fc_exch.c

/*
 * Copyright(c) 2007 Intel Corporation. All rights reserved.
 * Copyright(c) 2008 Red Hat, Inc.  All rights reserved.
 * Copyright(c) 2008 Mike Christie
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Maintained at www.Open-FCoE.org
 */

/*
 * Fibre Channel exchange and sequence handling.
 */

#include <linux/timer.h>
#include <linux/gfp.h>
#include <linux/err.h>

#include <scsi/fc/fc_fc2.h>

#include <scsi/libfc.h>
#include <scsi/fc_encode.h>

/*
 * fc_exch_debug can be set in debugger or at compile time to get more logs.
 */
static int fc_exch_debug;

#define FC_DEBUG_EXCH(fmt...)			\
	do {					\
		if (fc_exch_debug)		\
			FC_DBG(fmt);		\
	} while (0)

static struct kmem_cache *fc_em_cachep;	/* cache for exchanges */

/*
 * Structure and function definitions for managing Fibre Channel Exchanges
 * and Sequences.
 *
 * The three primary structures used here are fc_exch_mgr, fc_exch, and fc_seq.
 *
 * fc_exch_mgr holds the exchange state for an N port
 *
 * fc_exch holds state for one exchange and links to its active sequence.
 *
 * fc_seq holds the state for an individual sequence.
 */

/*
 * Exchange manager.
 *
 * This structure is the center for creating exchanges and sequences.
 * It manages the allocation of exchange IDs.
 */
struct fc_exch_mgr {
	enum fc_class	class;		/* default class for sequences */
	spinlock_t	em_lock;	/* exchange manager lock,
					   must be taken before ex_lock */
	u16		last_xid;	/* last allocated exchange ID */
	u16		min_xid;	/* min exchange ID */
	u16		max_xid;	/* max exchange ID */
	u16		max_read;	/* max exchange ID for read */
	u16		last_read;	/* last xid allocated for read */
	u32	total_exches;		/* total allocated exchanges */
	struct list_head	ex_list;	/* allocated exchanges list */
	struct fc_lport	*lp;		/* fc device instance */
	mempool_t	*ep_pool;	/* reserve ep's */

	/*
	 * currently exchange mgr stats are updated but not used.
	 * either stats can be expose via sysfs or remove them
	 * all together if not used XXX
	 */
	struct {
		atomic_t no_free_exch;
		atomic_t no_free_exch_xid;
		atomic_t xid_not_found;
		atomic_t xid_busy;
		atomic_t seq_not_found;
		atomic_t non_bls_resp;
	} stats;
	struct fc_exch **exches;	/* for exch pointers indexed by xid */
};
#define	fc_seq_exch(sp) container_of(sp, struct fc_exch, seq)

static void fc_exch_rrq(struct fc_exch *);
static void fc_seq_ls_acc(struct fc_seq *);
static void fc_seq_ls_rjt(struct fc_seq *, enum fc_els_rjt_reason,
			  enum fc_els_rjt_explan);
static void fc_exch_els_rec(struct fc_seq *, struct fc_frame *);
static void fc_exch_els_rrq(struct fc_seq *, struct fc_frame *);
static struct fc_seq *fc_seq_start_next_locked(struct fc_seq *sp);

/*
 * Internal implementation notes.
 *
 * The exchange manager is one by default in libfc but LLD may choose
 * to have one per CPU. The sequence manager is one per exchange manager
 * and currently never separated.
 *
 * Section 9.8 in FC-FS-2 specifies:  "The SEQ_ID is a one-byte field
 * assigned by the Sequence Initiator that shall be unique for a specific
 * D_ID and S_ID pair while the Sequence is open."   Note that it isn't
 * qualified by exchange ID, which one might think it would be.
 * In practice this limits the number of open sequences and exchanges to 256
 * per session.	 For most targets we could treat this limit as per exchange.
 *
 * The exchange and its sequence are freed when the last sequence is received.
 * It's possible for the remote port to leave an exchange open without
 * sending any sequences.
 *
 * Notes on reference counts:
 *
 * Exchanges are reference counted and exchange gets freed when the reference
 * count becomes zero.
 *
 * Timeouts:
 * Sequences are timed out for E_D_TOV and R_A_TOV.
 *
 * Sequence event handling:
 *
 * The following events may occur on initiator sequences:
 *
 *	Send.
 *	    For now, the whole thing is sent.
 *	Receive ACK
 *	    This applies only to class F.
 *	    The sequence is marked complete.
 *	ULP completion.
 *	    The upper layer calls fc_exch_done() when done
 *	    with exchange and sequence tuple.
 *	RX-inferred completion.
 *	    When we receive the next sequence on the same exchange, we can
 *	    retire the previous sequence ID.  (XXX not implemented).
 *	Timeout.
 *	    R_A_TOV frees the sequence ID.  If we're waiting for ACK,
 *	    E_D_TOV causes abort and calls upper layer response handler
 *	    with FC_EX_TIMEOUT error.
 *	Receive RJT
 *	    XXX defer.
 *	Send ABTS
 *	    On timeout.
 *
 * The following events may occur on recipient sequences:
 *
 *	Receive
 *	    Allocate sequence for first frame received.
 *	    Hold during receive handler.
 *	    Release when final frame received.
 *	    Keep status of last N of these for the ELS RES command.  XXX TBD.
 *	Receive ABTS
 *	    Deallocate sequence
 *	Send RJT
 *	    Deallocate
 *
 * For now, we neglect conditions where only part of a sequence was
 * received or transmitted, or where out-of-order receipt is detected.
 */

/*
 * Locking notes:
 *
 * The EM code run in a per-CPU worker thread.
 *
 * To protect against concurrency between a worker thread code and timers,
 * sequence allocation and deallocation must be locked.
 *  - exchange refcnt can be done atomicly without locks.
 *  - sequence allocation must be locked by exch lock.
 *  - If the em_lock and ex_lock must be taken at the same time, then the
 *    em_lock must be taken before the ex_lock.
 */

/*
 * opcode names for debugging.
 */
static char *fc_exch_rctl_names[] = FC_RCTL_NAMES_INIT;

#define FC_TABLE_SIZE(x)   (sizeof(x) / sizeof(x[0]))

static inline const char *fc_exch_name_lookup(unsigned int op, char **table,
					      unsigned int max_index)
{
	const char *name = NULL;

	if (op < max_index)
		name = table[op];
	if (!name)
		name = "unknown";
	return name;
}

static const char *fc_exch_rctl_name(unsigned int op)
{
	return fc_exch_name_lookup(op, fc_exch_rctl_names,
				   FC_TABLE_SIZE(fc_exch_rctl_names));
}

/*
 * Hold an exchange - keep it from being freed.
 */
static void fc_exch_hold(struct fc_exch *ep)
{
	atomic_inc(&ep->ex_refcnt);
}

/*
 * setup fc hdr by initializing few more FC header fields and sof/eof.
 * Initialized fields by this func:
 *	- fh_ox_id, fh_rx_id, fh_seq_id, fh_seq_cnt
 *	- sof and eof
 */
static void fc_exch_setup_hdr(struct fc_exch *ep, struct fc_frame *fp,
			      u32 f_ctl)
{
	struct fc_frame_header *fh = fc_frame_header_get(fp);
	u16 fill;

	fr_sof(fp) = ep->class;
	if (ep->seq.cnt)
		fr_sof(fp) = fc_sof_normal(ep->class);

	if (f_ctl & FC_FC_END_SEQ) {
		fr_eof(fp) = FC_EOF_T;
		if (fc_sof_needs_ack(ep->class))
			fr_eof(fp) = FC_EOF_N;
		/*
		 * Form f_ctl.
		 * The number of fill bytes to make the length a 4-byte
		 * multiple is the low order 2-bits of the f_ctl.
		 * The fill itself will have been cleared by the frame
		 * allocation.
		 * After this, the length will be even, as expected by
		 * the transport.
		 */
		fill = fr_len(fp) & 3;
		if (fill) {
			fill = 4 - fill;
			/* TODO, this may be a problem with fragmented skb */
			skb_put(fp_skb(fp), fill);
			hton24(fh->fh_f_ctl, f_ctl | fill);
		}
	} else {
		WARN_ON(fr_len(fp) % 4 != 0);	/* no pad to non last frame */
		fr_eof(fp) = FC_EOF_N;
	}

	/*
	 * Initialize remainig fh fields
	 * from fc_fill_fc_hdr
	 */
	fh->fh_ox_id = htons(ep->oxid);
	fh->fh_rx_id = htons(ep->rxid);
	fh->fh_seq_id = ep->seq.id;
	fh->fh_seq_cnt = htons(ep->seq.cnt);
}


