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authorDavid Howells <dhowells@redhat.com>2009-04-03 11:42:38 -0400
committerDavid Howells <dhowells@redhat.com>2009-04-03 11:42:38 -0400
commit36c9559022850f919269564a74bf17fdabf4bb30 (patch)
treef163afcf8f8a9eb1a5d63fd6198fcb3e29564493 /fs/fscache/object.c
parent2868cbea72dc89ae0eb17693596b1dedaafff1c5 (diff)
FS-Cache: Object management state machine
Implement the cache object management state machine. The following documentation is added to illuminate the working of this state machine. It will also be added as: Documentation/filesystems/caching/object.txt ==================================================== IN-KERNEL CACHE OBJECT REPRESENTATION AND MANAGEMENT ==================================================== ============== REPRESENTATION ============== FS-Cache maintains an in-kernel representation of each object that a netfs is currently interested in. Such objects are represented by the fscache_cookie struct and are referred to as cookies. FS-Cache also maintains a separate in-kernel representation of the objects that a cache backend is currently actively caching. Such objects are represented by the fscache_object struct. The cache backends allocate these upon request, and are expected to embed them in their own representations. These are referred to as objects. There is a 1:N relationship between cookies and objects. A cookie may be represented by multiple objects - an index may exist in more than one cache - or even by no objects (it may not be cached). Furthermore, both cookies and objects are hierarchical. The two hierarchies correspond, but the cookies tree is a superset of the union of the object trees of multiple caches: NETFS INDEX TREE : CACHE 1 : CACHE 2 : : : +-----------+ : +----------->| IObject | : +-----------+ | : +-----------+ : | ICookie |-------+ : | : +-----------+ | : | : +-----------+ | +------------------------------>| IObject | | : | : +-----------+ | : V : | | : +-----------+ : | V +----------->| IObject | : | +-----------+ | : +-----------+ : | | ICookie |-------+ : | : V +-----------+ | : | : +-----------+ | +------------------------------>| IObject | +-----+-----+ : | : +-----------+ | | : | : | V | : V : | +-----------+ | : +-----------+ : | | ICookie |------------------------->| IObject | : | +-----------+ | : +-----------+ : | | V : | : V | +-----------+ : | : +-----------+ | | ICookie |-------------------------------->| IObject | | +-----------+ : | : +-----------+ V | : V : | +-----------+ | : +-----------+ : | | DCookie |------------------------->| DObject | : | +-----------+ | : +-----------+ : | | : : | +-------+-------+ : : | | | : : | V V : : V +-----------+ +-----------+ : : +-----------+ | DCookie | | DCookie |------------------------>| DObject | +-----------+ +-----------+ : : +-----------+ : : In the above illustration, ICookie and IObject represent indices and DCookie and DObject represent data storage objects. Indices may have representation in multiple caches, but currently, non-index objects may not. Objects of any type may also be entirely unrepresented. As far as the netfs API goes, the netfs is only actually permitted to see pointers to the cookies. The cookies themselves and any objects attached to those cookies are hidden from it. =============================== OBJECT MANAGEMENT STATE MACHINE =============================== Within FS-Cache, each active object is managed by its own individual state machine. The state for an object is kept in the fscache_object struct, in object->state. A cookie may point to a set of objects that are in different states. Each state has an action associated with it that is invoked when the machine wakes up in that state. There are four logical sets of states: (1) Preparation: states that wait for the parent objects to become ready. The representations are hierarchical, and it is expected that an object must be created or accessed with respect to its parent object. (2) Initialisation: states that perform lookups in the cache and validate what's found and that create on disk any missing metadata. (3) Normal running: states that allow netfs operations on objects to proceed and that update the state of objects. (4) Termination: states that detach objects from their netfs cookies, that delete objects from disk, that handle disk and system errors and that free up in-memory resources. In most cases, transitioning between states is in response to signalled events. When a state has finished processing, it will usually set the mask of events in which it is interested (object->event_mask) and relinquish the worker thread. Then when an event is raised (by calling fscache_raise_event()), if the event is not masked, the object will be queued for processing (by calling fscache_enqueue_object()). PROVISION OF CPU TIME --------------------- The work to be done by the various states is given CPU time by the threads of the slow work facility (see Documentation/slow-work.txt). This is used in preference to the workqueue facility because: (1) Threads may be completely occupied for very long periods of time by a particular work item. These state actions may be doing sequences of synchronous, journalled disk accesses (lookup, mkdir, create, setxattr, getxattr, truncate, unlink, rmdir, rename). (2) Threads may do little actual work, but may rather spend a lot of time sleeping on I/O. This means that single-threaded and 1-per-CPU-threaded workqueues don't necessarily have the right numbers of threads. LOCKING SIMPLIFICATION ---------------------- Because only one worker thread may be operating on any particular object's state machine at once, this simplifies the locking, particularly with respect to disconnecting the netfs's representation of a cache object (fscache_cookie) from the cache backend's representation (fscache_object) - which may be requested from either end. ================= THE SET OF STATES ================= The object state machine has a set of states that it can be in. There are preparation states in which the object sets itself up and waits for its parent object to transit to a state that allows access to its