drivers/block/aoe/aoecmd.c

/* Copyright (c) 2013 Coraid, Inc.  See COPYING for GPL terms. */
/*
 * aoecmd.c
 * Filesystem request handling methods
 */

#include <linux/ata.h>
#include <linux/slab.h>
#include <linux/hdreg.h>
#include <linux/blkdev.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/genhd.h>
#include <linux/moduleparam.h>
#include <linux/workqueue.h>
#include <linux/kthread.h>
#include <net/net_namespace.h>
#include <asm/unaligned.h>
#include <linux/uio.h>
#include "aoe.h"

#define MAXIOC (8192)	/* default meant to avoid most soft lockups */

static void ktcomplete(struct frame *, struct sk_buff *);
static int count_targets(struct aoedev *d, int *untainted);

static struct buf *nextbuf(struct aoedev *);

static int aoe_deadsecs = 60 * 3;
module_param(aoe_deadsecs, int, 0644);
MODULE_PARM_DESC(aoe_deadsecs, "After aoe_deadsecs seconds, give up and fail dev.");

static int aoe_maxout = 64;
module_param(aoe_maxout, int, 0644);
MODULE_PARM_DESC(aoe_maxout,
	"Only aoe_maxout outstanding packets for every MAC on eX.Y.");

/* The number of online cpus during module initialization gives us a
 * convenient heuristic cap on the parallelism used for ktio threads
 * doing I/O completion.  It is not important that the cap equal the
 * actual number of running CPUs at any given time, but because of CPU
 * hotplug, we take care to use ncpus instead of using
 * num_online_cpus() after module initialization.
 */
static int ncpus;

/* mutex lock used for synchronization while thread spawning */
static DEFINE_MUTEX(ktio_spawn_lock);

static wait_queue_head_t *ktiowq;
static struct ktstate *kts;

/* io completion queue */
struct iocq_ktio {
	struct list_head head;
	spinlock_t lock;
};
static struct iocq_ktio *iocq;

static struct page *empty_page;

static struct sk_buff *
new_skb(ulong len)
{
	struct sk_buff *skb;

	skb = alloc_skb(len + MAX_HEADER, GFP_ATOMIC);
	if (skb) {
		skb_reserve(skb, MAX_HEADER);
		skb_reset_mac_header(skb);
		skb_reset_network_header(skb);
		skb->protocol = __constant_htons(ETH_P_AOE);
		skb_checksum_none_assert(skb);
	}
	return skb;
}

static struct frame *
getframe_deferred(struct aoedev *d, u32 tag)
{
	struct list_head *head, *pos, *nx;
	struct frame *f;

	head = &d->rexmitq;
	list_for_each_safe(pos, nx, head) {
		f = list_entry(pos, struct frame, head);
		if (f->tag == tag) {
			list_del(pos);
			return f;
		}
	}
	return NULL;
}

static struct frame *
getframe(struct aoedev *d, u32 tag)
{
	struct frame *f;
	struct list_head *head, *pos, *nx;
	u32 n;

	n = tag % NFACTIVE;
	head = &d->factive[n];
	list_for_each_safe(pos, nx, head) {
		f = list_entry(pos, struct frame, head);
		if (f->tag == tag) {
			list_del(pos);
			return f;
		}
	}
	return NULL;
}

/*
 * Leave the top bit clear so we have tagspace for userland.
 * The bottom 16 bits are the xmit tick for rexmit/rttavg processing.
 * This driver reserves tag -1 to mean "unused frame."
 */
static int
newtag(struct aoedev *d)
{
	register ulong n;

	n = jiffies & 0xffff;
	return n |= (++d->lasttag & 0x7fff) << 16;
}

static u32
aoehdr_atainit(struct aoedev *d, struct aoetgt *t, struct aoe_hdr *h)
{
	u32 host_tag = newtag(d);

	memcpy(h->src, t->ifp->nd->dev_addr, sizeof h->src);
	memcpy(h->dst, t->addr, sizeof h->dst);
	h->type = __constant_cpu_to_be16(ETH_P_AOE);
	h->verfl = AOE_HVER;
	h->major = cpu_to_be16(d->aoemajor);
	h->minor = d->aoeminor;
	h->cmd = AOECMD_ATA;
	h->tag = cpu_to_be32(host_tag);

	return host_tag;
}

static inline void
put_lba(struct aoe_atahdr *ah, sector_t lba)
{
	ah->lba0 = lba;
	ah->lba1 = lba >>= 8;
	ah->lba2 = lba >>= 8;
	ah->lba3 = lba >>= 8;
	ah->lba4 = lba >>= 8;
	ah->lba5 = lba >>= 8;
}

static struct aoeif *
ifrotate(struct aoetgt *t)
{
	struct aoeif *ifp;

	ifp = t->ifp;
	ifp++;
	if (ifp >= &t->ifs[NAOEIFS] || ifp->nd == NULL)
		ifp = t->ifs;
	if (ifp->nd == NULL)
		return NULL;
	return t->ifp = ifp;
}

static void
skb_pool_put(struct aoedev *d, struct sk_buff *skb)
{
	__skb_queue_tail(&d->skbpool, skb);
}

static struct sk_buff *
skb_pool_get(struct aoedev *d)
{
	struct sk_buff *skb = skb_peek(&d->skbpool);

	if (skb && atomic_read(&skb_shinfo(skb)->dataref) == 1) {
		__skb_unlink(skb, &d->skbpool);
		return skb;
	}
	if (skb_queue_len(&d->skbpool) < NSKBPOOLMAX &&
	    (skb = new_skb(ETH_ZLEN)))
		return skb;

	return NULL;
}

void
aoe_freetframe(struct frame *f)
{
	struct aoetgt *t;

	t = f->t;
	f->buf = NULL;
	f->lba = 0;
	f->bv = NULL;
	f->r_skb = NULL;
	f->flags = 0;
	list_add(&f->head, &t->ffree);
}

static struct frame *
newtframe(struct aoedev *d, struct aoetgt *t)
{
	struct frame *f;
	struct sk_buff *skb;
	struct list_head *pos;

	if (list_empty(&t->ffree)) {
		if (t->falloc >= NSKBPOOLMAX*2)
			return NULL;
		f = kcalloc(1, sizeof(*f), GFP_ATOMIC);
		if (f == NULL)
			return NULL;
		t->falloc++;
		f->t = t;
	} else {
		pos = t->ffree.next;
		list_del(pos);
		f = list_entry(pos, struct frame, head);
	}

	skb = f->skb;
	if (skb == NULL) {
		f->skb = skb = new_skb(ETH_ZLEN);
		if (!skb) {
bail:			aoe_freetframe(f);
			return NULL;
		}
	}

