blob: e7fd76975d86ff433912040bee03ba8416fc7a2d [file] [log] [blame]
Trond Myklebust80b14d52015-02-14 20:31:59 -05001/*
2 * Multipath support for RPC
3 *
4 * Copyright (c) 2015, 2016, Primary Data, Inc. All rights reserved.
5 *
6 * Trond Myklebust <trond.myklebust@primarydata.com>
7 *
8 */
9#include <linux/types.h>
10#include <linux/kref.h>
11#include <linux/list.h>
12#include <linux/rcupdate.h>
13#include <linux/rculist.h>
14#include <linux/slab.h>
15#include <asm/cmpxchg.h>
16#include <linux/spinlock.h>
17#include <linux/sunrpc/xprt.h>
18#include <linux/sunrpc/xprtmultipath.h>
19
20typedef struct rpc_xprt *(*xprt_switch_find_xprt_t)(struct list_head *head,
21 const struct rpc_xprt *cur);
22
23static const struct rpc_xprt_iter_ops rpc_xprt_iter_singular;
24static const struct rpc_xprt_iter_ops rpc_xprt_iter_roundrobin;
25static const struct rpc_xprt_iter_ops rpc_xprt_iter_listall;
26
27static void xprt_switch_add_xprt_locked(struct rpc_xprt_switch *xps,
28 struct rpc_xprt *xprt)
29{
30 if (unlikely(xprt_get(xprt) == NULL))
31 return;
32 list_add_tail_rcu(&xprt->xprt_switch, &xps->xps_xprt_list);
33 smp_wmb();
34 if (xps->xps_nxprts == 0)
35 xps->xps_net = xprt->xprt_net;
36 xps->xps_nxprts++;
37}
38
39/**
40 * rpc_xprt_switch_add_xprt - Add a new rpc_xprt to an rpc_xprt_switch
41 * @xps: pointer to struct rpc_xprt_switch
42 * @xprt: pointer to struct rpc_xprt
43 *
44 * Adds xprt to the end of the list of struct rpc_xprt in xps.
45 */
46void rpc_xprt_switch_add_xprt(struct rpc_xprt_switch *xps,
47 struct rpc_xprt *xprt)
48{
49 if (xprt == NULL)
50 return;
51 spin_lock(&xps->xps_lock);
52 if (xps->xps_net == xprt->xprt_net || xps->xps_net == NULL)
53 xprt_switch_add_xprt_locked(xps, xprt);
54 spin_unlock(&xps->xps_lock);
55}
56
57static void xprt_switch_remove_xprt_locked(struct rpc_xprt_switch *xps,
58 struct rpc_xprt *xprt)
59{
60 if (unlikely(xprt == NULL))
61 return;
62 xps->xps_nxprts--;
63 if (xps->xps_nxprts == 0)
64 xps->xps_net = NULL;
65 smp_wmb();
66 list_del_rcu(&xprt->xprt_switch);
67}
68
69/**
70 * rpc_xprt_switch_remove_xprt - Removes an rpc_xprt from a rpc_xprt_switch
71 * @xps: pointer to struct rpc_xprt_switch
72 * @xprt: pointer to struct rpc_xprt
73 *
74 * Removes xprt from the list of struct rpc_xprt in xps.
75 */
76void rpc_xprt_switch_remove_xprt(struct rpc_xprt_switch *xps,
77 struct rpc_xprt *xprt)
78{
79 spin_lock(&xps->xps_lock);
80 xprt_switch_remove_xprt_locked(xps, xprt);
81 spin_unlock(&xps->xps_lock);
82 xprt_put(xprt);
83}
84
85/**
86 * xprt_switch_alloc - Allocate a new struct rpc_xprt_switch
87 * @xprt: pointer to struct rpc_xprt
88 * @gfp_flags: allocation flags
89 *
90 * On success, returns an initialised struct rpc_xprt_switch, containing
91 * the entry xprt. Returns NULL on failure.