/*
 * Release a reference to an exchange.
 * If the refcnt goes to zero and the exchange is complete, it is freed.
 */
static void fc_exch_release(struct fc_exch *ep)
{
	struct fc_exch_mgr *mp;

	if (atomic_dec_and_test(&ep->ex_refcnt)) {
		mp = ep->em;
		if (ep->destructor)
			ep->destructor(&ep->seq, ep->arg);
		if (ep->lp->tt.exch_put)
			ep->lp->tt.exch_put(ep->lp, mp, ep->xid);
		WARN_ON(!ep->esb_stat & ESB_ST_COMPLETE);
		mempool_free(ep, mp->ep_pool);
	}
}

static int fc_exch_done_locked(struct fc_exch *ep)
{
	int rc = 1;

	/*
	 * We must check for completion in case there are two threads
	 * tyring to complete this. But the rrq code will reuse the
	 * ep, and in that case we only clear the resp and set it as
	 * complete, so it can be reused by the timer to send the rrq.
	 */
	ep->resp = NULL;
	if (ep->state & FC_EX_DONE)
		return rc;
	ep->esb_stat |= ESB_ST_COMPLETE;

	if (!(ep->esb_stat & ESB_ST_REC_QUAL)) {
		ep->state |= FC_EX_DONE;
		if (cancel_delayed_work(&ep->timeout_work))
			atomic_dec(&ep->ex_refcnt); /* drop hold for timer */
		rc = 0;
	}
	return rc;
}

static void fc_exch_mgr_delete_ep(struct fc_exch *ep)
{
	struct fc_exch_mgr *mp;

	mp = ep->em;
	spin_lock_bh(&mp->em_lock);
	WARN_ON(mp->total_exches <= 0);
	mp->total_exches--;
	mp->exches[ep->xid - mp->min_xid] = NULL;
	list_del(&ep->ex_list);
	spin_unlock_bh(&mp->em_lock);
	fc_exch_release(ep);	/* drop hold for exch in mp */
}

/*
 * Internal version of fc_exch_timer_set - used with lock held.
 */
static inline void fc_exch_timer_set_locked(struct fc_exch *ep,
					    unsigned int timer_msec)
{
	if (ep->state & (FC_EX_RST_CLEANUP | FC_EX_DONE))
		return;

	FC_DEBUG_EXCH("Exchange (%4x) timed out, notifying the upper layer\n",
		      ep->xid);
	if (schedule_delayed_work(&ep->timeout_work,
				  msecs_to_jiffies(timer_msec)))
		fc_exch_hold(ep);		/* hold for timer */
}

/*
 * Set timer for an exchange.
 * The time is a minimum delay in milliseconds until the timer fires.
 * Used for upper level protocols to time out the exchange.
 * The timer is cancelled when it fires or when the exchange completes.
 * Returns non-zero if a timer couldn't be allocated.
 */
static void fc_exch_timer_set(struct fc_exch *ep, unsigned int timer_msec)
{
	spin_lock_bh(&ep->ex_lock);
	fc_exch_timer_set_locked(ep, timer_msec);
	spin_unlock_bh(&ep->ex_lock);
}

int fc_seq_exch_abort(const struct fc_seq *req_sp, unsigned int timer_msec)
{
	struct fc_seq *sp;
	struct fc_exch *ep;
	struct fc_frame *fp;
	int error;

	ep = fc_seq_exch(req_sp);

	spin_lock_bh(&ep->ex_lock);
	if (ep->esb_stat & (ESB_ST_COMPLETE | ESB_ST_ABNORMAL) ||
	    ep->state & (FC_EX_DONE | FC_EX_RST_CLEANUP)) {
		spin_unlock_bh(&ep->ex_lock);
		return -ENXIO;
	}

	/*
	 * Send the abort on a new sequence if possible.
	 */
	sp = fc_seq_start_next_locked(&ep->seq);
	if (!sp) {
		spin_unlock_bh(&ep->ex_lock);
		return -ENOMEM;
	}

	ep->esb_stat |= ESB_ST_SEQ_INIT | ESB_ST_ABNORMAL;
	if (timer_msec)
		fc_exch_timer_set_locked(ep, timer_msec);
	spin_unlock_bh(&ep->ex_lock);

	/*
	 * If not logged into the fabric, don't send ABTS but leave
	 * sequence active until next timeout.
	 */
	if (!ep->sid)
		return 0;

	/*
	 * Send an abort for the sequence that timed out.
	 */
	fp = fc_frame_alloc(ep->lp, 0);
	if (fp) {
		fc_fill_fc_hdr(fp, FC_RCTL_BA_ABTS, ep->did, ep->sid,
			       FC_TYPE_BLS, FC_FC_END_SEQ | FC_FC_SEQ_INIT, 0);
		error = fc_seq_send(ep->lp, sp, fp);
	} else
		error = -ENOBUFS;
	return error;
}
EXPORT_SYMBOL(fc_seq_exch_abort);

/*
 * Exchange timeout - handle exchange timer expiration.
 * The timer will have been cancelled before this is called.
 */
static void fc_exch_timeout(struct work_struct *work)
{
	struct fc_exch *ep = container_of(work, struct fc_exch,
					  timeout_work.work);
	struct fc_seq *sp = &ep->seq;
	void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
	void *arg;
	u32 e_stat;
	int rc = 1;

	spin_lock_bh(&ep->ex_lock);
	if (ep->state & (FC_EX_RST_CLEANUP | FC_EX_DONE))
		goto unlock;

	e_stat = ep->esb_stat;
	if (e_stat & ESB_ST_COMPLETE) {
		ep->esb_stat = e_stat & ~ESB_ST_REC_QUAL;
		if (e_stat & ESB_ST_REC_QUAL)
			fc_exch_rrq(ep);
		spin_unlock_bh(&ep->ex_lock);
		goto done;
	} else {
		resp = ep->resp;
		arg = ep->arg;
		ep->resp = NULL;
		if (e_stat & ESB_ST_ABNORMAL)
			rc = fc_exch_done_locked(ep);
		spin_unlock_bh(&ep->ex_lock);
		if (!rc)
			fc_exch_mgr_delete_ep(ep);
		if (resp)
			resp(sp, ERR_PTR(-FC_EX_TIMEOUT), arg);
		fc_seq_exch_abort(sp, 2 * ep->r_a_tov);
		goto done;
	}
unlock:
	spin_unlock_bh(&ep->ex_lock);
done:
	/*
	 * This release matches the hold taken when the timer was set.
	 */
	fc_exch_release(ep);
}

/*
 * Allocate a sequence.
 *
 * We don't support multiple originated sequences on the same exchange.
 * By implication, any previously originated sequence on this exchange
 * is complete, and we reallocate the same sequence.
 */
static struct fc_seq *fc_seq_alloc(struct fc_exch *ep, u8 seq_id)
{
	struct fc_seq *sp;

	sp = &ep->seq;
	sp->ssb_stat = 0;
	sp->cnt = 0;
	sp->id = seq_id;
	return sp;
}

/*
 * fc_em_alloc_xid - returns an xid based on request type
 * @lp : ptr to associated lport
 * @fp : ptr to the assocated frame
 *
 * check the associated fc_fsp_pkt to get scsi command type and
 * command direction to decide from which range this exch id
 * will be allocated from.
 *
 * Returns : 0 or an valid xid
 */
static u16 fc_em_alloc_xid(struct fc_exch_mgr *mp, const struct fc_frame *fp)
{
	u16 xid, min, max;
	u16 *plast;
	struct fc_exch *ep = NULL;

	if (mp->max_read) {
		if (fc_frame_is_read(fp)) {
			min = mp->min_xid;
			max = mp->max_read;
			plast = &mp->last_read;
		} else {
			min = mp->max_read + 1;
			max = mp->max_xid;
			plast = &mp->last_xid;
		}
	} else {
		min = mp->min_xid;
		max = mp->max_xid;
		plast = &mp->last_xid;
	}
	xid = *plast;
	do {
		xid = (xid == max) ? min : xid + 1;
		ep = mp->exches[xid - mp->min_xid];
	} while ((ep != NULL) && (xid != *plast));

	if (unlikely(ep))
		xid = 0;
	else
		*plast = xid;

	return xid;
}

/*
 * fc_exch_alloc - allocate an exchange.
 * @mp : ptr to the exchange manager
 * @xid: input xid
 *
 * if xid is supplied zero then assign next free exchange ID
 * from exchange manager, otherwise use supplied xid.
 * Returns with exch lock held.
 */
struct fc_exch *fc_exch_alloc(struct fc_exch_mgr *mp,
			      struct fc_frame *fp, u16 xid)
{
	struct fc_exch *ep;