	if (atomic_read(&skb_shinfo(skb)->dataref) != 1) {
		skb = skb_pool_get(d);
		if (skb == NULL)
			goto bail;
		skb_pool_put(d, f->skb);
		f->skb = skb;
	}

	skb->truesize -= skb->data_len;
	skb_shinfo(skb)->nr_frags = skb->data_len = 0;
	skb_trim(skb, 0);
	return f;
}

static struct frame *
newframe(struct aoedev *d)
{
	struct frame *f;
	struct aoetgt *t, **tt;
	int totout = 0;
	int use_tainted;
	int has_untainted;

	if (!d->targets || !d->targets[0]) {
		printk(KERN_ERR "aoe: NULL TARGETS!\n");
		return NULL;
	}
	tt = d->tgt;	/* last used target */
	for (use_tainted = 0, has_untainted = 0;;) {
		tt++;
		if (tt >= &d->targets[d->ntargets] || !*tt)
			tt = d->targets;
		t = *tt;
		if (!t->taint) {
			has_untainted = 1;
			totout += t->nout;
		}
		if (t->nout < t->maxout
		&& (use_tainted || !t->taint)
		&& t->ifp->nd) {
			f = newtframe(d, t);
			if (f) {
				ifrotate(t);
				d->tgt = tt;
				return f;
			}
		}
		if (tt == d->tgt) {	/* we've looped and found nada */
			if (!use_tainted && !has_untainted)
				use_tainted = 1;
			else
				break;
		}
	}
	if (totout == 0) {
		d->kicked++;
		d->flags |= DEVFL_KICKME;
	}
	return NULL;
}

static void
skb_fillup(struct sk_buff *skb, struct bio_vec *bv, ulong off, ulong cnt)
{
	int frag = 0;
	ulong fcnt;
loop:
	fcnt = bv->bv_len - (off - bv->bv_offset);
	if (fcnt > cnt)
		fcnt = cnt;
	skb_fill_page_desc(skb, frag++, bv->bv_page, off, fcnt);
	cnt -= fcnt;
	if (cnt <= 0)
		return;
	bv++;
	off = bv->bv_offset;
	goto loop;
}

static void
fhash(struct frame *f)
{
	struct aoedev *d = f->t->d;
	u32 n;

	n = f->tag % NFACTIVE;
	list_add_tail(&f->head, &d->factive[n]);
}

static void
ata_rw_frameinit(struct frame *f)
{
	struct aoetgt *t;
	struct aoe_hdr *h;
	struct aoe_atahdr *ah;
	struct sk_buff *skb;
	char writebit, extbit;

	skb = f->skb;
	h = (struct aoe_hdr *) skb_mac_header(skb);
	ah = (struct aoe_atahdr *) (h + 1);
	skb_put(skb, sizeof(*h) + sizeof(*ah));
	memset(h, 0, skb->len);

	writebit = 0x10;
	extbit = 0x4;

	t = f->t;
	f->tag = aoehdr_atainit(t->d, t, h);
	fhash(f);
	t->nout++;
	f->waited = 0;
	f->waited_total = 0;
	if (f->buf)
		f->lba = f->buf->sector;

	/* set up ata header */
	ah->scnt = f->bcnt >> 9;
	put_lba(ah, f->lba);
	if (t->d->flags & DEVFL_EXT) {
		ah->aflags |= AOEAFL_EXT;
	} else {
		extbit = 0;
		ah->lba3 &= 0x0f;
		ah->lba3 |= 0xe0;	/* LBA bit + obsolete 0xa0 */
	}
	if (f->buf && bio_data_dir(f->buf->bio) == WRITE) {
		skb_fillup(skb, f->bv, f->bv_off, f->bcnt);
		ah->aflags |= AOEAFL_WRITE;
		skb->len += f->bcnt;
		skb->data_len = f->bcnt;
		skb->truesize += f->bcnt;
		t->wpkts++;
	} else {
		t->rpkts++;
		writebit = 0;
	}

	ah->cmdstat = ATA_CMD_PIO_READ | writebit | extbit;
	skb->dev = t->ifp->nd;
}

static int
aoecmd_ata_rw(struct aoedev *d)
{
	struct frame *f;
	struct buf *buf;
	struct sk_buff *skb;
	struct sk_buff_head queue;
	ulong bcnt, fbcnt;

	buf = nextbuf(d);
	if (buf == NULL)
		return 0;
	f = newframe(d);
	if (f == NULL)
		return 0;
	bcnt = d->maxbcnt;
	if (bcnt == 0)
		bcnt = DEFAULTBCNT;
	if (bcnt > buf->resid)
		bcnt = buf->resid;
	fbcnt = bcnt;
	f->bv = buf->bv;
	f->bv_off = f->bv->bv_offset + (f->bv->bv_len - buf->bv_resid);
	do {
		if (fbcnt < buf->bv_resid) {
			buf->bv_resid -= fbcnt;
			buf->resid -= fbcnt;
			break;
		}
		fbcnt -= buf->bv_resid;
		buf->resid -= buf->bv_resid;
		if (buf->resid == 0) {
			d->ip.buf = NULL;
			break;
		}
		buf->bv++;
		buf->bv_resid = buf->bv->bv_len;
		WARN_ON(buf->bv_resid == 0);
	} while (fbcnt);

	/* initialize the headers & frame */
	f->buf = buf;
	f->bcnt = bcnt;
	ata_rw_frameinit(f);

	/* mark all tracking fields and load out */
	buf->nframesout += 1;
	buf->sector += bcnt >> 9;

	skb = skb_clone(f->skb, GFP_ATOMIC);
	if (skb) {
		do_gettimeofday(&f->sent);
		f->sent_jiffs = (u32) jiffies;
		__skb_queue_head_init(&queue);
		__skb_queue_tail(&queue, skb);
		aoenet_xmit(&queue);
	}
	return 1;
}