92 */
93struct rpc_xprt_switch *xprt_switch_alloc(struct rpc_xprt *xprt,
94 gfp_t gfp_flags)
95{
96 struct rpc_xprt_switch *xps;
97
98 xps = kmalloc(sizeof(*xps), gfp_flags);
99 if (xps != NULL) {
100 spin_lock_init(&xps->xps_lock);
101 kref_init(&xps->xps_kref);
102 xps->xps_nxprts = 0;
103 INIT_LIST_HEAD(&xps->xps_xprt_list);
104 xps->xps_iter_ops = &rpc_xprt_iter_singular;
105 xprt_switch_add_xprt_locked(xps, xprt);
106 }
107
108 return xps;
109}
110
111static void xprt_switch_free_entries(struct rpc_xprt_switch *xps)
112{
113 spin_lock(&xps->xps_lock);
114 while (!list_empty(&xps->xps_xprt_list)) {
115 struct rpc_xprt *xprt;
116
117 xprt = list_first_entry(&xps->xps_xprt_list,
118 struct rpc_xprt, xprt_switch);
119 xprt_switch_remove_xprt_locked(xps, xprt);
120 spin_unlock(&xps->xps_lock);
121 xprt_put(xprt);
122 spin_lock(&xps->xps_lock);
123 }
124 spin_unlock(&xps->xps_lock);
125}
126
127static void xprt_switch_free(struct kref *kref)
128{
129 struct rpc_xprt_switch *xps = container_of(kref,
130 struct rpc_xprt_switch, xps_kref);
131
132 xprt_switch_free_entries(xps);
133 kfree_rcu(xps, xps_rcu);
134}
135
136/**
137 * xprt_switch_get - Return a reference to a rpc_xprt_switch
138 * @xps: pointer to struct rpc_xprt_switch
139 *
140 * Returns a reference to xps unless the refcount is already zero.
141 */
142struct rpc_xprt_switch *xprt_switch_get(struct rpc_xprt_switch *xps)
143{
144 if (xps != NULL && kref_get_unless_zero(&xps->xps_kref))
145 return xps;
146 return NULL;
147}
148
149/**
150 * xprt_switch_put - Release a reference to a rpc_xprt_switch
151 * @xps: pointer to struct rpc_xprt_switch
152 *
153 * Release the reference to xps, and free it once the refcount is zero.
154 */
155void xprt_switch_put(struct rpc_xprt_switch *xps)
156{
157 if (xps != NULL)
158 kref_put(&xps->xps_kref, xprt_switch_free);
159}
160
161/**
162 * rpc_xprt_switch_set_roundrobin - Set a round-robin policy on rpc_xprt_switch
163 * @xps: pointer to struct rpc_xprt_switch
164 *
165 * Sets a round-robin default policy for iterators acting on xps.
166 */
167void rpc_xprt_switch_set_roundrobin(struct rpc_xprt_switch *xps)
168{
169 if (READ_ONCE(xps->xps_iter_ops) != &rpc_xprt_iter_roundrobin)
170 WRITE_ONCE(xps->xps_iter_ops, &rpc_xprt_iter_roundrobin);
171}
172
173static
174const struct rpc_xprt_iter_ops *xprt_iter_ops(const struct rpc_xprt_iter *xpi)
175{
176 if (xpi->xpi_ops != NULL)
177 return xpi->xpi_ops;
178 return rcu_dereference(xpi->xpi_xpswitch)->xps_iter_ops;
179}
180
181static
182void xprt_iter_no_rewind(struct rpc_xprt_iter *xpi)
183{
184}
185
186static
187void xprt_iter_default_rewind(struct rpc_xprt_iter *xpi)
188{
189 WRITE_ONCE(xpi->xpi_cursor, NULL);
190}
191
192static
193struct rpc_xprt *xprt_switch_find_first_entry(struct list_head *head)
194{
195 return list_first_or_null_rcu(head, struct rpc_xprt, xprt_switch);
196}
197
198static
199struct rpc_xprt *xprt_iter_first_entry(struct rpc_xprt_iter *xpi)
200{
201 struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
202
203 if (xps == NULL)
204 return NULL;
205 return xprt_switch_find_first_entry(&xps->xps_xprt_list);
206}
207
208static
209struct rpc_xprt *xprt_switch_find_current_entry(struct list_head *head,
210 const struct rpc_xprt *cur)
211{
212 struct rpc_xprt *pos;
213
214 list_for_each_entry_rcu(pos, head, xprt_switch) {
215 if (cur == pos)
216 return pos;
217 }
218 return NULL;
219}
220
221static
222struct rpc_xprt *xprt_iter_current_entry(struct rpc_xprt_iter *xpi)
223{
224 struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
225 struct list_head *head;
226
227 if (xps == NULL)
228 return NULL;
229 head = &xps->xps_xprt_list;
230 if (xpi->xpi_cursor == NULL || xps->xps_nxprts < 2)