	/* allocate memory for exchange */
	ep = mempool_alloc(mp->ep_pool, GFP_ATOMIC);
	if (!ep) {
		atomic_inc(&mp->stats.no_free_exch);
		goto out;
	}
	memset(ep, 0, sizeof(*ep));

	spin_lock_bh(&mp->em_lock);
	/* alloc xid if input xid 0 */
	if (!xid) {
		/* alloc a new xid */
		xid = fc_em_alloc_xid(mp, fp);
		if (!xid) {
			printk(KERN_ERR "fc_em_alloc_xid() failed\n");
			goto err;
		}
	}

	fc_exch_hold(ep);	/* hold for exch in mp */
	spin_lock_init(&ep->ex_lock);
	/*
	 * Hold exch lock for caller to prevent fc_exch_reset()
	 * from releasing exch	while fc_exch_alloc() caller is
	 * still working on exch.
	 */
	spin_lock_bh(&ep->ex_lock);

	mp->exches[xid - mp->min_xid] = ep;
	list_add_tail(&ep->ex_list, &mp->ex_list);
	fc_seq_alloc(ep, ep->seq_id++);
	mp->total_exches++;
	spin_unlock_bh(&mp->em_lock);

	/*
	 *  update exchange
	 */
	ep->oxid = ep->xid = xid;
	ep->em = mp;
	ep->lp = mp->lp;
	ep->f_ctl = FC_FC_FIRST_SEQ;	/* next seq is first seq */
	ep->rxid = FC_XID_UNKNOWN;
	ep->class = mp->class;
	INIT_DELAYED_WORK(&ep->timeout_work, fc_exch_timeout);
out:
	return ep;
err:
	spin_unlock_bh(&mp->em_lock);
	atomic_inc(&mp->stats.no_free_exch_xid);
	mempool_free(ep, mp->ep_pool);
	return NULL;
}
EXPORT_SYMBOL(fc_exch_alloc);

/*
 * Lookup and hold an exchange.
 */
static struct fc_exch *fc_exch_find(struct fc_exch_mgr *mp, u16 xid)
{
	struct fc_exch *ep = NULL;

	if ((xid >= mp->min_xid) && (xid <= mp->max_xid)) {
		spin_lock_bh(&mp->em_lock);
		ep = mp->exches[xid - mp->min_xid];
		if (ep) {
			fc_exch_hold(ep);
			WARN_ON(ep->xid != xid);
		}
		spin_unlock_bh(&mp->em_lock);
	}
	return ep;
}

void fc_exch_done(struct fc_seq *sp)
{
	struct fc_exch *ep = fc_seq_exch(sp);
	int rc;

	spin_lock_bh(&ep->ex_lock);
	rc = fc_exch_done_locked(ep);
	spin_unlock_bh(&ep->ex_lock);
	if (!rc)
		fc_exch_mgr_delete_ep(ep);
}
EXPORT_SYMBOL(fc_exch_done);

/*
 * Allocate a new exchange as responder.
 * Sets the responder ID in the frame header.
 */
static struct fc_exch *fc_exch_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
	struct fc_exch *ep;
	struct fc_frame_header *fh;
	u16 rxid;

	ep = mp->lp->tt.exch_get(mp->lp, fp);
	if (ep) {
		ep->class = fc_frame_class(fp);

		/*
		 * Set EX_CTX indicating we're responding on this exchange.
		 */
		ep->f_ctl |= FC_FC_EX_CTX;	/* we're responding */
		ep->f_ctl &= ~FC_FC_FIRST_SEQ;	/* not new */
		fh = fc_frame_header_get(fp);
		ep->sid = ntoh24(fh->fh_d_id);
		ep->did = ntoh24(fh->fh_s_id);
		ep->oid = ep->did;

		/*
		 * Allocated exchange has placed the XID in the
		 * originator field. Move it to the responder field,
		 * and set the originator XID from the frame.
		 */
		ep->rxid = ep->xid;
		ep->oxid = ntohs(fh->fh_ox_id);
		ep->esb_stat |= ESB_ST_RESP | ESB_ST_SEQ_INIT;
		if ((ntoh24(fh->fh_f_ctl) & FC_FC_SEQ_INIT) == 0)
			ep->esb_stat &= ~ESB_ST_SEQ_INIT;

		/*
		 * Set the responder ID in the frame header.
		 * The old one should've been 0xffff.
		 * If it isn't, don't assign one.
		 * Incoming basic link service frames may specify
		 * a referenced RX_ID.
		 */
		if (fh->fh_type != FC_TYPE_BLS) {
			rxid = ntohs(fh->fh_rx_id);
			WARN_ON(rxid != FC_XID_UNKNOWN);
			fh->fh_rx_id = htons(ep->rxid);
		}
		fc_exch_hold(ep);	/* hold for caller */
		spin_unlock_bh(&ep->ex_lock);	/* lock from exch_get */
	}
	return ep;
}

/*
 * Find a sequence for receive where the other end is originating the sequence.
 * If fc_pf_rjt_reason is FC_RJT_NONE then this function will have a hold
 * on the ep that should be released by the caller.
 */
static enum fc_pf_rjt_reason
fc_seq_lookup_recip(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
	struct fc_frame_header *fh = fc_frame_header_get(fp);
	struct fc_exch *ep = NULL;
	struct fc_seq *sp = NULL;
	enum fc_pf_rjt_reason reject = FC_RJT_NONE;
	u32 f_ctl;
	u16 xid;

	f_ctl = ntoh24(fh->fh_f_ctl);
	WARN_ON((f_ctl & FC_FC_SEQ_CTX) != 0);

	/*
	 * Lookup or create the exchange if we will be creating the sequence.
	 */
	if (f_ctl & FC_FC_EX_CTX) {
		xid = ntohs(fh->fh_ox_id);	/* we originated exch */
		ep = fc_exch_find(mp, xid);
		if (!ep) {
			atomic_inc(&mp->stats.xid_not_found);
			reject = FC_RJT_OX_ID;
			goto out;
		}
		if (ep->rxid == FC_XID_UNKNOWN)
			ep->rxid = ntohs(fh->fh_rx_id);
		else if (ep->rxid != ntohs(fh->fh_rx_id)) {
			reject = FC_RJT_OX_ID;
			goto rel;
		}
	} else {
		xid = ntohs(fh->fh_rx_id);	/* we are the responder */

		/*
		 * Special case for MDS issuing an ELS TEST with a
		 * bad rxid of 0.
		 * XXX take this out once we do the proper reject.
		 */
		if (xid == 0 && fh->fh_r_ctl == FC_RCTL_ELS_REQ &&
		    fc_frame_payload_op(fp) == ELS_TEST) {
			fh->fh_rx_id = htons(FC_XID_UNKNOWN);
			xid = FC_XID_UNKNOWN;
		}

		/*
		 * new sequence - find the exchange
		 */
		ep = fc_exch_find(mp, xid);
		if ((f_ctl & FC_FC_FIRST_SEQ) && fc_sof_is_init(fr_sof(fp))) {
			if (ep) {
				atomic_inc(&mp->stats.xid_busy);
				reject = FC_RJT_RX_ID;
				goto rel;
			}
			ep = fc_exch_resp(mp, fp);
			if (!ep) {
				reject = FC_RJT_EXCH_EST;	/* XXX */
				goto out;
			}
			xid = ep->xid;	/* get our XID */
		} else if (!ep) {
			atomic_inc(&mp->stats.xid_not_found);
			reject = FC_RJT_RX_ID;	/* XID not found */
			goto out;
		}
	}

	/*
	 * At this point, we have the exchange held.
	 * Find or create the sequence.
	 */
	if (fc_sof_is_init(fr_sof(fp))) {
		sp = fc_seq_start_next(&ep->seq);
		if (!sp) {
			reject = FC_RJT_SEQ_XS;	/* exchange shortage */
			goto rel;
		}
		sp->id = fh->fh_seq_id;
		sp->ssb_stat |= SSB_ST_RESP;
	} else {
		sp = &ep->seq;
		if (sp->id != fh->fh_seq_id) {
			atomic_inc(&mp->stats.seq_not_found);
			reject = FC_RJT_SEQ_ID;	/* sequence/exch should exist */
			goto rel;
		}
	}
	WARN_ON(ep != fc_seq_exch(sp));

	if (f_ctl & FC_FC_SEQ_INIT)
		ep->esb_stat |= ESB_ST_SEQ_INIT;

	fr_seq(fp) = sp;
out:
	return reject;
rel:
	fc_exch_done(&ep->seq);
	fc_exch_release(ep);	/* hold from fc_exch_find/fc_exch_resp */
	return reject;
}