/* some callers cannot sleep, and they can call this function,
 * transmitting the packets later, when interrupts are on
 */
static void
aoecmd_cfg_pkts(ushort aoemajor, unsigned char aoeminor, struct sk_buff_head *queue)
{
	struct aoe_hdr *h;
	struct aoe_cfghdr *ch;
	struct sk_buff *skb;
	struct net_device *ifp;

	rcu_read_lock();
	for_each_netdev_rcu(&init_net, ifp) {
		dev_hold(ifp);
		if (!is_aoe_netif(ifp))
			goto cont;

		skb = new_skb(sizeof *h + sizeof *ch);
		if (skb == NULL) {
			printk(KERN_INFO "aoe: skb alloc failure\n");
			goto cont;
		}
		skb_put(skb, sizeof *h + sizeof *ch);
		skb->dev = ifp;
		__skb_queue_tail(queue, skb);
		h = (struct aoe_hdr *) skb_mac_header(skb);
		memset(h, 0, sizeof *h + sizeof *ch);

		memset(h->dst, 0xff, sizeof h->dst);
		memcpy(h->src, ifp->dev_addr, sizeof h->src);
		h->type = __constant_cpu_to_be16(ETH_P_AOE);
		h->verfl = AOE_HVER;
		h->major = cpu_to_be16(aoemajor);
		h->minor = aoeminor;
		h->cmd = AOECMD_CFG;

cont:
		dev_put(ifp);
	}
	rcu_read_unlock();
}

static void
resend(struct aoedev *d, struct frame *f)
{
	struct sk_buff *skb;
	struct sk_buff_head queue;
	struct aoe_hdr *h;
	struct aoetgt *t;
	char buf[128];
	u32 n;

	t = f->t;
	n = newtag(d);
	skb = f->skb;
	if (ifrotate(t) == NULL) {
		/* probably can't happen, but set it up to fail anyway */
		pr_info("aoe: resend: no interfaces to rotate to.\n");
		ktcomplete(f, NULL);
		return;
	}
	h = (struct aoe_hdr *) skb_mac_header(skb);

	if (!(f->flags & FFL_PROBE)) {
		snprintf(buf, sizeof(buf),
			"%15s e%ld.%d oldtag=%08x@%08lx newtag=%08x s=%pm d=%pm nout=%d\n",
			"retransmit", d->aoemajor, d->aoeminor,
			f->tag, jiffies, n,
			h->src, h->dst, t->nout);
		aoechr_error(buf);
	}

	f->tag = n;
	fhash(f);
	h->tag = cpu_to_be32(n);
	memcpy(h->dst, t->addr, sizeof h->dst);
	memcpy(h->src, t->ifp->nd->dev_addr, sizeof h->src);

	skb->dev = t->ifp->nd;
	skb = skb_clone(skb, GFP_ATOMIC);
	if (skb == NULL)
		return;
	do_gettimeofday(&f->sent);
	f->sent_jiffs = (u32) jiffies;
	__skb_queue_head_init(&queue);
	__skb_queue_tail(&queue, skb);
	aoenet_xmit(&queue);
}

static int
tsince_hr(struct frame *f)
{
	struct timeval now;
	int n;

	do_gettimeofday(&now);
	n = now.tv_usec - f->sent.tv_usec;
	n += (now.tv_sec - f->sent.tv_sec) * USEC_PER_SEC;

	if (n < 0)
		n = -n;

	/* For relatively long periods, use jiffies to avoid
	 * discrepancies caused by updates to the system time.
	 *
	 * On system with HZ of 1000, 32-bits is over 49 days
	 * worth of jiffies, or over 71 minutes worth of usecs.
	 *
	 * Jiffies overflow is handled by subtraction of unsigned ints:
	 * (gdb) print (unsigned) 2 - (unsigned) 0xfffffffe
	 * $3 = 4
	 * (gdb)
	 */
	if (n > USEC_PER_SEC / 4) {
		n = ((u32) jiffies) - f->sent_jiffs;
		n *= USEC_PER_SEC / HZ;
	}

	return n;
}

static int
tsince(u32 tag)
{
	int n;

	n = jiffies & 0xffff;
	n -= tag & 0xffff;
	if (n < 0)
		n += 1<<16;
	return jiffies_to_usecs(n + 1);
}

static struct aoeif *
getif(struct aoetgt *t, struct net_device *nd)
{
	struct aoeif *p, *e;

	p = t->ifs;
	e = p + NAOEIFS;
	for (; p < e; p++)
		if (p->nd == nd)
			return p;
	return NULL;
}

static void
ejectif(struct aoetgt *t, struct aoeif *ifp)
{
	struct aoeif *e;
	struct net_device *nd;
	ulong n;

	nd = ifp->nd;
	e = t->ifs + NAOEIFS - 1;
	n = (e - ifp) * sizeof *ifp;
	memmove(ifp, ifp+1, n);
	e->nd = NULL;
	dev_put(nd);
}

static struct frame *
reassign_frame(struct frame *f)
{
	struct frame *nf;
	struct sk_buff *skb;

	nf = newframe(f->t->d);
	if (!nf)
		return NULL;
	if (nf->t == f->t) {
		aoe_freetframe(nf);
		return NULL;
	}

	skb = nf->skb;
	nf->skb = f->skb;
	nf->buf = f->buf;
	nf->bcnt = f->bcnt;
	nf->lba = f->lba;
	nf->bv = f->bv;
	nf->bv_off = f->bv_off;
	nf->waited = 0;
	nf->waited_total = f->waited_total;
	nf->sent = f->sent;
	nf->sent_jiffs = f->sent_jiffs;
	f->skb = skb;

	return nf;
}

static void
probe(struct aoetgt *t)
{
	struct aoedev *d;
	struct frame *f;
	struct sk_buff *skb;
	struct sk_buff_head queue;
	size_t n, m;
	int frag;

	d = t->d;
	f = newtframe(d, t);
	if (!f) {
		pr_err("%s %pm for e%ld.%d: %s\n",
			"aoe: cannot probe remote address",
			t->addr,
			(long) d->aoemajor, d->aoeminor,
			"no frame available");
		return;
	}
	f->flags |= FFL_PROBE;
	ifrotate(t);
	f->bcnt = t->d->maxbcnt ? t->d->maxbcnt : DEFAULTBCNT;
	ata_rw_frameinit(f);
	skb = f->skb;
	for (frag = 0, n = f->bcnt; n > 0; ++frag, n -= m) {
		if (n < PAGE_SIZE)
			m = n;
		else
			m = PAGE_SIZE;
		skb_fill_page_desc(skb, frag, empty_page, 0, m);
	}
	skb->len += f->bcnt;
	skb->data_len = f->bcnt;
	skb->truesize += f->bcnt;

	skb = skb_clone(f->skb, GFP_ATOMIC);
	if (skb) {
		do_gettimeofday(&f->sent);
		f->sent_jiffs = (u32) jiffies;
		__skb_queue_head_init(&queue);
		__skb_queue_tail(&queue, skb);
		aoenet_xmit(&queue);
	}
}

static long
rto(struct aoedev *d)
{
	long t;

	t = 2 * d->rttavg >> RTTSCALE;
	t += 8 * d->rttdev >> RTTDSCALE;
	if (t == 0)
		t = 1;

	return t;
}

static void
rexmit_deferred(struct aoedev *d)
{
	struct aoetgt *t;
	struct frame *f;
	struct frame *nf;
	struct list_head *pos, *nx, *head;
	int since;
	int untainted;

	count_targets(d, &untainted);