children: (1) State FSCACHE_OBJECT_INIT. Initialise the object and wait for the parent object to become active. In the cache, it is expected that it will not be possible to look an object up from the parent object, until that parent object itself has been looked up. There are initialisation states in which the object sets itself up and accesses disk for the object metadata: (2) State FSCACHE_OBJECT_LOOKING_UP. Look up the object on disk, using the parent as a starting point. FS-Cache expects the cache backend to probe the cache to see whether this object is represented there, and if it is, to see if it's valid (coherency management). The cache should call fscache_object_lookup_negative() to indicate lookup failure for whatever reason, and should call fscache_obtained_object() to indicate success. At the completion of lookup, FS-Cache will let the netfs go ahead with read operations, no matter whether the file is yet cached. If not yet cached, read operations will be immediately rejected with ENODATA until the first known page is uncached - as to that point there can be no data to be read out of the cache for that file that isn't currently also held in the pagecache. (3) State FSCACHE_OBJECT_CREATING. Create an object on disk, using the parent as a starting point. This happens if the lookup failed to find the object, or if the object's coherency data indicated what's on disk is out of date. In this state, FS-Cache expects the cache to create The cache should call fscache_obtained_object() if creation completes successfully, fscache_object_lookup_negative() otherwise. At the completion of creation, FS-Cache will start processing write operations the netfs has queued for an object. If creation failed, the write ops will be transparently discarded, and nothing recorded in the cache. There are some normal running states in which the object spends its time servicing netfs requests: (4) State FSCACHE_OBJECT_AVAILABLE. A transient state in which pending operations are started, child objects are permitted to advance from FSCACHE_OBJECT_INIT state, and temporary lookup data is freed. (5) State FSCACHE_OBJECT_ACTIVE. The normal running state. In this state, requests the netfs makes will be passed on to the cache. (6) State FSCACHE_OBJECT_UPDATING. The state machine comes here to update the object in the cache from the netfs's records. This involves updating the auxiliary data that is used to maintain coherency. And there are terminal states in which an object cleans itself up, deallocates memory and potentially deletes stuff from disk: (7) State FSCACHE_OBJECT_LC_DYING. The object comes here if it is dying because of a lookup or creation error. This would be due to a disk error or system error of some sort. Temporary data is cleaned up, and the parent is released. (8) State FSCACHE_OBJECT_DYING. The object comes here if it is dying due to an error, because its parent cookie has been relinquished by the netfs or because the cache is being withdrawn. Any child objects waiting on this one are given CPU time so that they too can destroy themselves. This object waits for all its children to go away before advancing to the next state. (9) State FSCACHE_OBJECT_ABORT_INIT. The object comes to this state if it was waiting on its parent in FSCACHE_OBJECT_INIT, but its parent died. The object will destroy itself so that the parent may proceed from the FSCACHE_OBJECT_DYING state. (10) State FSCACHE_OBJECT_RELEASING. (11) State FSCACHE_OBJECT_RECYCLING. The object comes to one of these two states when dying once it is rid of all its children, if it is dying because the netfs relinquished its cookie. In the first state, the cached data is expected to persist, and in the second it will be deleted. (12) State FSCACHE_OBJECT_WITHDRAWING. The object transits to this state if the cache decides it wants to withdraw the object from service, perhaps to make space, but also due to error or just because the whole cache is being withdrawn. (13) State FSCACHE_OBJECT_DEAD. The object transits to this state when the in-memory object record is ready to be deleted. The object processor shouldn't ever see an object in this state. THE SET OF EVENTS ----------------- There are a number of events that can be raised to an object state machine: (*) FSCACHE_OBJECT_EV_UPDATE The netfs requested that an object be updated. The state machine will ask the cache backend to update the object, and the cache backend will ask the netfs for details of the change through its cookie definition ops. (*) FSCACHE_OBJECT_EV_CLEARED This is signalled in two circumstances: (a) when an object's last child object is dropped and (b) when the last operation outstanding on an object is completed. This is used to proceed from the dying state. (*) FSCACHE_OBJECT_EV_ERROR This is signalled when an I/O error occurs during the processing of some object. (*) FSCACHE_OBJECT_EV_RELEASE (*) FSCACHE_OBJECT_EV_RETIRE These are signalled when the netfs relinquishes a cookie it was using. The event selected depends on whether the netfs asks for the backing object to be retired (deleted) or retained. (*) FSCACHE_OBJECT_EV_WITHDRAW This is signalled when the cache backend wants to withdraw an object. This means that the object will have to be detached from the netfs's cookie. Because the withdrawing releasing/retiring events are all handled by the object state machine, it doesn't matter if there's a collision with both ends trying to sever the connection at the same time. The state machine can just pick which one it wants to honour, and that effects the other. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com>
Diffstat (limited to 'fs/fscache/object.c')
-rw-r--r--fs/fscache/object.c810
1 files changed, 810 insertions, 0 deletions
diff --git a/fs/fscache/object.c b/fs/fscache/object.c
new file mode 100644
index 000000000000..392a41b1b79d
--- /dev/null
+++ b/fs/fscache/object.c
@@ -0,0 +1,810 @@
1/* FS-Cache object state machine handler
2 *
3 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 *
11 * See Documentation/filesystems/caching/object.txt for a description of the
12 * object state machine and the in-kernel representations.
