                if ((1 == resp->done) && (!resp->sg_io_owned) &&
                    ((-1 == pack_id) || (resp->header.pack_id == pack_id))) {
                        resp->done = 2; /* guard against other readers */
                        break;
                }
        }
        write_unlock_irqrestore(&sfp->rq_list_lock, iflags);
        return resp;
}

/* always adds to end of list */
static Sg_request *
sg_add_request(Sg_fd * sfp)
{
        int k;
        unsigned long iflags;
        Sg_request *resp;
        Sg_request *rp = sfp->req_arr;

        write_lock_irqsave(&sfp->rq_list_lock, iflags);
        resp = sfp->headrp;
        if (!resp) {
                memset(rp, 0, sizeof (Sg_request));
                rp->parentfp = sfp;
                resp = rp;
                sfp->headrp = resp;
        } else {
                if (0 == sfp->cmd_q)

                        resp = NULL;    /* command queuing disallowed */
                else {
                        for (k = 0; k < SG_MAX_QUEUE; ++k, ++rp) {
                                if (!rp->parentfp)
                                        break;
                        }
                        if (k < SG_MAX_QUEUE) {
                                memset(rp, 0, sizeof (Sg_request));
                                rp->parentfp = sfp;
                                while (resp->nextrp)
                                        resp = resp->nextrp;
                                resp->nextrp = rp;
                                resp = rp;
                        } else
                                resp = NULL;
                }
        }
        if (resp) {
                resp->nextrp = NULL;
                resp->header.duration = jiffies_to_msecs(jiffies);
        }
        write_unlock_irqrestore(&sfp->rq_list_lock, iflags);
        return resp;
}

/* Return of 1 for found; 0 for not found */
static int
sg_remove_request(Sg_fd * sfp, Sg_request * srp)
{
        Sg_request *prev_rp;
        Sg_request *rp;
        unsigned long iflags;
        int res = 0;

        if ((!sfp) || (!srp) || (!sfp->headrp))
                return res;
        write_lock_irqsave(&sfp->rq_list_lock, iflags);
        prev_rp = sfp->headrp;
        if (srp == prev_rp) {
                sfp->headrp = prev_rp->nextrp;
                prev_rp->parentfp = NULL;
                res = 1;
        } else {
                while ((rp = prev_rp->nextrp)) {
                        if (srp == rp) {
                                prev_rp->nextrp = rp->nextrp;
                                rp->parentfp = NULL;
                                res = 1;
                                break;
                        }
                        prev_rp = rp;
                }
        }
        write_unlock_irqrestore(&sfp->rq_list_lock, iflags);
        return res;
}

static Sg_fd *
sg_add_sfp(Sg_device * sdp, int dev)
{
        Sg_fd *sfp;
        unsigned long iflags;
        int bufflen;

        sfp = kzalloc(sizeof(*sfp), GFP_ATOMIC | __GFP_NOWARN);
        if (!sfp)
                return NULL;

        init_waitqueue_head(&sfp->read_wait);
        rwlock_init(&sfp->rq_list_lock);

        kref_init(&sfp->f_ref);
        sfp->timeout = SG_DEFAULT_TIMEOUT;
        sfp->timeout_user = SG_DEFAULT_TIMEOUT_USER;
        sfp->force_packid = SG_DEF_FORCE_PACK_ID;
        sfp->low_dma = (SG_DEF_FORCE_LOW_DMA == 0) ?
            sdp->device->host->unchecked_isa_dma : 1;
        sfp->cmd_q = SG_DEF_COMMAND_Q;
        sfp->keep_orphan = SG_DEF_KEEP_ORPHAN;
        sfp->parentdp = sdp;
        write_lock_irqsave(&sg_index_lock, iflags);
        list_add_tail(&sfp->sfd_siblings, &sdp->sfds);
        write_unlock_irqrestore(&sg_index_lock, iflags);
        SCSI_LOG_TIMEOUT(3, printk("sg_add_sfp: sfp=0x%p\n", sfp));
        if (unlikely(sg_big_buff != def_reserved_size))
                sg_big_buff = def_reserved_size;

        bufflen = min_t(int, sg_big_buff,
                        queue_max_sectors(sdp->device->request_queue) * 512);
        sg_build_reserve(sfp, bufflen);
        SCSI_LOG_TIMEOUT(3, printk("sg_add_sfp:   bufflen=%d, k_use_sg=%d\n",
                           sfp->reserve.bufflen, sfp->reserve.k_use_sg));

        kref_get(&sdp->d_ref);
        __module_get(THIS_MODULE);
        return sfp;
}

static void sg_remove_sfp_usercontext(struct work_struct *work)
{
        struct sg_fd *sfp = container_of(work, struct sg_fd, ew.work);
        struct sg_device *sdp = sfp->parentdp;

