FS-Cache: Add the FS-Cache cache backend API and documentation

Add the API for a generic facility (FS-Cache) by which caches may declare them
selves open for business, and may obtain work to be done from network
filesystems.  The header file is included by:

	#include <linux/fscache-cache.h>

Documentation for the API is also added to:

	Documentation/filesystems/caching/backend-api.txt

This API is not usable without the implementation of the utility functions
which will be added in further patches.

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>

1 files changed, 509 insertions, 0 deletions

diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
new file mode 100644
index 000000000000..b2a9a484c4cf
--- /dev/null
+++ b/include/linux/fscache-cache.h
@@ -0,0 +1,509 @@
+/* General filesystem caching backing cache interface
+ *
+ * Copyright (C) 2004-2007 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.
+ *
+ * NOTE!!! See:
+ *
+ *      Documentation/filesystems/caching/backend-api.txt
+ *
+ * for a description of the cache backend interface declared here.
+ */
+
+#ifndef _LINUX_FSCACHE_CACHE_H
+#define _LINUX_FSCACHE_CACHE_H
+
+#include <linux/fscache.h>
+#include <linux/sched.h>
+#include <linux/slow-work.h>
+
+#define NR_MAXCACHES BITS_PER_LONG
+
+struct fscache_cache;
+struct fscache_cache_ops;
+struct fscache_object;
+struct fscache_operation;
+
+#ifdef CONFIG_FSCACHE_PROC
+extern struct proc_dir_entry *proc_fscache;
+#endif
+
+/*
+ * cache tag definition
+ */
+struct fscache_cache_tag {
+        struct list_head        link;
+        struct fscache_cache    *cache;         /* cache referred to by this tag */
+        unsigned long           flags;
+#define FSCACHE_TAG_RESERVED    0               /* T if tag is reserved for a cache */
+        atomic_t                usage;
+        char                    name[0];        /* tag name */
+};
+
+/*
+ * cache definition
+ */
+struct fscache_cache {
+        const struct fscache_cache_ops *ops;
+        struct fscache_cache_tag *tag;          /* tag representing this cache */
+        struct kobject          *kobj;          /* system representation of this cache */
+        struct list_head        link;           /* link in list of caches */
+        size_t                  max_index_size; /* maximum size of index data */
+        char                    identifier[36]; /* cache label */
+
+        /* node management */
+        struct work_struct      op_gc;          /* operation garbage collector */
+        struct list_head        object_list;    /* list of data/index objects */
+        struct list_head        op_gc_list;     /* list of ops to be deleted */
+        spinlock_t              object_list_lock;
+        spinlock_t              op_gc_list_lock;
+        atomic_t                object_count;   /* no. of live objects in this cache */
+        struct fscache_object   *fsdef;         /* object for the fsdef index */
+        unsigned long           flags;
+#define FSCACHE_IOERROR         0       /* cache stopped on I/O error */
+#define FSCACHE_CACHE_WITHDRAWN 1       /* cache has been withdrawn */
+};
+
+extern wait_queue_head_t fscache_cache_cleared_wq;
+
+/*
+ * operation to be applied to a cache object
+ * - retrieval initiation operations are done in the context of the process
+ *   that issued them, and not in an async thread pool
+ */
+typedef void (*fscache_operation_release_t)(struct fscache_operation *op);
+typedef void (*fscache_operation_processor_t)(struct fscache_operation *op);
+
+struct fscache_operation {
+        union {
+                struct work_struct fast_work;   /* record for fast ops */
+                struct slow_work slow_work;     /* record for (very) slow ops */
+        };
+        struct list_head        pend_link;      /* link in object->pending_ops */
+        struct fscache_object   *object;        /* object to be operated upon */
+
+        unsigned long           flags;
+#define FSCACHE_OP_TYPE         0x000f  /* operation type */
+#define FSCACHE_OP_FAST         0x0001  /* - fast op, processor may not sleep for disk */
+#define FSCACHE_OP_SLOW         0x0002  /* - (very) slow op, processor may sleep for disk */
+#define FSCACHE_OP_MYTHREAD     0x0003  /* - processing is done be issuing thread, not pool */
+#define FSCACHE_OP_WAITING      4       /* cleared when op is woken */
+#define FSCACHE_OP_EXCLUSIVE    5       /* exclusive op, other ops must wait */
+#define FSCACHE_OP_DEAD         6       /* op is now dead */
+
+        atomic_t                usage;
+        unsigned                debug_id;       /* debugging ID */
+
+        /* operation processor callback
+         * - can be NULL if FSCACHE_OP_WAITING is going to be used to perform
+         *   the op in a non-pool thread */
+        fscache_operation_processor_t processor;
+
+        /* operation releaser */
+        fscache_operation_release_t release;