13 */
14
15#define FSCACHE_DEBUG_LEVEL COOKIE
16#include <linux/module.h>
17#include "internal.h"
18
19const char *fscache_object_states[] = {
20 [FSCACHE_OBJECT_INIT] = "OBJECT_INIT",
21 [FSCACHE_OBJECT_LOOKING_UP] = "OBJECT_LOOKING_UP",
22 [FSCACHE_OBJECT_CREATING] = "OBJECT_CREATING",
23 [FSCACHE_OBJECT_AVAILABLE] = "OBJECT_AVAILABLE",
24 [FSCACHE_OBJECT_ACTIVE] = "OBJECT_ACTIVE",
25 [FSCACHE_OBJECT_UPDATING] = "OBJECT_UPDATING",
26 [FSCACHE_OBJECT_DYING] = "OBJECT_DYING",
27 [FSCACHE_OBJECT_LC_DYING] = "OBJECT_LC_DYING",
28 [FSCACHE_OBJECT_ABORT_INIT] = "OBJECT_ABORT_INIT",
29 [FSCACHE_OBJECT_RELEASING] = "OBJECT_RELEASING",
30 [FSCACHE_OBJECT_RECYCLING] = "OBJECT_RECYCLING",
31 [FSCACHE_OBJECT_WITHDRAWING] = "OBJECT_WITHDRAWING",
32 [FSCACHE_OBJECT_DEAD] = "OBJECT_DEAD",
33};
34EXPORT_SYMBOL(fscache_object_states);
35
36static void fscache_object_slow_work_put_ref(struct slow_work *);
37static int fscache_object_slow_work_get_ref(struct slow_work *);
38static void fscache_object_slow_work_execute(struct slow_work *);
39static void fscache_initialise_object(struct fscache_object *);
40static void fscache_lookup_object(struct fscache_object *);
41static void fscache_object_available(struct fscache_object *);
42static void fscache_release_object(struct fscache_object *);
43static void fscache_withdraw_object(struct fscache_object *);
44static void fscache_enqueue_dependents(struct fscache_object *);
45static void fscache_dequeue_object(struct fscache_object *);
46
47const struct slow_work_ops fscache_object_slow_work_ops = {
48 .get_ref = fscache_object_slow_work_get_ref,
49 .put_ref = fscache_object_slow_work_put_ref,
50 .execute = fscache_object_slow_work_execute,
51};
52EXPORT_SYMBOL(fscache_object_slow_work_ops);
53
54/*
55 * we need to notify the parent when an op completes that we had outstanding
56 * upon it
57 */
58static inline void fscache_done_parent_op(struct fscache_object *object)
59{
60 struct fscache_object *parent = object->parent;
61
62 _enter("OBJ%x {OBJ%x,%x}",
63 object->debug_id, parent->debug_id, parent->n_ops);
64
65 spin_lock_nested(&parent->lock, 1);
66 parent->n_ops--;
67 parent->n_obj_ops--;
68 if (parent->n_ops == 0)
69 fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED);
70 spin_unlock(&parent->lock);
71}
72
73/*
74 * process events that have been sent to an object's state machine
75 * - initiates parent lookup
76 * - does object lookup
77 * - does object creation
78 * - does object recycling and retirement
79 * - does object withdrawal
80 */
81static void fscache_object_state_machine(struct fscache_object *object)
82{
83 enum fscache_object_state new_state;
84
85 ASSERT(object != NULL);
86
87 _enter("{OBJ%x,%s,%lx}",
88 object->debug_id, fscache_object_states[object->state],
89 object->events);
90
91 switch (object->state) {
92 /* wait for the parent object to become ready */
93 case FSCACHE_OBJECT_INIT:
94 object->event_mask =
95 ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED);
96 fscache_initialise_object(object);
97 goto done;
98
99 /* look up the object metadata on disk */
100 case FSCACHE_OBJECT_LOOKING_UP:
101 fscache_lookup_object(object);
102 goto lookup_transit;
103
104 /* create the object metadata on disk */
105 case FSCACHE_OBJECT_CREATING:
106 fscache_lookup_object(object);
107 goto lookup_transit;
108
109 /* handle an object becoming available; start pending
110 * operations and queue dependent operations for processing */
111 case FSCACHE_OBJECT_AVAILABLE:
112 fscache_object_available(object);
113 goto active_transit;
114
115 /* normal running state */
116 case FSCACHE_OBJECT_ACTIVE:
117 goto active_transit;
118
119 /* update the object metadata on disk */
120 case FSCACHE_OBJECT_UPDATING:
121 clear_bit(FSCACHE_OBJECT_EV_UPDATE, &object->events);
122 fscache_stat(&fscache_n_updates_run);
123 object->cache->ops->update_object(object);
124 goto active_transit;
125
126 /* handle an object dying during lookup or creation */
