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/*
 * The low performance USB storage driver (ub).
 *
 * Copyright (c) 1999, 2000 Matthew Dharm (mdharm-usb@one-eyed-alien.net)
 * Copyright (C) 2004 Pete Zaitcev (zaitcev@yahoo.com)
 *
 * This work is a part of Linux kernel, is derived from it,
 * and is not licensed separately. See file COPYING for details.
 *
 * TODO (sorted by decreasing priority)
 *  -- set readonly flag for CDs, set removable flag for CF readers
 *  -- do inquiry and verify we got a disk and not a tape (for LUN mismatch)
 *  -- verify the 13 conditions and do bulk resets
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 *  -- highmem
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 *  -- move top_sense and work_bcs into separate allocations (if they survive)
 *     for cache purists and esoteric architectures.
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 *  -- Allocate structure for LUN 0 before the first ub_sync_tur, avoid NULL. ?
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 *  -- prune comments, they are too volumnous
 *  -- Resove XXX's
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 *  -- CLEAR, CLR2STS, CLRRS seem to be ripe for refactoring.
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 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/usb.h>
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#include <linux/usb_usual.h>
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#include <linux/blkdev.h>
#include <linux/timer.h>
#include <scsi/scsi.h>

#define DRV_NAME "ub"

#define UB_MAJOR 180

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/*
 * The command state machine is the key model for understanding of this driver.
 *
 * The general rule is that all transitions are done towards the bottom
 * of the diagram, thus preventing any loops.
 *
 * An exception to that is how the STAT state is handled. A counter allows it
 * to be re-entered along the path marked with [C].
 *
 *       +--------+
 *       ! INIT   !
 *       +--------+
 *           !
 *        ub_scsi_cmd_start fails ->--------------------------------------\
 *           !                                                            !
 *           V                                                            !
 *       +--------+                                                       !
 *       ! CMD    !                                                       !
 *       +--------+                                                       !
 *           !                                            +--------+      !
 *         was -EPIPE -->-------------------------------->! CLEAR  !      !
 *           !                                            +--------+      !
 *           !                                                !           !
 *         was error -->------------------------------------- ! --------->\
 *           !                                                !           !
 *  /--<-- cmd->dir == NONE ?                                 !           !
 *  !        !                                                !           !
 *  !        V                                                !           !
 *  !    +--------+                                           !           !
 *  !    ! DATA   !                                           !           !
 *  !    +--------+                                           !           !
 *  !        !                           +---------+          !           !
 *  !      was -EPIPE -->--------------->! CLR2STS !          !           !
 *  !        !                           +---------+          !           !
 *  !        !                                !               !           !
 *  !        !                              was error -->---- ! --------->\
 *  !      was error -->--------------------- ! ------------- ! --------->\
 *  !        !                                !               !           !
 *  !        V                                !               !           !
 *  \--->+--------+                           !               !           !
 *       ! STAT   !<--------------------------/               !           !
 *  /--->+--------+                                           !           !
 *  !        !                                                !           !
 * [C]     was -EPIPE -->-----------\                         !           !
 *  !        !                      !                         !           !
 *  +<---- len == 0                 !                         !           !
 *  !        !                      !                         !           !
 *  !      was error -->--------------------------------------!---------->\
 *  !        !                      !                         !           !
 *  +<---- bad CSW                  !                         !           !
 *  +<---- bad tag                  !                         !           !
 *  !        !                      V                         !           !
 *  !        !                 +--------+                     !           !
 *  !        !                 ! CLRRS  !                     !           !
 *  !        !                 +--------+                     !           !
 *  !        !                      !                         !           !
 *  \------- ! --------------------[C]--------\               !           !
 *           !                                !               !           !
 *         cmd->error---\                +--------+           !           !
 *           !          +--------------->! SENSE  !<----------/           !
 *         STAT_FAIL----/                +--------+                       !
 *           !                                !                           V
 *           !                                V                      +--------+
 *           \--------------------------------\--------------------->! DONE   !
 *                                                                   +--------+
 */

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/*
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 * This many LUNs per USB device.
 * Every one of them takes a host, see UB_MAX_HOSTS.
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 */
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#define UB_MAX_LUNS   9
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/*
 */

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#define UB_PARTS_PER_LUN      8
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#define UB_MAX_CDB_SIZE      16		/* Corresponds to Bulk */

#define UB_SENSE_SIZE  18

/*
 */

/* command block wrapper */
struct bulk_cb_wrap {
	__le32	Signature;		/* contains 'USBC' */
	u32	Tag;			/* unique per command id */
	__le32	DataTransferLength;	/* size of data */
	u8	Flags;			/* direction in bit 0 */
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	u8	Lun;			/* LUN */
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	u8	Length;			/* of of the CDB */
	u8	CDB[UB_MAX_CDB_SIZE];	/* max command */
};

#define US_BULK_CB_WRAP_LEN	31
#define US_BULK_CB_SIGN		0x43425355	/*spells out USBC */
#define US_BULK_FLAG_IN		1
#define US_BULK_FLAG_OUT	0

/* command status wrapper */
struct bulk_cs_wrap {
	__le32	Signature;		/* should = 'USBS' */
	u32	Tag;			/* same as original command */
	__le32	Residue;		/* amount not transferred */
	u8	Status;			/* see below */
};

#define US_BULK_CS_WRAP_LEN	13
#define US_BULK_CS_SIGN		0x53425355	/* spells out 'USBS' */
#define US_BULK_STAT_OK		0
#define US_BULK_STAT_FAIL	1
#define US_BULK_STAT_PHASE	2

/* bulk-only class specific requests */
#define US_BULK_RESET_REQUEST	0xff
#define US_BULK_GET_MAX_LUN	0xfe

/*
 */
struct ub_dev;