	head = &d->rexmitq;
	list_for_each_safe(pos, nx, head) {
		f = list_entry(pos, struct frame, head);
		t = f->t;
		if (t->taint) {
			if (!(f->flags & FFL_PROBE)) {
				nf = reassign_frame(f);
				if (nf) {
					if (t->nout_probes == 0
					&& untainted > 0) {
						probe(t);
						t->nout_probes++;
					}
					list_replace(&f->head, &nf->head);
					pos = &nf->head;
					aoe_freetframe(f);
					f = nf;
					t = f->t;
				}
			} else if (untainted < 1) {
				/* don't probe w/o other untainted aoetgts */
				goto stop_probe;
			} else if (tsince_hr(f) < t->taint * rto(d)) {
				/* reprobe slowly when taint is high */
				continue;
			}
		} else if (f->flags & FFL_PROBE) {
stop_probe:		/* don't probe untainted aoetgts */
			list_del(pos);
			aoe_freetframe(f);
			/* leaving d->kicked, because this is routine */
			f->t->d->flags |= DEVFL_KICKME;
			continue;
		}
		if (t->nout >= t->maxout)
			continue;
		list_del(pos);
		t->nout++;
		if (f->flags & FFL_PROBE)
			t->nout_probes++;
		since = tsince_hr(f);
		f->waited += since;
		f->waited_total += since;
		resend(d, f);
	}
}

/* An aoetgt accumulates demerits quickly, and successful
 * probing redeems the aoetgt slowly.
 */
static void
scorn(struct aoetgt *t)
{
	int n;

	n = t->taint++;
	t->taint += t->taint * 2;
	if (n > t->taint)
		t->taint = n;
	if (t->taint > MAX_TAINT)
		t->taint = MAX_TAINT;
}

static int
count_targets(struct aoedev *d, int *untainted)
{
	int i, good;

	for (i = good = 0; i < d->ntargets && d->targets[i]; ++i)
		if (d->targets[i]->taint == 0)
			good++;

	if (untainted)
		*untainted = good;
	return i;
}

static void
rexmit_timer(ulong vp)
{
	struct aoedev *d;
	struct aoetgt *t;
	struct aoeif *ifp;
	struct frame *f;
	struct list_head *head, *pos, *nx;
	LIST_HEAD(flist);
	register long timeout;
	ulong flags, n;
	int i;
	int utgts;	/* number of aoetgt descriptors (not slots) */
	int since;

	d = (struct aoedev *) vp;

	spin_lock_irqsave(&d->lock, flags);

	/* timeout based on observed timings and variations */
	timeout = rto(d);

	utgts = count_targets(d, NULL);

	if (d->flags & DEVFL_TKILL) {
		spin_unlock_irqrestore(&d->lock, flags);
		return;
	}

	/* collect all frames to rexmit into flist */
	for (i = 0; i < NFACTIVE; i++) {
		head = &d->factive[i];
		list_for_each_safe(pos, nx, head) {
			f = list_entry(pos, struct frame, head);
			if (tsince_hr(f) < timeout)
				break;	/* end of expired frames */
			/* move to flist for later processing */
			list_move_tail(pos, &flist);
		}
	}

	/* process expired frames */
	while (!list_empty(&flist)) {
		pos = flist.next;
		f = list_entry(pos, struct frame, head);
		since = tsince_hr(f);
		n = f->waited_total + since;
		n /= USEC_PER_SEC;
		if (aoe_deadsecs
		&& n > aoe_deadsecs
		&& !(f->flags & FFL_PROBE)) {
			/* Waited too long.  Device failure.
			 * Hang all frames on first hash bucket for downdev
			 * to clean up.
			 */
			list_splice(&flist, &d->factive[0]);
			aoedev_downdev(d);
			goto out;
		}

		t = f->t;
		n = f->waited + since;
		n /= USEC_PER_SEC;
		if (aoe_deadsecs && utgts > 0
		&& (n > aoe_deadsecs / utgts || n > HARD_SCORN_SECS))
			scorn(t); /* avoid this target */

		if (t->maxout != 1) {
			t->ssthresh = t->maxout / 2;
			t->maxout = 1;
		}

		if (f->flags & FFL_PROBE) {
			t->nout_probes--;
		} else {
			ifp = getif(t, f->skb->dev);
			if (ifp && ++ifp->lost > (t->nframes << 1)
			&& (ifp != t->ifs || t->ifs[1].nd)) {
				ejectif(t, ifp);
				ifp = NULL;
			}
		}
		list_move_tail(pos, &d->rexmitq);
		t->nout--;
	}
	rexmit_deferred(d);

out:
	if ((d->flags & DEVFL_KICKME) && d->blkq) {
		d->flags &= ~DEVFL_KICKME;
		d->blkq->request_fn(d->blkq);
	}

	d->timer.expires = jiffies + TIMERTICK;
	add_timer(&d->timer);

	spin_unlock_irqrestore(&d->lock, flags);
}

static unsigned long
rqbiocnt(struct request *r)
{
	struct bio *bio;
	unsigned long n = 0;

	__rq_for_each_bio(bio, r)
		n++;
	return n;
}

/* This can be removed if we are certain that no users of the block
 * layer will ever use zero-count pages in bios.  Otherwise we have to
 * protect against the put_page sometimes done by the network layer.
 *
 * See http://oss.sgi.com/archives/xfs/2007-01/msg00594.html for
 * discussion.
 *
 * We cannot use get_page in the workaround, because it insists on a
 * positive page count as a precondition.  So we use _count directly.
 */
static void
bio_pageinc(struct bio *bio)
{
	struct bio_vec *bv;
	struct page *page;
	int i;

	bio_for_each_segment(bv, bio, i) {
		/* Non-zero page count for non-head members of
		 * compound pages is no longer allowed by the kernel.
		 */
		page = compound_trans_head(bv->bv_page);
		atomic_inc(&page->_count);
	}
}

static void
bio_pagedec(struct bio *bio)
{
	struct bio_vec *bv;
	struct page *page;
	int i;

	bio_for_each_segment(bv, bio, i) {
		page = compound_trans_head(bv->bv_page);
		atomic_dec(&page->_count);
	}
}

static void
bufinit(struct buf *buf, struct request *rq, struct bio *bio)
{
	memset(buf, 0, sizeof(*buf));
	buf->rq = rq;
	buf->bio = bio;
	buf->resid = bio->bi_size;
	buf->sector = bio->bi_sector;
	bio_pageinc(bio);
	buf->bv = bio_iovec(bio);
	buf->bv_resid = buf->bv->bv_len;
	WARN_ON(buf->bv_resid == 0);
}

static struct buf *
nextbuf(struct aoedev *d)
{
	struct request *rq;
	struct request_queue *q;
	struct buf *buf;
	struct bio *bio;

	q = d->blkq;
	if (q == NULL)
		return NULL;	/* initializing */
	if (d->ip.buf)
		return d->ip.buf;
	rq = d->ip.rq;
	if (rq == NULL) {
		rq = blk_peek_request(q);
		if (rq == NULL)
			return NULL;
		blk_start_request(rq);
		d->ip.rq = rq;
		d->ip.nxbio = rq->bio;
		rq->special = (void *) rqbiocnt(rq);
	}
	buf = mempool_alloc(d->bufpool, GFP_ATOMIC);
	if (buf == NULL) {
		pr_err("aoe: nextbuf: unable to mempool_alloc!\n");
		return NULL;
	}
	bio = d->ip.nxbio;
	bufinit(buf, rq, bio);
	bio = bio->bi_next;
	d->ip.nxbio = bio;
	if (bio == NULL)
		d->ip.rq = NULL;
	return d->ip.buf = buf;
}