127 case FSCACHE_OBJECT_LC_DYING:
128 object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE);
129 object->cache->ops->lookup_complete(object);
130
131 spin_lock(&object->lock);
132 object->state = FSCACHE_OBJECT_DYING;
133 if (test_and_clear_bit(FSCACHE_COOKIE_CREATING,
134 &object->cookie->flags))
135 wake_up_bit(&object->cookie->flags,
136 FSCACHE_COOKIE_CREATING);
137 spin_unlock(&object->lock);
138
139 fscache_done_parent_op(object);
140
141 /* wait for completion of all active operations on this object
142 * and the death of all child objects of this object */
143 case FSCACHE_OBJECT_DYING:
144 dying:
145 clear_bit(FSCACHE_OBJECT_EV_CLEARED, &object->events);
146 spin_lock(&object->lock);
147 _debug("dying OBJ%x {%d,%d}",
148 object->debug_id, object->n_ops, object->n_children);
149 if (object->n_ops == 0 && object->n_children == 0) {
150 object->event_mask &=
151 ~(1 << FSCACHE_OBJECT_EV_CLEARED);
152 object->event_mask |=
153 (1 << FSCACHE_OBJECT_EV_WITHDRAW) |
154 (1 << FSCACHE_OBJECT_EV_RETIRE) |
155 (1 << FSCACHE_OBJECT_EV_RELEASE) |
156 (1 << FSCACHE_OBJECT_EV_ERROR);
157 } else {
158 object->event_mask &=
159 ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
160 (1 << FSCACHE_OBJECT_EV_RETIRE) |
161 (1 << FSCACHE_OBJECT_EV_RELEASE) |
162 (1 << FSCACHE_OBJECT_EV_ERROR));
163 object->event_mask |=
164 1 << FSCACHE_OBJECT_EV_CLEARED;
165 }
166 spin_unlock(&object->lock);
167 fscache_enqueue_dependents(object);
168 goto terminal_transit;
169
170 /* handle an abort during initialisation */
171 case FSCACHE_OBJECT_ABORT_INIT:
172 _debug("handle abort init %lx", object->events);
173 object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE);
174
175 spin_lock(&object->lock);
176 fscache_dequeue_object(object);
177
178 object->state = FSCACHE_OBJECT_DYING;
179 if (test_and_clear_bit(FSCACHE_COOKIE_CREATING,
180 &object->cookie->flags))
181 wake_up_bit(&object->cookie->flags,
182 FSCACHE_COOKIE_CREATING);
183 spin_unlock(&object->lock);
184 goto dying;
185
186 /* handle the netfs releasing an object and possibly marking it
187 * obsolete too */
188 case FSCACHE_OBJECT_RELEASING:
189 case FSCACHE_OBJECT_RECYCLING:
190 object->event_mask &=
191 ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
192 (1 << FSCACHE_OBJECT_EV_RETIRE) |
193 (1 << FSCACHE_OBJECT_EV_RELEASE) |
194 (1 << FSCACHE_OBJECT_EV_ERROR));
195 fscache_release_object(object);
196 spin_lock(&object->lock);
197 object->state = FSCACHE_OBJECT_DEAD;
198 spin_unlock(&object->lock);
199 fscache_stat(&fscache_n_object_dead);
200 goto terminal_transit;
201
202 /* handle the parent cache of this object being withdrawn from
203 * active service */
204 case FSCACHE_OBJECT_WITHDRAWING:
205 object->event_mask &=
206 ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
207 (1 << FSCACHE_OBJECT_EV_RETIRE) |
208 (1 << FSCACHE_OBJECT_EV_RELEASE) |
209 (1 << FSCACHE_OBJECT_EV_ERROR));
210 fscache_withdraw_object(object);
211 spin_lock(&object->lock);
212 object->state = FSCACHE_OBJECT_DEAD;
213 spin_unlock(&object->lock);
214 fscache_stat(&fscache_n_object_dead);
215 goto terminal_transit;
216
217 /* complain about the object being woken up once it is
218 * deceased */
219 case FSCACHE_OBJECT_DEAD:
220 printk(KERN_ERR "FS-Cache:"
221 " Unexpected event in dead state %lx\n",
222 object->events & object->event_mask);
223 BUG();
224
225 default:
226 printk(KERN_ERR "FS-Cache: Unknown object state %u\n",
227 object->state);
228 BUG();
229 }
230
231 /* determine the transition from a lookup state */
232lookup_transit:
233 switch (fls(object->events & object->event_mask) - 1) {
234 case FSCACHE_OBJECT_EV_WITHDRAW:
235 case FSCACHE_OBJECT_EV_RETIRE:
236 case FSCACHE_OBJECT_EV_RELEASE:
237 case FSCACHE_OBJECT_EV_ERROR:
238 new_state = FSCACHE_OBJECT_LC_DYING;
239 goto change_state;
240 case FSCACHE_OBJECT_EV_REQUEUE:
241 goto done;
242 case -1:
243 goto done; /* sleep until event */
244 default:
245 goto unsupported_event;
246 }
247