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#define UB_MAX_REQ_SG	9	/* cdrecord requires 32KB and maybe a header */
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#define UB_MAX_SECTORS 64

/*
 * A second is more than enough for a 32K transfer (UB_MAX_SECTORS)
 * even if a webcam hogs the bus, but some devices need time to spin up.
 */
#define UB_URB_TIMEOUT	(HZ*2)
#define UB_DATA_TIMEOUT	(HZ*5)	/* ZIP does spin-ups in the data phase */
#define UB_STAT_TIMEOUT	(HZ*5)	/* Same spinups and eject for a dataless cmd. */
#define UB_CTRL_TIMEOUT	(HZ/2)	/* 500ms ought to be enough to clear a stall */

/*
 * An instance of a SCSI command in transit.
 */
#define UB_DIR_NONE	0
#define UB_DIR_READ	1
#define UB_DIR_ILLEGAL2	2
#define UB_DIR_WRITE	3

#define UB_DIR_CHAR(c)  (((c)==UB_DIR_WRITE)? 'w': \
			 (((c)==UB_DIR_READ)? 'r': 'n'))

enum ub_scsi_cmd_state {
	UB_CMDST_INIT,			/* Initial state */
	UB_CMDST_CMD,			/* Command submitted */
	UB_CMDST_DATA,			/* Data phase */
	UB_CMDST_CLR2STS,		/* Clearing before requesting status */
	UB_CMDST_STAT,			/* Status phase */
	UB_CMDST_CLEAR,			/* Clearing a stall (halt, actually) */
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	UB_CMDST_CLRRS,			/* Clearing before retrying status */
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	UB_CMDST_SENSE,			/* Sending Request Sense */
	UB_CMDST_DONE			/* Final state */
};

struct ub_scsi_cmd {
	unsigned char cdb[UB_MAX_CDB_SIZE];
	unsigned char cdb_len;

	unsigned char dir;		/* 0 - none, 1 - read, 3 - write. */
	enum ub_scsi_cmd_state state;
	unsigned int tag;
	struct ub_scsi_cmd *next;

	int error;			/* Return code - valid upon done */
	unsigned int act_len;		/* Return size */
	unsigned char key, asc, ascq;	/* May be valid if error==-EIO */

	int stat_count;			/* Retries getting status. */

	unsigned int len;		/* Requested length */
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	unsigned int current_sg;
	unsigned int nsg;		/* sgv[nsg] */
	struct scatterlist sgv[UB_MAX_REQ_SG];
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	struct ub_lun *lun;
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	void (*done)(struct ub_dev *, struct ub_scsi_cmd *);
	void *back;
};

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struct ub_request {
	struct request *rq;
	unsigned int current_try;
	unsigned int nsg;		/* sgv[nsg] */
	struct scatterlist sgv[UB_MAX_REQ_SG];
};

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/*
 */
struct ub_capacity {
	unsigned long nsec;		/* Linux size - 512 byte sectors */
	unsigned int bsize;		/* Linux hardsect_size */
	unsigned int bshift;		/* Shift between 512 and hard sects */
};

/*
 * This is a direct take-off from linux/include/completion.h
 * The difference is that I do not wait on this thing, just poll.
 * When I want to wait (ub_probe), I just use the stock completion.
 *
 * Note that INIT_COMPLETION takes no lock. It is correct. But why
 * in the bloody hell that thing takes struct instead of pointer to struct
 * is quite beyond me. I just copied it from the stock completion.
 */
struct ub_completion {
	unsigned int done;
	spinlock_t lock;
};

static inline void ub_init_completion(struct ub_completion *x)
{
	x->done = 0;
	spin_lock_init(&x->lock);
}

#define UB_INIT_COMPLETION(x)	((x).done = 0)

static void ub_complete(struct ub_completion *x)
{
	unsigned long flags;

	spin_lock_irqsave(&x->lock, flags);
	x->done++;
	spin_unlock_irqrestore(&x->lock, flags);
}

static int ub_is_completed(struct ub_completion *x)
{
	unsigned long flags;
	int ret;

	spin_lock_irqsave(&x->lock, flags);
	ret = x->done;
	spin_unlock_irqrestore(&x->lock, flags);
	return ret;
}

/*
 */
struct ub_scsi_cmd_queue {
	int qlen, qmax;
	struct ub_scsi_cmd *head, *tail;
};

/*
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 * The block device instance (one per LUN).
 */
struct ub_lun {
	struct ub_dev *udev;
	struct list_head link;
	struct gendisk *disk;
	int id;				/* Host index */
	int num;			/* LUN number */
	char name[16];

	int changed;			/* Media was changed */
	int removable;
	int readonly;

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	struct ub_request urq;

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	/* Use Ingo's mempool if or when we have more than one command. */
	/*
	 * Currently we never need more than one command for the whole device.
	 * However, giving every LUN a command is a cheap and automatic way
	 * to enforce fairness between them.
	 */
	int cmda[1];
	struct ub_scsi_cmd cmdv[1];

	struct ub_capacity capacity; 
};

/*
 * The USB device instance.
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 */
struct ub_dev {
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	spinlock_t *lock;
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	atomic_t poison;		/* The USB device is disconnected */
	int openc;			/* protected by ub_lock! */
					/* kref is too implicit for our taste */
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	int reset;			/* Reset is running */
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	unsigned int tagcnt;
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	char name[12];
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	struct usb_device *dev;
	struct usb_interface *intf;

