xref: /freebsd/sys/netinet/tcp_hostcache.c (revision 6549718b70f0e660a15685369afb4f9caf2215ce)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 2002 Andre Oppermann, Internet Business Solutions AG
5  * Copyright (c) 2021 Gleb Smirnoff <glebius@FreeBSD.org>
6  * All rights reserved.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. The name of the author may not be used to endorse or promote
17  *    products derived from this software without specific prior written
18  *    permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30  * SUCH DAMAGE.
31  */
32 
33 /*
34  * The tcp_hostcache moves the tcp-specific cached metrics from the routing
35  * table to a dedicated structure indexed by the remote IP address.  It keeps
36  * information on the measured TCP parameters of past TCP sessions to allow
37  * better initial start values to be used with later connections to/from the
38  * same source.  Depending on the network parameters (delay, max MTU,
39  * congestion window) between local and remote sites, this can lead to
40  * significant speed-ups for new TCP connections after the first one.
41  *
42  * Due to the tcp_hostcache, all TCP-specific metrics information in the
43  * routing table have been removed.  The inpcb no longer keeps a pointer to
44  * the routing entry, and protocol-initiated route cloning has been removed
45  * as well.  With these changes, the routing table has gone back to being
46  * more lightwight and only carries information related to packet forwarding.
47  *
48  * tcp_hostcache is designed for multiple concurrent access in SMP
49  * environments and high contention.  It is a straight hash.  Each bucket row
50  * is protected by its own lock for modification.  Readers are protected by
51  * SMR.  This puts certain restrictions on writers, e.g. a writer shall only
52  * insert a fully populated entry into a row.  Writer can't reuse least used
53  * entry if a hash is full.  Value updates for an entry shall be atomic.
54  *
55  * TCP stack(s) communication with tcp_hostcache() is done via KBI functions
56  * tcp_hc_*() and the hc_metrics_lite structure.
57  *
58  * Since tcp_hostcache is only caching information, there are no fatal
59  * consequences if we either can't allocate a new entry or have to drop
60  * an existing entry, or return somewhat stale information.
61  */
62 
63 /*
64  * Many thanks to jlemon for basic structure of tcp_syncache which is being
65  * followed here.
66  */
67 
68 #include <sys/cdefs.h>
69 #include "opt_inet6.h"
70 
71 #include <sys/param.h>
72 #include <sys/systm.h>
73 #include <sys/hash.h>
74 #include <sys/jail.h>
75 #include <sys/kernel.h>
76 #include <sys/lock.h>
77 #include <sys/mutex.h>
78 #include <sys/malloc.h>
79 #include <sys/proc.h>
80 #include <sys/sbuf.h>
81 #include <sys/smr.h>
82 #include <sys/socket.h>
83 #include <sys/sysctl.h>
84 
85 #include <net/vnet.h>
86 
87 #include <netinet/in.h>
88 #include <netinet/in_pcb.h>
89 #include <netinet/tcp.h>
90 #include <netinet/tcp_var.h>
91 
92 #include <vm/uma.h>
93 
94 struct hc_head {
95 	CK_SLIST_HEAD(hc_qhead, hc_metrics) hch_bucket;
96 	u_int		hch_length;
97 	struct mtx	hch_mtx;
98 };
99 
100 struct hc_metrics {
101 	/* housekeeping */
102 	CK_SLIST_ENTRY(hc_metrics) rmx_q;
103 	struct		in_addr ip4;	/* IP address */
104 	struct		in6_addr ip6;	/* IP6 address */
105 	uint32_t	ip6_zoneid;	/* IPv6 scope zone id */
106 	/* endpoint specific values for tcp */
107 	uint32_t	rmx_mtu;	/* MTU for this path */
108 	uint32_t	rmx_ssthresh;	/* outbound gateway buffer limit */
109 	uint32_t	rmx_rtt;	/* estimated round trip time */
110 	uint32_t	rmx_rttvar;	/* estimated rtt variance */
111 	uint32_t	rmx_cwnd;	/* congestion window */
112 	uint32_t	rmx_sendpipe;	/* outbound delay-bandwidth product */
113 	uint32_t	rmx_recvpipe;	/* inbound delay-bandwidth product */
114 	/* TCP hostcache internal data */
115 	int		rmx_expire;	/* lifetime for object */
116 #ifdef	TCP_HC_COUNTERS
117 	u_long		rmx_hits;	/* number of hits */
118 	u_long		rmx_updates;	/* number of updates */
119 #endif
120 };
121 
122 struct tcp_hostcache {
123 	struct hc_head	*hashbase;
124 	uma_zone_t	zone;