248 /* determine the transition from an active state */
249active_transit:
250 switch (fls(object->events & object->event_mask) - 1) {
251 case FSCACHE_OBJECT_EV_WITHDRAW:
252 case FSCACHE_OBJECT_EV_RETIRE:
253 case FSCACHE_OBJECT_EV_RELEASE:
254 case FSCACHE_OBJECT_EV_ERROR:
255 new_state = FSCACHE_OBJECT_DYING;
256 goto change_state;
257 case FSCACHE_OBJECT_EV_UPDATE:
258 new_state = FSCACHE_OBJECT_UPDATING;
259 goto change_state;
260 case -1:
261 new_state = FSCACHE_OBJECT_ACTIVE;
262 goto change_state; /* sleep until event */
263 default:
264 goto unsupported_event;
265 }
266
267 /* determine the transition from a terminal state */
268terminal_transit:
269 switch (fls(object->events & object->event_mask) - 1) {
270 case FSCACHE_OBJECT_EV_WITHDRAW:
271 new_state = FSCACHE_OBJECT_WITHDRAWING;
272 goto change_state;
273 case FSCACHE_OBJECT_EV_RETIRE:
274 new_state = FSCACHE_OBJECT_RECYCLING;
275 goto change_state;
276 case FSCACHE_OBJECT_EV_RELEASE:
277 new_state = FSCACHE_OBJECT_RELEASING;
278 goto change_state;
279 case FSCACHE_OBJECT_EV_ERROR:
280 new_state = FSCACHE_OBJECT_WITHDRAWING;
281 goto change_state;
282 case FSCACHE_OBJECT_EV_CLEARED:
283 new_state = FSCACHE_OBJECT_DYING;
284 goto change_state;
285 case -1:
286 goto done; /* sleep until event */
287 default:
288 goto unsupported_event;
289 }
290
291change_state:
292 spin_lock(&object->lock);
293 object->state = new_state;
294 spin_unlock(&object->lock);
295
296done:
297 _leave(" [->%s]", fscache_object_states[object->state]);
298 return;
299
300unsupported_event:
301 printk(KERN_ERR "FS-Cache:"
302 " Unsupported event %lx [mask %lx] in state %s\n",
303 object->events, object->event_mask,
304 fscache_object_states[object->state]);
305 BUG();
306}
307
308/*
309 * execute an object
310 */
311static void fscache_object_slow_work_execute(struct slow_work *work)
312{
313 struct fscache_object *object =
314 container_of(work, struct fscache_object, work);
315 unsigned long start;
316
317 _enter("{OBJ%x}", object->debug_id);
318
319 clear_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
320
321 start = jiffies;
322 fscache_object_state_machine(object);
323 fscache_hist(fscache_objs_histogram, start);
324 if (object->events & object->event_mask)
325 fscache_enqueue_object(object);
326}
327
328/*
329 * initialise an object
330 * - check the specified object's parent to see if we can make use of it
331 * immediately to do a creation
332 * - we may need to start the process of creating a parent and we need to wait
333 * for the parent's lookup and creation to complete if it's not there yet
334 * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the
335 * leaf-most cookies of the object and all its children
336 */
337static void fscache_initialise_object(struct fscache_object *object)
338{
339 struct fscache_object *parent;
340
341 _enter("");
342 ASSERT(object->cookie != NULL);
343 ASSERT(object->cookie->parent != NULL);
344 ASSERT(list_empty(&object->work.link));
345
346 if (object->events & ((1 << FSCACHE_OBJECT_EV_ERROR) |
347 (1 << FSCACHE_OBJECT_EV_RELEASE) |
348 (1 << FSCACHE_OBJECT_EV_RETIRE) |
349 (1 << FSCACHE_OBJECT_EV_WITHDRAW))) {
350 _debug("abort init %lx", object->events);
351 spin_lock(&object->lock);
352 object->state = FSCACHE_OBJECT_ABORT_INIT;
353 spin_unlock(&object->lock);
354 return;
355 }
356
357 spin_lock(&object->cookie->lock);
358 spin_lock_nested(&object->cookie->parent->lock, 1);
359
360 parent = object->parent;
361 if (!parent) {
362 _debug("no parent");
363 set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
364 } else {
365 spin_lock(&object->lock);
366 spin_lock_nested(&parent->lock, 1);
367 _debug("parent %s", fscache_object_states[parent->state]);
368
369 if (parent->state >= FSCACHE_OBJECT_DYING) {
370 _debug("bad parent");
371 set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
372 } else if (parent->state < FSCACHE_OBJECT_AVAILABLE) {
373 _debug("wait");
374
375 /* we may get woken up in this state by child objects