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	struct list_head luns;
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	unsigned int send_bulk_pipe;	/* cached pipe values */
	unsigned int recv_bulk_pipe;
	unsigned int send_ctrl_pipe;
	unsigned int recv_ctrl_pipe;

	struct tasklet_struct tasklet;

	struct ub_scsi_cmd_queue cmd_queue;
	struct ub_scsi_cmd top_rqs_cmd;	/* REQUEST SENSE */
	unsigned char top_sense[UB_SENSE_SIZE];

	struct ub_completion work_done;
	struct urb work_urb;
	struct timer_list work_timer;
	int last_pipe;			/* What might need clearing */
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	__le32 signature;		/* Learned signature */
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	struct bulk_cb_wrap work_bcb;
	struct bulk_cs_wrap work_bcs;
	struct usb_ctrlrequest work_cr;

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	struct work_struct reset_work;
	wait_queue_head_t reset_wait;

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	int sg_stat[6];
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};

/*
 */
static void ub_cleanup(struct ub_dev *sc);
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static int ub_request_fn_1(struct ub_lun *lun, struct request *rq);
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static void ub_cmd_build_block(struct ub_dev *sc, struct ub_lun *lun,
    struct ub_scsi_cmd *cmd, struct ub_request *urq);
static void ub_cmd_build_packet(struct ub_dev *sc, struct ub_lun *lun,
    struct ub_scsi_cmd *cmd, struct ub_request *urq);
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static void ub_rw_cmd_done(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
static void ub_end_rq(struct request *rq, int uptodate);
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static int ub_rw_cmd_retry(struct ub_dev *sc, struct ub_lun *lun,
    struct ub_request *urq, struct ub_scsi_cmd *cmd);
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static int ub_submit_scsi(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
static void ub_urb_complete(struct urb *urb, struct pt_regs *pt);
static void ub_scsi_action(unsigned long _dev);
static void ub_scsi_dispatch(struct ub_dev *sc);
static void ub_scsi_urb_compl(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
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static void ub_data_start(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
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static void ub_state_done(struct ub_dev *sc, struct ub_scsi_cmd *cmd, int rc);
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static int __ub_state_stat(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
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static void ub_state_stat(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
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static void ub_state_stat_counted(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
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static void ub_state_sense(struct ub_dev *sc, struct ub_scsi_cmd *cmd);
static int ub_submit_clear_stall(struct ub_dev *sc, struct ub_scsi_cmd *cmd,
    int stalled_pipe);
static void ub_top_sense_done(struct ub_dev *sc, struct ub_scsi_cmd *scmd);
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static void ub_reset_enter(struct ub_dev *sc, int try);
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static void ub_reset_task(void *arg);
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static int ub_sync_tur(struct ub_dev *sc, struct ub_lun *lun);
static int ub_sync_read_cap(struct ub_dev *sc, struct ub_lun *lun,
    struct ub_capacity *ret);
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static int ub_sync_reset(struct ub_dev *sc);
static int ub_probe_clear_stall(struct ub_dev *sc, int stalled_pipe);
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static int ub_probe_lun(struct ub_dev *sc, int lnum);
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/*
 */
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#ifdef CONFIG_USB_LIBUSUAL

#define ub_usb_ids  storage_usb_ids
#else

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static struct usb_device_id ub_usb_ids[] = {
	{ USB_INTERFACE_INFO(USB_CLASS_MASS_STORAGE, US_SC_SCSI, US_PR_BULK) },
	{ }
};

MODULE_DEVICE_TABLE(usb, ub_usb_ids);
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#endif /* CONFIG_USB_LIBUSUAL */
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/*
 * Find me a way to identify "next free minor" for add_disk(),
 * and the array disappears the next day. However, the number of
 * hosts has something to do with the naming and /proc/partitions.
 * This has to be thought out in detail before changing.
 * If UB_MAX_HOST was 1000, we'd use a bitmap. Or a better data structure.
 */
#define UB_MAX_HOSTS  26
static char ub_hostv[UB_MAX_HOSTS];
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#define UB_QLOCK_NUM 5
static spinlock_t ub_qlockv[UB_QLOCK_NUM];
static int ub_qlock_next = 0;

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static DEFINE_SPINLOCK(ub_lock);	/* Locks globals and ->openc */

/*
 * The id allocator.
 *
 * This also stores the host for indexing by minor, which is somewhat dirty.
 */
static int ub_id_get(void)
{
	unsigned long flags;
	int i;

	spin_lock_irqsave(&ub_lock, flags);
	for (i = 0; i < UB_MAX_HOSTS; i++) {
		if (ub_hostv[i] == 0) {
			ub_hostv[i] = 1;
			spin_unlock_irqrestore(&ub_lock, flags);
			return i;
		}
	}
	spin_unlock_irqrestore(&ub_lock, flags);
	return -1;
}

static void ub_id_put(int id)
{
	unsigned long flags;

	if (id < 0 || id >= UB_MAX_HOSTS) {
		printk(KERN_ERR DRV_NAME ": bad host ID %d\n", id);
		return;
	}

	spin_lock_irqsave(&ub_lock, flags);
	if (ub_hostv[id] == 0) {
		spin_unlock_irqrestore(&ub_lock, flags);
		printk(KERN_ERR DRV_NAME ": freeing free host ID %d\n", id);
		return;
	}
	ub_hostv[id] = 0;
	spin_unlock_irqrestore(&ub_lock, flags);
}

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/*
 * This is necessitated by the fact that blk_cleanup_queue does not
 * necesserily destroy the queue. Instead, it may merely decrease q->refcnt.
 * Since our blk_init_queue() passes a spinlock common with ub_dev,
 * we have life time issues when ub_cleanup frees ub_dev.
 */
static spinlock_t *ub_next_lock(void)
{
	unsigned long flags;
	spinlock_t *ret;

	spin_lock_irqsave(&ub_lock, flags);
	ret = &ub_qlockv[ub_qlock_next];
	ub_qlock_next = (ub_qlock_next + 1) % UB_QLOCK_NUM;
	spin_unlock_irqrestore(&ub_lock, flags);
	return ret;
}