/*
 * Find the sequence for a frame being received.
 * We originated the sequence, so it should be found.
 * We may or may not have originated the exchange.
 * Does not hold the sequence for the caller.
 */
static struct fc_seq *fc_seq_lookup_orig(struct fc_exch_mgr *mp,
					 struct fc_frame *fp)
{
	struct fc_frame_header *fh = fc_frame_header_get(fp);
	struct fc_exch *ep;
	struct fc_seq *sp = NULL;
	u32 f_ctl;
	u16 xid;

	f_ctl = ntoh24(fh->fh_f_ctl);
	WARN_ON((f_ctl & FC_FC_SEQ_CTX) != FC_FC_SEQ_CTX);
	xid = ntohs((f_ctl & FC_FC_EX_CTX) ? fh->fh_ox_id : fh->fh_rx_id);
	ep = fc_exch_find(mp, xid);
	if (!ep)
		return NULL;
	if (ep->seq.id == fh->fh_seq_id) {
		/*
		 * Save the RX_ID if we didn't previously know it.
		 */
		sp = &ep->seq;
		if ((f_ctl & FC_FC_EX_CTX) != 0 &&
		    ep->rxid == FC_XID_UNKNOWN) {
			ep->rxid = ntohs(fh->fh_rx_id);
		}
	}
	fc_exch_release(ep);
	return sp;
}

/*
 * Set addresses for an exchange.
 * Note this must be done before the first sequence of the exchange is sent.
 */
static void fc_exch_set_addr(struct fc_exch *ep,
			     u32 orig_id, u32 resp_id)
{
	ep->oid = orig_id;
	if (ep->esb_stat & ESB_ST_RESP) {
		ep->sid = resp_id;
		ep->did = orig_id;
	} else {
		ep->sid = orig_id;
		ep->did = resp_id;
	}
}

static struct fc_seq *fc_seq_start_next_locked(struct fc_seq *sp)
{
	struct fc_exch *ep = fc_seq_exch(sp);

	sp = fc_seq_alloc(ep, ep->seq_id++);
	FC_DEBUG_EXCH("exch %4x f_ctl %6x seq %2x\n",
		      ep->xid, ep->f_ctl, sp->id);
	return sp;
}
/*
 * Allocate a new sequence on the same exchange as the supplied sequence.
 * This will never return NULL.
 */
struct fc_seq *fc_seq_start_next(struct fc_seq *sp)
{
	struct fc_exch *ep = fc_seq_exch(sp);

	spin_lock_bh(&ep->ex_lock);
	WARN_ON((ep->esb_stat & ESB_ST_COMPLETE) != 0);
	sp = fc_seq_start_next_locked(sp);
	spin_unlock_bh(&ep->ex_lock);

	return sp;
}
EXPORT_SYMBOL(fc_seq_start_next);

int fc_seq_send(struct fc_lport *lp, struct fc_seq *sp, struct fc_frame *fp)
{
	struct fc_exch *ep;
	struct fc_frame_header *fh = fc_frame_header_get(fp);
	int error;
	u32	f_ctl;

	ep = fc_seq_exch(sp);
	WARN_ON((ep->esb_stat & ESB_ST_SEQ_INIT) != ESB_ST_SEQ_INIT);

	f_ctl = ntoh24(fh->fh_f_ctl);
	fc_exch_setup_hdr(ep, fp, f_ctl);

	/*
	 * update sequence count if this frame is carrying
	 * multiple FC frames when sequence offload is enabled
	 * by LLD.
	 */
	if (fr_max_payload(fp))
		sp->cnt += DIV_ROUND_UP((fr_len(fp) - sizeof(*fh)),
					fr_max_payload(fp));
	else
		sp->cnt++;

	/*
	 * Send the frame.
	 */
	error = lp->tt.frame_send(lp, fp);

	/*
	 * Update the exchange and sequence flags,
	 * assuming all frames for the sequence have been sent.
	 * We can only be called to send once for each sequence.
	 */
	spin_lock_bh(&ep->ex_lock);
	ep->f_ctl = f_ctl & ~FC_FC_FIRST_SEQ;	/* not first seq */
	if (f_ctl & (FC_FC_END_SEQ | FC_FC_SEQ_INIT))
		ep->esb_stat &= ~ESB_ST_SEQ_INIT;
	spin_unlock_bh(&ep->ex_lock);
	return error;
}
EXPORT_SYMBOL(fc_seq_send);

void fc_seq_els_rsp_send(struct fc_seq *sp, enum fc_els_cmd els_cmd,
			 struct fc_seq_els_data *els_data)
{
	switch (els_cmd) {
	case ELS_LS_RJT:
		fc_seq_ls_rjt(sp, els_data->reason, els_data->explan);
		break;
	case ELS_LS_ACC:
		fc_seq_ls_acc(sp);
		break;
	case ELS_RRQ:
		fc_exch_els_rrq(sp, els_data->fp);
		break;
	case ELS_REC:
		fc_exch_els_rec(sp, els_data->fp);
		break;
	default:
		FC_DBG("Invalid ELS CMD:%x\n", els_cmd);
	}
}
EXPORT_SYMBOL(fc_seq_els_rsp_send);

/*
 * Send a sequence, which is also the last sequence in the exchange.
 */
static void fc_seq_send_last(struct fc_seq *sp, struct fc_frame *fp,
			     enum fc_rctl rctl, enum fc_fh_type fh_type)
{
	u32 f_ctl;
	struct fc_exch *ep = fc_seq_exch(sp);

	f_ctl = FC_FC_LAST_SEQ | FC_FC_END_SEQ | FC_FC_SEQ_INIT;
	f_ctl |= ep->f_ctl;
	fc_fill_fc_hdr(fp, rctl, ep->did, ep->sid, fh_type, f_ctl, 0);
	fc_seq_send(ep->lp, sp, fp);
}

/*
 * Send ACK_1 (or equiv.) indicating we received something.
 * The frame we're acking is supplied.
 */
static void fc_seq_send_ack(struct fc_seq *sp, const struct fc_frame *rx_fp)
{
	struct fc_frame *fp;
	struct fc_frame_header *rx_fh;
	struct fc_frame_header *fh;
	struct fc_exch *ep = fc_seq_exch(sp);
	struct fc_lport *lp = ep->lp;
	unsigned int f_ctl;

	/*
	 * Don't send ACKs for class 3.
	 */
	if (fc_sof_needs_ack(fr_sof(rx_fp))) {
		fp = fc_frame_alloc(lp, 0);
		if (!fp)
			return;

		fh = fc_frame_header_get(fp);
		fh->fh_r_ctl = FC_RCTL_ACK_1;
		fh->fh_type = FC_TYPE_BLS;

		/*
		 * Form f_ctl by inverting EX_CTX and SEQ_CTX (bits 23, 22).
		 * Echo FIRST_SEQ, LAST_SEQ, END_SEQ, END_CONN, SEQ_INIT.
		 * Bits 9-8 are meaningful (retransmitted or unidirectional).
		 * Last ACK uses bits 7-6 (continue sequence),
		 * bits 5-4 are meaningful (what kind of ACK to use).
		 */
		rx_fh = fc_frame_header_get(rx_fp);
		f_ctl = ntoh24(rx_fh->fh_f_ctl);
		f_ctl &= FC_FC_EX_CTX | FC_FC_SEQ_CTX |
			FC_FC_FIRST_SEQ | FC_FC_LAST_SEQ |
			FC_FC_END_SEQ | FC_FC_END_CONN | FC_FC_SEQ_INIT |
			FC_FC_RETX_SEQ | FC_FC_UNI_TX;
		f_ctl ^= FC_FC_EX_CTX | FC_FC_SEQ_CTX;
		hton24(fh->fh_f_ctl, f_ctl);

		fc_exch_setup_hdr(ep, fp, f_ctl);
		fh->fh_seq_id = rx_fh->fh_seq_id;
		fh->fh_seq_cnt = rx_fh->fh_seq_cnt;
		fh->fh_parm_offset = htonl(1);	/* ack single frame */

		fr_sof(fp) = fr_sof(rx_fp);
		if (f_ctl & FC_FC_END_SEQ)
			fr_eof(fp) = FC_EOF_T;
		else
			fr_eof(fp) = FC_EOF_N;

		(void) lp->tt.frame_send(lp, fp);
	}
}

/*
 * Send BLS Reject.
 * This is for rejecting BA_ABTS only.
 */
static void
fc_exch_send_ba_rjt(struct fc_frame *rx_fp, enum fc_ba_rjt_reason reason,
		    enum fc_ba_rjt_explan explan)
{
	struct fc_frame *fp;
	struct fc_frame_header *rx_fh;
	struct fc_frame_header *fh;
	struct fc_ba_rjt *rp;
	struct fc_lport *lp;
	unsigned int f_ctl;

	lp = fr_dev(rx_fp);
	fp = fc_frame_alloc(lp, sizeof(*rp));
	if (!fp)
		return;
	fh = fc_frame_header_get(fp);
	rx_fh = fc_frame_header_get(rx_fp);

	memset(fh, 0, sizeof(*fh) + sizeof(*rp));

	rp = fc_frame_payload_get(fp, sizeof(*rp));
	rp->br_reason = reason;
	rp->br_explan = explan;

