diff options
| -rw-r--r-- | Documentation/filesystems/caching/fscache.txt | 5 | ||||
| -rw-r--r-- | Documentation/filesystems/caching/object.txt | 313 | ||||
| -rw-r--r-- | fs/fscache/Makefile | 3 | ||||
| -rw-r--r-- | fs/fscache/internal.h | 26 | ||||
| -rw-r--r-- | fs/fscache/object.c | 810 |
5 files changed, 1155 insertions, 2 deletions
diff --git a/Documentation/filesystems/caching/fscache.txt b/Documentation/filesystems/caching/fscache.txt index 0a751f3..9e94b94 100644 --- a/Documentation/filesystems/caching/fscache.txt +++ b/Documentation/filesystems/caching/fscache.txt @@ -188,6 +188,11 @@ The cache backend API to FS-Cache can be found in: Documentation/filesystems/caching/backend-api.txt +A description of the internal representations and object state machine can be +found in: + + Documentation/filesystems/caching/object.txt + ======================= STATISTICAL INFORMATION diff --git a/Documentation/filesystems/caching/object.txt b/Documentation/filesystems/caching/object.txt new file mode 100644 index 0000000..e8b0a35 --- /dev/null +++ b/Documentation/filesystems/caching/object.txt @@ -0,0 +1,313 @@ + ==================================================== + IN-KERNEL CACHE OBJECT REPRESENTATION AND MANAGEMENT + ==================================================== + +By: David Howells <dhowells@redhat.com> + +Contents: + + (*) Representation + + (*) Object management state machine. + + - Provision of cpu time. + - Locking simplification. + + (*) The set of states. + + (*) The set of events. + + +============== +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. diff --git a/fs/fscache/Makefile b/fs/fscache/Makefile index ecf6946..4420ac6 100644 --- a/fs/fscache/Makefile +++ b/fs/fscache/Makefile @@ -7,7 +7,8 @@ fscache-y := \ cookie.o \ fsdef.o \ main.o \ - netfs.o + netfs.o \ + object.o fscache-$(CONFIG_PROC_FS) += proc.o fscache-$(CONFIG_FSCACHE_STATS) += stats.o diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h index 1638994..529f4de 100644 --- a/fs/fscache/internal.h +++ b/fs/fscache/internal.h @@ -86,6 +86,18 @@ extern int fscache_wait_bit(void *); extern int fscache_wait_bit_interruptible(void *); /* + * fsc-object.c + */ +extern void fscache_withdrawing_object(struct fscache_cache *, + struct fscache_object *); +extern void fscache_enqueue_object(struct fscache_object *); + +/* + * fsc-operation.c + */ +#define fscache_start_operations(obj) BUG() + +/* * fsc-proc.c */ #ifdef CONFIG_PROC_FS @@ -196,7 +208,19 @@ extern const struct file_operations fscache_stats_fops; static inline void fscache_raise_event(struct fscache_object *object, unsigned event) { - BUG(); // TODO + if (!test_and_set_bit(event, &object->events) && + test_bit(event, &object->event_mask)) + fscache_enqueue_object(object); +} + +/* + * drop a reference to a cookie + */ +static inline void fscache_cookie_put(struct fscache_cookie *cookie) +{ + BUG_ON(atomic_read(&cookie->usage) <= 0); + if (atomic_dec_and_test(&cookie->usage)) + __fscache_cookie_put(cookie); } /*****************************************************************************/ diff --git a/fs/fscache/object.c b/fs/fscache/object.c new file mode 100644 index 0000000..392a41b --- /dev/null +++ b/fs/fscache/object.c @@ -0,0 +1,810 @@ +/* FS-Cache object state machine handler + * + * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + * + * See Documentation/filesystems/caching/object.txt for a description of the + * object state machine and the in-kernel representations. + */ + +#define FSCACHE_DEBUG_LEVEL COOKIE +#include <linux/module.h> +#include "internal.h" + +const char *fscache_object_states[] = { + [FSCACHE_OBJECT_INIT] = "OBJECT_INIT", + [FSCACHE_OBJECT_LOOKING_UP] = "OBJECT_LOOKING_UP", + [FSCACHE_OBJECT_CREATING] = "OBJECT_CREATING", + [FSCACHE_OBJECT_AVAILABLE] = "OBJECT_AVAILABLE", + [FSCACHE_OBJECT_ACTIVE] = "OBJECT_ACTIVE", + [FSCACHE_OBJECT_UPDATING] = "OBJECT_UPDATING", + [FSCACHE_OBJECT_DYING] = "OBJECT_DYING", + [FSCACHE_OBJECT_LC_DYING] = "OBJECT_LC_DYING", + [FSCACHE_OBJECT_ABORT_INIT] = "OBJECT_ABORT_INIT", + [FSCACHE_OBJECT_RELEASING] = "OBJECT_RELEASING", + [FSCACHE_OBJECT_RECYCLING] = "OBJECT_RECYCLING", + [FSCACHE_OBJECT_WITHDRAWING] = "OBJECT_WITHDRAWING", + [FSCACHE_OBJECT_DEAD] = "OBJECT_DEAD", +}; +EXPORT_SYMBOL(fscache_object_states); + +static void fscache_object_slow_work_put_ref(struct slow_work *); +static int fscache_object_slow_work_get_ref(struct slow_work *); +static void fscache_object_slow_work_execute(struct slow_work *); +static void fscache_initialise_object(struct fscache_object *); +static void fscache_lookup_object(struct fscache_object *); +static void fscache_object_available(struct fscache_object *); +static void fscache_release_object(struct fscache_object *); +static void fscache_withdraw_object(struct fscache_object *); +static void fscache_enqueue_dependents(struct fscache_object *); +static void fscache_dequeue_object(struct fscache_object *); + +const struct slow_work_ops fscache_object_slow_work_ops = { + .get_ref = fscache_object_slow_work_get_ref, + .put_ref = fscache_object_slow_work_put_ref, + .execute = fscache_object_slow_work_execute, +}; +EXPORT_SYMBOL(fscache_object_slow_work_ops); + +/* + * we need to notify the parent when an op completes that we had outstanding + * upon it + */ +static inline void fscache_done_parent_op(struct fscache_object *object) +{ + struct fscache_object *parent = object->parent; + + _enter("OBJ%x {OBJ%x,%x}", + object->debug_id, parent->debug_id, parent->n_ops); + + spin_lock_nested(&parent->lock, 1); + parent->n_ops--; + parent->n_obj_ops--; + if (parent->n_ops == 0) + fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED); + spin_unlock(&parent->lock); +} + +/* + * process events that have been sent to an object's state machine + * - initiates parent lookup + * - does object lookup + * - does object creation + * - does object recycling and retirement + * - does object withdrawal + */ +static void fscache_object_state_machine(struct fscache_object *object) +{ + enum fscache_object_state new_state; + + ASSERT(object != NULL); + + _enter("{OBJ%x,%s,%lx}", + object->debug_id, fscache_object_states[object->state], + object->events); + + switch (object->state) { + /* wait for the parent object to become ready */ + case FSCACHE_OBJECT_INIT: + object->event_mask = + ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED); + fscache_initialise_object(object); + goto done; + + /* look up the object metadata on disk */ + case FSCACHE_OBJECT_LOOKING_UP: + fscache_lookup_object(object); + goto lookup_transit; + + /* create the object metadata on disk */ + case FSCACHE_OBJECT_CREATING: + fscache_lookup_object(object); + goto lookup_transit; + + /* handle an object becoming available; start pending + * operations and queue dependent operations for processing */ + case FSCACHE_OBJECT_AVAILABLE: + fscache_object_available(object); + goto active_transit; + + /* normal running state */ + case FSCACHE_OBJECT_ACTIVE: + goto active_transit; + + /* update the object metadata on disk */ + case FSCACHE_OBJECT_UPDATING: + clear_bit(FSCACHE_OBJECT_EV_UPDATE, &object->events); + fscache_stat(&fscache_n_updates_run); + object->cache->ops->update_object(object); + goto active_transit; + + /* handle an object dying during lookup or creation */ + case FSCACHE_OBJECT_LC_DYING: + object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE); + object->cache->ops->lookup_complete(object); + + spin_lock(&object->lock); + object->state = FSCACHE_OBJECT_DYING; + if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, + &object->cookie->flags)) + wake_up_bit(&object->cookie->flags, + FSCACHE_COOKIE_CREATING); + spin_unlock(&object->lock); + + fscache_done_parent_op(object); + + /* wait