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/*
 * Downcount for deallocation. This rides on two assumptions:
 *  - once something is poisoned, its refcount cannot grow
 *  - opens cannot happen at this time (del_gendisk was done)
 * If the above is true, we can drop the lock, which we need for
 * blk_cleanup_queue(): the silly thing may attempt to sleep.
 * [Actually, it never needs to sleep for us, but it calls might_sleep()]
 */
static void ub_put(struct ub_dev *sc)
{
	unsigned long flags;

	spin_lock_irqsave(&ub_lock, flags);
	--sc->openc;
	if (sc->openc == 0 && atomic_read(&sc->poison)) {
		spin_unlock_irqrestore(&ub_lock, flags);
		ub_cleanup(sc);
	} else {
		spin_unlock_irqrestore(&ub_lock, flags);
	}
}

/*
 * Final cleanup and deallocation.
 */
static void ub_cleanup(struct ub_dev *sc)
{
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	struct list_head *p;
	struct ub_lun *lun;
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	request_queue_t *q;

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	while (!list_empty(&sc->luns)) {
		p = sc->luns.next;
		lun = list_entry(p, struct ub_lun, link);
		list_del(p);
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		/* I don't think queue can be NULL. But... Stolen from sx8.c */
		if ((q = lun->disk->queue) != NULL)
			blk_cleanup_queue(q);
		/*
		 * If we zero disk->private_data BEFORE put_disk, we have
		 * to check for NULL all over the place in open, release,
		 * check_media and revalidate, because the block level
		 * semaphore is well inside the put_disk.
		 * But we cannot zero after the call, because *disk is gone.
		 * The sd.c is blatantly racy in this area.
		 */
		/* disk->private_data = NULL; */
		put_disk(lun->disk);
		lun->disk = NULL;

		ub_id_put(lun->id);
		kfree(lun);
	}
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	usb_set_intfdata(sc->intf, NULL);
	usb_put_intf(sc->intf);
	usb_put_dev(sc->dev);
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	kfree(sc);
}

/*
 * The "command allocator".
 */
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static struct ub_scsi_cmd *ub_get_cmd(struct ub_lun *lun)
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{
	struct ub_scsi_cmd *ret;

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	if (lun->cmda[0])
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		return NULL;
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	ret = &lun->cmdv[0];
	lun->cmda[0] = 1;
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	return ret;
}

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static void ub_put_cmd(struct ub_lun *lun, struct ub_scsi_cmd *cmd)
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{
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	if (cmd != &lun->cmdv[0]) {
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		printk(KERN_WARNING "%s: releasing a foreign cmd %p\n",
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		    lun->name, cmd);
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		return;
	}
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	if (!lun->cmda[0]) {
		printk(KERN_WARNING "%s: releasing a free cmd\n", lun->name);
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		return;
	}
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	lun->cmda[0] = 0;
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}

/*
 * The command queue.
 */
static void ub_cmdq_add(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
	struct ub_scsi_cmd_queue *t = &sc->cmd_queue;

	if (t->qlen++ == 0) {
		t->head = cmd;
		t->tail = cmd;
	} else {
		t->tail->next = cmd;
		t->tail = cmd;
	}

	if (t->qlen > t->qmax)
		t->qmax = t->qlen;
}

static void ub_cmdq_insert(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
	struct ub_scsi_cmd_queue *t = &sc->cmd_queue;

	if (t->qlen++ == 0) {
		t->head = cmd;
		t->tail = cmd;
	} else {
		cmd->next = t->head;
		t->head = cmd;
	}

	if (t->qlen > t->qmax)
		t->qmax = t->qlen;
}

static struct ub_scsi_cmd *ub_cmdq_pop(struct ub_dev *sc)
{
	struct ub_scsi_cmd_queue *t = &sc->cmd_queue;
	struct ub_scsi_cmd *cmd;

	if (t->qlen == 0)
		return NULL;
	if (--t->qlen == 0)
		t->tail = NULL;
	cmd = t->head;
	t->head = cmd->next;
	cmd->next = NULL;
	return cmd;
}

#define ub_cmdq_peek(sc)  ((sc)->cmd_queue.head)

/*
 * The request function is our main entry point
 */

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static void ub_request_fn(request_queue_t *q)
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{
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	struct ub_lun *lun = q->queuedata;
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	struct request *rq;

	while ((rq = elv_next_request(q)) != NULL) {
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		if (ub_request_fn_1(lun, rq) != 0) {
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			blk_stop_queue(q);
			break;
		}
	}
}

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static int ub_request_fn_1(struct ub_lun *lun, struct request *rq)
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{
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	struct ub_dev *sc = lun->udev;
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	struct ub_scsi_cmd *cmd;
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	struct ub_request *urq;
	int n_elem;
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	if (atomic_read(&sc->poison) || lun->changed) {
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		blkdev_dequeue_request(rq);
		ub_end_rq(rq, 0);
		return 0;
	}

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	if (lun->urq.rq != NULL)
		return -1;
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	if ((cmd = ub_get_cmd(lun)) == NULL)
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		return -1;
	memset(cmd, 0, sizeof(struct ub_scsi_cmd));

	blkdev_dequeue_request(rq);
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	urq = &lun->urq;
	memset(urq, 0, sizeof(struct ub_request));
	urq->rq = rq;

	/*
	 * get scatterlist from block layer
	 */
	n_elem = blk_rq_map_sg(lun->disk->queue, rq, &urq->sgv[0]);
	if (n_elem < 0) {
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		/* Impossible, because blk_rq_map_sg should not hit ENOMEM. */
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		printk(KERN_INFO "%s: failed request map (%d)\n",
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		    lun->name, n_elem);
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		goto drop;
	}
	if (n_elem > UB_MAX_REQ_SG) {	/* Paranoia */
		printk(KERN_WARNING "%s: request with %d segments\n",
		    lun->name, n_elem);
		goto drop;
	}
	urq->nsg = n_elem;
	sc->sg_stat[n_elem < 5 ? n_elem : 5]++;