        /* Cleanup any responses which were never read(). */
        while (sfp->headrp)
                sg_finish_rem_req(sfp->headrp);

        if (sfp->reserve.bufflen > 0) {
                SCSI_LOG_TIMEOUT(6,
                        printk("sg_remove_sfp:    bufflen=%d, k_use_sg=%d\n",
                                (int) sfp->reserve.bufflen,
                                (int) sfp->reserve.k_use_sg));
                sg_remove_scat(&sfp->reserve);
        }

        SCSI_LOG_TIMEOUT(6,
                printk("sg_remove_sfp: %s, sfp=0x%p\n",
                        sdp->disk->disk_name,
                        sfp));
        kfree(sfp);

        scsi_device_put(sdp->device);
        sg_put_dev(sdp);
        module_put(THIS_MODULE);
}

static void sg_remove_sfp(struct kref *kref)
{
        struct sg_fd *sfp = container_of(kref, struct sg_fd, f_ref);
        struct sg_device *sdp = sfp->parentdp;
        unsigned long iflags;

        write_lock_irqsave(&sg_index_lock, iflags);
        list_del(&sfp->sfd_siblings);
        write_unlock_irqrestore(&sg_index_lock, iflags);
        wake_up_interruptible(&sdp->o_excl_wait);

        INIT_WORK(&sfp->ew.work, sg_remove_sfp_usercontext);
        schedule_work(&sfp->ew.work);
}

static int
sg_res_in_use(Sg_fd * sfp)
{
        const Sg_request *srp;
        unsigned long iflags;

        read_lock_irqsave(&sfp->rq_list_lock, iflags);
        for (srp = sfp->headrp; srp; srp = srp->nextrp)
                if (srp->res_used)
                        break;
        read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
        return srp ? 1 : 0;
}

#ifdef CONFIG_SCSI_PROC_FS
static int
sg_idr_max_id(int id, void *p, void *data)
{
        int *k = data;

        if (*k < id)
                *k = id;

        return 0;
}

static int
sg_last_dev(void)
{
        int k = -1;
        unsigned long iflags;

        read_lock_irqsave(&sg_index_lock, iflags);
        idr_for_each(&sg_index_idr, sg_idr_max_id, &k);
        read_unlock_irqrestore(&sg_index_lock, iflags);
        return k + 1;           /* origin 1 */
}
#endif

/* must be called with sg_index_lock held */
static Sg_device *sg_lookup_dev(int dev)
{
        return idr_find(&sg_index_idr, dev);
}

static Sg_device *sg_get_dev(int dev)
{
        struct sg_device *sdp;
        unsigned long flags;

        read_lock_irqsave(&sg_index_lock, flags);
        sdp = sg_lookup_dev(dev);
        if (!sdp)
                sdp = ERR_PTR(-ENXIO);
        else if (sdp->detached) {
                /* If sdp->detached, then the refcount may already be 0, in
                 * which case it would be a bug to do kref_get().
                 */
                sdp = ERR_PTR(-ENODEV);
        } else
                kref_get(&sdp->d_ref);
        read_unlock_irqrestore(&sg_index_lock, flags);

        return sdp;
}

static void sg_put_dev(struct sg_device *sdp)
{
        kref_put(&sdp->d_ref, sg_device_destroy);
}

#ifdef CONFIG_SCSI_PROC_FS

static struct proc_dir_entry *sg_proc_sgp = NULL;

static char sg_proc_sg_dirname[] = "scsi/sg";

static int sg_proc_seq_show_int(struct seq_file *s, void *v);

static int sg_proc_single_open_adio(struct inode *inode, struct file *file);
static ssize_t sg_proc_write_adio(struct file *filp, const char __user *buffer,
                                  size_t count, loff_t *off);
static const struct file_operations adio_fops = {
        .owner = THIS_MODULE,
        .open = sg_proc_single_open_adio,
        .read = seq_read,
        .llseek = seq_lseek,
        .write = sg_proc_write_adio,
        .release = single_release,
};

