aboutsummaryrefslogtreecommitdiff
path: root/net/core/netpoll.c
blob: b5873bdff61207e13b89650c535393db0c44a830 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
/*
 * Common framework for low-level network console, dump, and debugger code
 *
 * Sep 8 2003  Matt Mackall <mpm@selenic.com>
 *
 * based on the netconsole code from:
 *
 * Copyright (C) 2001  Ingo Molnar <mingo@redhat.com>
 * Copyright (C) 2002  Red Hat, Inc.
 */

#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/string.h>
#include <linux/if_arp.h>
#include <linux/inetdevice.h>
#include <linux/inet.h>
#include <linux/interrupt.h>
#include <linux/netpoll.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <asm/unaligned.h>

/*
 * We maintain a small pool of fully-sized skbs, to make sure the
 * message gets out even in extreme OOM situations.
 */

#define MAX_UDP_CHUNK 1460
#define MAX_SKBS 32
#define MAX_QUEUE_DEPTH (MAX_SKBS / 2)

static struct sk_buff_head skb_pool;

static atomic_t trapped;

#define USEC_PER_POLL	50
#define NETPOLL_RX_ENABLED  1
#define NETPOLL_RX_DROP     2

#define MAX_SKB_SIZE \
		(MAX_UDP_CHUNK + sizeof(struct udphdr) + \
				sizeof(struct iphdr) + sizeof(struct ethhdr))

static void zap_completion_queue(void);
static void arp_reply(struct sk_buff *skb);

static void queue_process(struct work_struct *work)
{
	struct netpoll_info *npinfo =
		container_of(work, struct netpoll_info, tx_work.work);
	struct sk_buff *skb;
	unsigned long flags;

	while ((skb = skb_dequeue(&npinfo->txq))) {
		struct net_device *dev = skb->dev;
		const struct net_device_ops *ops = dev->netdev_ops;
		struct netdev_queue *txq;

		if (!netif_device_present(dev) || !netif_running(dev)) {
			__kfree_skb(skb);
			continue;
		}

		txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));

		local_irq_save(flags);
		__netif_tx_lock(txq, smp_processor_id());
		if (netif_tx_queue_stopped(txq) ||
		    netif_tx_queue_frozen(txq) ||
		    ops->ndo_start_xmit(skb, dev) != NETDEV_TX_OK) {
			skb_queue_head(&npinfo->txq, skb);
			__netif_tx_unlock(txq);
			local_irq_restore(flags);

			schedule_delayed_work(&npinfo->tx_work, HZ/10);
			return;
		}
		__netif_tx_unlock(txq);
		local_irq_restore(flags);
	}
}

static __sum16 checksum_udp(struct sk_buff *skb, struct udphdr *uh,
			    unsigned short ulen, __be32 saddr, __be32 daddr)
{
	__wsum psum;

	if (uh->check == 0 || skb_csum_unnecessary(skb))
		return 0;

	psum = csum_tcpudp_nofold(saddr, daddr, ulen, IPPROTO_UDP, 0);

	if (skb->ip_summed == CHECKSUM_COMPLETE &&
	    !csum_fold(csum_add(psum, skb->csum)))
		return 0;

	skb->csum = psum;

	return __skb_checksum_complete(skb);
}

/*
 * Check whether delayed processing was scheduled for our NIC. If so,
 * we attempt to grab the poll lock and use ->poll() to pump the card.
 * If this fails, either we've recursed in ->poll() or it's already
 * running on another CPU.
 *
 * Note: we don't mask interrupts with this lock because we're using
 * trylock here and interrupts are already disabled in the softirq
 * case. Further, we test the poll_owner to avoid recursion on UP
 * systems where the lock doesn't exist.
 *
 * In cases where there is bi-directional communications, reading only
 * one message at a time can lead to packets being dropped by the
 * network adapter, forcing superfluous retries and possibly timeouts.
 * Thus, we set our budget to greater than 1.
 */
static int poll_one_napi(struct netpoll_info *npinfo,
			 struct napi_struct *napi, int budget)
{
	int work;