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	if (blk_pc_request(rq)) {
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		ub_cmd_build_packet(sc, lun, cmd, urq);
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	} else {
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		ub_cmd_build_block(sc, lun, cmd, urq);
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	}
	cmd->state = UB_CMDST_INIT;
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	cmd->lun = lun;
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	cmd->done = ub_rw_cmd_done;
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	cmd->back = urq;
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	cmd->tag = sc->tagcnt++;
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	if (ub_submit_scsi(sc, cmd) != 0)
		goto drop;

	return 0;
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drop:
	ub_put_cmd(lun, cmd);
	ub_end_rq(rq, 0);
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	return 0;
}

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static void ub_cmd_build_block(struct ub_dev *sc, struct ub_lun *lun,
    struct ub_scsi_cmd *cmd, struct ub_request *urq)
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{
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	struct request *rq = urq->rq;
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	unsigned int block, nblks;
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	if (rq_data_dir(rq) == WRITE)
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		cmd->dir = UB_DIR_WRITE;
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	else
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		cmd->dir = UB_DIR_READ;
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	cmd->nsg = urq->nsg;
	memcpy(cmd->sgv, urq->sgv, sizeof(struct scatterlist) * cmd->nsg);
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	/*
	 * build the command
	 *
	 * The call to blk_queue_hardsect_size() guarantees that request
	 * is aligned, but it is given in terms of 512 byte units, always.
	 */
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	block = rq->sector >> lun->capacity.bshift;
	nblks = rq->nr_sectors >> lun->capacity.bshift;
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	cmd->cdb[0] = (cmd->dir == UB_DIR_READ)? READ_10: WRITE_10;
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	/* 10-byte uses 4 bytes of LBA: 2147483648KB, 2097152MB, 2048GB */
	cmd->cdb[2] = block >> 24;
	cmd->cdb[3] = block >> 16;
	cmd->cdb[4] = block >> 8;
	cmd->cdb[5] = block;
	cmd->cdb[7] = nblks >> 8;
	cmd->cdb[8] = nblks;
	cmd->cdb_len = 10;

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	cmd->len = rq->nr_sectors * 512;
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}

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static void ub_cmd_build_packet(struct ub_dev *sc, struct ub_lun *lun,
    struct ub_scsi_cmd *cmd, struct ub_request *urq)
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{
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	struct request *rq = urq->rq;
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	if (rq->data_len == 0) {
		cmd->dir = UB_DIR_NONE;
	} else {
		if (rq_data_dir(rq) == WRITE)
			cmd->dir = UB_DIR_WRITE;
		else
			cmd->dir = UB_DIR_READ;
	}
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	cmd->nsg = urq->nsg;
	memcpy(cmd->sgv, urq->sgv, sizeof(struct scatterlist) * cmd->nsg);
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	memcpy(&cmd->cdb, rq->cmd, rq->cmd_len);
	cmd->cdb_len = rq->cmd_len;

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	cmd->len = rq->data_len;
}

static void ub_rw_cmd_done(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
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	struct ub_lun *lun = cmd->lun;
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	struct ub_request *urq = cmd->back;
	struct request *rq;
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	int uptodate;

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	rq = urq->rq;

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	if (cmd->error == 0) {
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		uptodate = 1;

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		if (blk_pc_request(rq)) {
			if (cmd->act_len >= rq->data_len)
				rq->data_len = 0;
			else
				rq->data_len -= cmd->act_len;
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		}
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	} else {
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		uptodate = 0;

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		if (blk_pc_request(rq)) {
			/* UB_SENSE_SIZE is smaller than SCSI_SENSE_BUFFERSIZE */
			memcpy(rq->sense, sc->top_sense, UB_SENSE_SIZE);
			rq->sense_len = UB_SENSE_SIZE;
			if (sc->top_sense[0] != 0)
				rq->errors = SAM_STAT_CHECK_CONDITION;
			else
				rq->errors = DID_ERROR << 16;
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		} else {
			if (cmd->error == -EIO) {
				if (ub_rw_cmd_retry(sc, lun, urq, cmd) == 0)
					return;
			}
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		}
	}
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	urq->rq = NULL;

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	ub_put_cmd(lun, cmd);
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	ub_end_rq(rq, uptodate);
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	blk_start_queue(lun->disk->queue);
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}

static void ub_end_rq(struct request *rq, int uptodate)
{
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	end_that_request_first(rq, uptodate, rq->hard_nr_sectors);
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	end_that_request_last(rq, uptodate);
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}

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static int ub_rw_cmd_retry(struct ub_dev *sc, struct ub_lun *lun,
    struct ub_request *urq, struct ub_scsi_cmd *cmd)
{

	if (atomic_read(&sc->poison))
		return -ENXIO;

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	ub_reset_enter(sc, urq->current_try);
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	if (urq->current_try >= 3)
		return -EIO;
	urq->current_try++;
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	/* Remove this if anyone complains of flooding. */
	printk(KERN_DEBUG "%s: dir %c len/act %d/%d "
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	    "[sense %x %02x %02x] retry %d\n",
	    sc->name, UB_DIR_CHAR(cmd->dir), cmd->len, cmd->act_len,
	    cmd->key, cmd->asc, cmd->ascq, urq->current_try);

	memset(cmd, 0, sizeof(struct ub_scsi_cmd));
	ub_cmd_build_block(sc, lun, cmd, urq);

	cmd->state = UB_CMDST_INIT;
	cmd->lun = lun;
	cmd->done = ub_rw_cmd_done;
	cmd->back = urq;

	cmd->tag = sc->tagcnt++;