231 return xprt_switch_find_first_entry(head);
232 return xprt_switch_find_current_entry(head, xpi->xpi_cursor);
233}
234
235static
236struct rpc_xprt *xprt_switch_find_next_entry(struct list_head *head,
237 const struct rpc_xprt *cur)
238{
239 struct rpc_xprt *pos, *prev = NULL;
240
241 list_for_each_entry_rcu(pos, head, xprt_switch) {
242 if (cur == prev)
243 return pos;
244 prev = pos;
245 }
246 return NULL;
247}
248
249static
250struct rpc_xprt *xprt_switch_set_next_cursor(struct list_head *head,
251 struct rpc_xprt **cursor,
252 xprt_switch_find_xprt_t find_next)
253{
254 struct rpc_xprt *cur, *pos, *old;
255
256 cur = READ_ONCE(*cursor);
257 for (;;) {
258 old = cur;
259 pos = find_next(head, old);
260 if (pos == NULL)
261 break;
262 cur = cmpxchg_relaxed(cursor, old, pos);
263 if (cur == old)
264 break;
265 }
266 return pos;
267}
268
269static
270struct rpc_xprt *xprt_iter_next_entry_multiple(struct rpc_xprt_iter *xpi,
271 xprt_switch_find_xprt_t find_next)
272{
273 struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
274 struct list_head *head;
275
276 if (xps == NULL)
277 return NULL;
278 head = &xps->xps_xprt_list;
279 if (xps->xps_nxprts < 2)
280 return xprt_switch_find_first_entry(head);
281 return xprt_switch_set_next_cursor(head, &xpi->xpi_cursor, find_next);
282}
283
284static
285struct rpc_xprt *xprt_switch_find_next_entry_roundrobin(struct list_head *head,
286 const struct rpc_xprt *cur)
287{
288 struct rpc_xprt *ret;
289
290 ret = xprt_switch_find_next_entry(head, cur);
291 if (ret != NULL)
292 return ret;
293 return xprt_switch_find_first_entry(head);
294}
295
296static
297struct rpc_xprt *xprt_iter_next_entry_roundrobin(struct rpc_xprt_iter *xpi)
298{
299 return xprt_iter_next_entry_multiple(xpi,
300 xprt_switch_find_next_entry_roundrobin);
301}
302
303static
304struct rpc_xprt *xprt_iter_next_entry_all(struct rpc_xprt_iter *xpi)
305{
306 return xprt_iter_next_entry_multiple(xpi, xprt_switch_find_next_entry);
307}
308
309/*
310 * xprt_iter_rewind - Resets the xprt iterator
311 * @xpi: pointer to rpc_xprt_iter
312 *
313 * Resets xpi to ensure that it points to the first entry in the list
314 * of transports.
315 */
316static
317void xprt_iter_rewind(struct rpc_xprt_iter *xpi)
318{
319 rcu_read_lock();
320 xprt_iter_ops(xpi)->xpi_rewind(xpi);
321 rcu_read_unlock();
322}
323
324static void __xprt_iter_init(struct rpc_xprt_iter *xpi,
325 struct rpc_xprt_switch *xps,
326 const struct rpc_xprt_iter_ops *ops)
327{
328 rcu_assign_pointer(xpi->xpi_xpswitch, xprt_switch_get(xps));
329 xpi->xpi_cursor = NULL;
330 xpi->xpi_ops = ops;
331}
332
333/**
334 * xprt_iter_init - Initialise an xprt iterator
335 * @xpi: pointer to rpc_xprt_iter
336 * @xps: pointer to rpc_xprt_switch
337 *
338 * Initialises the iterator to use the default iterator ops
339 * as set in xps. This function is mainly intended for internal
340 * use in the rpc_client.
341 */
342void xprt_iter_init(struct rpc_xprt_iter *xpi,
343 struct rpc_xprt_switch *xps)
344{
345 __xprt_iter_init(xpi, xps, NULL);
346}
347
348/**
349 * xprt_iter_init_listall - Initialise an xprt iterator
350 * @xpi: pointer to rpc_xprt_iter
351 * @xps: pointer to rpc_xprt_switch
352 *
353 * Initialises the iterator to iterate once through the entire list
354 * of entries in xps.
355 */
356void xprt_iter_init_listall(struct rpc_xprt_iter *xpi,
357 struct rpc_xprt_switch *xps)
358{
359 __xprt_iter_init(xpi, xps, &rpc_xprt_iter_listall);
360}
361
362/**
363 * xprt_iter_xchg_switch - Atomically swap out the rpc_xprt_switch
364 * @xpi: pointer to rpc_xprt_iter
365 * @xps: pointer to a new rpc_xprt_switch or NULL
366 *
367 * Swaps out the existing xpi->xpi_xpswitch with a new value.