+};
+
+extern atomic_t fscache_op_debug_id;
+extern const struct slow_work_ops fscache_op_slow_work_ops;
+
+extern void fscache_enqueue_operation(struct fscache_operation *);
+extern void fscache_put_operation(struct fscache_operation *);
+
+/**
+ * fscache_operation_init - Do basic initialisation of an operation
+ * @op: The operation to initialise
+ * @release: The release function to assign
+ *
+ * Do basic initialisation of an operation.  The caller must still set flags,
+ * object, either fast_work or slow_work if necessary, and processor if needed.
+ */
+static inline void fscache_operation_init(struct fscache_operation *op,
+                                          fscache_operation_release_t release)
+{
+        atomic_set(&op->usage, 1);
+        op->debug_id = atomic_inc_return(&fscache_op_debug_id);
+        op->release = release;
+        INIT_LIST_HEAD(&op->pend_link);
+}
+
+/**
+ * fscache_operation_init_slow - Do additional initialisation of a slow op
+ * @op: The operation to initialise
+ * @processor: The processor function to assign
+ *
+ * Do additional initialisation of an operation as required for slow work.
+ */
+static inline
+void fscache_operation_init_slow(struct fscache_operation *op,
+                                 fscache_operation_processor_t processor)
+{
+        op->processor = processor;
+        slow_work_init(&op->slow_work, &fscache_op_slow_work_ops);
+}
+
+/*
+ * data read operation
+ */
+struct fscache_retrieval {
+        struct fscache_operation op;
+        struct address_space    *mapping;       /* netfs pages */
+        fscache_rw_complete_t   end_io_func;    /* function to call on I/O completion */
+        void                    *context;       /* netfs read context (pinned) */
+        struct list_head        to_do;          /* list of things to be done by the backend */
+        unsigned long           start_time;     /* time at which retrieval started */
+};
+
+typedef int (*fscache_page_retrieval_func_t)(struct fscache_retrieval *op,
+                                             struct page *page,
+                                             gfp_t gfp);
+
+typedef int (*fscache_pages_retrieval_func_t)(struct fscache_retrieval *op,
+                                              struct list_head *pages,
+                                              unsigned *nr_pages,
+                                              gfp_t gfp);
+
+/**
+ * fscache_get_retrieval - Get an extra reference on a retrieval operation
+ * @op: The retrieval operation to get a reference on
+ *
+ * Get an extra reference on a retrieval operation.
+ */
+static inline
+struct fscache_retrieval *fscache_get_retrieval(struct fscache_retrieval *op)
+{
+        atomic_inc(&op->op.usage);
+        return op;
+}
+
+/**
+ * fscache_enqueue_retrieval - Enqueue a retrieval operation for processing
+ * @op: The retrieval operation affected
+ *
+ * Enqueue a retrieval operation for processing by the FS-Cache thread pool.
+ */
+static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
+{
+        fscache_enqueue_operation(&op->op);
+}
+
+/**
+ * fscache_put_retrieval - Drop a reference to a retrieval operation
+ * @op: The retrieval operation affected
+ *
+ * Drop a reference to a retrieval operation.
+ */
+static inline void fscache_put_retrieval(struct fscache_retrieval *op)
+{
+        fscache_put_operation(&op->op);
+}
+
+/*
+ * cached page storage work item
+ * - used to do three things:
+ *   - batch writes to the cache
+ *   - do cache writes asynchronously
+ *   - defer writes until cache object lookup completion
+ */
+struct fscache_storage {
+        struct fscache_operation op;
+        pgoff_t                 store_limit;    /* don't write more than this */
+};
+
+/*
+ * cache operations
+ */
+struct fscache_cache_ops {
+        /* name of cache provider */
+        const char *name;
+
+        /* allocate an object record for a cookie */
+        struct fscache_object *(*alloc_object)(struct fscache_cache *cache,
+                                               struct fscache_cookie *cookie);
+
+        /* look up the object for a cookie */
+        void (*lookup_object)(struct fscache_object *object);
+
+        /* finished looking up */
+        void (*lookup_complete)(struct fscache_object *object);
+
+        /* increment the usage count on this object (may fail if unmounting) */
+        struct fscache_object *(*grab_object)(struct fscache_object *object);
+
+        /* pin an object in the cache */
+        int (*pin_object)(struct fscache_object *object);
+
+        /* unpin an object in the cache */
+        void (*unpin_object)(struct fscache_object *object);
+
+        /* store the updated auxilliary data on an object */
+        void (*update_object)(struct fscache_object *object);
+
+        /* discard the resources pinned by an object and effect retirement if