	/* net_rx_action's ->poll() invocations and our's are
	 * synchronized by this test which is only made while
	 * holding the napi->poll_lock.
	 */
	if (!test_bit(NAPI_STATE_SCHED, &napi->state))
		return budget;

	npinfo->rx_flags |= NETPOLL_RX_DROP;
	atomic_inc(&trapped);
	set_bit(NAPI_STATE_NPSVC, &napi->state);

	work = napi->poll(napi, budget);

	clear_bit(NAPI_STATE_NPSVC, &napi->state);
	atomic_dec(&trapped);
	npinfo->rx_flags &= ~NETPOLL_RX_DROP;

	return budget - work;
}

static void poll_napi(struct net_device *dev)
{
	struct napi_struct *napi;
	int budget = 16;

	list_for_each_entry(napi, &dev->napi_list, dev_list) {
		if (napi->poll_owner != smp_processor_id() &&
		    spin_trylock(&napi->poll_lock)) {
			budget = poll_one_napi(dev->npinfo, napi, budget);
			spin_unlock(&napi->poll_lock);

			if (!budget)
				break;
		}
	}
}

static void service_arp_queue(struct netpoll_info *npi)
{
	if (npi) {
		struct sk_buff *skb;

		while ((skb = skb_dequeue(&npi->arp_tx)))
			arp_reply(skb);
	}
}

void netpoll_poll(struct netpoll *np)
{
	struct net_device *dev = np->dev;
	const struct net_device_ops *ops = dev->netdev_ops;

	if (!dev || !netif_running(dev) || !ops->ndo_poll_controller)
		return;

	/* Process pending work on NIC */
	ops->ndo_poll_controller(dev);

	poll_napi(dev);

	service_arp_queue(dev->npinfo);

	zap_completion_queue();
}

static void refill_skbs(void)
{
	struct sk_buff *skb;
	unsigned long flags;

	spin_lock_irqsave(&skb_pool.lock, flags);
	while (skb_pool.qlen < MAX_SKBS) {
		skb = alloc_skb(MAX_SKB_SIZE, GFP_ATOMIC);
		if (!skb)
			break;

		__skb_queue_tail(&skb_pool, skb);
	}
	spin_unlock_irqrestore(&skb_pool.lock, flags);
}

static void zap_completion_queue(void)
{
	unsigned long flags;
	struct softnet_data *sd = &get_cpu_var(softnet_data);

	if (sd->completion_queue) {
		struct sk_buff *clist;

		local_irq_save(flags);
		clist = sd->completion_queue;
		sd->completion_queue = NULL;
		local_irq_restore(flags);

		while (clist != NULL) {
			struct sk_buff *skb = clist;
			clist = clist->next;
			if (skb->destructor) {
				atomic_inc(&skb->users);
				dev_kfree_skb_any(skb); /* put this one back */
			} else {
				__kfree_skb(skb);
			}
		}
	}

	put_cpu_var(softnet_data);
}

static struct sk_buff *find_skb(struct netpoll *np, int len, int reserve)
{
	int count = 0;
	struct sk_buff *skb;

	zap_completion_queue();
	refill_skbs();
repeat:

	skb = alloc_skb(len, GFP_ATOMIC);
	if (!skb)
		skb = skb_dequeue(&skb_pool);

	if (!skb) {
		if (++count < 10) {
			netpoll_poll(np);
			goto repeat;
		}
		return NULL;
	}

	atomic_set(&skb->users, 1);
	skb_reserve(skb, reserve);
	return skb;
}

static int netpoll_owner_active(struct net_device *dev)
{
	struct napi_struct *napi;

	list_for_each_entry(napi, &dev->napi_list, dev_list) {
		if (napi->poll_owner == smp_processor_id())
			return 1;
	}
	return 0;
}

static void netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
{
	int status = NETDEV_TX_BUSY;
	unsigned long tries;
	struct net_device *dev = np->dev;
	const struct net_device_ops *ops = dev->netdev_ops;
	struct netpoll_info *npinfo = np->dev->npinfo;

	if (!npinfo || !netif_running(dev) || !netif_device_present(dev)) {
		__kfree_skb(skb);
		return;
	}

	/* don't get messages out of order, and no recursion */
	if (skb_queue_len(&npinfo->txq) == 0 && !netpoll_owner_active(dev)) {
		struct netdev_queue *txq;
		unsigned long flags;

		txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));

		local_irq_save(flags);
		/* try until next clock tick */
		for (tries = jiffies_to_usecs(1)/USEC_PER_POLL;
		     tries > 0; --tries) {
			if (__netif_tx_trylock(txq)) {
				if (!netif_tx_queue_stopped(txq))
					status = ops->ndo_start_xmit(skb, dev);
				__netif_tx_unlock(txq);

				if (status == NETDEV_TX_OK)
					break;