125 	smr_t		smr;
126 	u_int		hashsize;
127 	u_int		hashmask;
128 	u_int		hashsalt;
129 	u_int		bucket_limit;
130 	u_int		cache_count;
131 	u_int		cache_limit;
132 	int		expire;
133 	int		prune;
134 	int		purgeall;
135 };
136 
137 /* Arbitrary values */
138 #define TCP_HOSTCACHE_HASHSIZE		512
139 #define TCP_HOSTCACHE_BUCKETLIMIT	30
140 #define TCP_HOSTCACHE_EXPIRE		60*60	/* one hour */
141 #define TCP_HOSTCACHE_PRUNE		5*60	/* every 5 minutes */
142 
143 VNET_DEFINE_STATIC(struct tcp_hostcache, tcp_hostcache);
144 #define	V_tcp_hostcache		VNET(tcp_hostcache)
145 
146 VNET_DEFINE_STATIC(struct callout, tcp_hc_callout);
147 #define	V_tcp_hc_callout	VNET(tcp_hc_callout)
148 
149 static struct hc_metrics *tcp_hc_lookup(struct in_conninfo *);
150 static int sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS);
151 static int sysctl_tcp_hc_histo(SYSCTL_HANDLER_ARGS);
152 static int sysctl_tcp_hc_purgenow(SYSCTL_HANDLER_ARGS);
153 static void tcp_hc_purge_internal(int);
154 static void tcp_hc_purge(void *);
155 
156 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, hostcache,
157     CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
158     "TCP Host cache");
159 
160 VNET_DEFINE(int, tcp_use_hostcache) = 1;
161 #define V_tcp_use_hostcache  VNET(tcp_use_hostcache)
162 SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
163     &VNET_NAME(tcp_use_hostcache), 0,
164     "Enable the TCP hostcache");
165 
166 SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
167     &VNET_NAME(tcp_hostcache.cache_limit), 0,
168     "Overall entry limit for hostcache");
169 
170 SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
171     &VNET_NAME(tcp_hostcache.hashsize), 0,
172     "Size of TCP hostcache hashtable");
173 
174 SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, bucketlimit,
175     CTLFLAG_VNET | CTLFLAG_RDTUN, &VNET_NAME(tcp_hostcache.bucket_limit), 0,
176     "Per-bucket hash limit for hostcache");
177 
178 SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, count, CTLFLAG_VNET | CTLFLAG_RD,
179     &VNET_NAME(tcp_hostcache.cache_count), 0,
180     "Current number of entries in hostcache");
181 
182 SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, expire, CTLFLAG_VNET | CTLFLAG_RW,
183     &VNET_NAME(tcp_hostcache.expire), 0,
184     "Expire time of TCP hostcache entries");
185 
186 SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, prune, CTLFLAG_VNET | CTLFLAG_RW,
187     &VNET_NAME(tcp_hostcache.prune), 0,
188     "Time between purge runs");
189 
190 SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, purge, CTLFLAG_VNET | CTLFLAG_RW,
191     &VNET_NAME(tcp_hostcache.purgeall), 0,
192     "Expire all entries on next purge run");
193 
194 SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, list,
195     CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_SKIP | CTLFLAG_MPSAFE,
196     0, 0, sysctl_tcp_hc_list, "A",
197     "List of all hostcache entries");
198 
199 SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, histo,
200     CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_SKIP | CTLFLAG_MPSAFE,
201     0, 0, sysctl_tcp_hc_histo, "A",
202     "Print a histogram of hostcache hashbucket utilization");
203 
204 SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, purgenow,
205     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
206     NULL, 0, sysctl_tcp_hc_purgenow, "I",
207     "Immediately purge all entries");
208 
209 static MALLOC_DEFINE(M_HOSTCACHE, "hostcache", "TCP hostcache");
210 
211 /* Use jenkins_hash32(), as in other parts of the tcp stack */
212 #define	HOSTCACHE_HASH(inc)						\
213 	((inc)->inc_flags & INC_ISIPV6) ?				\
214 		(jenkins_hash32((inc)->inc6_faddr.s6_addr32, 4,		\
215 		V_tcp_hostcache.hashsalt) & V_tcp_hostcache.hashmask)	\
216 	:								\
217 		(jenkins_hash32(&(inc)->inc_faddr.s_addr, 1,		\
218 		V_tcp_hostcache.hashsalt) & V_tcp_hostcache.hashmask)
219 
220 #define THC_LOCK(h)		mtx_lock(&(h)->hch_mtx)
221 #define THC_UNLOCK(h)		mtx_unlock(&(h)->hch_mtx)
222 
223 void
224 tcp_hc_init(void)
225 {
226 	u_int cache_limit;
227 	int i;
228 
229 	/*
230 	 * Initialize hostcache structures.