/* enters with d->lock held */
void
aoecmd_work(struct aoedev *d)
{
	rexmit_deferred(d);
	while (aoecmd_ata_rw(d))
		;
}

/* this function performs work that has been deferred until sleeping is OK
 */
void
aoecmd_sleepwork(struct work_struct *work)
{
	struct aoedev *d = container_of(work, struct aoedev, work);
	struct block_device *bd;
	u64 ssize;

	if (d->flags & DEVFL_GDALLOC)
		aoeblk_gdalloc(d);

	if (d->flags & DEVFL_NEWSIZE) {
		ssize = get_capacity(d->gd);
		bd = bdget_disk(d->gd, 0);
		if (bd) {
			mutex_lock(&bd->bd_inode->i_mutex);
			i_size_write(bd->bd_inode, (loff_t)ssize<<9);
			mutex_unlock(&bd->bd_inode->i_mutex);
			bdput(bd);
		}
		spin_lock_irq(&d->lock);
		d->flags |= DEVFL_UP;
		d->flags &= ~DEVFL_NEWSIZE;
		spin_unlock_irq(&d->lock);
	}
}

static void
ata_ident_fixstring(u16 *id, int ns)
{
	u16 s;

	while (ns-- > 0) {
		s = *id;
		*id++ = s >> 8 | s << 8;
	}
}

static void
ataid_complete(struct aoedev *d, struct aoetgt *t, unsigned char *id)
{
	u64 ssize;
	u16 n;

	/* word 83: command set supported */
	n = get_unaligned_le16(&id[83 << 1]);

	/* word 86: command set/feature enabled */
	n |= get_unaligned_le16(&id[86 << 1]);

	if (n & (1<<10)) {	/* bit 10: LBA 48 */
		d->flags |= DEVFL_EXT;

		/* word 100: number lba48 sectors */
		ssize = get_unaligned_le64(&id[100 << 1]);

		/* set as in ide-disk.c:init_idedisk_capacity */
		d->geo.cylinders = ssize;
		d->geo.cylinders /= (255 * 63);
		d->geo.heads = 255;
		d->geo.sectors = 63;
	} else {
		d->flags &= ~DEVFL_EXT;

		/* number lba28 sectors */
		ssize = get_unaligned_le32(&id[60 << 1]);

		/* NOTE: obsolete in ATA 6 */
		d->geo.cylinders = get_unaligned_le16(&id[54 << 1]);
		d->geo.heads = get_unaligned_le16(&id[55 << 1]);
		d->geo.sectors = get_unaligned_le16(&id[56 << 1]);
	}

	ata_ident_fixstring((u16 *) &id[10<<1], 10);	/* serial */
	ata_ident_fixstring((u16 *) &id[23<<1], 4);	/* firmware */
	ata_ident_fixstring((u16 *) &id[27<<1], 20);	/* model */
	memcpy(d->ident, id, sizeof(d->ident));

	if (d->ssize != ssize)
		printk(KERN_INFO
			"aoe: %pm e%ld.%d v%04x has %llu sectors\n",
			t->addr,
			d->aoemajor, d->aoeminor,
			d->fw_ver, (long long)ssize);
	d->ssize = ssize;
	d->geo.start = 0;
	if (d->flags & (DEVFL_GDALLOC|DEVFL_NEWSIZE))
		return;
	if (d->gd != NULL) {
		set_capacity(d->gd, ssize);
		d->flags |= DEVFL_NEWSIZE;
	} else
		d->flags |= DEVFL_GDALLOC;
	schedule_work(&d->work);
}

static void
calc_rttavg(struct aoedev *d, struct aoetgt *t, int rtt)
{
	register long n;

	n = rtt;

	/* cf. Congestion Avoidance and Control, Jacobson & Karels, 1988 */
	n -= d->rttavg >> RTTSCALE;
	d->rttavg += n;
	if (n < 0)
		n = -n;
	n -= d->rttdev >> RTTDSCALE;
	d->rttdev += n;

	if (!t || t->maxout >= t->nframes)
		return;
	if (t->maxout < t->ssthresh)
		t->maxout += 1;
	else if (t->nout == t->maxout && t->next_cwnd-- == 0) {
		t->maxout += 1;
		t->next_cwnd = t->maxout;
	}
}

static struct aoetgt *
gettgt(struct aoedev *d, char *addr)
{
	struct aoetgt **t, **e;

	t = d->targets;
	e = t + d->ntargets;
	for (; t < e && *t; t++)
		if (memcmp((*t)->addr, addr, sizeof((*t)->addr)) == 0)
			return *t;
	return NULL;
}

static void
bvcpy(struct bio_vec *bv, ulong off, struct sk_buff *skb, long cnt)
{
	ulong fcnt;
	char *p;
	int soff = 0;
loop:
	fcnt = bv->bv_len - (off - bv->bv_offset);
	if (fcnt > cnt)
		fcnt = cnt;
	p = page_address(bv->bv_page) + off;
	skb_copy_bits(skb, soff, p, fcnt);
	soff += fcnt;
	cnt -= fcnt;
	if (cnt <= 0)
		return;
	bv++;
	off = bv->bv_offset;
	goto loop;
}

void
aoe_end_request(struct aoedev *d, struct request *rq, int fastfail)
{
	struct bio *bio;
	int bok;
	struct request_queue *q;

	q = d->blkq;
	if (rq == d->ip.rq)
		d->ip.rq = NULL;
	do {
		bio = rq->bio;
		bok = !fastfail && test_bit(BIO_UPTODATE, &bio->bi_flags);
	} while (__blk_end_request(rq, bok ? 0 : -EIO, bio->bi_size));