			}

			/* tickle device maybe there is some cleanup */
			netpoll_poll(np);

			udelay(USEC_PER_POLL);
		}
		local_irq_restore(flags);
	}

	if (status != NETDEV_TX_OK) {
		skb_queue_tail(&npinfo->txq, skb);
		schedule_delayed_work(&npinfo->tx_work,0);
	}
}

void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
{
	int total_len, eth_len, ip_len, udp_len;
	struct sk_buff *skb;
	struct udphdr *udph;
	struct iphdr *iph;
	struct ethhdr *eth;

	udp_len = len + sizeof(*udph);
	ip_len = eth_len = udp_len + sizeof(*iph);
	total_len = eth_len + ETH_HLEN + NET_IP_ALIGN;

	skb = find_skb(np, total_len, total_len - len);
	if (!skb)
		return;

	skb_copy_to_linear_data(skb, msg, len);
	skb->len += len;

	skb_push(skb, sizeof(*udph));
	skb_reset_transport_header(skb);
	udph = udp_hdr(skb);
	udph->source = htons(np->local_port);
	udph->dest = htons(np->remote_port);
	udph->len = htons(udp_len);
	udph->check = 0;
	udph->check = csum_tcpudp_magic(np->local_ip,
					np->remote_ip,
					udp_len, IPPROTO_UDP,
					csum_partial(udph, udp_len, 0));
	if (udph->check == 0)
		udph->check = CSUM_MANGLED_0;

	skb_push(skb, sizeof(*iph));
	skb_reset_network_header(skb);
	iph = ip_hdr(skb);

	/* iph->version = 4; iph->ihl = 5; */
	put_unaligned(0x45, (unsigned char *)iph);
	iph->tos      = 0;
	put_unaligned(htons(ip_len), &(iph->tot_len));
	iph->id       = 0;
	iph->frag_off = 0;
	iph->ttl      = 64;
	iph->protocol = IPPROTO_UDP;
	iph->check    = 0;
	put_unaligned(np->local_ip, &(iph->saddr));
	put_unaligned(np->remote_ip, &(iph->daddr));
	iph->check    = ip_fast_csum((unsigned char *)iph, iph->ihl);

	eth = (struct ethhdr *) skb_push(skb, ETH_HLEN);
	skb_reset_mac_header(skb);
	skb->protocol = eth->h_proto = htons(ETH_P_IP);
	memcpy(eth->h_source, np->dev->dev_addr, ETH_ALEN);
	memcpy(eth->h_dest, np->remote_mac, ETH_ALEN);

	skb->dev = np->dev;

	netpoll_send_skb(np, skb);
}

static void arp_reply(struct sk_buff *skb)
{
	struct netpoll_info *npinfo = skb->dev->npinfo;
	struct arphdr *arp;
	unsigned char *arp_ptr;
	int size, type = ARPOP_REPLY, ptype = ETH_P_ARP;
	__be32 sip, tip;
	unsigned char *sha;
	struct sk_buff *send_skb;
	struct netpoll *np = NULL;

	if (npinfo->rx_np && npinfo->rx_np->dev == skb->dev)
		np = npinfo->rx_np;
	if (!np)
		return;

	/* No arp on this interface */
	if (skb->dev->flags & IFF_NOARP)
		return;

	if (!pskb_may_pull(skb, arp_hdr_len(skb->dev)))
		return;

	skb_reset_network_header(skb);
	skb_reset_transport_header(skb);
	arp = arp_hdr(skb);

	if ((arp->ar_hrd != htons(ARPHRD_ETHER) &&
	     arp->ar_hrd != htons(ARPHRD_IEEE802)) ||
	    arp->ar_pro != htons(ETH_P_IP) ||
	    arp->ar_op != htons(ARPOP_REQUEST))
		return;

	arp_ptr = (unsigned char *)(arp+1);
	/* save the location of the src hw addr */
	sha = arp_ptr;
	arp_ptr += skb->dev->addr_len;
	memcpy(&sip, arp_ptr, 4);
	arp_ptr += 4;
	/* if we actually cared about dst hw addr, it would get copied here */
	arp_ptr += skb->dev->addr_len;
	memcpy(&tip, arp_ptr, 4);