for completion of all active operations on this object + * and the death of all child objects of this object */ + case FSCACHE_OBJECT_DYING: + dying: + clear_bit(FSCACHE_OBJECT_EV_CLEARED, &object->events); + spin_lock(&object->lock); + _debug("dying OBJ%x {%d,%d}", + object->debug_id, object->n_ops, object->n_children); + if (object->n_ops == 0 && object->n_children == 0) { + object->event_mask &= + ~(1 << FSCACHE_OBJECT_EV_CLEARED); + object->event_mask |= + (1 << FSCACHE_OBJECT_EV_WITHDRAW) | + (1 << FSCACHE_OBJECT_EV_RETIRE) | + (1 << FSCACHE_OBJECT_EV_RELEASE) | + (1 << FSCACHE_OBJECT_EV_ERROR); + } else { + object->event_mask &= + ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) | + (1 << FSCACHE_OBJECT_EV_RETIRE) | + (1 << FSCACHE_OBJECT_EV_RELEASE) | + (1 << FSCACHE_OBJECT_EV_ERROR)); + object->event_mask |= + 1 << FSCACHE_OBJECT_EV_CLEARED; + } + spin_unlock(&object->lock); + fscache_enqueue_dependents(object); + goto terminal_transit; + + /* handle an abort during initialisation */ + case FSCACHE_OBJECT_ABORT_INIT: + _debug("handle abort init %lx", object->events); + object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE); + + spin_lock(&object->lock); + fscache_dequeue_object(object); + + object->state = FSCACHE_OBJECT_DYING; + if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, + &object->cookie->flags)) + wake_up_bit(&object->cookie->flags, + FSCACHE_COOKIE_CREATING); + spin_unlock(&object->lock); + goto dying; + + /* handle the netfs releasing an object and possibly marking it + * obsolete too */ + case FSCACHE_OBJECT_RELEASING: + case FSCACHE_OBJECT_RECYCLING: + object->event_mask &= + ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) | + (1 << FSCACHE_OBJECT_EV_RETIRE) | + (1 << FSCACHE_OBJECT_EV_RELEASE) | + (1 << FSCACHE_OBJECT_EV_ERROR)); + fscache_release_object(object); + spin_lock(&object->lock); + object->state = FSCACHE_OBJECT_DEAD; + spin_unlock(&object->lock); + fscache_stat(&fscache_n_object_dead); + goto terminal_transit; + + /* handle the parent cache of this object being withdrawn from + * active service */ + case FSCACHE_OBJECT_WITHDRAWING: + object->event_mask &= + ~((1 << FSCACHE_OBJECT_EV_WITHDRAW) | + (1 << FSCACHE_OBJECT_EV_RETIRE) | + (1 << FSCACHE_OBJECT_EV_RELEASE) | + (1 << FSCACHE_OBJECT_EV_ERROR)); + fscache_withdraw_object(object); + spin_lock(&object->lock); + object->state = FSCACHE_OBJECT_DEAD; + spin_unlock(&object->lock); + fscache_stat(&fscache_n_object_dead); + goto terminal_transit; + + /* complain about the object being woken up once it is + * deceased */ + case FSCACHE_OBJECT_DEAD: + printk(KERN_ERR "FS-Cache:" + " Unexpected event in dead state %lx\n", + object->events & object->event_mask); + BUG(); + + default: + printk(KERN_ERR "FS-Cache: Unknown object state %u\n", + object->state); + BUG(); + } + + /* determine the transition from a lookup state */ +lookup_transit: + switch (fls(object->events & object->event_mask) - 1) { + case FSCACHE_OBJECT_EV_WITHDRAW: + case FSCACHE_OBJECT_EV_RETIRE: + case FSCACHE_OBJECT_EV_RELEASE: + case FSCACHE_OBJECT_EV_ERROR: + new_state = FSCACHE_OBJECT_LC_DYING; + goto change_state; + case FSCACHE_OBJECT_EV_REQUEUE: + goto done; + case -1: + goto done; /* sleep until event */ + default: + goto unsupported_event; + } + + /* determine the transition from an active state */ +active_transit: + switch (fls(object->events & object->event_mask) - 1) { + case FSCACHE_OBJECT_EV_WITHDRAW: + case FSCACHE_OBJECT_EV_RETIRE: + case FSCACHE_OBJECT_EV_RELEASE: + case FSCACHE_OBJECT_EV_ERROR: + new_state = FSCACHE_OBJECT_DYING; + goto change_state; + case FSCACHE_OBJECT_EV_UPDATE: + new_state = FSCACHE_OBJECT_UPDATING; + goto change_state; + case -1: + new_state = FSCACHE_OBJECT_ACTIVE; + goto change_state; /* sleep until event */ + default: + goto unsupported_event; + } + + /* determine the transition from a terminal state */ +terminal_transit: + switch (fls(object->events & object->event_mask) - 1) { + case FSCACHE_OBJECT_EV_WITHDRAW: + new_state = FSCACHE_OBJECT_WITHDRAWING; + goto change_state; + case FSCACHE_OBJECT_EV_RETIRE: + new_state = FSCACHE_OBJECT_RECYCLING; + goto change_state; + case FSCACHE_OBJECT_EV_RELEASE: + new_state = FSCACHE_OBJECT_RELEASING; + goto change_state; + case FSCACHE_OBJECT_EV_ERROR: + new_state = FSCACHE_OBJECT_WITHDRAWING; + goto change_state; + case FSCACHE_OBJECT_EV_CLEARED: + new_state = FSCACHE_OBJECT_DYING; + goto change_state; + case -1: + goto done; /* sleep until event */ + default: + goto unsupported_event; + } + +change_state: + spin_lock(&object->lock); + object->state = new_state; + spin_unlock(&object->lock); + +done: + _leave(" [->%s]", fscache_object_states[object->state]); + return; + +unsupported_event: + printk(KERN_ERR "FS-Cache:" + " Unsupported event %lx [mask %lx] in state %s\n", + object->events, object->event_mask, + fscache_object_states[object->state]); + BUG(); +} + +/* + * execute an object + */ +static void fscache_object_slow_work_execute(struct slow_work *work) +{ + struct fscache_object *object = + container_of(work, struct fscache_object, work); + unsigned long start; + + _enter("{OBJ%x}", object->debug_id); + + clear_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events); + + start = jiffies; + fscache_object_state_machine(object); + fscache_hist(fscache_objs_histogram, start); + if (object->events & object->event_mask) + fscache_enqueue_object(object); +} + +/* + * initialise an object + * - check the specified object's parent to see if we can make use of it + * immediately to do a creation + * - we may need to start the process of creating a parent and we need to wait + * for the parent's lookup and creation to complete if it's not there yet + * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the + * leaf-most cookies of the object and all its children + */ +static void fscache_initialise_object(struct fscache_object *object) +{ + struct fscache_object *parent; + + _enter(""); + ASSERT(object->cookie != NULL); + ASSERT(object->cookie->parent != NULL); + ASSERT(list_empty(&object->work.link)); + + if (object->events & ((1 << FSCACHE_OBJECT_EV_ERROR) | + (1 << FSCACHE_OBJECT_EV_RELEASE) | + (1 << FSCACHE_OBJECT_EV_RETIRE) | + (1 << FSCACHE_OBJECT_EV_WITHDRAW))) { + _debug("abort init %lx", object->events); + spin_lock(&object->lock); + object->state = FSCACHE_OBJECT_ABORT_INIT; + spin_unlock(&object->lock); + return; + } + + spin_lock(&object->cookie->lock); + spin_lock_nested(&object->cookie->parent->lock, 1); + + parent = object->parent; + if (!parent) { + _debug("no parent"); + set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events); + } else { + spin_lock(&object->lock); + spin_lock_nested(&parent->lock, 1); + _debug("parent %s", fscache_object_states[parent->state]); + + if (parent->state >= FSCACHE_OBJECT_DYING) { + _debug("bad parent"); + set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events); + } else if (parent->state < FSCACHE_OBJECT_AVAILABLE) { + _debug("wait"); + + /* we may get woken up in this state by child objects + * binding on to us, so we need to make sure we don't + * add ourself to the list multiple times */ + if (list_empty(&object->dep_link)) { + object->cache->ops->grab_object(object); + list_add(&object->dep_link, + &parent->dependents); + + /* fscache_acquire_non_index_cookie() uses this + * to wake the chain up */ + if (parent->state == FSCACHE_OBJECT_INIT) + fscache_enqueue_object(parent); + } + } else { + _debug("go"); + parent->n_ops++; + parent->n_obj_ops++; + object->lookup_jif = jiffies; + object->state = FSCACHE_OBJECT_LOOKING_UP; + set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events); + } + + spin_unlock(&parent->lock); + spin_unlock(&object->lock); + } + + spin_unlock(&object->cookie->parent->lock); + spin_unlock(&object->cookie->lock); + _leave(""); +} + +/* + * look an object up in the cache from which it was allocated + * - we hold an "access lock" on the parent object, so the parent object cannot + * be withdrawn by either party till we've finished + * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the + * leaf-most cookies of the object and all its children + */ +static void fscache_lookup_object(struct fscache_object *object) +{ + struct fscache_cookie *cookie = object->cookie; + struct fscache_object *parent; + + _enter(""); + + parent = object->parent; + ASSERT(parent != NULL); + ASSERTCMP(parent->n_ops, >, 0); + ASSERTCMP(parent->n_obj_ops, >, 0); + + /* make sure the parent is still available */ + ASSERTCMP(parent->state, >=, FSCACHE_OBJECT_AVAILABLE); + + if (parent->state >= FSCACHE_OBJECT_DYING || + test_bit(FSCACHE_IOERROR, &object->cache->flags)) { + _debug("unavailable"); + set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events); + _leave(""); + return; + } + + _debug("LOOKUP \"%s/%s\" in \"%s\"", + parent->cookie->def->name, cookie->def->name, + object->cache->tag->name); + + fscache_stat(&fscache_n_object_lookups); + object->cache->ops->lookup_object(object); + + if (test_bit(FSCACHE_OBJECT_EV_ERROR, &object->events)) + set_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags); + + _leave(""); +} + +/** + * fscache_object_lookup_negative - Note negative cookie lookup + * @object: Object pointing to cookie to mark + * + * Note negative lookup, permitting those waiting to read data from an already + * existing backing object to continue as there's no data for them to read. + */ +void fscache_object_lookup_negative(struct fscache_object *object) +{ + struct fscache_cookie *cookie = object->cookie; + + _enter("{OBJ%x,%s}", + object->debug_id, fscache_object_states[object->state]); + + spin_lock(&object->lock); + if (object->state == FSCACHE_OBJECT_LOOKING_UP) { + fscache_stat(&fscache_n_object_lookups_negative); + + /* transit here to allow write requests to begin stacking up + * and read requests to begin returning ENODATA */ + object->state = FSCACHE_OBJECT_CREATING; + spin_unlock(&object->lock); + + set_bit(FSCACHE_COOKIE_PENDING_FILL, &cookie->flags); + set_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags); + + _debug("wake up lookup %p", &cookie->flags); + smp_mb__before_clear_bit(); + clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags); + smp_mb__after_clear_bit(); + wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP); + set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events); + } else { + ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING); + spin_unlock(&object->lock); + } + + _leave(""); +} +EXPORT_SYMBOL(fscache_object_lookup_negative); + +/** + * fscache_obtained_object - Note successful object lookup or creation + * @object: Object pointing to cookie to mark + * + * Note successful lookup and/or creation, permitting those waiting to write + * data to a backing object to continue. + * + * Note that after calling this, an object's cookie may be relinquished by the + * netfs, and so must be accessed with object lock held. + */ +void fscache_obtained_object(struct fscache_object *object) +{ + struct fscache_cookie *cookie = object->cookie; + + _enter("{OBJ%x,%s}", + object->debug_id, fscache_object_states[object->state]); + + /* if we were still looking up, then we must have a positive lookup + * result, in which case there may be data available */ + spin_lock(&object->lock); + if (object->state == FSCACHE_OBJECT_LOOKING_UP) { + fscache_stat(&fscache_n_object_lookups_positive); + + clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags); + + object->state = FSCACHE_OBJECT_AVAILABLE; + spin_unlock(&object->lock); + + smp_mb__before_clear_bit(); + clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags); + smp_mb__after_clear_bit(); + wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP); + set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events); + } else { + ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING); + fscache_stat(&fscache_n_object_created); + + object->state = FSCACHE_OBJECT_AVAILABLE; + spin_unlock(&object->lock); + set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events); + smp_wmb(); + } + + if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, &cookie->flags)) + wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING); + + _leave(""); +} +EXPORT_SYMBOL(fscache_obtained_object); + +/* + * handle an object that has just become available + */ +static void fscache_object_available(struct fscache_object *object) +{ + _enter("{OBJ%x}", object->debug_id); + + spin_lock(&object->lock); + + if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, &object->cookie->flags)) + wake_up_bit(&object->cookie->flags, FSCACHE_COOKIE_CREATING); + + fscache_done_parent_op(object); + if (object->n_in_progress == 0) { + if (object->n_ops > 0) { + ASSERTCMP(object->n_ops, >=, object->n_obj_ops); + ASSERTIF(object->n_ops > object->n_obj_ops, + !list_empty(&object->pending_ops)); + fscache_start_operations(object); + } else { + ASSERT(list_empty(&object->pending_ops)); + } + } + spin_unlock(&object->lock); + + object->cache->ops->lookup_complete(object); + fscache_enqueue_dependents(object); + + fscache_hist(fscache_obj_instantiate_histogram, object->lookup_jif); + fscache_stat(&fscache_n_object_avail); + + _leave(""); +} + +/* + * drop an object's attachments + */ +static void fscache_drop_object(struct fscache_object *object) +{ + struct fscache_object *parent = object->parent; + struct fscache_cache *cache = object->cache; + + _enter("{OBJ%x,%d}", object->debug_id, object->n_children); + + spin_lock(&cache->object_list_lock); + list_del_init(&object->cache_link); + spin_unlock(&cache->object_list_lock); + + cache->ops->drop_object(object); + + if (parent) { + _debug("release parent OBJ%x {%d}", + parent->debug_id, parent->n_children); + + spin_lock(&parent->lock); + parent->n_children--; + if (parent->n_children == 0) + fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED); + spin_unlock(&parent->lock); + object->parent = NULL; + } + + /* this just shifts the object release to the slow work processor */ + object->cache->ops->put_object(object); + + _leave(""); +} + +/* + * release or recycle an object that the netfs has discarded + */ +static void fscache_release_object(struct fscache_object *object) +{ + _enter(""); + + fscache_drop_object(object); +} + +/* + * withdraw an object from active service + */ +static void fscache_withdraw_object(struct fscache_object *object) +{ + struct fscache_cookie *cookie; + bool detached; + + _enter(""); + + spin_lock(&object->lock); + cookie = object->cookie; + if (cookie) { + /* need to get the cookie lock before the object lock, starting + * from the object pointer */ + atomic_inc(&cookie->usage); + spin_unlock(&object->lock); + + detached = false; + spin_lock(&cookie->lock); + spin_lock(&object->lock); + + if (object->cookie == cookie) { + hlist_del_init(&object->cookie_link); + object->cookie = NULL; + detached = true; + } + spin_unlock(&cookie->lock); + fscache_cookie_put(cookie); + if (detached) + fscache_cookie_put(cookie); + } + + spin_unlock(&object->lock); + + fscache_drop_object(object); +} + +/* + * withdraw an object from active service at the behest of the cache + * - need break the links to a cached