	/* cf. http://lkml.org/lkml/2006/10/31/28 */
	if (!fastfail)
		__blk_run_queue(q);
}

static void
aoe_end_buf(struct aoedev *d, struct buf *buf)
{
	struct request *rq;
	unsigned long n;

	if (buf == d->ip.buf)
		d->ip.buf = NULL;
	rq = buf->rq;
	bio_pagedec(buf->bio);
	mempool_free(buf, d->bufpool);
	n = (unsigned long) rq->special;
	rq->special = (void *) --n;
	if (n == 0)
		aoe_end_request(d, rq, 0);
}

static void
ktiocomplete(struct frame *f)
{
	struct aoe_hdr *hin, *hout;
	struct aoe_atahdr *ahin, *ahout;
	struct buf *buf;
	struct sk_buff *skb;
	struct aoetgt *t;
	struct aoeif *ifp;
	struct aoedev *d;
	long n;
	int untainted;

	if (f == NULL)
		return;

	t = f->t;
	d = t->d;
	skb = f->r_skb;
	buf = f->buf;
	if (f->flags & FFL_PROBE)
		goto out;
	if (!skb)		/* just fail the buf. */
		goto noskb;

	hout = (struct aoe_hdr *) skb_mac_header(f->skb);
	ahout = (struct aoe_atahdr *) (hout+1);

	hin = (struct aoe_hdr *) skb->data;
	skb_pull(skb, sizeof(*hin));
	ahin = (struct aoe_atahdr *) skb->data;
	skb_pull(skb, sizeof(*ahin));
	if (ahin->cmdstat & 0xa9) {	/* these bits cleared on success */
		pr_err("aoe: ata error cmd=%2.2Xh stat=%2.2Xh from e%ld.%d\n",
			ahout->cmdstat, ahin->cmdstat,
			d->aoemajor, d->aoeminor);
noskb:		if (buf)
			clear_bit(BIO_UPTODATE, &buf->bio->bi_flags);
		goto out;
	}

	n = ahout->scnt << 9;
	switch (ahout->cmdstat) {
	case ATA_CMD_PIO_READ:
	case ATA_CMD_PIO_READ_EXT:
		if (skb->len < n) {
			pr_err("%s e%ld.%d.  skb->len=%d need=%ld\n",
				"aoe: runt data size in read from",
				(long) d->aoemajor, d->aoeminor,
			       skb->len, n);
			clear_bit(BIO_UPTODATE, &buf->bio->bi_flags);
			break;
		}
		bvcpy(f->bv, f->bv_off, skb, n);
	case ATA_CMD_PIO_WRITE:
	case ATA_CMD_PIO_WRITE_EXT:
		spin_lock_irq(&d->lock);
		ifp = getif(t, skb->dev);
		if (ifp)
			ifp->lost = 0;
		spin_unlock_irq(&d->lock);
		break;
	case ATA_CMD_ID_ATA:
		if (skb->len < 512) {
			pr_info("%s e%ld.%d.  skb->len=%d need=512\n",
				"aoe: runt data size in ataid from",
				(long) d->aoemajor, d->aoeminor,
				skb->len);
			break;
		}
		if (skb_linearize(skb))
			break;
		spin_lock_irq(&d->lock);
		ataid_complete(d, t, skb->data);
		spin_unlock_irq(&d->lock);
		break;
	default:
		pr_info("aoe: unrecognized ata command %2.2Xh for %d.%d\n",
			ahout->cmdstat,
			be16_to_cpu(get_unaligned(&hin->major)),
			hin->minor);
	}
out:
	spin_lock_irq(&d->lock);
	if (t->taint > 0
	&& --t->taint > 0
	&& t->nout_probes == 0) {
		count_targets(d, &untainted);
		if (untainted > 0) {
			probe(t);
			t->nout_probes++;
		}
	}

	aoe_freetframe(f);

	if (buf && --buf->nframesout == 0 && buf->resid == 0)
		aoe_end_buf(d, buf);

	spin_unlock_irq(&d->lock);
	aoedev_put(d);
	dev_kfree_skb(skb);
}

/* Enters with iocq.lock held.
 * Returns true iff responses needing processing remain.
 */
static int
ktio(int id)
{
	struct frame *f;
	struct list_head *pos;
	int i;
	int actual_id;

	for (i = 0; ; ++i) {
		if (i == MAXIOC)
			return 1;
		if (list_empty(&iocq[id].head))
			return 0;
		pos = iocq[id].head.next;
		list_del(pos);
		f = list_entry(pos, struct frame, head);
		spin_unlock_irq(&iocq[id].lock);
		ktiocomplete(f);

		/* Figure out if extra threads are required. */
		actual_id = f->t->d->aoeminor % ncpus;

		if (!kts[actual_id].active) {
			BUG_ON(id != 0);
			mutex_lock(&ktio_spawn_lock);
			if (!kts[actual_id].active
				&& aoe_ktstart(&kts[actual_id]) == 0)
				kts[actual_id].active = 1;
			mutex_unlock(&ktio_spawn_lock);
		}
		spin_lock_irq(&iocq[id].lock);
	}
}

static int
kthread(void *vp)
{
	struct ktstate *k;
	DECLARE_WAITQUEUE(wait, current);
	int more;

	k = vp;
	current->flags |= PF_NOFREEZE;
	set_user_nice(current, -10);
	complete(&k->rendez);	/* tell spawner we're running */
	do {
		spin_lock_irq(k->lock);
		more = k->fn(k->id);
		if (!more) {
			add_wait_queue(k->waitq, &wait);
			__set_current_state(TASK_INTERRUPTIBLE);
		}
		spin_unlock_irq(k->lock);
		if (!more) {
			schedule();
			remove_wait_queue(k->waitq, &wait);
		} else
			cond_resched();
	} while (!kthread_should_stop());
	complete(&k->rendez);	/* tell spawner we're stopping */
	return 0;
}

void
aoe_ktstop(struct ktstate *k)
{
	kthread_stop(k->task);
	wait_for_completion(&k->rendez);
}

int
aoe_ktstart(struct ktstate *k)
{
	struct task_struct *task;

	init_completion(&k->rendez);
	task = kthread_run(kthread, k, "%s", k->name);
	if (task == NULL || IS_ERR(task))
		return -ENOMEM;
	k->task = task;
	wait_for_completion(&k->rendez); /* allow kthread to start */
	init_completion(&k->rendez);	/* for waiting for exit later */
	return 0;
}