static int sg_proc_single_open_dressz(struct inode *inode, struct file *file);
static ssize_t sg_proc_write_dressz(struct file *filp, 
                const char __user *buffer, size_t count, loff_t *off);
static const struct file_operations dressz_fops = {
        .owner = THIS_MODULE,
        .open = sg_proc_single_open_dressz,
        .read = seq_read,
        .llseek = seq_lseek,
        .write = sg_proc_write_dressz,
        .release = single_release,
};

static int sg_proc_seq_show_version(struct seq_file *s, void *v);
static int sg_proc_single_open_version(struct inode *inode, struct file *file);
static const struct file_operations version_fops = {
        .owner = THIS_MODULE,
        .open = sg_proc_single_open_version,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = single_release,
};

static int sg_proc_seq_show_devhdr(struct seq_file *s, void *v);
static int sg_proc_single_open_devhdr(struct inode *inode, struct file *file);
static const struct file_operations devhdr_fops = {
        .owner = THIS_MODULE,
        .open = sg_proc_single_open_devhdr,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = single_release,
};

static int sg_proc_seq_show_dev(struct seq_file *s, void *v);
static int sg_proc_open_dev(struct inode *inode, struct file *file);
static void * dev_seq_start(struct seq_file *s, loff_t *pos);
static void * dev_seq_next(struct seq_file *s, void *v, loff_t *pos);
static void dev_seq_stop(struct seq_file *s, void *v);
static const struct file_operations dev_fops = {
        .owner = THIS_MODULE,
        .open = sg_proc_open_dev,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = seq_release,
};
static const struct seq_operations dev_seq_ops = {
        .start = dev_seq_start,
        .next  = dev_seq_next,
        .stop  = dev_seq_stop,
        .show  = sg_proc_seq_show_dev,
};

static int sg_proc_seq_show_devstrs(struct seq_file *s, void *v);
static int sg_proc_open_devstrs(struct inode *inode, struct file *file);
static const struct file_operations devstrs_fops = {
        .owner = THIS_MODULE,
        .open = sg_proc_open_devstrs,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = seq_release,
};
static const struct seq_operations devstrs_seq_ops = {
        .start = dev_seq_start,
        .next  = dev_seq_next,
        .stop  = dev_seq_stop,
        .show  = sg_proc_seq_show_devstrs,
};

static int sg_proc_seq_show_debug(struct seq_file *s, void *v);
static int sg_proc_open_debug(struct inode *inode, struct file *file);
static const struct file_operations debug_fops = {
        .owner = THIS_MODULE,
        .open = sg_proc_open_debug,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = seq_release,
};
static const struct seq_operations debug_seq_ops = {
        .start = dev_seq_start,
        .next  = dev_seq_next,
        .stop  = dev_seq_stop,
        .show  = sg_proc_seq_show_debug,
};


struct sg_proc_leaf {
        const char * name;
        const struct file_operations * fops;
};

static const struct sg_proc_leaf sg_proc_leaf_arr[] = {
        {"allow_dio", &adio_fops},
        {"debug", &debug_fops},
        {"def_reserved_size", &dressz_fops},
        {"device_hdr", &devhdr_fops},
        {"devices", &dev_fops},
        {"device_strs", &devstrs_fops},
        {"version", &version_fops}
};

static int
sg_proc_init(void)
{
        int num_leaves = ARRAY_SIZE(sg_proc_leaf_arr);
        int k;

        sg_proc_sgp = proc_mkdir(sg_proc_sg_dirname, NULL);
        if (!sg_proc_sgp)
                return 1;
        for (k = 0; k < num_leaves; ++k) {
                const struct sg_proc_leaf *leaf = &sg_proc_leaf_arr[k];
                umode_t mask = leaf->fops->write ? S_IRUGO | S_IWUSR : S_IRUGO;
                proc_create(leaf->name, mask, sg_proc_sgp, leaf->fops);
        }
        return 0;
}

static void
sg_proc_cleanup(void)
{
        int k;
        int num_leaves = ARRAY_SIZE(sg_proc_leaf_arr);

        if (!sg_proc_sgp)
                return;
        for (k = 0; k < num_leaves; ++k)
                remove_proc_entry(sg_proc_leaf_arr[k].name, sg_proc_sgp);
        remove_proc_entry(sg_proc_sg_dirname, NULL);
}


static int sg_proc_seq_show_int(struct seq_file *s, void *v)
{
        seq_printf(s, "%d\n", *((int *)s->private));
        return 0;
}

static int sg_proc_single_open_adio(struct inode *inode, struct file *file)
{
        return single_open(file, sg_proc_seq_show_int, &sg_allow_dio);
}