+         * necessary */
+        void (*drop_object)(struct fscache_object *object);
+
+        /* dispose of a reference to an object */
+        void (*put_object)(struct fscache_object *object);
+
+        /* sync a cache */
+        void (*sync_cache)(struct fscache_cache *cache);
+
+        /* notification that the attributes of a non-index object (such as
+         * i_size) have changed */
+        int (*attr_changed)(struct fscache_object *object);
+
+        /* reserve space for an object's data and associated metadata */
+        int (*reserve_space)(struct fscache_object *object, loff_t i_size);
+
+        /* request a backing block for a page be read or allocated in the
+         * cache */
+        fscache_page_retrieval_func_t read_or_alloc_page;
+
+        /* request backing blocks for a list of pages be read or allocated in
+         * the cache */
+        fscache_pages_retrieval_func_t read_or_alloc_pages;
+
+        /* request a backing block for a page be allocated in the cache so that
+         * it can be written directly */
+        fscache_page_retrieval_func_t allocate_page;
+
+        /* request backing blocks for pages be allocated in the cache so that
+         * they can be written directly */
+        fscache_pages_retrieval_func_t allocate_pages;
+
+        /* write a page to its backing block in the cache */
+        int (*write_page)(struct fscache_storage *op, struct page *page);
+
+        /* detach backing block from a page (optional)
+         * - must release the cookie lock before returning
+         * - may sleep
+         */
+        void (*uncache_page)(struct fscache_object *object,
+                             struct page *page);
+
+        /* dissociate a cache from all the pages it was backing */
+        void (*dissociate_pages)(struct fscache_cache *cache);
+};
+
+/*
+ * data file or index object cookie
+ * - a file will only appear in one cache
+ * - a request to cache a file may or may not be honoured, subject to
+ *   constraints such as disk space
+ * - indices are created on disk just-in-time
+ */
+struct fscache_cookie {
+        atomic_t                        usage;          /* number of users of this cookie */
+        atomic_t                        n_children;     /* number of children of this cookie */
+        spinlock_t                      lock;
+        struct hlist_head               backing_objects; /* object(s) backing this file/index */
+        const struct fscache_cookie_def *def;           /* definition */
+        struct fscache_cookie           *parent;        /* parent of this entry */
+        void                            *netfs_data;    /* back pointer to netfs */
+        struct radix_tree_root          stores;         /* pages to be stored on this cookie */
+#define FSCACHE_COOKIE_PENDING_TAG      0               /* pages tag: pending write to cache */
+
+        unsigned long                   flags;
+#define FSCACHE_COOKIE_LOOKING_UP       0       /* T if non-index cookie being looked up still */
+#define FSCACHE_COOKIE_CREATING         1       /* T if non-index object being created still */
+#define FSCACHE_COOKIE_NO_DATA_YET      2       /* T if new object with no cached data yet */
+#define FSCACHE_COOKIE_PENDING_FILL     3       /* T if pending initial fill on object */
+#define FSCACHE_COOKIE_FILLING          4       /* T if filling object incrementally */
+#define FSCACHE_COOKIE_UNAVAILABLE      5       /* T if cookie is unavailable (error, etc) */
+};
+
+extern struct fscache_cookie fscache_fsdef_index;
+
+/*
+ * on-disk cache file or index handle
+ */
+struct fscache_object {
+        enum fscache_object_state {
+                FSCACHE_OBJECT_INIT,            /* object in initial unbound state */
+                FSCACHE_OBJECT_LOOKING_UP,      /* looking up object */
+                FSCACHE_OBJECT_CREATING,        /* creating object */
+
+                /* active states */
+                FSCACHE_OBJECT_AVAILABLE,       /* cleaning up object after creation */
+                FSCACHE_OBJECT_ACTIVE,          /* object is usable */
+                FSCACHE_OBJECT_UPDATING,        /* object is updating */
+
+                /* terminal states */
+                FSCACHE_OBJECT_DYING,           /* object waiting for accessors to finish */
+                FSCACHE_OBJECT_LC_DYING,        /* object cleaning up after lookup/create */
+                FSCACHE_OBJECT_ABORT_INIT,      /* abort the init state */
+                FSCACHE_OBJECT_RELEASING,       /* releasing object */
+                FSCACHE_OBJECT_RECYCLING,       /* retiring object */
+                FSCACHE_OBJECT_WITHDRAWING,     /* withdrawing object */
+                FSCACHE_OBJECT_DEAD,            /* object is now dead */
+        } state;
+
+        int                     debug_id;       /* debugging ID */
+        int                     n_children;     /* number of child objects */