	/* Should we ignore arp? */
	if (tip != np->local_ip ||
	    ipv4_is_loopback(tip) || ipv4_is_multicast(tip))
		return;

	size = arp_hdr_len(skb->dev);
	send_skb = find_skb(np, size + LL_ALLOCATED_SPACE(np->dev),
			    LL_RESERVED_SPACE(np->dev));

	if (!send_skb)
		return;

	skb_reset_network_header(send_skb);
	arp = (struct arphdr *) skb_put(send_skb, size);
	send_skb->dev = skb->dev;
	send_skb->protocol = htons(ETH_P_ARP);

	/* Fill the device header for the ARP frame */
	if (dev_hard_header(send_skb, skb->dev, ptype,
			    sha, np->dev->dev_addr,
			    send_skb->len) < 0) {
		kfree_skb(send_skb);
		return;
	}

	/*
	 * Fill out the arp protocol part.
	 *
	 * we only support ethernet device type,
	 * which (according to RFC 1390) should always equal 1 (Ethernet).
	 */

	arp->ar_hrd = htons(np->dev->type);
	arp->ar_pro = htons(ETH_P_IP);
	arp->ar_hln = np->dev->addr_len;
	arp->ar_pln = 4;
	arp->ar_op = htons(type);

	arp_ptr=(unsigned char *)(arp + 1);
	memcpy(arp_ptr, np->dev->dev_addr, np->dev->addr_len);
	arp_ptr += np->dev->addr_len;
	memcpy(arp_ptr, &tip, 4);
	arp_ptr += 4;
	memcpy(arp_ptr, sha, np->dev->addr_len);
	arp_ptr += np->dev->addr_len;
	memcpy(arp_ptr, &sip, 4);

	netpoll_send_skb(np, send_skb);
}

int __netpoll_rx(struct sk_buff *skb)
{
	int proto, len, ulen;
	struct iphdr *iph;
	struct udphdr *uh;
	struct netpoll_info *npi = skb->dev->npinfo;
	struct netpoll *np = npi->rx_np;

	if (!np)
		goto out;
	if (skb->dev->type != ARPHRD_ETHER)
		goto out;

	/* check if netpoll clients need ARP */
	if (skb->protocol == htons(ETH_P_ARP) &&
	    atomic_read(&trapped)) {
		skb_queue_tail(&npi->arp_tx, skb);
		return 1;
	}

	proto = ntohs(eth_hdr(skb)->h_proto);
	if (proto != ETH_P_IP)
		goto out;
	if (skb->pkt_type == PACKET_OTHERHOST)
		goto out;
	if (skb_shared(skb))
		goto out;

	iph = (struct iphdr *)skb->data;
	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
		goto out;
	if (iph->ihl < 5 || iph->version != 4)
		goto out;
	if (!pskb_may_pull(skb, iph->ihl*4))
		goto out;
	if (ip_fast_csum((u8 *)iph, iph->ihl) != 0)
		goto out;

	len = ntohs(iph->tot_len);
	if (skb->len < len || len < iph->ihl*4)
		goto out;

	/*
	 * Our transport medium may have padded the buffer out.
	 * Now We trim to the true length of the frame.
	 */
	if (pskb_trim_rcsum(skb, len))
		goto out;

	if (iph->protocol != IPPROTO_UDP)
		goto out;

	len -= iph->ihl*4;
	uh = (struct udphdr *)(((char *)iph) + iph->ihl*4);
	ulen = ntohs(uh->len);

	if (ulen != len)
		goto out;
	if (checksum_udp(skb, uh, ulen, iph->saddr, iph->daddr))
		goto out;
	if (np->local_ip && np->local_ip != iph->daddr)
		goto out;
	if (np->remote_ip && np->remote_ip != iph->saddr)
		goto out;
	if (np->local_port && np->local_port != ntohs(uh->dest))
		goto out;

	np->rx_hook(np, ntohs(uh->source),
		    (char *)(uh+1),
		    ulen - sizeof(struct udphdr));

	kfree_skb(skb);
	return 1;