#if 0 /* Wasteful */
	return ub_submit_scsi(sc, cmd);
#else
	ub_cmdq_add(sc, cmd);
	return 0;
#endif
}

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/*
 * Submit a regular SCSI operation (not an auto-sense).
 *
 * The Iron Law of Good Submit Routine is:
 * Zero return - callback is done, Nonzero return - callback is not done.
 * No exceptions.
 *
 * Host is assumed locked.
 */
static int ub_submit_scsi(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{

	if (cmd->state != UB_CMDST_INIT ||
	    (cmd->dir != UB_DIR_NONE && cmd->len == 0)) {
		return -EINVAL;
	}

	ub_cmdq_add(sc, cmd);
	/*
	 * We can call ub_scsi_dispatch(sc) right away here, but it's a little
	 * safer to jump to a tasklet, in case upper layers do something silly.
	 */
	tasklet_schedule(&sc->tasklet);
	return 0;
}

/*
 * Submit the first URB for the queued command.
 * This function does not deal with queueing in any way.
 */
static int ub_scsi_cmd_start(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
	struct bulk_cb_wrap *bcb;
	int rc;

	bcb = &sc->work_bcb;

	/*
	 * ``If the allocation length is eighteen or greater, and a device
	 * server returns less than eithteen bytes of data, the application
	 * client should assume that the bytes not transferred would have been
	 * zeroes had the device server returned those bytes.''
	 *
	 * We zero sense for all commands so that when a packet request
	 * fails it does not return a stale sense.
	 */
	memset(&sc->top_sense, 0, UB_SENSE_SIZE);

	/* set up the command wrapper */
	bcb->Signature = cpu_to_le32(US_BULK_CB_SIGN);
	bcb->Tag = cmd->tag;		/* Endianness is not important */
	bcb->DataTransferLength = cpu_to_le32(cmd->len);
	bcb->Flags = (cmd->dir == UB_DIR_READ) ? 0x80 : 0;
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	bcb->Lun = (cmd->lun != NULL) ? cmd->lun->num : 0;
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	bcb->Length = cmd->cdb_len;

	/* copy the command payload */
	memcpy(bcb->CDB, cmd->cdb, UB_MAX_CDB_SIZE);

	UB_INIT_COMPLETION(sc->work_done);

	sc->last_pipe = sc->send_bulk_pipe;
	usb_fill_bulk_urb(&sc->work_urb, sc->dev, sc->send_bulk_pipe,
	    bcb, US_BULK_CB_WRAP_LEN, ub_urb_complete, sc);

	/* Fill what we shouldn't be filling, because usb-storage did so. */
	sc->work_urb.actual_length = 0;
	sc->work_urb.error_count = 0;
	sc->work_urb.status = 0;

	if ((rc = usb_submit_urb(&sc->work_urb, GFP_ATOMIC)) != 0) {
		/* XXX Clear stalls */
		ub_complete(&sc->work_done);
		return rc;
	}

	sc->work_timer.expires = jiffies + UB_URB_TIMEOUT;
	add_timer(&sc->work_timer);

	cmd->state = UB_CMDST_CMD;
	return 0;
}

/*
 * Timeout handler.
 */
static void ub_urb_timeout(unsigned long arg)
{
	struct ub_dev *sc = (struct ub_dev *) arg;
	unsigned long flags;

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	spin_lock_irqsave(sc->lock, flags);
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	if (!ub_is_completed(&sc->work_done))
		usb_unlink_urb(&sc->work_urb);
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	spin_unlock_irqrestore(sc->lock, flags);
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}

/*
 * Completion routine for the work URB.
 *
 * This can be called directly from usb_submit_urb (while we have
 * the sc->lock taken) and from an interrupt (while we do NOT have
 * the sc->lock taken). Therefore, bounce this off to a tasklet.
 */
static void ub_urb_complete(struct urb *urb, struct pt_regs *pt)
{
	struct ub_dev *sc = urb->context;

	ub_complete(&sc->work_done);
	tasklet_schedule(&sc->tasklet);
}

static void ub_scsi_action(unsigned long _dev)
{
	struct ub_dev *sc = (struct ub_dev *) _dev;
	unsigned long flags;

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	spin_lock_irqsave(sc->lock, flags);
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	ub_scsi_dispatch(sc);
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	spin_unlock_irqrestore(sc->lock, flags);
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}

static void ub_scsi_dispatch(struct ub_dev *sc)
{
	struct ub_scsi_cmd *cmd;
	int rc;

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	while (!sc->reset && (cmd = ub_cmdq_peek(sc)) != NULL) {
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		if (cmd->state == UB_CMDST_DONE) {
			ub_cmdq_pop(sc);
			(*cmd->done)(sc, cmd);
		} else if (cmd->state == UB_CMDST_INIT) {
			if ((rc = ub_scsi_cmd_start(sc, cmd)) == 0)
				break;
			cmd->error = rc;
			cmd->state = UB_CMDST_DONE;
		} else {
			if (!ub_is_completed(&sc->work_done))
				break;
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			del_timer(&sc->work_timer);
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			ub_scsi_urb_compl(sc, cmd);
		}
	}
}

static void ub_scsi_urb_compl(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
	struct urb *urb = &sc->work_urb;
	struct bulk_cs_wrap *bcs;
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	int len;
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	int rc;

	if (atomic_read(&sc->poison)) {
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		ub_state_done(sc, cmd, -ENODEV);
		return;
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	}

	if (cmd->state == UB_CMDST_CLEAR) {
		if (urb->status == -EPIPE) {
			/*
			 * STALL while clearning STALL.
			 * The control pipe clears itself - nothing to do.
			 */
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			printk(KERN_NOTICE "%s: stall on control pipe\n",
			    sc->name);
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			goto Bad_End;
		}