	/*
	 * seq_id, cs_ctl, df_ctl and param/offset are zero.
	 */
	memcpy(fh->fh_s_id, rx_fh->fh_d_id, 3);
	memcpy(fh->fh_d_id, rx_fh->fh_s_id, 3);
	fh->fh_ox_id = rx_fh->fh_rx_id;
	fh->fh_rx_id = rx_fh->fh_ox_id;
	fh->fh_seq_cnt = rx_fh->fh_seq_cnt;
	fh->fh_r_ctl = FC_RCTL_BA_RJT;
	fh->fh_type = FC_TYPE_BLS;

	/*
	 * Form f_ctl by inverting EX_CTX and SEQ_CTX (bits 23, 22).
	 * Echo FIRST_SEQ, LAST_SEQ, END_SEQ, END_CONN, SEQ_INIT.
	 * Bits 9-8 are meaningful (retransmitted or unidirectional).
	 * Last ACK uses bits 7-6 (continue sequence),
	 * bits 5-4 are meaningful (what kind of ACK to use).
	 * Always set LAST_SEQ, END_SEQ.
	 */
	f_ctl = ntoh24(rx_fh->fh_f_ctl);
	f_ctl &= FC_FC_EX_CTX | FC_FC_SEQ_CTX |
		FC_FC_END_CONN | FC_FC_SEQ_INIT |
		FC_FC_RETX_SEQ | FC_FC_UNI_TX;
	f_ctl ^= FC_FC_EX_CTX | FC_FC_SEQ_CTX;
	f_ctl |= FC_FC_LAST_SEQ | FC_FC_END_SEQ;
	f_ctl &= ~FC_FC_FIRST_SEQ;
	hton24(fh->fh_f_ctl, f_ctl);

	fr_sof(fp) = fc_sof_class(fr_sof(rx_fp));
	fr_eof(fp) = FC_EOF_T;
	if (fc_sof_needs_ack(fr_sof(fp)))
		fr_eof(fp) = FC_EOF_N;

	(void) lp->tt.frame_send(lp, fp);
}

/*
 * Handle an incoming ABTS.  This would be for target mode usually,
 * but could be due to lost FCP transfer ready, confirm or RRQ.
 * We always handle this as an exchange abort, ignoring the parameter.
 */
static void fc_exch_recv_abts(struct fc_exch *ep, struct fc_frame *rx_fp)
{
	struct fc_frame *fp;
	struct fc_ba_acc *ap;
	struct fc_frame_header *fh;
	struct fc_seq *sp;

	if (!ep)
		goto reject;
	spin_lock_bh(&ep->ex_lock);
	if (ep->esb_stat & ESB_ST_COMPLETE) {
		spin_unlock_bh(&ep->ex_lock);
		goto reject;
	}
	if (!(ep->esb_stat & ESB_ST_REC_QUAL))
		fc_exch_hold(ep);		/* hold for REC_QUAL */
	ep->esb_stat |= ESB_ST_ABNORMAL | ESB_ST_REC_QUAL;
	fc_exch_timer_set_locked(ep, ep->r_a_tov);

	fp = fc_frame_alloc(ep->lp, sizeof(*ap));
	if (!fp) {
		spin_unlock_bh(&ep->ex_lock);
		goto free;
	}
	fh = fc_frame_header_get(fp);
	ap = fc_frame_payload_get(fp, sizeof(*ap));
	memset(ap, 0, sizeof(*ap));
	sp = &ep->seq;
	ap->ba_high_seq_cnt = htons(0xffff);
	if (sp->ssb_stat & SSB_ST_RESP) {
		ap->ba_seq_id = sp->id;
		ap->ba_seq_id_val = FC_BA_SEQ_ID_VAL;
		ap->ba_high_seq_cnt = fh->fh_seq_cnt;
		ap->ba_low_seq_cnt = htons(sp->cnt);
	}
	sp = fc_seq_start_next_locked(sp);
	spin_unlock_bh(&ep->ex_lock);
	fc_seq_send_last(sp, fp, FC_RCTL_BA_ACC, FC_TYPE_BLS);
	fc_frame_free(rx_fp);
	return;

reject:
	fc_exch_send_ba_rjt(rx_fp, FC_BA_RJT_UNABLE, FC_BA_RJT_INV_XID);
free:
	fc_frame_free(rx_fp);
}

/*
 * Handle receive where the other end is originating the sequence.
 */
static void fc_exch_recv_req(struct fc_lport *lp, struct fc_exch_mgr *mp,
			     struct fc_frame *fp)
{
	struct fc_frame_header *fh = fc_frame_header_get(fp);
	struct fc_seq *sp = NULL;
	struct fc_exch *ep = NULL;
	enum fc_sof sof;
	enum fc_eof eof;
	u32 f_ctl;
	enum fc_pf_rjt_reason reject;

	fr_seq(fp) = NULL;
	reject = fc_seq_lookup_recip(mp, fp);
	if (reject == FC_RJT_NONE) {
		sp = fr_seq(fp);	/* sequence will be held */
		ep = fc_seq_exch(sp);
		sof = fr_sof(fp);
		eof = fr_eof(fp);
		f_ctl = ntoh24(fh->fh_f_ctl);
		fc_seq_send_ack(sp, fp);

		/*
		 * Call the receive function.
		 *
		 * The receive function may allocate a new sequence
		 * over the old one, so we shouldn't change the
		 * sequence after this.
		 *
		 * The frame will be freed by the receive function.
		 * If new exch resp handler is valid then call that
		 * first.
		 */
		if (ep->resp)
			ep->resp(sp, fp, ep->arg);
		else
			lp->tt.lport_recv(lp, sp, fp);
		fc_exch_release(ep);	/* release from lookup */
	} else {
		FC_DEBUG_EXCH("exch/seq lookup failed: reject %x\n", reject);
		fc_frame_free(fp);
	}
}

/*
 * Handle receive where the other end is originating the sequence in
 * response to our exchange.
 */
static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
	struct fc_frame_header *fh = fc_frame_header_get(fp);
	struct fc_seq *sp;
	struct fc_exch *ep;
	enum fc_sof sof;
	u32 f_ctl;
	void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
	void *ex_resp_arg;
	int rc;

	ep = fc_exch_find(mp, ntohs(fh->fh_ox_id));
	if (!ep) {
		atomic_inc(&mp->stats.xid_not_found);
		goto out;
	}
	if (ep->rxid == FC_XID_UNKNOWN)
		ep->rxid = ntohs(fh->fh_rx_id);
	if (ep->sid != 0 && ep->sid != ntoh24(fh->fh_d_id)) {
		atomic_inc(&mp->stats.xid_not_found);
		goto rel;
	}
	if (ep->did != ntoh24(fh->fh_s_id) &&
	    ep->did != FC_FID_FLOGI) {
		atomic_inc(&mp->stats.xid_not_found);
		goto rel;
	}
	sof = fr_sof(fp);
	if (fc_sof_is_init(sof)) {
		sp = fc_seq_start_next(&ep->seq);
		sp->id = fh->fh_seq_id;
		sp->ssb_stat |= SSB_ST_RESP;
	} else {
		sp = &ep->seq;
		if (sp->id != fh->fh_seq_id) {
			atomic_inc(&mp->stats.seq_not_found);
			goto rel;
		}
	}
	f_ctl = ntoh24(fh->fh_f_ctl);
	fr_seq(fp) = sp;
	if (f_ctl & FC_FC_SEQ_INIT)
		ep->esb_stat |= ESB_ST_SEQ_INIT;

	if (fc_sof_needs_ack(sof))
		fc_seq_send_ack(sp, fp);
	resp = ep->resp;
	ex_resp_arg = ep->arg;

	if (fh->fh_type != FC_TYPE_FCP && fr_eof(fp) == FC_EOF_T &&
	    (f_ctl & (FC_FC_LAST_SEQ | FC_FC_END_SEQ)) ==
	    (FC_FC_LAST_SEQ | FC_FC_END_SEQ)) {
		spin_lock_bh(&ep->ex_lock);
		rc = fc_exch_done_locked(ep);
		WARN_ON(fc_seq_exch(sp) != ep);
		spin_unlock_bh(&ep->ex_lock);
		if (!rc)
			fc_exch_mgr_delete_ep(ep);
	}