231 	 */
232 	atomic_store_int(&V_tcp_hostcache.cache_count, 0);
233 	V_tcp_hostcache.hashsize = TCP_HOSTCACHE_HASHSIZE;
234 	V_tcp_hostcache.bucket_limit = TCP_HOSTCACHE_BUCKETLIMIT;
235 	V_tcp_hostcache.expire = TCP_HOSTCACHE_EXPIRE;
236 	V_tcp_hostcache.prune = TCP_HOSTCACHE_PRUNE;
237 	V_tcp_hostcache.hashsalt = arc4random();
238 
239 	TUNABLE_INT_FETCH("net.inet.tcp.hostcache.hashsize",
240 	    &V_tcp_hostcache.hashsize);
241 	if (!powerof2(V_tcp_hostcache.hashsize)) {
242 		printf("WARNING: hostcache hash size is not a power of 2.\n");
243 		V_tcp_hostcache.hashsize = TCP_HOSTCACHE_HASHSIZE; /* default */
244 	}
245 	V_tcp_hostcache.hashmask = V_tcp_hostcache.hashsize - 1;
246 
247 	TUNABLE_INT_FETCH("net.inet.tcp.hostcache.bucketlimit",
248 	    &V_tcp_hostcache.bucket_limit);
249 
250 	cache_limit = V_tcp_hostcache.hashsize * V_tcp_hostcache.bucket_limit;
251 	V_tcp_hostcache.cache_limit = cache_limit;
252 	TUNABLE_INT_FETCH("net.inet.tcp.hostcache.cachelimit",
253 	    &V_tcp_hostcache.cache_limit);
254 	if (V_tcp_hostcache.cache_limit > cache_limit)
255 		V_tcp_hostcache.cache_limit = cache_limit;
256 
257 	/*
258 	 * Allocate the hash table.
259 	 */
260 	V_tcp_hostcache.hashbase = (struct hc_head *)
261 	    malloc(V_tcp_hostcache.hashsize * sizeof(struct hc_head),
262 		   M_HOSTCACHE, M_WAITOK | M_ZERO);
263 
264 	/*
265 	 * Initialize the hash buckets.
266 	 */
267 	for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
268 		CK_SLIST_INIT(&V_tcp_hostcache.hashbase[i].hch_bucket);
269 		V_tcp_hostcache.hashbase[i].hch_length = 0;
270 		mtx_init(&V_tcp_hostcache.hashbase[i].hch_mtx, "tcp_hc_entry",
271 			  NULL, MTX_DEF);
272 	}
273 
274 	/*
275 	 * Allocate the hostcache entries.
276 	 */
277 	V_tcp_hostcache.zone =
278 	    uma_zcreate("hostcache", sizeof(struct hc_metrics),
279 	    NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_SMR);
280 	uma_zone_set_max(V_tcp_hostcache.zone, V_tcp_hostcache.cache_limit);
281 	V_tcp_hostcache.smr = uma_zone_get_smr(V_tcp_hostcache.zone);
282 
283 	/*
284 	 * Set up periodic cache cleanup.
285 	 */
286 	callout_init(&V_tcp_hc_callout, 1);
287 	callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
288 	    tcp_hc_purge, curvnet);
289 }
290 
291 #ifdef VIMAGE
292 void
293 tcp_hc_destroy(void)
294 {
295 	int i;
296 
297 	callout_drain(&V_tcp_hc_callout);
298 
299 	/* Purge all hc entries. */
300 	tcp_hc_purge_internal(1);
301 
302 	/* Free the uma zone and the allocated hash table. */
303 	uma_zdestroy(V_tcp_hostcache.zone);
304 
305 	for (i = 0; i < V_tcp_hostcache.hashsize; i++)
306 		mtx_destroy(&V_tcp_hostcache.hashbase[i].hch_mtx);
307 	free(V_tcp_hostcache.hashbase, M_HOSTCACHE);
308 }
309 #endif
310 
311 /*
312  * Internal function: compare cache entry to a connection.