out:
	if (atomic_read(&trapped)) {
		kfree_skb(skb);
		return 1;
	}

	return 0;
}

void netpoll_print_options(struct netpoll *np)
{
	printk(KERN_INFO "%s: local port %d\n",
			 np->name, np->local_port);
	printk(KERN_INFO "%s: local IP %pI4\n",
			 np->name, &np->local_ip);
	printk(KERN_INFO "%s: interface %s\n",
			 np->name, np->dev_name);
	printk(KERN_INFO "%s: remote port %d\n",
			 np->name, np->remote_port);
	printk(KERN_INFO "%s: remote IP %pI4\n",
			 np->name, &np->remote_ip);
	printk(KERN_INFO "%s: remote ethernet address %pM\n",
	                 np->name, np->remote_mac);
}

int netpoll_parse_options(struct netpoll *np, char *opt)
{
	char *cur=opt, *delim;

	if (*cur != '@') {
		if ((delim = strchr(cur, '@')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->local_port = simple_strtol(cur, NULL, 10);
		cur = delim;
	}
	cur++;

	if (*cur != '/') {
		if ((delim = strchr(cur, '/')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->local_ip = in_aton(cur);
		cur = delim;
	}
	cur++;

	if (*cur != ',') {
		/* parse out dev name */
		if ((delim = strchr(cur, ',')) == NULL)
			goto parse_failed;
		*delim = 0;
		strlcpy(np->dev_name, cur, sizeof(np->dev_name));
		cur = delim;
	}
	cur++;

	if (*cur != '@') {
		/* dst port */
		if ((delim = strchr(cur, '@')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->remote_port = simple_strtol(cur, NULL, 10);
		cur = delim;
	}
	cur++;

	/* dst ip */
	if ((delim = strchr(cur, '/')) == NULL)
		goto parse_failed;
	*delim = 0;
	np->remote_ip = in_aton(cur);
	cur = delim + 1;

	if (*cur != 0) {
		/* MAC address */
		if ((delim = strchr(cur, ':')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->remote_mac[0] = simple_strtol(cur, NULL, 16);
		cur = delim + 1;
		if ((delim = strchr(cur, ':')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->remote_mac[1] = simple_strtol(cur, NULL, 16);
		cur = delim + 1;
		if ((delim = strchr(cur, ':')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->remote_mac[2] = simple_strtol(cur, NULL, 16);
		cur = delim + 1;
		if ((delim = strchr(cur, ':')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->remote_mac[3] = simple_strtol(cur, NULL, 16);
		cur = delim + 1;
		if ((delim = strchr(cur, ':')) == NULL)
			goto parse_failed;
		*delim = 0;
		np->remote_mac[4] = simple_strtol(cur, NULL, 16);
		cur = delim + 1;
		np->remote_mac[5] = simple_strtol(cur, NULL, 16);
	}

	netpoll_print_options(np);

	return 0;

 parse_failed:
	printk(KERN_INFO "%s: couldn't parse config at %s!\n",
	       np->name, cur);
	return -1;
}

int netpoll_setup(struct netpoll *np)
{
	struct net_device *ndev = NULL;
	struct in_device *in_dev;
	struct netpoll_info *npinfo;
	unsigned long flags;
	int err;

	if (np->dev_name)
		ndev = dev_get_by_name(&init_net, np->dev_name);
	if (!ndev) {
		printk(KERN_ERR "%s: %s doesn't exist, aborting.\n",
		       np->name, np->dev_name);
		return -ENODEV;
	}

	np->dev = ndev;
	if (!ndev->npinfo) {
		npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL);
		if (!npinfo) {
			err = -ENOMEM;
			goto release;
		}

		npinfo->rx_flags = 0;
		npinfo->rx_np = NULL;

		spin_lock_init(&npinfo->rx_lock);
		skb_queue_head_init(&npinfo->arp_tx);
		skb_queue_head_init(&npinfo->txq);
		INIT_DELAYED_WORK(&npinfo->tx_work, queue_process);

		atomic_set(&npinfo->refcnt, 1);
	} else {
		npinfo = ndev->npinfo;
		atomic_inc(&npinfo->refcnt);
	}

	if (!ndev->netdev_ops->ndo_poll_controller) {
		printk(KERN_ERR "%s: %s doesn't support polling, aborting.\n",
		       np->name, np->dev_name);
		err = -ENOTSUPP;
		goto release;
	}