368 */
369struct rpc_xprt_switch *xprt_iter_xchg_switch(struct rpc_xprt_iter *xpi,
370 struct rpc_xprt_switch *newswitch)
371{
372 struct rpc_xprt_switch __rcu *oldswitch;
373
374 /* Atomically swap out the old xpswitch */
375 oldswitch = xchg(&xpi->xpi_xpswitch, RCU_INITIALIZER(newswitch));
376 if (newswitch != NULL)
377 xprt_iter_rewind(xpi);
378 return rcu_dereference_protected(oldswitch, true);
379}
380
381/**
382 * xprt_iter_destroy - Destroys the xprt iterator
383 * @xpi pointer to rpc_xprt_iter
384 */
385void xprt_iter_destroy(struct rpc_xprt_iter *xpi)
386{
387 xprt_switch_put(xprt_iter_xchg_switch(xpi, NULL));
388}
389
390/**
391 * xprt_iter_xprt - Returns the rpc_xprt pointed to by the cursor
392 * @xpi: pointer to rpc_xprt_iter
393 *
394 * Returns a pointer to the struct rpc_xprt that is currently
395 * pointed to by the cursor.
396 * Caller must be holding rcu_read_lock().
397 */
398struct rpc_xprt *xprt_iter_xprt(struct rpc_xprt_iter *xpi)
399{
400 WARN_ON_ONCE(!rcu_read_lock_held());
401 return xprt_iter_ops(xpi)->xpi_xprt(xpi);
402}
403
404static
405struct rpc_xprt *xprt_iter_get_helper(struct rpc_xprt_iter *xpi,
406 struct rpc_xprt *(*fn)(struct rpc_xprt_iter *))
407{
408 struct rpc_xprt *ret;
409
410 do {
411 ret = fn(xpi);
412 if (ret == NULL)
413 break;
414 ret = xprt_get(ret);
415 } while (ret == NULL);
416 return ret;
417}
418
419/**
420 * xprt_iter_get_xprt - Returns the rpc_xprt pointed to by the cursor
421 * @xpi: pointer to rpc_xprt_iter
422 *
423 * Returns a reference to the struct rpc_xprt that is currently
424 * pointed to by the cursor.
425 */
426struct rpc_xprt *xprt_iter_get_xprt(struct rpc_xprt_iter *xpi)
427{
428 struct rpc_xprt *xprt;
429
430 rcu_read_lock();
431 xprt = xprt_iter_get_helper(xpi, xprt_iter_ops(xpi)->xpi_xprt);
432 rcu_read_unlock();
433 return xprt;
434}
435
436/**
437 * xprt_iter_get_next - Returns the next rpc_xprt following the cursor
438 * @xpi: pointer to rpc_xprt_iter
439 *
440 * Returns a reference to the struct rpc_xprt that immediately follows the
441 * entry pointed to by the cursor.
442 */
443struct rpc_xprt *xprt_iter_get_next(struct rpc_xprt_iter *xpi)
444{
445 struct rpc_xprt *xprt;
446
447 rcu_read_lock();
448 xprt = xprt_iter_get_helper(xpi, xprt_iter_ops(xpi)->xpi_next);
449 rcu_read_unlock();
450 return xprt;
451}
452
453/* Policy for always returning the first entry in the rpc_xprt_switch */
454static
455const struct rpc_xprt_iter_ops rpc_xprt_iter_singular = {
456 .xpi_rewind = xprt_iter_no_rewind,
457 .xpi_xprt = xprt_iter_first_entry,
458 .xpi_next = xprt_iter_first_entry,
459};
460
461/* Policy for round-robin iteration of entries in the rpc_xprt_switch */
462static
463const struct rpc_xprt_iter_ops rpc_xprt_iter_roundrobin = {
464 .xpi_rewind = xprt_iter_default_rewind,
465 .xpi_xprt = xprt_iter_current_entry,
466 .xpi_next = xprt_iter_next_entry_roundrobin,
467};
468
469/* Policy for once-through iteration of entries in the rpc_xprt_switch */
470static
471const struct rpc_xprt_iter_ops rpc_xprt_iter_listall = {
472 .xpi_rewind = xprt_iter_default_rewind,
473 .xpi_xprt = xprt_iter_current_entry,
474 .xpi_next = xprt_iter_next_entry_all,
475};