313  */
314 static bool
315 tcp_hc_cmp(struct hc_metrics *hc_entry, struct in_conninfo *inc)
316 {
317 
318 	if (inc->inc_flags & INC_ISIPV6) {
319 		/* XXX: check ip6_zoneid */
320 		if (memcmp(&inc->inc6_faddr, &hc_entry->ip6,
321 		    sizeof(inc->inc6_faddr)) == 0)
322 			return (true);
323 	} else {
324 		if (memcmp(&inc->inc_faddr, &hc_entry->ip4,
325 		    sizeof(inc->inc_faddr)) == 0)
326 			return (true);
327 	}
328 
329 	return (false);
330 }
331 
332 /*
333  * Internal function: look up an entry in the hostcache for read.
334  * On success returns in SMR section.
335  */
336 static struct hc_metrics *
337 tcp_hc_lookup(struct in_conninfo *inc)
338 {
339 	struct hc_head *hc_head;
340 	struct hc_metrics *hc_entry;
341 
342 	KASSERT(inc != NULL, ("%s: NULL in_conninfo", __func__));
343 
344 	hc_head = &V_tcp_hostcache.hashbase[HOSTCACHE_HASH(inc)];
345 
346 	/*
347 	 * Iterate through entries in bucket row looking for a match.
348 	 */
349 	smr_enter(V_tcp_hostcache.smr);
350 	CK_SLIST_FOREACH(hc_entry, &hc_head->hch_bucket, rmx_q)
351 		if (tcp_hc_cmp(hc_entry, inc))
352 			break;
353 
354 	if (hc_entry != NULL) {
355 		if (atomic_load_int(&hc_entry->rmx_expire) !=
356 		    V_tcp_hostcache.expire)
357 			atomic_store_int(&hc_entry->rmx_expire,
358 			    V_tcp_hostcache.expire);
359 #ifdef	TCP_HC_COUNTERS
360 		hc_entry->rmx_hits++;
361 #endif
362 	} else
363 		smr_exit(V_tcp_hostcache.smr);
364 
365 	return (hc_entry);
366 }
367 
368 /*
369  * External function: look up an entry in the hostcache and fill out the
370  * supplied TCP metrics structure.  Fills in NULL when no entry was found or
371  * a value is not set.
372  */
373 void
374 tcp_hc_get(struct in_conninfo *inc, struct hc_metrics_lite *hc_metrics_lite)
375 {
376 	struct hc_metrics *hc_entry;
377 
378 	if (!V_tcp_use_hostcache) {
379 		bzero(hc_metrics_lite, sizeof(*hc_metrics_lite));
380 		return;
381 	}
382 
383 	/*
384 	 * Find the right bucket.
385 	 */
386 	hc_entry = tcp_hc_lookup(inc);
387 
388 	/*
389 	 * If we don't have an existing object.
390 	 */
391 	if (hc_entry == NULL) {
392 		bzero(hc_metrics_lite, sizeof(*hc_metrics_lite));
393 		return;
394 	}
395 
396 	hc_metrics_lite->rmx_mtu = atomic_load_32(&hc_entry->rmx_mtu);
397 	hc_metrics_lite->rmx_ssthresh = atomic_load_32(&hc_entry->rmx_ssthresh);
398 	hc_metrics_lite->rmx_rtt = atomic_load_32(&hc_entry->rmx_rtt);
399 	hc_metrics_lite->rmx_rttvar = atomic_load_32(&hc_entry->rmx_rttvar);
400 	hc_metrics_lite->rmx_cwnd = atomic_load_32(&hc_entry->rmx_cwnd);
401 	hc_metrics_lite->rmx_sendpipe = atomic_load_32(&hc_entry->rmx_sendpipe);
402 	hc_metrics_lite->rmx_recvpipe = atomic_load_32(&hc_entry->rmx_recvpipe);
403 
404 	smr_exit(V_tcp_hostcache.smr);
405 }
406 
407 /*
408  * External function: look up an entry in the hostcache and return the
409  * discovered path MTU.  Returns 0 if no entry is found or value is not
410  * set.
411  */
412 uint32_t
413 tcp_hc_getmtu(struct in_conninfo *inc)
414 {
415 	struct hc_metrics *hc_entry;
416 	uint32_t mtu;
417 
418 	if (!V_tcp_use_hostcache)
419 		return (0);
420 
421 	hc_entry = tcp_hc_lookup(inc);
422 	if (hc_entry == NULL) {
423 		return (0);
424 	}
425 
426 	mtu = atomic_load_32(&hc_entry->rmx_mtu);
427 	smr_exit(V_tcp_hostcache.smr);
428 
429 	return (mtu);
430 }
431 
432 /*
433  * External function: update the MTU value of an entry in the hostcache.