	/*
	 * Call the receive function.
	 * The sequence is held (has a refcnt) for us,
	 * but not for the receive function.
	 *
	 * The receive function may allocate a new sequence
	 * over the old one, so we shouldn't change the
	 * sequence after this.
	 *
	 * The frame will be freed by the receive function.
	 * If new exch resp handler is valid then call that
	 * first.
	 */
	if (resp)
		resp(sp, fp, ex_resp_arg);
	else
		fc_frame_free(fp);
	fc_exch_release(ep);
	return;
rel:
	fc_exch_release(ep);
out:
	fc_frame_free(fp);
}

/*
 * Handle receive for a sequence where other end is responding to our sequence.
 */
static void fc_exch_recv_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
	struct fc_seq *sp;

	sp = fc_seq_lookup_orig(mp, fp);	/* doesn't hold sequence */
	if (!sp) {
		atomic_inc(&mp->stats.xid_not_found);
		FC_DEBUG_EXCH("seq lookup failed\n");
	} else {
		atomic_inc(&mp->stats.non_bls_resp);
		FC_DEBUG_EXCH("non-BLS response to sequence");
	}
	fc_frame_free(fp);
}

/*
 * Handle the response to an ABTS for exchange or sequence.
 * This can be BA_ACC or BA_RJT.
 */
static void fc_exch_abts_resp(struct fc_exch *ep, struct fc_frame *fp)
{
	void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
	void *ex_resp_arg;
	struct fc_frame_header *fh;
	struct fc_ba_acc *ap;
	struct fc_seq *sp;
	u16 low;
	u16 high;
	int rc = 1, has_rec = 0;

	fh = fc_frame_header_get(fp);
	FC_DEBUG_EXCH("exch: BLS rctl %x - %s\n",
		      fh->fh_r_ctl, fc_exch_rctl_name(fh->fh_r_ctl));

	if (cancel_delayed_work_sync(&ep->timeout_work))
		fc_exch_release(ep);	/* release from pending timer hold */

	spin_lock_bh(&ep->ex_lock);
	switch (fh->fh_r_ctl) {
	case FC_RCTL_BA_ACC:
		ap = fc_frame_payload_get(fp, sizeof(*ap));
		if (!ap)
			break;

		/*
		 * Decide whether to establish a Recovery Qualifier.
		 * We do this if there is a non-empty SEQ_CNT range and
		 * SEQ_ID is the same as the one we aborted.
		 */
		low = ntohs(ap->ba_low_seq_cnt);
		high = ntohs(ap->ba_high_seq_cnt);
		if ((ep->esb_stat & ESB_ST_REC_QUAL) == 0 &&
		    (ap->ba_seq_id_val != FC_BA_SEQ_ID_VAL ||
		     ap->ba_seq_id == ep->seq_id) && low != high) {
			ep->esb_stat |= ESB_ST_REC_QUAL;
			fc_exch_hold(ep);  /* hold for recovery qualifier */
			has_rec = 1;
		}
		break;
	case FC_RCTL_BA_RJT:
		break;
	default:
		break;
	}

	resp = ep->resp;
	ex_resp_arg = ep->arg;

	/* do we need to do some other checks here. Can we reuse more of
	 * fc_exch_recv_seq_resp
	 */
	sp = &ep->seq;
	/*
	 * do we want to check END_SEQ as well as LAST_SEQ here?
	 */
	if (ep->fh_type != FC_TYPE_FCP &&
	    ntoh24(fh->fh_f_ctl) & FC_FC_LAST_SEQ)
		rc = fc_exch_done_locked(ep);
	spin_unlock_bh(&ep->ex_lock);
	if (!rc)
		fc_exch_mgr_delete_ep(ep);

	if (resp)
		resp(sp, fp, ex_resp_arg);
	else
		fc_frame_free(fp);

	if (has_rec)
		fc_exch_timer_set(ep, ep->r_a_tov);

}

/*
 * Receive BLS sequence.
 * This is always a sequence initiated by the remote side.
 * We may be either the originator or recipient of the exchange.
 */
static void fc_exch_recv_bls(struct fc_exch_mgr *mp, struct fc_frame *fp)
{
	struct fc_frame_header *fh;
	struct fc_exch *ep;
	u32 f_ctl;

	fh = fc_frame_header_get(fp);
	f_ctl = ntoh24(fh->fh_f_ctl);
	fr_seq(fp) = NULL;

	ep = fc_exch_find(mp, (f_ctl & FC_FC_EX_CTX) ?
			  ntohs(fh->fh_ox_id) : ntohs(fh->fh_rx_id));
	if (ep && (f_ctl & FC_FC_SEQ_INIT)) {
		spin_lock_bh(&ep->ex_lock);
		ep->esb_stat |= ESB_ST_SEQ_INIT;
		spin_unlock_bh(&ep->ex_lock);
	}
	if (f_ctl & FC_FC_SEQ_CTX) {
		/*
		 * A response to a sequence we initiated.
		 * This should only be ACKs for class 2 or F.
		 */
		switch (fh->fh_r_ctl) {
		case FC_RCTL_ACK_1:
		case FC_RCTL_ACK_0:
			break;
		default:
			FC_DEBUG_EXCH("BLS rctl %x - %s received",
				      fh->fh_r_ctl,
				      fc_exch_rctl_name(fh->fh_r_ctl));
			break;
		}
		fc_frame_free(fp);
	} else {
		switch (fh->fh_r_ctl) {
		case FC_RCTL_BA_RJT:
		case FC_RCTL_BA_ACC:
			if (ep)
				fc_exch_abts_resp(ep, fp);
			else
				fc_frame_free(fp);
			break;
		case FC_RCTL_BA_ABTS:
			fc_exch_recv_abts(ep, fp);
			break;
		default:			/* ignore junk */
			fc_frame_free(fp);
			break;
		}
	}
	if (ep)
		fc_exch_release(ep);	/* release hold taken by fc_exch_find */
}

/*
 * Accept sequence with LS_ACC.
 * If this fails due to allocation or transmit congestion, assume the
 * originator will repeat the sequence.
 */
static void fc_seq_ls_acc(struct fc_seq *req_sp)
{
	struct fc_seq *sp;
	struct fc_els_ls_acc *acc;
	struct fc_frame *fp;

	sp = fc_seq_start_next(req_sp);
	fp = fc_frame_alloc(fc_seq_exch(sp)->lp, sizeof(*acc));
	if (fp) {
		acc = fc_frame_payload_get(fp, sizeof(*acc));
		memset(acc, 0, sizeof(*acc));
		acc->la_cmd = ELS_LS_ACC;
		fc_seq_send_last(sp, fp, FC_RCTL_ELS_REP, FC_TYPE_ELS);
	}
}

/*
 * Reject sequence with ELS LS_RJT.
 * If this fails due to allocation or transmit congestion, assume the
 * originator will repeat the sequence.
 */
static void fc_seq_ls_rjt(struct fc_seq *req_sp, enum fc_els_rjt_reason reason,
			  enum fc_els_rjt_explan explan)
{
	struct fc_seq *sp;
	struct fc_els_ls_rjt *rjt;
	struct fc_frame *fp;

	sp = fc_seq_start_next(req_sp);
	fp = fc_frame_alloc(fc_seq_exch(sp)->lp, sizeof(*rjt));
	if (fp) {
		rjt = fc_frame_payload_get(fp, sizeof(*rjt));
		memset(rjt, 0, sizeof(*rjt));
		rjt->er_cmd = ELS_LS_RJT;
		rjt->er_reason = reason;
		rjt->er_explan = explan;
		fc_seq_send_last(sp, fp, FC_RCTL_ELS_REP, FC_TYPE_ELS);
	}
}

static void fc_exch_reset(struct fc_exch *ep)
{
	struct fc_seq *sp;
	void (*resp)(struct fc_seq *, struct fc_frame *, void *);
	void *arg;
	int rc = 1;

	spin_lock_bh(&ep->ex_lock);
	ep->state |= FC_EX_RST_CLEANUP;
	/*
	 * we really want to call del_timer_sync, but cannot due
	 * to the lport calling with the lport lock held (some resp
	 * functions can also grab the lport lock which could cause
	 * a deadlock).
	 */
	if (cancel_delayed_work(&ep->timeout_work))
		atomic_dec(&ep->ex_refcnt);	/* drop hold for timer */
	resp = ep->resp;
	ep->resp = NULL;
	if (ep->esb_stat & ESB_ST_REC_QUAL)
		atomic_dec(&ep->ex_refcnt);	/* drop hold for rec_qual */
	ep->esb_stat &= ~ESB_ST_REC_QUAL;
	arg = ep->arg;
	sp = &ep->seq;
	rc = fc_exch_done_locked(ep);
	spin_unlock_bh(&ep->ex_lock);
	if (!rc)
		fc_exch_mgr_delete_ep(ep);

	if (resp)
		resp(sp, ERR_PTR(-FC_EX_CLOSED), arg);
}

/*
 * Reset an exchange manager, releasing all sequences and exchanges.
 * If sid is non-zero, reset only exchanges we source from that FID.
 * If did is non-zero, reset only exchanges destined to that FID.
 */
void fc_exch_mgr_reset(struct fc_lport *lp, u32 sid, u32 did)
{
	struct fc_exch *ep;
	struct fc_exch *next;
	struct fc_exch_mgr *mp = lp->emp;

	spin_lock_bh(&mp->em_lock);
restart:
	list_for_each_entry_safe(ep, next, &mp->ex_list, ex_list) {
		if ((sid == 0 || sid == ep->sid) &&
		    (did == 0 || did == ep->did)) {
			fc_exch_hold(ep);
			spin_unlock_bh(&mp->em_lock);

			fc_exch_reset(ep);

			fc_exch_release(ep);
			spin_lock_bh(&mp->em_lock);