376 * binding on to us, so we need to make sure we don't
377 * add ourself to the list multiple times */
378 if (list_empty(&object->dep_link)) {
379 object->cache->ops->grab_object(object);
380 list_add(&object->dep_link,
381 &parent->dependents);
382
383 /* fscache_acquire_non_index_cookie() uses this
384 * to wake the chain up */
385 if (parent->state == FSCACHE_OBJECT_INIT)
386 fscache_enqueue_object(parent);
387 }
388 } else {
389 _debug("go");
390 parent->n_ops++;
391 parent->n_obj_ops++;
392 object->lookup_jif = jiffies;
393 object->state = FSCACHE_OBJECT_LOOKING_UP;
394 set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
395 }
396
397 spin_unlock(&parent->lock);
398 spin_unlock(&object->lock);
399 }
400
401 spin_unlock(&object->cookie->parent->lock);
402 spin_unlock(&object->cookie->lock);
403 _leave("");
404}
405
406/*
407 * look an object up in the cache from which it was allocated
408 * - we hold an "access lock" on the parent object, so the parent object cannot
409 * be withdrawn by either party till we've finished
410 * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the
411 * leaf-most cookies of the object and all its children
412 */
413static void fscache_lookup_object(struct fscache_object *object)
414{
415 struct fscache_cookie *cookie = object->cookie;
416 struct fscache_object *parent;
417
418 _enter("");
419
420 parent = object->parent;
421 ASSERT(parent != NULL);
422 ASSERTCMP(parent->n_ops, >, 0);
423 ASSERTCMP(parent->n_obj_ops, >, 0);
424
425 /* make sure the parent is still available */
426 ASSERTCMP(parent->state, >=, FSCACHE_OBJECT_AVAILABLE);
427
428 if (parent->state >= FSCACHE_OBJECT_DYING ||
429 test_bit(FSCACHE_IOERROR, &object->cache->flags)) {
430 _debug("unavailable");
431 set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
432 _leave("");
433 return;
434 }
435
436 _debug("LOOKUP \"%s/%s\" in \"%s\"",
437 parent->cookie->def->name, cookie->def->name,
438 object->cache->tag->name);
439
440 fscache_stat(&fscache_n_object_lookups);
441 object->cache->ops->lookup_object(object);
442
443 if (test_bit(FSCACHE_OBJECT_EV_ERROR, &object->events))
444 set_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags);
445
446 _leave("");
447}
448
449/**
450 * fscache_object_lookup_negative - Note negative cookie lookup
451 * @object: Object pointing to cookie to mark
452 *
453 * Note negative lookup, permitting those waiting to read data from an already
454 * existing backing object to continue as there's no data for them to read.
455 */
456void fscache_object_lookup_negative(struct fscache_object *object)
457{
458 struct fscache_cookie *cookie = object->cookie;
459
460 _enter("{OBJ%x,%s}",
461 object->debug_id, fscache_object_states[object->state]);
462
463 spin_lock(&object->lock);
464 if (object->state == FSCACHE_OBJECT_LOOKING_UP) {
465 fscache_stat(&fscache_n_object_lookups_negative);
466
467 /* transit here to allow write requests to begin stacking up
468 * and read requests to begin returning ENODATA */
469 object->state = FSCACHE_OBJECT_CREATING;
470 spin_unlock(&object->lock);
471
472 set_bit(FSCACHE_COOKIE_PENDING_FILL, &cookie->flags);
473 set_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
474
475 _debug("wake up lookup %p", &cookie->flags);
476 smp_mb__before_clear_bit();
477 clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
478 smp_mb__after_clear_bit();
479 wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
480 set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
481 } else {
482 ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING);
483 spin_unlock(&object->lock);
484 }
485
486 _leave("");
487}
488EXPORT_SYMBOL(fscache_object_lookup_negative);
489
490/**
491 * fscache_obtained_object - Note successful object lookup or creation
492 * @object: Object pointing to cookie to mark
493 *
494 * Note successful lookup and/or creation, permitting those waiting to write
495 * data to a backing object to continue.