434  * Creates a new entry if none was found.
435  */
436 void
437 tcp_hc_updatemtu(struct in_conninfo *inc, uint32_t mtu)
438 {
439 	struct hc_metrics_lite hcml = { .rmx_mtu = mtu };
440 
441 	return (tcp_hc_update(inc, &hcml));
442 }
443 
444 /*
445  * External function: update the TCP metrics of an entry in the hostcache.
446  * Creates a new entry if none was found.
447  */
448 void
449 tcp_hc_update(struct in_conninfo *inc, struct hc_metrics_lite *hcml)
450 {
451 	struct hc_head *hc_head;
452 	struct hc_metrics *hc_entry, *hc_prev;
453 	uint32_t v;
454 	bool new;
455 
456 	if (!V_tcp_use_hostcache)
457 		return;
458 
459 	hc_head = &V_tcp_hostcache.hashbase[HOSTCACHE_HASH(inc)];
460 	hc_prev = NULL;
461 
462 	THC_LOCK(hc_head);
463 	CK_SLIST_FOREACH(hc_entry, &hc_head->hch_bucket, rmx_q) {
464 		if (tcp_hc_cmp(hc_entry, inc))
465 			break;
466 		if (CK_SLIST_NEXT(hc_entry, rmx_q) != NULL)
467 			hc_prev = hc_entry;
468 	}
469 
470 	if (hc_entry != NULL) {
471 		if (atomic_load_int(&hc_entry->rmx_expire) !=
472 		    V_tcp_hostcache.expire)
473 			atomic_store_int(&hc_entry->rmx_expire,
474 			    V_tcp_hostcache.expire);
475 #ifdef	TCP_HC_COUNTERS
476 		hc_entry->rmx_updates++;
477 #endif
478 		new = false;
479 	} else {
480 		/*
481 		 * Try to allocate a new entry.  If the bucket limit is
482 		 * reached, delete the least-used element, located at the end
483 		 * of the CK_SLIST.  During lookup we saved the pointer to
484 		 * the second to last element, in case if list has at least 2
485 		 * elements.  This will allow to delete last element without
486 		 * extra traversal.
487 		 *
488 		 * Give up if the row is empty.
489 		 */
490 		if (hc_head->hch_length >= V_tcp_hostcache.bucket_limit ||
491 		    atomic_load_int(&V_tcp_hostcache.cache_count) >=
492 		    V_tcp_hostcache.cache_limit) {
493 			if (hc_prev != NULL) {
494 				hc_entry = CK_SLIST_NEXT(hc_prev, rmx_q);
495 				KASSERT(CK_SLIST_NEXT(hc_entry, rmx_q) == NULL,
496 				    ("%s: %p is not one to last",
497 				    __func__, hc_prev));
498 				CK_SLIST_REMOVE_AFTER(hc_prev, rmx_q);
499 			} else if ((hc_entry =
500 			    CK_SLIST_FIRST(&hc_head->hch_bucket)) != NULL) {
501 				KASSERT(CK_SLIST_NEXT(hc_entry, rmx_q) == NULL,
502 				    ("%s: %p is not the only element",
503 				    __func__, hc_entry));
504 				CK_SLIST_REMOVE_HEAD(&hc_head->hch_bucket,
505 				    rmx_q);
506 			} else {
507 				THC_UNLOCK(hc_head);
508 				return;
509 			}
510 			KASSERT(hc_head->hch_length > 0 &&
511 			    hc_head->hch_length <= V_tcp_hostcache.bucket_limit,
512 			    ("tcp_hostcache: bucket length violated at %p",
513 			    hc_head));
514 			hc_head->hch_length--;
515 			atomic_subtract_int(&V_tcp_hostcache.cache_count, 1);
516 			TCPSTAT_INC(tcps_hc_bucketoverflow);
517 			uma_zfree_smr(V_tcp_hostcache.zone, hc_entry);
518 		}
519 
520 		/*
521 		 * Allocate a new entry, or balk if not possible.
522 		 */
523 		hc_entry = uma_zalloc_smr(V_tcp_hostcache.zone, M_NOWAIT);
524 		if (hc_entry == NULL) {
525 			THC_UNLOCK(hc_head);
526 			return;
527 		}
528 
529 		/*
530 		 * Initialize basic information of hostcache entry.
