Release 4.11 drivers/scsi/sg.c

/*
 *  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 - 2014 Douglas Gilbert
 *
 * 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 = 30536;	
/* 2 digits for each component */

#define SG_VERSION_STR "3.5.36"

/*
 *  D. P. Gilbert (dgilbert@interlog.com), 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/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/atomic.h>
#include <linux/ratelimit.h>
#include <linux/uio.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 = "20140603";

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


#define SG_ALLOW_DIO_DEF 0


#define SG_MAX_DEVS 32768

/* SG_MAX_CDB_SIZE should be 260 (spc4r37 section 3.1.30) however the type
 * of sg_io_hdr::cmd_len can only represent 255. All SCSI commands greater
 * than 16 bytes are "variable length" whose length is a multiple of 4
 */

#define SG_MAX_CDB_SIZE 252


#define SG_DEFAULT_TIMEOUT mult_frac(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_device(struct device *, struct class_interface *);
static void sg_remove_device(struct device *, struct class_interface *);

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_device,
	.remove_dev     = sg_remove_device,
};


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 */
	
struct list_head sfd_siblings;  /* protected by device's sfd_lock */
	
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 */
	
unsigned char next_cmd_len; /* 0: automatic, >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 open_wait;    /* queue open() when O_EXCL present */
	
struct mutex open_rel_lock;     /* held when in open() or release() */
	
int sg_tablesize;	/* adapter's max scatter-gather table size */
	
u32 index;		/* device index number */
	
struct list_head sfds;
	
rwlock_t sfd_lock;      /* protect access to sfd list */
	
atomic_t detaching;     /* 0->device usable, 1->device detaching */
	
bool exclude;		/* 1->open(O_EXCL) succeeded and is active */
	
int open_cnt;		/* count of opens (perhaps < num(sfds) ) */
	
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_fd * sfp, 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);
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_device_destroy(struct kref *kref);


#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)


#define sg_printk(prefix, sdp, fmt, a...) \
	sdev_prefix_printk(prefix, (sdp)->device,               \
                           (sdp)->disk->disk_name, fmt, ##a)



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);
}

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FUJITA Tomonori
52
100.00%
1
100.00%
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52
100.00%
1
100.00%


static int

open_wait(Sg_device *sdp, int flags)
{
	int retval = 0;

	if (flags & O_EXCL) {
		while (sdp->open_cnt > 0) {
			mutex_unlock(&sdp->open_rel_lock);
			retval = wait_event_interruptible(sdp->open_wait,
					(atomic_read(&sdp->detaching) ||
					 !sdp->open_cnt));
			mutex_lock(&sdp->open_rel_lock);

			if (retval) /* -ERESTARTSYS */
				return retval;
			if (atomic_read(&sdp->detaching))
				return -ENODEV;
		}
	} else {
		while (sdp->exclude) {
			mutex_unlock(&sdp->open_rel_lock);
			retval = wait_event_interruptible(sdp->open_wait,
					(atomic_read(&sdp->detaching) ||
					 !sdp->exclude));
			mutex_lock(&sdp->open_rel_lock);

			if (retval) /* -ERESTARTSYS */
				return retval;
			if (atomic_read(&sdp->detaching))
				return -ENODEV;
		}
	}

	return retval;
}

Contributors
Person
Tokens
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CommitProp
Douglas Gilbert
122
70.11%
1
33.33%
James Bottomley
32
18.39%
1
33.33%
Jörn Engel
20
11.49%
1
33.33%
Total
174
100.00%
3
100.00%

/* Returns 0 on success, else a negated errno value */

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 retval;

	nonseekable_open(inode, filp);
	if ((flags & O_EXCL) && (O_RDONLY == (flags & O_ACCMODE)))
		return -EPERM; /* Can't lock it with read only access */
	sdp = sg_get_dev(dev);
	if (IS_ERR(sdp))
		return PTR_ERR(sdp);

	SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp,
				      "sg_open: flags=0x%x\n", flags));

	/* 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;

	/* scsi_block_when_processing_errors() may block so bypass
         * check if O_NONBLOCK. Permits SCSI commands to be issued
         * during error recovery. Tread carefully. */
	if (!((flags & O_NONBLOCK) ||
	      scsi_block_when_processing_errors(sdp->device))) {
		retval = -ENXIO;
		/* we are in error recovery for this device */
		goto error_out;
	}

	mutex_lock(&sdp->open_rel_lock);
	if (flags & O_NONBLOCK) {
		if (flags & O_EXCL) {
			if (sdp->open_cnt > 0) {
				retval = -EBUSY;
				goto error_mutex_locked;
			}
		} else {
			if (sdp->exclude) {
				retval = -EBUSY;
				goto error_mutex_locked;
			}
		}
	} else {
		retval = open_wait(sdp, flags);
		if (retval) /* -ERESTARTSYS or -ENODEV */
			goto error_mutex_locked;
	}