496 *
497 * Note that after calling this, an object's cookie may be relinquished by the
498 * netfs, and so must be accessed with object lock held.
499 */
500void fscache_obtained_object(struct fscache_object *object)
501{
502 struct fscache_cookie *cookie = object->cookie;
503
504 _enter("{OBJ%x,%s}",
505 object->debug_id, fscache_object_states[object->state]);
506
507 /* if we were still looking up, then we must have a positive lookup
508 * result, in which case there may be data available */
509 spin_lock(&object->lock);
510 if (object->state == FSCACHE_OBJECT_LOOKING_UP) {
511 fscache_stat(&fscache_n_object_lookups_positive);
512
513 clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
514
515 object->state = FSCACHE_OBJECT_AVAILABLE;
516 spin_unlock(&object->lock);
517
518 smp_mb__before_clear_bit();
519 clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
520 smp_mb__after_clear_bit();
521 wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
522 set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
523 } else {
524 ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING);
525 fscache_stat(&fscache_n_object_created);
526
527 object->state = FSCACHE_OBJECT_AVAILABLE;
528 spin_unlock(&object->lock);
529 set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
530 smp_wmb();
531 }
532
533 if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, &cookie->flags))
534 wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING);
535
536 _leave("");
537}
538EXPORT_SYMBOL(fscache_obtained_object);
539
540/*
541 * handle an object that has just become available
542 */
543static void fscache_object_available(struct fscache_object *object)
544{
545 _enter("{OBJ%x}", object->debug_id);
546
547 spin_lock(&object->lock);
548
549 if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, &object->cookie->flags))
550 wake_up_bit(&object->cookie->flags, FSCACHE_COOKIE_CREATING);
551
552 fscache_done_parent_op(object);
553 if (object->n_in_progress == 0) {
554 if (object->n_ops > 0) {
555 ASSERTCMP(object->n_ops, >=, object->n_obj_ops);
556 ASSERTIF(object->n_ops > object->n_obj_ops,
557 !list_empty(&object->pending_ops));
558 fscache_start_operations(object);
559 } else {
560 ASSERT(list_empty(&object->pending_ops));
561 }
562 }
563 spin_unlock(&object->lock);
564
565 object->cache->ops->lookup_complete(object);
566 fscache_enqueue_dependents(object);
567
568 fscache_hist(fscache_obj_instantiate_histogram, object->lookup_jif);
569 fscache_stat(&fscache_n_object_avail);
570
571 _leave("");
572}
573
574/*
575 * drop an object's attachments
576 */
577static void fscache_drop_object(struct fscache_object *object)
578{
579 struct fscache_object *parent = object->parent;
580 struct fscache_cache *cache = object->cache;
581
582 _enter("{OBJ%x,%d}", object->debug_id, object->n_children);
583
584 spin_lock(&cache->object_list_lock);
585 list_del_init(&object->cache_link);
586 spin_unlock(&cache->object_list_lock);
587
588 cache->ops->drop_object(object);
589
590 if (parent) {
591 _debug("release parent OBJ%x {%d}",
592 parent->debug_id, parent->n_children);
593
594 spin_lock(&parent->lock);
595 parent->n_children--;
596 if (parent->n_children == 0)
597 fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED);
598 spin_unlock(&parent->lock);
599 object->parent = NULL;
600 }
601
602 /* this just shifts the object release to the slow work processor */
603 object->cache->ops->put_object(object);
604
605 _leave("");
606}
607
608/*
609 * release or recycle an object that the netfs has discarded
610 */
611static void fscache_release_object(struct fscache_object *object)
612{
613 _enter("");
614
615 fscache_drop_object(object);
616}
617
618/*
619 * withdraw an object from active service
620 */
621static void fscache_withdraw_object(struct fscache_object *object)
622{
623 struct fscache_cookie *cookie;
624 bool detached;
625
626 _enter("");
627
628 spin_lock(&object->lock);
629 cookie = object->cookie;
630 if (cookie) {
631 /* need to get the cookie lock before the object lock, starting
632 * from the object pointer */
633 atomic_inc(&cookie->usage);
634 spin_unlock(&object->lock);
635
636 detached = false;
637 spin_lock(&cookie->lock);
638 spin_lock(&object->lock);
639
640 if (object->cookie == cookie) {
641 hlist_del_init(&object->cookie_link);
642 object->cookie = NULL;
643 detached = true;
644 }
645 spin_unlock(&cookie->lock);
646 fscache_cookie_put(cookie);