531 		 */
532 		bzero(hc_entry, sizeof(*hc_entry));
533 		if (inc->inc_flags & INC_ISIPV6) {
534 			hc_entry->ip6 = inc->inc6_faddr;
535 			hc_entry->ip6_zoneid = inc->inc6_zoneid;
536 		} else
537 			hc_entry->ip4 = inc->inc_faddr;
538 		hc_entry->rmx_expire = V_tcp_hostcache.expire;
539 		new = true;
540 	}
541 
542 	/*
543 	 * Fill in data.  Use atomics, since an existing entry is
544 	 * accessible by readers in SMR section.
545 	 */
546 	if (hcml->rmx_mtu != 0) {
547 		atomic_store_32(&hc_entry->rmx_mtu, hcml->rmx_mtu);
548 	}
549 	if (hcml->rmx_rtt != 0) {
550 		if (hc_entry->rmx_rtt == 0)
551 			v = hcml->rmx_rtt;
552 		else
553 			v = ((uint64_t)hc_entry->rmx_rtt +
554 			    (uint64_t)hcml->rmx_rtt) / 2;
555 		atomic_store_32(&hc_entry->rmx_rtt, v);
556 		TCPSTAT_INC(tcps_cachedrtt);
557 	}
558 	if (hcml->rmx_rttvar != 0) {
559 	        if (hc_entry->rmx_rttvar == 0)
560 			v = hcml->rmx_rttvar;
561 		else
562 			v = ((uint64_t)hc_entry->rmx_rttvar +
563 			    (uint64_t)hcml->rmx_rttvar) / 2;
564 		atomic_store_32(&hc_entry->rmx_rttvar, v);
565 		TCPSTAT_INC(tcps_cachedrttvar);
566 	}
567 	if (hcml->rmx_ssthresh != 0) {
568 		if (hc_entry->rmx_ssthresh == 0)
569 			v = hcml->rmx_ssthresh;
570 		else
571 			v = (hc_entry->rmx_ssthresh + hcml->rmx_ssthresh) / 2;
572 		atomic_store_32(&hc_entry->rmx_ssthresh, v);
573 		TCPSTAT_INC(tcps_cachedssthresh);
574 	}
575 	if (hcml->rmx_cwnd != 0) {
576 		if (hc_entry->rmx_cwnd == 0)
577 			v = hcml->rmx_cwnd;
578 		else
579 			v = ((uint64_t)hc_entry->rmx_cwnd +
580 			    (uint64_t)hcml->rmx_cwnd) / 2;
581 		atomic_store_32(&hc_entry->rmx_cwnd, v);
582 		/* TCPSTAT_INC(tcps_cachedcwnd); */
583 	}
584 	if (hcml->rmx_sendpipe != 0) {
585 		if (hc_entry->rmx_sendpipe == 0)
586 			v = hcml->rmx_sendpipe;
587 		else
588 			v = ((uint64_t)hc_entry->rmx_sendpipe +
589 			    (uint64_t)hcml->rmx_sendpipe) /2;
590 		atomic_store_32(&hc_entry->rmx_sendpipe, v);
591 		/* TCPSTAT_INC(tcps_cachedsendpipe); */
592 	}
593 	if (hcml->rmx_recvpipe != 0) {
594 		if (hc_entry->rmx_recvpipe == 0)
595 			v = hcml->rmx_recvpipe;
596 		else
597 			v = ((uint64_t)hc_entry->rmx_recvpipe +
598 			    (uint64_t)hcml->rmx_recvpipe) /2;
599 		atomic_store_32(&hc_entry->rmx_recvpipe, v);
600 		/* TCPSTAT_INC(tcps_cachedrecvpipe); */
601 	}
602 
603 	/*
604 	 * Put it upfront.
605 	 */
606 	if (new) {
607 		CK_SLIST_INSERT_HEAD(&hc_head->hch_bucket, hc_entry, rmx_q);
608 		hc_head->hch_length++;
609 		KASSERT(hc_head->hch_length <= V_tcp_hostcache.bucket_limit,
610 		    ("tcp_hostcache: bucket length too high at %p", hc_head));
611 		atomic_add_int(&V_tcp_hostcache.cache_count, 1);
612 		TCPSTAT_INC(tcps_hc_added);
613 	} else if (hc_entry != CK_SLIST_FIRST(&hc_head->hch_bucket)) {
614 		KASSERT(CK_SLIST_NEXT(hc_prev, rmx_q) == hc_entry,
615 		    ("%s: %p next is not %p", __func__, hc_prev, hc_entry));
616 		CK_SLIST_REMOVE_AFTER(hc_prev, rmx_q);
617 		CK_SLIST_INSERT_HEAD(&hc_head->hch_bucket, hc_entry, rmx_q);
618 	}
619 	THC_UNLOCK(hc_head);
620 }
621 
622 /*
623  * Sysctl function: prints the list and values of all hostcache entries in
624  * unsorted order.