		/*
		 * We ignore the result for the halt clear.
		 */

		/* reset the endpoint toggle */
		usb_settoggle(sc->dev, usb_pipeendpoint(sc->last_pipe),
			usb_pipeout(sc->last_pipe), 0);

		ub_state_sense(sc, cmd);

	} else if (cmd->state == UB_CMDST_CLR2STS) {
		if (urb->status == -EPIPE) {
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			printk(KERN_NOTICE "%s: stall on control pipe\n",
			    sc->name);
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			goto Bad_End;
		}

		/*
		 * We ignore the result for the halt clear.
		 */

		/* reset the endpoint toggle */
		usb_settoggle(sc->dev, usb_pipeendpoint(sc->last_pipe),
			usb_pipeout(sc->last_pipe), 0);

		ub_state_stat(sc, cmd);

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	} else if (cmd->state == UB_CMDST_CLRRS) {
		if (urb->status == -EPIPE) {
			printk(KERN_NOTICE "%s: stall on control pipe\n",
			    sc->name);
			goto Bad_End;
		}

		/*
		 * We ignore the result for the halt clear.
		 */

		/* reset the endpoint toggle */
		usb_settoggle(sc->dev, usb_pipeendpoint(sc->last_pipe),
			usb_pipeout(sc->last_pipe), 0);

		ub_state_stat_counted(sc, cmd);

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	} else if (cmd->state == UB_CMDST_CMD) {
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		switch (urb->status) {
		case 0:
			break;
		case -EOVERFLOW:
			goto Bad_End;
		case -EPIPE:
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			rc = ub_submit_clear_stall(sc, cmd, sc->last_pipe);
			if (rc != 0) {
				printk(KERN_NOTICE "%s: "
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				    "unable to submit clear (%d)\n",
				    sc->name, rc);
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				/*
				 * This is typically ENOMEM or some other such shit.
				 * Retrying is pointless. Just do Bad End on it...
				 */
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				ub_state_done(sc, cmd, rc);
				return;
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			}
			cmd->state = UB_CMDST_CLEAR;
			return;
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		case -ESHUTDOWN:	/* unplug */
		case -EILSEQ:		/* unplug timeout on uhci */
			ub_state_done(sc, cmd, -ENODEV);
			return;
		default:
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			goto Bad_End;
		}
		if (urb->actual_length != US_BULK_CB_WRAP_LEN) {
			goto Bad_End;
		}

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		if (cmd->dir == UB_DIR_NONE || cmd->nsg < 1) {
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			ub_state_stat(sc, cmd);
			return;
		}

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		// udelay(125);		// usb-storage has this
		ub_data_start(sc, cmd);
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	} else if (cmd->state == UB_CMDST_DATA) {
		if (urb->status == -EPIPE) {
			rc = ub_submit_clear_stall(sc, cmd, sc->last_pipe);
			if (rc != 0) {
				printk(KERN_NOTICE "%s: "
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				    "unable to submit clear (%d)\n",
				    sc->name, rc);
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				ub_state_done(sc, cmd, rc);
				return;
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			}
			cmd->state = UB_CMDST_CLR2STS;
			return;
		}
		if (urb->status == -EOVERFLOW) {
			/*
			 * A babble? Failure, but we must transfer CSW now.
			 */
			cmd->error = -EOVERFLOW;	/* A cheap trick... */
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			ub_state_stat(sc, cmd);
			return;
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		}
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		if (cmd->dir == UB_DIR_WRITE) {
			/*
			 * Do not continue writes in case of a failure.
			 * Doing so would cause sectors to be mixed up,
			 * which is worse than sectors lost.
			 *
			 * We must try to read the CSW, or many devices
			 * get confused.
			 */
			len = urb->actual_length;
			if (urb->status != 0 ||
			    len != cmd->sgv[cmd->current_sg].length) {
				cmd->act_len += len;

				cmd->error = -EIO;
				ub_state_stat(sc, cmd);
				return;
			}

		} else {
			/*
			 * If an error occurs on read, we record it, and
			 * continue to fetch data in order to avoid bubble.
			 *
			 * As a small shortcut, we stop if we detect that
			 * a CSW mixed into data.
			 */
			if (urb->status != 0)
				cmd->error = -EIO;

			len = urb->actual_length;
			if (urb->status != 0 ||
			    len != cmd->sgv[cmd->current_sg].length) {
				if ((len & 0x1FF) == US_BULK_CS_WRAP_LEN)
					goto Bad_End;
			}
		}
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		cmd->act_len += urb->actual_length;
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		if (++cmd->current_sg < cmd->nsg) {
			ub_data_start(sc, cmd);
			return;
		}
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		ub_state_stat(sc, cmd);

	} else if (cmd->state == UB_CMDST_STAT) {
		if (urb->status == -EPIPE) {
			rc = ub_submit_clear_stall(sc, cmd, sc->last_pipe);
			if (rc != 0) {
				printk(KERN_NOTICE "%s: "
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				    "unable to submit clear (%d)\n",
				    sc->name, rc);
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				ub_state_done(sc, cmd, rc);
				return;
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			}
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			/*
			 * Having a stall when getting CSW is an error, so
			 * make sure uppper levels are not oblivious to it.
			 */
			cmd->error = -EIO;		/* A cheap trick... */

			cmd->state = UB_CMDST_CLRRS;
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			return;
		}
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		/* Catch everything, including -EOVERFLOW and other nasties. */
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		if (urb->status != 0)
			goto Bad_End;

		if (urb->actual_length == 0) {
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			ub_state_stat_counted(sc, cmd);
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			return;
		}