647 if (detached)
648 fscache_cookie_put(cookie);
649 }
650
651 spin_unlock(&object->lock);
652
653 fscache_drop_object(object);
654}
655
656/*
657 * withdraw an object from active service at the behest of the cache
658 * - need break the links to a cached object cookie
659 * - called under two situations:
660 * (1) recycler decides to reclaim an in-use object
661 * (2) a cache is unmounted
662 * - have to take care as the cookie can be being relinquished by the netfs
663 * simultaneously
664 * - the object is pinned by the caller holding a refcount on it
665 */
666void fscache_withdrawing_object(struct fscache_cache *cache,
667 struct fscache_object *object)
668{
669 bool enqueue = false;
670
671 _enter(",OBJ%x", object->debug_id);
672
673 spin_lock(&object->lock);
674 if (object->state < FSCACHE_OBJECT_WITHDRAWING) {
675 object->state = FSCACHE_OBJECT_WITHDRAWING;
676 enqueue = true;
677 }
678 spin_unlock(&object->lock);
679
680 if (enqueue)
681 fscache_enqueue_object(object);
682
683 _leave("");
684}
685
686/*
687 * allow the slow work item processor to get a ref on an object
688 */
689static int fscache_object_slow_work_get_ref(struct slow_work *work)
690{
691 struct fscache_object *object =
692 container_of(work, struct fscache_object, work);
693
694 return object->cache->ops->grab_object(object) ? 0 : -EAGAIN;
695}
696
697/*
698 * allow the slow work item processor to discard a ref on a work item
699 */
700static void fscache_object_slow_work_put_ref(struct slow_work *work)
701{
702 struct fscache_object *object =
703 container_of(work, struct fscache_object, work);
704
705 return object->cache->ops->put_object(object);
706}
707
708/*
709 * enqueue an object for metadata-type processing
710 */
711void fscache_enqueue_object(struct fscache_object *object)
712{
713 _enter("{OBJ%x}", object->debug_id);
714
715 slow_work_enqueue(&object->work);
716}
717
718/*
719 * enqueue the dependents of an object for metadata-type processing
720 * - the caller must hold the object's lock
721 * - this may cause an already locked object to wind up being processed again
722 */
723static void fscache_enqueue_dependents(struct fscache_object *object)
724{
725 struct fscache_object *dep;
726
727 _enter("{OBJ%x}", object->debug_id);
728
729 if (list_empty(&object->dependents))
730 return;
731
732 spin_lock(&object->lock);
733
734 while (!list_empty(&object->dependents)) {
735 dep = list_entry(object->dependents.next,
736 struct fscache_object, dep_link);
737 list_del_init(&dep->dep_link);
738
739
740 /* sort onto appropriate lists */
741 fscache_enqueue_object(dep);
742 dep->cache->ops->put_object(dep);
743
744 if (!list_empty(&object->dependents))
745 cond_resched_lock(&object->lock);
746 }
747
748 spin_unlock(&object->lock);
749}
750
751/*
752 * remove an object from whatever queue it's waiting on
753 * - the caller must hold object->lock
754 */
755void fscache_dequeue_object(struct fscache_object *object)
756{
757 _enter("{OBJ%x}", object->debug_id);
758
759 if (!list_empty(&object->dep_link)) {
760 spin_lock(&object->parent->lock);
761 list_del_init(&object->dep_link);
762 spin_unlock(&object->parent->lock);
763 }
764
765 _leave("");
766}
767
768/**
769 * fscache_check_aux - Ask the netfs whether an object on disk is still valid
770 * @object: The object to ask about
771 * @data: The auxiliary data for the object
772 * @datalen: The size of the auxiliary data
773 *
774 * This function consults the netfs about the coherency state of an object
775 */
776enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
777 const void *data, uint16_t datalen)
778{
779 enum fscache_checkaux result;
780
781 if (!object->cookie->def->check_aux) {
782 fscache_stat(&fscache_n_checkaux_none);
783 return FSCACHE_CHECKAUX_OKAY;
784 }
785
786 result = object->cookie->def->check_aux(object->cookie->netfs_data,
787 data, datalen);
788 switch (result) {
789 /* entry okay as is */
790 case FSCACHE_CHECKAUX_OKAY:
791 fscache_stat(&fscache_n_checkaux_okay);
792 break;
793
794 /* entry requires update */
795 case FSCACHE_CHECKAUX_NEEDS_UPDATE:
796 fscache_stat(&fscache_n_checkaux_update);
797 break;
798
799 /* entry requires deletion */
800 case FSCACHE_CHECKAUX_OBSOLETE:
801 fscache_stat(&fscache_n_checkaux_obsolete);
802 break;
803
804 default:
805 BUG();
806 }
807
808 return result;
809}
810EXPORT_SYMBOL(fscache_check_aux);
generated by cgit v1.2.2 (git 2.25.0) at 2024-10-26 21:44:34 -0400