/* pass it off to kthreads for processing */
static void
ktcomplete(struct frame *f, struct sk_buff *skb)
{
	int id;
	ulong flags;

	f->r_skb = skb;
	id = f->t->d->aoeminor % ncpus;
	spin_lock_irqsave(&iocq[id].lock, flags);
	if (!kts[id].active) {
		spin_unlock_irqrestore(&iocq[id].lock, flags);
		/* The thread with id has not been spawned yet,
		 * so delegate the work to the main thread and
		 * try spawning a new thread.
		 */
		id = 0;
		spin_lock_irqsave(&iocq[id].lock, flags);
	}
	list_add_tail(&f->head, &iocq[id].head);
	spin_unlock_irqrestore(&iocq[id].lock, flags);
	wake_up(&ktiowq[id]);
}

struct sk_buff *
aoecmd_ata_rsp(struct sk_buff *skb)
{
	struct aoedev *d;
	struct aoe_hdr *h;
	struct frame *f;
	u32 n;
	ulong flags;
	char ebuf[128];
	u16 aoemajor;

	h = (struct aoe_hdr *) skb->data;
	aoemajor = be16_to_cpu(get_unaligned(&h->major));
	d = aoedev_by_aoeaddr(aoemajor, h->minor, 0);
	if (d == NULL) {
		snprintf(ebuf, sizeof ebuf, "aoecmd_ata_rsp: ata response "
			"for unknown device %d.%d\n",
			aoemajor, h->minor);
		aoechr_error(ebuf);
		return skb;
	}

	spin_lock_irqsave(&d->lock, flags);

	n = be32_to_cpu(get_unaligned(&h->tag));
	f = getframe(d, n);
	if (f) {
		calc_rttavg(d, f->t, tsince_hr(f));
		f->t->nout--;
		if (f->flags & FFL_PROBE)
			f->t->nout_probes--;
	} else {
		f = getframe_deferred(d, n);
		if (f) {
			calc_rttavg(d, NULL, tsince_hr(f));
		} else {
			calc_rttavg(d, NULL, tsince(n));
			spin_unlock_irqrestore(&d->lock, flags);
			aoedev_put(d);
			snprintf(ebuf, sizeof(ebuf),
				 "%15s e%d.%d    tag=%08x@%08lx s=%pm d=%pm\n",
				 "unexpected rsp",
				 get_unaligned_be16(&h->major),
				 h->minor,
				 get_unaligned_be32(&h->tag),
				 jiffies,
				 h->src,
				 h->dst);
			aoechr_error(ebuf);
			return skb;
		}
	}
	aoecmd_work(d);

	spin_unlock_irqrestore(&d->lock, flags);

	ktcomplete(f, skb);

	/*
	 * Note here that we do not perform an aoedev_put, as we are
	 * leaving this reference for the ktio to release.
	 */
	return NULL;
}

void
aoecmd_cfg(ushort aoemajor, unsigned char aoeminor)
{
	struct sk_buff_head queue;

	__skb_queue_head_init(&queue);
	aoecmd_cfg_pkts(aoemajor, aoeminor, &queue);
	aoenet_xmit(&queue);
}

struct sk_buff *
aoecmd_ata_id(struct aoedev *d)
{
	struct aoe_hdr *h;
	struct aoe_atahdr *ah;
	struct frame *f;
	struct sk_buff *skb;
	struct aoetgt *t;

	f = newframe(d);
	if (f == NULL)
		return NULL;

	t = *d->tgt;

	/* initialize the headers & frame */
	skb = f->skb;
	h = (struct aoe_hdr *) skb_mac_header(skb);
	ah = (struct aoe_atahdr *) (h+1);
	skb_put(skb, sizeof *h + sizeof *ah);
	memset(h, 0, skb->len);
	f->tag = aoehdr_atainit(d, t, h);
	fhash(f);
	t->nout++;
	f->waited = 0;
	f->waited_total = 0;

	/* set up ata header */
	ah->scnt = 1;
	ah->cmdstat = ATA_CMD_ID_ATA;
	ah->lba3 = 0xa0;

	skb->dev = t->ifp->nd;

	d->rttavg = RTTAVG_INIT;
	d->rttdev = RTTDEV_INIT;
	d->timer.function = rexmit_timer;

	skb = skb_clone(skb, GFP_ATOMIC);
	if (skb) {
		do_gettimeofday(&f->sent);
		f->sent_jiffs = (u32) jiffies;
	}

	return skb;
}

static struct aoetgt **
grow_targets(struct aoedev *d)
{
	ulong oldn, newn;
	struct aoetgt **tt;

	oldn = d->ntargets;
	newn = oldn * 2;
	tt = kcalloc(newn, sizeof(*d->targets), GFP_ATOMIC);
	if (!tt)
		return NULL;
	memmove(tt, d->targets, sizeof(*d->targets) * oldn);
	d->tgt = tt + (d->tgt - d->targets);
	kfree(d->targets);
	d->targets = tt;
	d->ntargets = newn;

	return &d->targets[oldn];
}

static struct aoetgt *
addtgt(struct aoedev *d, char *addr, ulong nframes)
{
	struct aoetgt *t, **tt, **te;

	tt = d->targets;
	te = tt + d->ntargets;
	for (; tt < te && *tt; tt++)
		;

	if (tt == te) {
		tt = grow_targets(d);
		if (!tt)
			goto nomem;
	}
	t = kzalloc(sizeof(*t), GFP_ATOMIC);
	if (!t)
		goto nomem;
	t->nframes = nframes;
	t->d = d;
	memcpy(t->addr, addr, sizeof t->addr);
	t->ifp = t->ifs;
	aoecmd_wreset(t);
	t->maxout = t->nframes / 2;
	INIT_LIST_HEAD(&t->ffree);
	return *tt = t;

 nomem:
	pr_info("aoe: cannot allocate memory to add target\n");
	return NULL;
}

static void
setdbcnt(struct aoedev *d)
{
	struct aoetgt **t, **e;
	int bcnt = 0;

	t = d->targets;
	e = t + d->ntargets;
	for (; t < e && *t; t++)
		if (bcnt == 0 || bcnt > (*t)->minbcnt)
			bcnt = (*t)->minbcnt;
	if (bcnt != d->maxbcnt) {
		d->maxbcnt = bcnt;
		pr_info("aoe: e%ld.%d: setting %d byte data frames\n",
			d->aoemajor, d->aoeminor, bcnt);
	}
}

static void
setifbcnt(struct aoetgt *t, struct net_device *nd, int bcnt)
{
	struct aoedev *d;
	struct aoeif *p, *e;
	int minbcnt;

	d = t->d;
	minbcnt = bcnt;
	p = t->ifs;
	e = p + NAOEIFS;
	for (; p < e; p++) {
		if (p->nd == NULL)
			break;		/* end of the valid interfaces */
		if (p->nd == nd) {
			p->bcnt = bcnt;	/* we're updating */
			nd = NULL;
		} else if (minbcnt > p->bcnt)
			minbcnt = p->bcnt; /* find the min interface */
	}
	if (nd) {
		if (p == e) {
			pr_err("aoe: device setifbcnt failure; too many interfaces.\n");
			return;
		}
		dev_hold(nd);
		p->nd = nd;
		p->bcnt = bcnt;
	}
	t->minbcnt = minbcnt;
	setdbcnt(d);
}

void
aoecmd_cfg_rsp(struct sk_buff *skb)
{
	struct aoedev *d;
	struct aoe_hdr *h;
	struct aoe_cfghdr *ch;
	struct aoetgt *t;
	ulong flags, aoemajor;
	struct sk_buff *sl;
	struct sk_buff_head queue;
	u16 n;

	sl = NULL;
	h = (struct aoe_hdr *) skb_mac_header(skb);
	ch = (struct aoe_cfghdr *) (h+1);