	if (!netif_running(ndev)) {
		unsigned long atmost, atleast;

		printk(KERN_INFO "%s: device %s not up yet, forcing it\n",
		       np->name, np->dev_name);

		rtnl_lock();
		err = dev_open(ndev);
		rtnl_unlock();

		if (err) {
			printk(KERN_ERR "%s: failed to open %s\n",
			       np->name, ndev->name);
			goto release;
		}

		atleast = jiffies + HZ/10;
		atmost = jiffies + 4*HZ;
		while (!netif_carrier_ok(ndev)) {
			if (time_after(jiffies, atmost)) {
				printk(KERN_NOTICE
				       "%s: timeout waiting for carrier\n",
				       np->name);
				break;
			}
			cond_resched();
		}

		/* If carrier appears to come up instantly, we don't
		 * trust it and pause so that we don't pump all our
		 * queued console messages into the bitbucket.
		 */

		if (time_before(jiffies, atleast)) {
			printk(KERN_NOTICE "%s: carrier detect appears"
			       " untrustworthy, waiting 4 seconds\n",
			       np->name);
			msleep(4000);
		}
	}

	if (!np->local_ip) {
		rcu_read_lock();
		in_dev = __in_dev_get_rcu(ndev);

		if (!in_dev || !in_dev->ifa_list) {
			rcu_read_unlock();
			printk(KERN_ERR "%s: no IP address for %s, aborting\n",
			       np->name, np->dev_name);
			err = -EDESTADDRREQ;
			goto release;
		}

		np->local_ip = in_dev->ifa_list->ifa_local;
		rcu_read_unlock();
		printk(KERN_INFO "%s: local IP %pI4\n", np->name, &np->local_ip);
	}

	if (np->rx_hook) {
		spin_lock_irqsave(&npinfo->rx_lock, flags);
		npinfo->rx_flags |= NETPOLL_RX_ENABLED;
		npinfo->rx_np = np;
		spin_unlock_irqrestore(&npinfo->rx_lock, flags);
	}

	/* fill up the skb queue */
	refill_skbs();

	/* last thing to do is link it to the net device structure */
	ndev->npinfo = npinfo;

	/* avoid racing with NAPI reading npinfo */
	synchronize_rcu();

	return 0;

 release:
	if (!ndev->npinfo)
		kfree(npinfo);
	np->dev = NULL;
	dev_put(ndev);
	return err;
}

static int __init netpoll_init(void)
{
	skb_queue_head_init(&skb_pool);
	return 0;
}
core_initcall(netpoll_init);

void netpoll_cleanup(struct netpoll *np)
{
	struct netpoll_info *npinfo;
	unsigned long flags;

	if (np->dev) {
		npinfo = np->dev->npinfo;
		if (npinfo) {
			if (npinfo->rx_np == np) {
				spin_lock_irqsave(&npinfo->rx_lock, flags);
				npinfo->rx_np = NULL;
				npinfo->rx_flags &= ~NETPOLL_RX_ENABLED;
				spin_unlock_irqrestore(&npinfo->rx_lock, flags);
			}

			if (atomic_dec_and_test(&npinfo->refcnt)) {
				skb_queue_purge(&npinfo->arp_tx);
				skb_queue_purge(&npinfo->txq);
				cancel_rearming_delayed_work(&npinfo->tx_work);

				/* clean after last, unfinished work */
				__skb_queue_purge(&npinfo->txq);
				kfree(npinfo);
				np->dev->npinfo = NULL;
			}
		}

		dev_put(np->dev);
	}

	np->dev = NULL;
}

int netpoll_trap(void)
{
	return atomic_read(&trapped);
}

void netpoll_set_trap(int trap)
{
	if (trap)
		atomic_inc(&trapped);
	else
		atomic_dec(&trapped);
}

EXPORT_SYMBOL(netpoll_set_trap);
EXPORT_SYMBOL(netpoll_trap);
EXPORT_SYMBOL(netpoll_print_options);
EXPORT_SYMBOL(netpoll_parse_options);
EXPORT_SYMBOL(netpoll_setup);
EXPORT_SYMBOL(netpoll_cleanup);
EXPORT_SYMBOL(netpoll_send_udp);
EXPORT_SYMBOL(netpoll_poll);