	/* N.B. at this point we are holding the open_rel_lock */
	if (flags & O_EXCL)
		sdp->exclude = true;

	if (sdp->open_cnt < 1) {  /* no existing opens */
		sdp->sgdebug = 0;
		q = sdp->device->request_queue;
		sdp->sg_tablesize = queue_max_segments(q);
	}
	sfp = sg_add_sfp(sdp);
	if (IS_ERR(sfp)) {
		retval = PTR_ERR(sfp);
		goto out_undo;
	}

	filp->private_data = sfp;
	sdp->open_cnt++;
	mutex_unlock(&sdp->open_rel_lock);

	retval = 0;
sg_put:
	kref_put(&sdp->d_ref, sg_device_destroy);
	return retval;

out_undo:
	if (flags & O_EXCL) {
		sdp->exclude = false;   /* undo if error */
		wake_up_interruptible(&sdp->open_wait);
	}
error_mutex_locked:
	mutex_unlock(&sdp->open_rel_lock);
error_out:
	scsi_autopm_put_device(sdp->device);
sdp_put:
	scsi_device_put(sdp->device);
	goto sg_put;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Douglas Gilbert
151
35.53%
2
7.41%
Linus Torvalds (pre-git)
119
28.00%
12
44.44%
Linus Torvalds
42
9.88%
2
7.41%
James Bottomley
29
6.82%
2
7.41%
Alan Stern
25
5.88%
1
3.70%
Tony Battersby
20
4.71%
1
3.70%
Hannes Reinecke
16
3.76%
1
3.70%
Christoph Hellwig
8
1.88%
1
3.70%
Mike Christie
7
1.65%
1
3.70%
Vaughan Cao
5
1.18%
1
3.70%
Al Viro
1
0.24%
1
3.70%
Martin K. Petersen
1
0.24%
1
3.70%
Doug Ledford
1
0.24%
1
3.70%
Total
425
100.00%
27
100.00%

/* Release resources associated with a successful sg_open()
 * Returns 0 on success, else a negated errno value */

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, sg_printk(KERN_INFO, sdp, "sg_release\n"));

	mutex_lock(&sdp->open_rel_lock);
	scsi_autopm_put_device(sdp->device);
	kref_put(&sfp->f_ref, sg_remove_sfp);
	sdp->open_cnt--;

	/* possibly many open()s waiting on exlude clearing, start many;
         * only open(O_EXCL)s wait on 0==open_cnt so only start one */
	if (sdp->exclude) {
		sdp->exclude = false;
		wake_up_interruptible_all(&sdp->open_wait);
	} else if (0 == sdp->open_cnt) {
		wake_up_interruptible(&sdp->open_wait);
	}
	mutex_unlock(&sdp->open_rel_lock);
	return 0;
}

Contributors
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Tokens
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Commits
CommitProp
Linus Torvalds (pre-git)
71
46.41%
3
37.50%
Douglas Gilbert
57
37.25%
1
12.50%
Tony Battersby
10
6.54%
1
12.50%
Alan Stern
7
4.58%
1
12.50%
Vaughan Cao
4
2.61%
1
12.50%
Hannes Reinecke
4
2.61%
1
12.50%
Total
153
100.00%
8
100.00%


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, sg_printk(KERN_INFO, sdp,
				      "sg_read: count=%d\n", (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 (atomic_read(&sdp->detaching)) {
			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,
			(atomic_read(&sdp->detaching) ||
			(srp = sg_get_rq_mark(sfp, req_pack_id))));
		if (atomic_read(&sdp->detaching)) {
			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;
}

Contributors
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CommitProp
Linus Torvalds (pre-git)
507
64.42%
12
54.55%
Douglas Gilbert
240
30.50%
4
18.18%
Linus Torvalds
29
3.68%
1
4.55%
Jesper Juhl
4
0.51%
1
4.55%
Hannes Reinecke
4
0.51%
1
4.55%
Jörn Engel
2
0.25%
2
9.09%
Al Viro
1
0.13%
1
4.55%
Total
787
100.00%
22
100.00%


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, err2;
	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:
	err2 = sg_finish_rem_req(srp);
	return err ? : err2 ? : count;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Linus Torvalds (pre-git)
184
77.64%
5
41.67%
Douglas Gilbert
22
9.28%
1
8.33%
Linus Torvalds
20
8.44%
1
8.33%
Tony Battersby
7
2.95%
1
8.33%
Al Viro
1
0.42%
1
8.33%
FUJITA Tomonori
1
0.42%
1
8.33%
Dave Jones
1
0.42%
1
8.33%
Mike Christie
1
0.42%
1
8.33%
Total
237
100.00%
12
100.00%


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[SG_MAX_CDB_SIZE];

	if (unlikely(segment_eq(get_fs(), KERNEL_DS)))
		return -EINVAL;

	if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
		return -ENXIO;
	SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp,
				      "sg_write: count=%d\n", (int) count));
	if (atomic_read(&sdp->detaching))
		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, sg_printk(KERN_INFO, sdp,
					      "sg_write: queue full\n"));
		return -EDOM;
	}
	buf += SZ_SG_HEADER;
	__get_user(opcode, buf);
	if (sfp->next_cmd_len > 0) {
		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, sg_printk(KERN_INFO, sdp,
		"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 */