	/*
	 * Enough people have their dip switches set backwards to
	 * warrant a loud message for this special case.
	 */
	aoemajor = get_unaligned_be16(&h->major);
	if (aoemajor == 0xfff) {
		printk(KERN_ERR "aoe: Warning: shelf address is all ones.  "
			"Check shelf dip switches.\n");
		return;
	}
	if (aoemajor == 0xffff) {
		pr_info("aoe: e%ld.%d: broadcast shelf number invalid\n",
			aoemajor, (int) h->minor);
		return;
	}
	if (h->minor == 0xff) {
		pr_info("aoe: e%ld.%d: broadcast slot number invalid\n",
			aoemajor, (int) h->minor);
		return;
	}

	n = be16_to_cpu(ch->bufcnt);
	if (n > aoe_maxout)	/* keep it reasonable */
		n = aoe_maxout;

	d = aoedev_by_aoeaddr(aoemajor, h->minor, 1);
	if (d == NULL) {
		pr_info("aoe: device allocation failure\n");
		return;
	}

	spin_lock_irqsave(&d->lock, flags);

	t = gettgt(d, h->src);
	if (t) {
		t->nframes = n;
		if (n < t->maxout)
			aoecmd_wreset(t);
	} else {
		t = addtgt(d, h->src, n);
		if (!t)
			goto bail;
	}
	n = skb->dev->mtu;
	n -= sizeof(struct aoe_hdr) + sizeof(struct aoe_atahdr);
	n /= 512;
	if (n > ch->scnt)
		n = ch->scnt;
	n = n ? n * 512 : DEFAULTBCNT;
	setifbcnt(t, skb->dev, n);

	/* don't change users' perspective */
	if (d->nopen == 0) {
		d->fw_ver = be16_to_cpu(ch->fwver);
		sl = aoecmd_ata_id(d);
	}
bail:
	spin_unlock_irqrestore(&d->lock, flags);
	aoedev_put(d);
	if (sl) {
		__skb_queue_head_init(&queue);
		__skb_queue_tail(&queue, sl);
		aoenet_xmit(&queue);
	}
}

void
aoecmd_wreset(struct aoetgt *t)
{
	t->maxout = 1;
	t->ssthresh = t->nframes / 2;
	t->next_cwnd = t->nframes;
}

void
aoecmd_cleanslate(struct aoedev *d)
{
	struct aoetgt **t, **te;

	d->rttavg = RTTAVG_INIT;
	d->rttdev = RTTDEV_INIT;
	d->maxbcnt = 0;

	t = d->targets;
	te = t + d->ntargets;
	for (; t < te && *t; t++)
		aoecmd_wreset(*t);
}

void
aoe_failbuf(struct aoedev *d, struct buf *buf)
{
	if (buf == NULL)
		return;
	buf->resid = 0;
	clear_bit(BIO_UPTODATE, &buf->bio->bi_flags);
	if (buf->nframesout == 0)
		aoe_end_buf(d, buf);
}

void
aoe_flush_iocq(void)
{
	int i;

	for (i = 0; i < ncpus; i++) {
		if (kts[i].active)
			aoe_flush_iocq_by_index(i);
	}
}

void
aoe_flush_iocq_by_index(int id)
{
	struct frame *f;
	struct aoedev *d;
	LIST_HEAD(flist);
	struct list_head *pos;
	struct sk_buff *skb;
	ulong flags;

	spin_lock_irqsave(&iocq[id].lock, flags);
	list_splice_init(&iocq[id].head, &flist);
	spin_unlock_irqrestore(&iocq[id].lock, flags);
	while (!list_empty(&flist)) {
		pos = flist.next;
		list_del(pos);
		f = list_entry(pos, struct frame, head);
		d = f->t->d;
		skb = f->r_skb;
		spin_lock_irqsave(&d->lock, flags);
		if (f->buf) {
			f->buf->nframesout--;
			aoe_failbuf(d, f->buf);
		}
		aoe_freetframe(f);
		spin_unlock_irqrestore(&d->lock, flags);
		dev_kfree_skb(skb);
		aoedev_put(d);
	}
}

int __init
aoecmd_init(void)
{
	void *p;
	int i;
	int ret;

	/* get_zeroed_page returns page with ref count 1 */
	p = (void *) get_zeroed_page(GFP_KERNEL | __GFP_REPEAT);
	if (!p)
		return -ENOMEM;
	empty_page = virt_to_page(p);

	ncpus = num_online_cpus();

	iocq = kcalloc(ncpus, sizeof(struct iocq_ktio), GFP_KERNEL);
	if (!iocq)
		return -ENOMEM;

	kts = kcalloc(ncpus, sizeof(struct ktstate), GFP_KERNEL);
	if (!kts) {
		ret = -ENOMEM;
		goto kts_fail;
	}

	ktiowq = kcalloc(ncpus, sizeof(wait_queue_head_t), GFP_KERNEL);
	if (!ktiowq) {
		ret = -ENOMEM;
		goto ktiowq_fail;
	}

	mutex_init(&ktio_spawn_lock);

	for (i = 0; i < ncpus; i++) {
		INIT_LIST_HEAD(&iocq[i].head);
		spin_lock_init(&iocq[i].lock);
		init_waitqueue_head(&ktiowq[i]);
		snprintf(kts[i].name, sizeof(kts[i].name), "aoe_ktio%d", i);
		kts[i].fn = ktio;
		kts[i].waitq = &ktiowq[i];
		kts[i].lock = &iocq[i].lock;
		kts[i].id = i;
		kts[i].active = 0;
	}
	kts[0].active = 1;
	if (aoe_ktstart(&kts[0])) {
		ret = -ENOMEM;
		goto ktstart_fail;
	}
	return 0;

ktstart_fail:
	kfree(ktiowq);
ktiowq_fail:
	kfree(kts);
kts_fail:
	kfree(iocq);

	return ret;
}

void
aoecmd_exit(void)
{
	int i;

	for (i = 0; i < ncpus; i++)
		if (kts[i].active)
			aoe_ktstop(&kts[i]);

	aoe_flush_iocq();

	/* Free up the iocq and thread speicific configuration
	* allocated during startup.
	*/
	kfree(iocq);
	kfree(kts);
	kfree(ktiowq);

	free_page((unsigned long) page_address(empty_page));
	empty_page = NULL;
}