625  */
626 static int
627 sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
628 {
629 	const int linesize = 128;
630 	struct sbuf sb;
631 	int i, error, len;
632 	struct hc_metrics *hc_entry;
633 	char ip4buf[INET_ADDRSTRLEN];
634 #ifdef INET6
635 	char ip6buf[INET6_ADDRSTRLEN];
636 #endif
637 
638 	if (jailed_without_vnet(curthread->td_ucred) != 0)
639 		return (EPERM);
640 
641 	/* Optimize Buffer length query by sbin/sysctl */
642 	if (req->oldptr == NULL) {
643 		len = (atomic_load_int(&V_tcp_hostcache.cache_count) + 1) *
644 			linesize;
645 		return (SYSCTL_OUT(req, NULL, len));
646 	}
647 
648 	error = sysctl_wire_old_buffer(req, 0);
649 	if (error != 0) {
650 		return(error);
651 	}
652 
653 	/* Use a buffer sized for one full bucket */
654 	sbuf_new_for_sysctl(&sb, NULL, V_tcp_hostcache.bucket_limit *
655 		linesize, req);
656 
657 	sbuf_printf(&sb,
658 		"\nIP address        MTU  SSTRESH      RTT   RTTVAR "
659 		"    CWND SENDPIPE RECVPIPE "
660 #ifdef	TCP_HC_COUNTERS
661 		"HITS  UPD  "
662 #endif
663 		"EXP\n");
664 	sbuf_drain(&sb);
665 
666 #define msec(u) (((u) + 500) / 1000)
667 	for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
668 		THC_LOCK(&V_tcp_hostcache.hashbase[i]);
669 		CK_SLIST_FOREACH(hc_entry,
670 		    &V_tcp_hostcache.hashbase[i].hch_bucket, rmx_q) {
671 			sbuf_printf(&sb,
672 			    "%-15s %5u %8u %6lums %6lums %8u %8u %8u "
673 #ifdef	TCP_HC_COUNTERS
674 			    "%4lu %4lu "
675 #endif
676 			    "%4i\n",
677 			    hc_entry->ip4.s_addr ?
678 			        inet_ntoa_r(hc_entry->ip4, ip4buf) :
679 #ifdef INET6
680 				ip6_sprintf(ip6buf, &hc_entry->ip6),
681 #else
682 				"IPv6?",
683 #endif
684 			    hc_entry->rmx_mtu,
685 			    hc_entry->rmx_ssthresh,
686 			    msec((u_long)hc_entry->rmx_rtt *
687 				(RTM_RTTUNIT / (hz * TCP_RTT_SCALE))),
688 			    msec((u_long)hc_entry->rmx_rttvar *
689 				(RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE))),
690 			    hc_entry->rmx_cwnd,
691 			    hc_entry->rmx_sendpipe,
692 			    hc_entry->rmx_recvpipe,
693 #ifdef	TCP_HC_COUNTERS
694 			    hc_entry->rmx_hits,
695 			    hc_entry->rmx_updates,
696 #endif
697 			    hc_entry->rmx_expire);
698 		}
699 		THC_UNLOCK(&V_tcp_hostcache.hashbase[i]);
700 		sbuf_drain(&sb);
701 	}
702 #undef msec
703 	error = sbuf_finish(&sb);
704 	sbuf_delete(&sb);
705 	return(error);
706 }
707 
708 /*
709  * Sysctl function: prints a histogram of the hostcache hashbucket
710  * utilization.