		/*
		 * Check the returned Bulk protocol status.
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		 * The status block has to be validated first.
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		 */

		bcs = &sc->work_bcs;
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		if (sc->signature == cpu_to_le32(0)) {
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			/*
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			 * This is the first reply, so do not perform the check.
			 * Instead, remember the signature the device uses
			 * for future checks. But do not allow a nul.
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			 */
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			sc->signature = bcs->Signature;
			if (sc->signature == cpu_to_le32(0)) {
				ub_state_stat_counted(sc, cmd);
				return;
			}
		} else {
			if (bcs->Signature != sc->signature) {
				ub_state_stat_counted(sc, cmd);
				return;
			}
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		}

		if (bcs->Tag != cmd->tag) {
			/*
			 * This usually happens when we disagree with the
			 * device's microcode about something. For instance,
			 * a few of them throw this after timeouts. They buffer
			 * commands and reply at commands we timed out before.
			 * Without flushing these replies we loop forever.
			 */
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			ub_state_stat_counted(sc, cmd);
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			return;
		}

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		len = le32_to_cpu(bcs->Residue);
		if (len != cmd->len - cmd->act_len) {
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			/*
			 * It is all right to transfer less, the caller has
			 * to check. But it's not all right if the device
			 * counts disagree with our counts.
			 */
			goto Bad_End;
		}

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		switch (bcs->Status) {
		case US_BULK_STAT_OK:
			break;
		case US_BULK_STAT_FAIL:
			ub_state_sense(sc, cmd);
			return;
		case US_BULK_STAT_PHASE:
			goto Bad_End;
		default:
			printk(KERN_INFO "%s: unknown CSW status 0x%x\n",
			    sc->name, bcs->Status);
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			ub_state_done(sc, cmd, -EINVAL);
			return;
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		}

		/* Not zeroing error to preserve a babble indicator */
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		if (cmd->error != 0) {
			ub_state_sense(sc, cmd);
			return;
		}
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		cmd->state = UB_CMDST_DONE;
		ub_cmdq_pop(sc);
		(*cmd->done)(sc, cmd);

	} else if (cmd->state == UB_CMDST_SENSE) {
		ub_state_done(sc, cmd, -EIO);

	} else {
		printk(KERN_WARNING "%s: "
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		    "wrong command state %d\n",
		    sc->name, cmd->state);
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		ub_state_done(sc, cmd, -EINVAL);
		return;
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	}
	return;

Bad_End: /* Little Excel is dead */
	ub_state_done(sc, cmd, -EIO);
}

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/*
 * Factorization helper for the command state machine:
 * Initiate a data segment transfer.
 */
static void ub_data_start(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
	struct scatterlist *sg = &cmd->sgv[cmd->current_sg];
	int pipe;
	int rc;

	UB_INIT_COMPLETION(sc->work_done);

	if (cmd->dir == UB_DIR_READ)
		pipe = sc->recv_bulk_pipe;
	else
		pipe = sc->send_bulk_pipe;
	sc->last_pipe = pipe;
	usb_fill_bulk_urb(&sc->work_urb, sc->dev, pipe,
	    page_address(sg->page) + sg->offset, sg->length,
	    ub_urb_complete, sc);
	sc->work_urb.actual_length = 0;
	sc->work_urb.error_count = 0;
	sc->work_urb.status = 0;

	if ((rc = usb_submit_urb(&sc->work_urb, GFP_ATOMIC)) != 0) {
		/* XXX Clear stalls */
		ub_complete(&sc->work_done);
		ub_state_done(sc, cmd, rc);
		return;
	}

	sc->work_timer.expires = jiffies + UB_DATA_TIMEOUT;
	add_timer(&sc->work_timer);

	cmd->state = UB_CMDST_DATA;
}

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/*
 * Factorization helper for the command state machine:
 * Finish the command.
 */
static void ub_state_done(struct ub_dev *sc, struct ub_scsi_cmd *cmd, int rc)
{

	cmd->error = rc;
	cmd->state = UB_CMDST_DONE;
	ub_cmdq_pop(sc);
	(*cmd->done)(sc, cmd);
}

/*
 * Factorization helper for the command state machine:
 * Submit a CSW read.
 */
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static int __ub_state_stat(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
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{
	int rc;

	UB_INIT_COMPLETION(sc->work_done);

	sc->last_pipe = sc->recv_bulk_pipe;
	usb_fill_bulk_urb(&sc->work_urb, sc->dev, sc->recv_bulk_pipe,
	    &sc->work_bcs, US_BULK_CS_WRAP_LEN, ub_urb_complete, sc);
	sc->work_urb.actual_length = 0;
	sc->work_urb.error_count = 0;
	sc->work_urb.status = 0;

	if ((rc = usb_submit_urb(&sc->work_urb, GFP_ATOMIC)) != 0) {
		/* XXX Clear stalls */
		ub_complete(&sc->work_done);
		ub_state_done(sc, cmd, rc);
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		return -1;
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	}

	sc->work_timer.expires = jiffies + UB_STAT_TIMEOUT;
	add_timer(&sc->work_timer);
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	return 0;
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}

/*
 * Factorization helper for the command state machine:
 * Submit a CSW read and go to STAT state.
 */
static void ub_state_stat(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
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	if (__ub_state_stat(sc, cmd) != 0)
		return;
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	cmd->stat_count = 0;
	cmd->state = UB_CMDST_STAT;
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}

/*
 * Factorization helper for the command state machine:
 * Submit a CSW read and go to STAT state with counter (along [C] path).
 */
static void ub_state_stat_counted(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{

	if (++cmd->stat_count >= 4) {
		ub_state_sense(sc, cmd);
		return;
	}

	if (__ub_state_stat(sc, cmd) != 0)
		return;

	cmd->state = UB_CMDST_STAT;
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}

/*
 * Factorization helper for the command state machine:
 * Submit a REQUEST SENSE and go to SENSE state.
 */
static void ub_state_sense(struct ub_dev *sc, struct ub_scsi_cmd *cmd)
{
	struct ub_scsi_cmd *scmd;
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	struct scatterlist *sg;