object cookie + * - called under two situations: + * (1) recycler decides to reclaim an in-use object + * (2) a cache is unmounted + * - have to take care as the cookie can be being relinquished by the netfs + * simultaneously + * - the object is pinned by the caller holding a refcount on it + */ +void fscache_withdrawing_object(struct fscache_cache *cache, + struct fscache_object *object) +{ + bool enqueue = false; + + _enter(",OBJ%x", object->debug_id); + + spin_lock(&object->lock); + if (object->state < FSCACHE_OBJECT_WITHDRAWING) { + object->state = FSCACHE_OBJECT_WITHDRAWING; + enqueue = true; + } + spin_unlock(&object->lock); + + if (enqueue) + fscache_enqueue_object(object); + + _leave(""); +} + +/* + * allow the slow work item processor to get a ref on an object + */ +static int fscache_object_slow_work_get_ref(struct slow_work *work) +{ + struct fscache_object *object = + container_of(work, struct fscache_object, work); + + return object->cache->ops->grab_object(object) ? 0 : -EAGAIN; +} + +/* + * allow the slow work item processor to discard a ref on a work item + */ +static void fscache_object_slow_work_put_ref(struct slow_work *work) +{ + struct fscache_object *object = + container_of(work, struct fscache_object, work); + + return object->cache->ops->put_object(object); +} + +/* + * enqueue an object for metadata-type processing + */ +void fscache_enqueue_object(struct fscache_object *object) +{ + _enter("{OBJ%x}", object->debug_id); + + slow_work_enqueue(&object->work); +} + +/* + * enqueue the dependents of an object for metadata-type processing + * - the caller must hold the object's lock + * - this may cause an already locked object to wind up being processed again + */ +static void fscache_enqueue_dependents(struct fscache_object *object) +{ + struct fscache_object *dep; + + _enter("{OBJ%x}", object->debug_id); + + if (list_empty(&object->dependents)) + return; + + spin_lock(&object->lock); + + while (!list_empty(&object->dependents)) { + dep = list_entry(object->dependents.next, + struct fscache_object, dep_link); + list_del_init(&dep->dep_link); + + + /* sort onto appropriate lists */ + fscache_enqueue_object(dep); + dep->cache->ops->put_object(dep); + + if (!list_empty(&object->dependents)) + cond_resched_lock(&object->lock); + } + + spin_unlock(&object->lock); +} + +/* + * remove an object from whatever queue it's waiting on + * - the caller must hold object->lock + */ +void fscache_dequeue_object(struct fscache_object *object) +{ + _enter("{OBJ%x}", object->debug_id); + + if (!list_empty(&object->dep_link)) { + spin_lock(&object->parent->lock); + list_del_init(&object->dep_link); + spin_unlock(&object->parent->lock); + } + + _leave(""); +} + +/** + * fscache_check_aux - Ask the netfs whether an object on disk is still valid + * @object: The object to ask about + * @data: The auxiliary data for the object + * @datalen: The size of the auxiliary data + * + * This function consults the netfs about the coherency state of an object + */ +enum fscache_checkaux fscache_check_aux(struct fscache_object *object, + const void *data, uint16_t datalen) +{ + enum fscache_checkaux result; + + if (!object->cookie->def->check_aux) { + fscache_stat(&fscache_n_checkaux_none); + return FSCACHE_CHECKAUX_OKAY; + } + + result = object->cookie->def->check_aux(object->cookie->netfs_data, + data, datalen); + switch (result) { + /* entry okay as is */ + case FSCACHE_CHECKAUX_OKAY: + fscache_stat(&fscache_n_checkaux_okay); + break; + + /* entry requires update */ + case FSCACHE_CHECKAUX_NEEDS_UPDATE: + fscache_stat(&fscache_n_checkaux_update); + break; + + /* entry requires deletion */ + case FSCACHE_CHECKAUX_OBSOLETE: + fscache_stat(&fscache_n_checkaux_obsolete); + break; + + default: + BUG(); + } + + return result; +} +EXPORT_SYMBOL(fscache_check_aux); |