			/*
			 * must restart loop incase while lock was down
			 * multiple eps were released.
			 */
			goto restart;
		}
	}
	spin_unlock_bh(&mp->em_lock);
}
EXPORT_SYMBOL(fc_exch_mgr_reset);

/*
 * Handle incoming ELS REC - Read Exchange Concise.
 * Note that the requesting port may be different than the S_ID in the request.
 */
static void fc_exch_els_rec(struct fc_seq *sp, struct fc_frame *rfp)
{
	struct fc_frame *fp;
	struct fc_exch *ep;
	struct fc_exch_mgr *em;
	struct fc_els_rec *rp;
	struct fc_els_rec_acc *acc;
	enum fc_els_rjt_reason reason = ELS_RJT_LOGIC;
	enum fc_els_rjt_explan explan;
	u32 sid;
	u16 rxid;
	u16 oxid;

	rp = fc_frame_payload_get(rfp, sizeof(*rp));
	explan = ELS_EXPL_INV_LEN;
	if (!rp)
		goto reject;
	sid = ntoh24(rp->rec_s_id);
	rxid = ntohs(rp->rec_rx_id);
	oxid = ntohs(rp->rec_ox_id);

	/*
	 * Currently it's hard to find the local S_ID from the exchange
	 * manager.  This will eventually be fixed, but for now it's easier
	 * to lookup the subject exchange twice, once as if we were
	 * the initiator, and then again if we weren't.
	 */
	em = fc_seq_exch(sp)->em;
	ep = fc_exch_find(em, oxid);
	explan = ELS_EXPL_OXID_RXID;
	if (ep && ep->oid == sid) {
		if (ep->rxid != FC_XID_UNKNOWN &&
		    rxid != FC_XID_UNKNOWN &&
		    ep->rxid != rxid)
			goto rel;
	} else {
		if (ep)
			fc_exch_release(ep);
		ep = NULL;
		if (rxid != FC_XID_UNKNOWN)
			ep = fc_exch_find(em, rxid);
		if (!ep)
			goto reject;
	}

	fp = fc_frame_alloc(fc_seq_exch(sp)->lp, sizeof(*acc));
	if (!fp) {
		fc_exch_done(sp);
		goto out;
	}
	sp = fc_seq_start_next(sp);
	acc = fc_frame_payload_get(fp, sizeof(*acc));
	memset(acc, 0, sizeof(*acc));
	acc->reca_cmd = ELS_LS_ACC;
	acc->reca_ox_id = rp->rec_ox_id;
	memcpy(acc->reca_ofid, rp->rec_s_id, 3);
	acc->reca_rx_id = htons(ep->rxid);
	if (ep->sid == ep->oid)
		hton24(acc->reca_rfid, ep->did);
	else
		hton24(acc->reca_rfid, ep->sid);
	acc->reca_fc4value = htonl(ep->seq.rec_data);
	acc->reca_e_stat = htonl(ep->esb_stat & (ESB_ST_RESP |
						 ESB_ST_SEQ_INIT |
						 ESB_ST_COMPLETE));
	sp = fc_seq_start_next(sp);
	fc_seq_send_last(sp, fp, FC_RCTL_ELS_REP, FC_TYPE_ELS);
out:
	fc_exch_release(ep);
	fc_frame_free(rfp);
	return;

rel:
	fc_exch_release(ep);
reject:
	fc_seq_ls_rjt(sp, reason, explan);
	fc_frame_free(rfp);
}

/*
 * Handle response from RRQ.
 * Not much to do here, really.
 * Should report errors.
 *
 * TODO: fix error handler.
 */
static void fc_exch_rrq_resp(struct fc_seq *sp, struct fc_frame *fp, void *arg)
{
	struct fc_exch *aborted_ep = arg;
	unsigned int op;

	if (IS_ERR(fp)) {
		int err = PTR_ERR(fp);

		if (err == -FC_EX_CLOSED || err == -FC_EX_TIMEOUT)
			goto cleanup;
		FC_DBG("Cannot process RRQ, because of frame error %d\n", err);
		return;
	}

	op = fc_frame_payload_op(fp);
	fc_frame_free(fp);

	switch (op) {
	case ELS_LS_RJT:
		FC_DBG("LS_RJT for RRQ");
		/* fall through */
	case ELS_LS_ACC:
		goto cleanup;
	default:
		FC_DBG("unexpected response op %x for RRQ", op);
		return;
	}

cleanup:
	fc_exch_done(&aborted_ep->seq);
	/* drop hold for rec qual */
	fc_exch_release(aborted_ep);
}

/*
 * Send ELS RRQ - Reinstate Recovery Qualifier.
 * This tells the remote port to stop blocking the use of
 * the exchange and the seq_cnt range.
 */
static void fc_exch_rrq(struct fc_exch *ep)
{
	struct fc_lport *lp;
	struct fc_els_rrq *rrq;
	struct fc_frame *fp;
	struct fc_seq *rrq_sp;
	u32 did;

	lp = ep->lp;

	fp = fc_frame_alloc(lp, sizeof(*rrq));
	if (!fp)
		return;
	rrq = fc_frame_payload_get(fp, sizeof(*rrq));
	memset(rrq, 0, sizeof(*rrq));
	rrq->rrq_cmd = ELS_RRQ;
	hton24(rrq->rrq_s_id, ep->sid);
	rrq->rrq_ox_id = htons(ep->oxid);
	rrq->rrq_rx_id = htons(ep->rxid);

	did = ep->did;
	if (ep->esb_stat & ESB_ST_RESP)
		did = ep->sid;

	fc_fill_fc_hdr(fp, FC_RCTL_ELS_REQ, did,
		       fc_host_port_id(lp->host), FC_TYPE_ELS,
		       FC_FC_FIRST_SEQ | FC_FC_END_SEQ | FC_FC_SEQ_INIT, 0);

	rrq_sp = fc_exch_seq_send(lp, fp, fc_exch_rrq_resp, NULL, ep,
				  lp->e_d_tov);
	if (!rrq_sp) {
		ep->esb_stat |= ESB_ST_REC_QUAL;
		fc_exch_timer_set_locked(ep, ep->r_a_tov);
		return;
	}
}


/*
 * Handle incoming ELS RRQ - Reset Recovery Qualifier.
 */
static void fc_exch_els_rrq(struct fc_seq *sp, struct fc_frame *fp)
{
	struct fc_exch *ep;		/* request or subject exchange */
	struct fc_els_rrq *rp;
	u32 sid;
	u16 xid;
	enum fc_els_rjt_explan explan;

	rp = fc_frame_payload_get(fp, sizeof(*rp));
	explan = ELS_EXPL_INV_LEN;
	if (!rp)
		goto reject;

	/*
	 * lookup subject exchange.
	 */
	ep = fc_seq_exch(sp);
	sid = ntoh24(rp->rrq_s_id);		/* subject source */
	xid = ep->did == sid ? ntohs(rp->rrq_ox_id) : ntohs(rp->rrq_rx_id);
	ep = fc_exch_find(ep->em, xid);

	explan = ELS_EXPL_OXID_RXID;
	if (!ep)
		goto reject;
	spin_lock_bh(&ep->ex_lock);
	if (ep->oxid != ntohs(rp->rrq_ox_id))
		goto unlock_reject;
	if (ep->rxid != ntohs(rp->rrq_rx_id) &&
	    ep->rxid != FC_XID_UNKNOWN)
		goto unlock_reject;
	explan = ELS_EXPL_SID;
	if (ep->sid != sid)
		goto unlock_reject;