static ssize_t 
sg_proc_write_adio(struct file *filp, const char __user *buffer,
                   size_t count, loff_t *off)
{
        int err;
        unsigned long num;

        if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
                return -EACCES;
        err = kstrtoul_from_user(buffer, count, 0, &num);
        if (err)
                return err;
        sg_allow_dio = num ? 1 : 0;
        return count;
}

static int sg_proc_single_open_dressz(struct inode *inode, struct file *file)
{
        return single_open(file, sg_proc_seq_show_int, &sg_big_buff);
}

static ssize_t 
sg_proc_write_dressz(struct file *filp, const char __user *buffer,
                     size_t count, loff_t *off)
{
        int err;
        unsigned long k = ULONG_MAX;

        if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
                return -EACCES;

        err = kstrtoul_from_user(buffer, count, 0, &k);
        if (err)
                return err;
        if (k <= 1048576) {     /* limit "big buff" to 1 MB */
                sg_big_buff = k;
                return count;
        }
        return -ERANGE;
}

static int sg_proc_seq_show_version(struct seq_file *s, void *v)
{
        seq_printf(s, "%d\t%s [%s]\n", sg_version_num, SG_VERSION_STR,
                   sg_version_date);
        return 0;
}

static int sg_proc_single_open_version(struct inode *inode, struct file *file)
{
        return single_open(file, sg_proc_seq_show_version, NULL);
}

static int sg_proc_seq_show_devhdr(struct seq_file *s, void *v)
{
        seq_printf(s, "host\tchan\tid\tlun\ttype\topens\tqdepth\tbusy\t"
                   "online\n");
        return 0;
}

static int sg_proc_single_open_devhdr(struct inode *inode, struct file *file)
{
        return single_open(file, sg_proc_seq_show_devhdr, NULL);
}

struct sg_proc_deviter {
        loff_t  index;
        size_t  max;
};

static void * dev_seq_start(struct seq_file *s, loff_t *pos)
{
        struct sg_proc_deviter * it = kmalloc(sizeof(*it), GFP_KERNEL);

        s->private = it;
        if (! it)
                return NULL;

        it->index = *pos;
        it->max = sg_last_dev();
        if (it->index >= it->max)
                return NULL;
        return it;
}

static void * dev_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
        struct sg_proc_deviter * it = s->private;

        *pos = ++it->index;
        return (it->index < it->max) ? it : NULL;
}

static void dev_seq_stop(struct seq_file *s, void *v)
{
        kfree(s->private);
}

static int sg_proc_open_dev(struct inode *inode, struct file *file)
{
        return seq_open(file, &dev_seq_ops);
}

static int sg_proc_seq_show_dev(struct seq_file *s, void *v)
{
        struct sg_proc_deviter * it = (struct sg_proc_deviter *) v;
        Sg_device *sdp;
        struct scsi_device *scsidp;
        unsigned long iflags;

        read_lock_irqsave(&sg_index_lock, iflags);
        sdp = it ? sg_lookup_dev(it->index) : NULL;
        if (sdp && (scsidp = sdp->device) && (!sdp->detached))
                seq_printf(s, "%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\n",
                              scsidp->host->host_no, scsidp->channel,
                              scsidp->id, scsidp->lun, (int) scsidp->type,
                              1,
                              (int) scsidp->queue_depth,
                              (int) scsidp->device_busy,
                              (int) scsi_device_online(scsidp));
        else
                seq_printf(s, "-1\t-1\t-1\t-1\t-1\t-1\t-1\t-1\t-1\n");
        read_unlock_irqrestore(&sg_index_lock, iflags);
        return 0;
}

static int sg_proc_open_devstrs(struct inode *inode, struct file *file)
{
        return seq_open(file, &devstrs_seq_ops);
}

static int sg_proc_seq_show_devstrs(struct seq_file *s, void *v)
{
        struct sg_proc_deviter * it = (struct sg_proc_deviter *) v;
        Sg_device *sdp;
        struct scsi_device *scsidp;
        unsigned long iflags;

        read_lock_irqsave(&sg_index_lock, iflags);
        sdp = it ? sg_lookup_dev(it->index) : NULL;
        if (sdp && (scsidp = sdp->device) && (!sdp->detached))
                seq_printf(s, "%8.8s\t%16.16s\t%4.4s\n",
                           scsidp->vendor, scsidp->model, scsidp->rev);
        else
                seq_printf(s, "<no active device>\n");
        read_unlock_irqrestore(&sg_index_lock, iflags);
        return 0;
}