711  */
712 static int
713 sysctl_tcp_hc_histo(SYSCTL_HANDLER_ARGS)
714 {
715 	const int linesize = 50;
716 	struct sbuf sb;
717 	int i, error;
718 	int *histo;
719 	u_int hch_length;
720 
721 	if (jailed_without_vnet(curthread->td_ucred) != 0)
722 		return (EPERM);
723 
724 	histo = (int *)malloc(sizeof(int) * (V_tcp_hostcache.bucket_limit + 1),
725 			M_TEMP, M_NOWAIT|M_ZERO);
726 	if (histo == NULL)
727 		return(ENOMEM);
728 
729 	for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
730 		hch_length = V_tcp_hostcache.hashbase[i].hch_length;
731 		KASSERT(hch_length <= V_tcp_hostcache.bucket_limit,
732 		    ("tcp_hostcache: bucket limit exceeded at %u: %u",
733 		    i, hch_length));
734 		histo[hch_length]++;
735 	}
736 
737 	/* Use a buffer for 16 lines */
738 	sbuf_new_for_sysctl(&sb, NULL, 16 * linesize, req);
739 
740 	sbuf_printf(&sb, "\nLength\tCount\n");
741 	for (i = 0; i <= V_tcp_hostcache.bucket_limit; i++) {
742 		sbuf_printf(&sb, "%u\t%u\n", i, histo[i]);
743 	}
744 	error = sbuf_finish(&sb);
745 	sbuf_delete(&sb);
746 	free(histo, M_TEMP);
747 	return(error);
748 }
749 
750 /*
751  * Caller has to make sure the curvnet is set properly.
752  */
753 static void
754 tcp_hc_purge_internal(int all)
755 {
756 	struct hc_head *head;
757 	struct hc_metrics *hc_entry, *hc_next, *hc_prev;
758 	int i;
759 
760 	for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
761 		head = &V_tcp_hostcache.hashbase[i];
762 		hc_prev = NULL;
763 		THC_LOCK(head);
764 		CK_SLIST_FOREACH_SAFE(hc_entry, &head->hch_bucket, rmx_q,
765 		    hc_next) {
766 			KASSERT(head->hch_length > 0 && head->hch_length <=
767 			    V_tcp_hostcache.bucket_limit, ("tcp_hostcache: "
768 			    "bucket length out of range at %u: %u", i,
769 			    head->hch_length));
770 			if (all ||
771 			    atomic_load_int(&hc_entry->rmx_expire) <= 0) {
772 				if (hc_prev != NULL) {
773 					KASSERT(hc_entry ==
774 					    CK_SLIST_NEXT(hc_prev, rmx_q),
775 					    ("%s: %p is not next to %p",
776 					    __func__, hc_entry, hc_prev));
777 					CK_SLIST_REMOVE_AFTER(hc_prev, rmx_q);
778 				} else {
779 					KASSERT(hc_entry ==
780 					    CK_SLIST_FIRST(&head->hch_bucket),
781 					    ("%s: %p is not first",
782 					    __func__, hc_entry));
783 					CK_SLIST_REMOVE_HEAD(&head->hch_bucket,
784 					    rmx_q);
785 				}
786 				uma_zfree_smr(V_tcp_hostcache.zone, hc_entry);
787 				head->hch_length--;
788 				atomic_subtract_int(&V_tcp_hostcache.cache_count, 1);
789 			} else {
790 				atomic_subtract_int(&hc_entry->rmx_expire,
791 				    V_tcp_hostcache.prune);
792 				hc_prev = hc_entry;
793 			}
794 		}
795 		THC_UNLOCK(head);
796 	}
797 }
798 
799 /*
800  * Expire and purge (old|all) entries in the tcp_hostcache.  Runs
801  * periodically from the callout.
802  */
803 static void
804 tcp_hc_purge(void *arg)
805 {
806 	CURVNET_SET((struct vnet *) arg);
807 	int all = 0;
808 
809 	if (V_tcp_hostcache.purgeall) {
810 		if (V_tcp_hostcache.purgeall == 2)
811 			V_tcp_hostcache.hashsalt = arc4random();
812 		all = 1;
813 		V_tcp_hostcache.purgeall = 0;
814 	}
815 
816 	tcp_hc_purge_internal(all);
817 
818 	callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
819 	    tcp_hc_purge, arg);
820 	CURVNET_RESTORE();
821 }
822 
823 /*
824  * Expire and purge all entries in hostcache immediately.
825  */
826 static int
827 sysctl_tcp_hc_purgenow(SYSCTL_HANDLER_ARGS)
828 {
829 	int error, val;
830 
831 	val = 0;
832 	error = sysctl_handle_int(oidp, &val, 0, req);
833 	if (error || !req->newptr)
834 		return (error);
835 
836 	if (val == 2)
837 		V_tcp_hostcache.hashsalt = arc4random();
838 	tcp_hc_purge_internal(1);
839 
840 	callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
841 	    tcp_hc_purge, curvnet);
842 
843 	return (0);
844 }
845