	/*
	 * Clear Recovery Qualifier state, and cancel timer if complete.
	 */
	if (ep->esb_stat & ESB_ST_REC_QUAL) {
		ep->esb_stat &= ~ESB_ST_REC_QUAL;
		atomic_dec(&ep->ex_refcnt);	/* drop hold for rec qual */
	}
	if (ep->esb_stat & ESB_ST_COMPLETE) {
		if (cancel_delayed_work(&ep->timeout_work))
			atomic_dec(&ep->ex_refcnt);	/* drop timer hold */
	}

	spin_unlock_bh(&ep->ex_lock);

	/*
	 * Send LS_ACC.
	 */
	fc_seq_ls_acc(sp);
	fc_frame_free(fp);
	return;

unlock_reject:
	spin_unlock_bh(&ep->ex_lock);
	fc_exch_release(ep);	/* drop hold from fc_exch_find */
reject:
	fc_seq_ls_rjt(sp, ELS_RJT_LOGIC, explan);
	fc_frame_free(fp);
}

struct fc_exch_mgr *fc_exch_mgr_alloc(struct fc_lport *lp,
				      enum fc_class class,
				      u16 min_xid, u16 max_xid)
{
	struct fc_exch_mgr *mp;
	size_t len;

	if (max_xid <= min_xid || min_xid == 0 || max_xid == FC_XID_UNKNOWN) {
		FC_DBG("Invalid min_xid 0x:%x and max_xid 0x:%x\n",
		       min_xid, max_xid);
		return NULL;
	}

	/*
	 * Memory need for EM
	 */
#define xid_ok(i, m1, m2) (((i) >= (m1)) && ((i) <= (m2)))
	len = (max_xid - min_xid + 1) * (sizeof(struct fc_exch *));
	len += sizeof(struct fc_exch_mgr);

	mp = kzalloc(len, GFP_ATOMIC);
	if (!mp)
		return NULL;

	mp->class = class;
	mp->total_exches = 0;
	mp->exches = (struct fc_exch **)(mp + 1);
	mp->lp = lp;
	/* adjust em exch xid range for offload */
	mp->min_xid = min_xid;
	mp->max_xid = max_xid;
	mp->last_xid = min_xid - 1;
	mp->max_read = 0;
	mp->last_read = 0;
	if (lp->lro_enabled && xid_ok(lp->lro_xid, min_xid, max_xid)) {
		mp->max_read = lp->lro_xid;
		mp->last_read = min_xid - 1;
		mp->last_xid = mp->max_read;
	} else {
		/* disable lro if no xid control over read */
		lp->lro_enabled = 0;
	}

	INIT_LIST_HEAD(&mp->ex_list);
	spin_lock_init(&mp->em_lock);

	mp->ep_pool = mempool_create_slab_pool(2, fc_em_cachep);
	if (!mp->ep_pool)
		goto free_mp;

	return mp;

free_mp:
	kfree(mp);
	return NULL;
}
EXPORT_SYMBOL(fc_exch_mgr_alloc);

void fc_exch_mgr_free(struct fc_exch_mgr *mp)
{
	WARN_ON(!mp);
	/*
	 * The total exch count must be zero
	 * before freeing exchange manager.
	 */
	WARN_ON(mp->total_exches != 0);
	mempool_destroy(mp->ep_pool);
	kfree(mp);
}
EXPORT_SYMBOL(fc_exch_mgr_free);

struct fc_exch *fc_exch_get(struct fc_lport *lp, struct fc_frame *fp)
{
	if (!lp || !lp->emp)
		return NULL;

	return fc_exch_alloc(lp->emp, fp, 0);
}
EXPORT_SYMBOL(fc_exch_get);

struct fc_seq *fc_exch_seq_send(struct fc_lport *lp,
				struct fc_frame *fp,
				void (*resp)(struct fc_seq *,
					     struct fc_frame *fp,
					     void *arg),
				void (*destructor)(struct fc_seq *, void *),
				void *arg, u32 timer_msec)
{
	struct fc_exch *ep;
	struct fc_seq *sp = NULL;
	struct fc_frame_header *fh;
	int rc = 1;

	ep = lp->tt.exch_get(lp, fp);
	if (!ep) {
		fc_frame_free(fp);
		return NULL;
	}
	ep->esb_stat |= ESB_ST_SEQ_INIT;
	fh = fc_frame_header_get(fp);
	fc_exch_set_addr(ep, ntoh24(fh->fh_s_id), ntoh24(fh->fh_d_id));
	ep->resp = resp;
	ep->destructor = destructor;
	ep->arg = arg;
	ep->r_a_tov = FC_DEF_R_A_TOV;
	ep->lp = lp;
	sp = &ep->seq;

	ep->fh_type = fh->fh_type; /* save for possbile timeout handling */
	ep->f_ctl = ntoh24(fh->fh_f_ctl);
	fc_exch_setup_hdr(ep, fp, ep->f_ctl);
	sp->cnt++;

	if (unlikely(lp->tt.frame_send(lp, fp)))
		goto err;

	if (timer_msec)
		fc_exch_timer_set_locked(ep, timer_msec);
	ep->f_ctl &= ~FC_FC_FIRST_SEQ;	/* not first seq */

	if (ep->f_ctl & FC_FC_SEQ_INIT)
		ep->esb_stat &= ~ESB_ST_SEQ_INIT;
	spin_unlock_bh(&ep->ex_lock);
	return sp;
err:
	rc = fc_exch_done_locked(ep);
	spin_unlock_bh(&ep->ex_lock);
	if (!rc)
		fc_exch_mgr_delete_ep(ep);
	return NULL;
}
EXPORT_SYMBOL(fc_exch_seq_send);

/*
 * Receive a frame
 */
void fc_exch_recv(struct fc_lport *lp, struct fc_exch_mgr *mp,
		  struct fc_frame *fp)
{
	struct fc_frame_header *fh = fc_frame_header_get(fp);
	u32 f_ctl;

	/* lport lock ? */
	if (!lp || !mp || (lp->state == LPORT_ST_NONE)) {
		FC_DBG("fc_lport or EM is not allocated and configured");
		fc_frame_free(fp);
		return;
	}

	/*
	 * If frame is marked invalid, just drop it.
	 */
	f_ctl = ntoh24(fh->fh_f_ctl);
	switch (fr_eof(fp)) {
	case FC_EOF_T:
		if (f_ctl & FC_FC_END_SEQ)
			skb_trim(fp_skb(fp), fr_len(fp) - FC_FC_FILL(f_ctl));
		/* fall through */
	case FC_EOF_N:
		if (fh->fh_type == FC_TYPE_BLS)
			fc_exch_recv_bls(mp, fp);
		else if ((f_ctl & (FC_FC_EX_CTX | FC_FC_SEQ_CTX)) ==
			 FC_FC_EX_CTX)
			fc_exch_recv_seq_resp(mp, fp);
		else if (f_ctl & FC_FC_SEQ_CTX)
			fc_exch_recv_resp(mp, fp);
		else
			fc_exch_recv_req(lp, mp, fp);
		break;
	default:
		FC_DBG("dropping invalid frame (eof %x)", fr_eof(fp));
		fc_frame_free(fp);
		break;
	}
}
EXPORT_SYMBOL(fc_exch_recv);

int fc_exch_init(struct fc_lport *lp)
{
	if (!lp->tt.exch_get) {
		/*
		 *  exch_put() should be NULL if
		 *  exch_get() is NULL
		 */
		WARN_ON(lp->tt.exch_put);
		lp->tt.exch_get = fc_exch_get;
	}

	if (!lp->tt.seq_start_next)
		lp->tt.seq_start_next = fc_seq_start_next;

	if (!lp->tt.exch_seq_send)
		lp->tt.exch_seq_send = fc_exch_seq_send;

	if (!lp->tt.seq_send)
		lp->tt.seq_send = fc_seq_send;

	if (!lp->tt.seq_els_rsp_send)
		lp->tt.seq_els_rsp_send = fc_seq_els_rsp_send;

	if (!lp->tt.exch_done)
		lp->tt.exch_done = fc_exch_done;

	if (!lp->tt.exch_mgr_reset)
		lp->tt.exch_mgr_reset = fc_exch_mgr_reset;

	if (!lp->tt.seq_exch_abort)
		lp->tt.seq_exch_abort = fc_seq_exch_abort;

	return 0;
}
EXPORT_SYMBOL(fc_exch_init);

int fc_setup_exch_mgr(void)
{
	fc_em_cachep = kmem_cache_create("libfc_em", sizeof(struct fc_exch),
					 0, SLAB_HWCACHE_ALIGN, NULL);
	if (!fc_em_cachep)
		return -ENOMEM;
	return 0;
}

void fc_destroy_exch_mgr(void)
{
	kmem_cache_destroy(fc_em_cachep);
}