/* must be called while holding sg_index_lock */
static void sg_proc_debug_helper(struct seq_file *s, Sg_device * sdp)
{
        int k, m, new_interface, blen, usg;
        Sg_request *srp;
        Sg_fd *fp;
        const sg_io_hdr_t *hp;
        const char * cp;
        unsigned int ms;

        k = 0;
        list_for_each_entry(fp, &sdp->sfds, sfd_siblings) {
                k++;
                read_lock(&fp->rq_list_lock); /* irqs already disabled */
                seq_printf(s, "   FD(%d): timeout=%dms bufflen=%d "
                           "(res)sgat=%d low_dma=%d\n", k,
                           jiffies_to_msecs(fp->timeout),
                           fp->reserve.bufflen,
                           (int) fp->reserve.k_use_sg,
                           (int) fp->low_dma);
                seq_printf(s, "   cmd_q=%d f_packid=%d k_orphan=%d closed=0\n",
                           (int) fp->cmd_q, (int) fp->force_packid,
                           (int) fp->keep_orphan);
                for (m = 0, srp = fp->headrp;
                                srp != NULL;
                                ++m, srp = srp->nextrp) {
                        hp = &srp->header;
                        new_interface = (hp->interface_id == '\0') ? 0 : 1;
                        if (srp->res_used) {
                                if (new_interface && 
                                    (SG_FLAG_MMAP_IO & hp->flags))
                                        cp = "     mmap>> ";
                                else
                                        cp = "     rb>> ";
                        } else {
                                if (SG_INFO_DIRECT_IO_MASK & hp->info)
                                        cp = "     dio>> ";
                                else
                                        cp = "     ";
                        }
                        seq_printf(s, cp);
                        blen = srp->data.bufflen;
                        usg = srp->data.k_use_sg;
                        seq_printf(s, srp->done ? 
                                   ((1 == srp->done) ?  "rcv:" : "fin:")
                                   : "act:");
                        seq_printf(s, " id=%d blen=%d",
                                   srp->header.pack_id, blen);
                        if (srp->done)
                                seq_printf(s, " dur=%d", hp->duration);
                        else {
                                ms = jiffies_to_msecs(jiffies);
                                seq_printf(s, " t_o/elap=%d/%d",
                                        (new_interface ? hp->timeout :
                                                  jiffies_to_msecs(fp->timeout)),
                                        (ms > hp->duration ? ms - hp->duration : 0));
                        }
                        seq_printf(s, "ms sgat=%d op=0x%02x\n", usg,
                                   (int) srp->data.cmd_opcode);
                }
                if (0 == m)
                        seq_printf(s, "     No requests active\n");
                read_unlock(&fp->rq_list_lock);
        }
}

static int sg_proc_open_debug(struct inode *inode, struct file *file)
{
        return seq_open(file, &debug_seq_ops);
}

static int sg_proc_seq_show_debug(struct seq_file *s, void *v)
{
        struct sg_proc_deviter * it = (struct sg_proc_deviter *) v;
        Sg_device *sdp;
        unsigned long iflags;

        if (it && (0 == it->index)) {
                seq_printf(s, "max_active_device=%d(origin 1)\n",
                           (int)it->max);
                seq_printf(s, " def_reserved_size=%d\n", sg_big_buff);
        }

        read_lock_irqsave(&sg_index_lock, iflags);
        sdp = it ? sg_lookup_dev(it->index) : NULL;
        if (sdp && !list_empty(&sdp->sfds)) {
                struct scsi_device *scsidp = sdp->device;

                seq_printf(s, " >>> device=%s ", sdp->disk->disk_name);
                if (sdp->detached)
                        seq_printf(s, "detached pending close ");
                else
                        seq_printf
                            (s, "scsi%d chan=%d id=%d lun=%d   em=%d",
                             scsidp->host->host_no,
                             scsidp->channel, scsidp->id,
                             scsidp->lun,
                             scsidp->host->hostt->emulated);
                seq_printf(s, " sg_tablesize=%d excl=%d\n",
                           sdp->sg_tablesize, get_exclude(sdp));
                sg_proc_debug_helper(s, sdp);
        }
        read_unlock_irqrestore(&sg_index_lock, iflags);
        return 0;
}

#endif                          /* CONFIG_SCSI_PROC_FS */

module_init(init_sg);
module_exit(exit_sg);