+        int                     n_ops;          /* number of ops outstanding on object */
+        int                     n_obj_ops;      /* number of object ops outstanding on object */
+        int                     n_in_progress;  /* number of ops in progress */
+        int                     n_exclusive;    /* number of exclusive ops queued */
+        spinlock_t              lock;           /* state and operations lock */
+
+        unsigned long           lookup_jif;     /* time at which lookup started */
+        unsigned long           event_mask;     /* events this object is interested in */
+        unsigned long           events;         /* events to be processed by this object
+                                                 * (order is important - using fls) */
+#define FSCACHE_OBJECT_EV_REQUEUE       0       /* T if object should be requeued */
+#define FSCACHE_OBJECT_EV_UPDATE        1       /* T if object should be updated */
+#define FSCACHE_OBJECT_EV_CLEARED       2       /* T if accessors all gone */
+#define FSCACHE_OBJECT_EV_ERROR         3       /* T if fatal error occurred during processing */
+#define FSCACHE_OBJECT_EV_RELEASE       4       /* T if netfs requested object release */
+#define FSCACHE_OBJECT_EV_RETIRE        5       /* T if netfs requested object retirement */
+#define FSCACHE_OBJECT_EV_WITHDRAW      6       /* T if cache requested object withdrawal */
+
+        unsigned long           flags;
+#define FSCACHE_OBJECT_LOCK             0       /* T if object is busy being processed */
+#define FSCACHE_OBJECT_PENDING_WRITE    1       /* T if object has pending write */
+#define FSCACHE_OBJECT_WAITING          2       /* T if object is waiting on its parent */
+
+        struct list_head        cache_link;     /* link in cache->object_list */
+        struct hlist_node       cookie_link;    /* link in cookie->backing_objects */
+        struct fscache_cache    *cache;         /* cache that supplied this object */
+        struct fscache_cookie   *cookie;        /* netfs's file/index object */
+        struct fscache_object   *parent;        /* parent object */
+        struct slow_work        work;           /* attention scheduling record */
+        struct list_head        dependents;     /* FIFO of dependent objects */
+        struct list_head        dep_link;       /* link in parent's dependents list */
+        struct list_head        pending_ops;    /* unstarted operations on this object */
+        pgoff_t                 store_limit;    /* current storage limit */
+};
+
+extern const char *fscache_object_states[];
+
+#define fscache_object_is_active(obj)                         \
+        (!test_bit(FSCACHE_IOERROR, &(obj)->cache->flags) &&  \
+         (obj)->state >= FSCACHE_OBJECT_AVAILABLE &&          \
+         (obj)->state < FSCACHE_OBJECT_DYING)
+
+extern const struct slow_work_ops fscache_object_slow_work_ops;
+
+/**
+ * fscache_object_init - Initialise a cache object description
+ * @object: Object description
+ *
+ * Initialise a cache object description to its basic values.
+ *
+ * See Documentation/filesystems/caching/backend-api.txt for a complete
+ * description.
+ */
+static inline
+void fscache_object_init(struct fscache_object *object,
+                         struct fscache_cookie *cookie,
+                         struct fscache_cache *cache)
+{
+        atomic_inc(&cache->object_count);
+
+        object->state = FSCACHE_OBJECT_INIT;
+        spin_lock_init(&object->lock);
+        INIT_LIST_HEAD(&object->cache_link);
+        INIT_HLIST_NODE(&object->cookie_link);
+        vslow_work_init(&object->work, &fscache_object_slow_work_ops);
+        INIT_LIST_HEAD(&object->dependents);
+        INIT_LIST_HEAD(&object->dep_link);
+        INIT_LIST_HEAD(&object->pending_ops);
+        object->n_children = 0;
+        object->n_ops = object->n_in_progress = object->n_exclusive = 0;
+        object->events = object->event_mask = 0;
+        object->flags = 0;
+        object->store_limit = 0;
+        object->cache = cache;
+        object->cookie = cookie;
+        object->parent = NULL;
+}
+
+extern void fscache_object_lookup_negative(struct fscache_object *object);
+extern void fscache_obtained_object(struct fscache_object *object);
+
+/**
+ * fscache_object_destroyed - Note destruction of an object in a cache
+ * @cache: The cache from which the object came
+ *
+ * Note the destruction and deallocation of an object record in a cache.
+ */
+static inline void fscache_object_destroyed(struct fscache_cache *cache)
+{
+        if (atomic_dec_and_test(&cache->object_count))
+                wake_up_all(&fscache_cache_cleared_wq);
+}
+
+/**
+ * fscache_object_lookup_error - Note an object encountered an error
+ * @object: The object on which the error was encountered
+ *
+ * Note that an object encountered a fatal error (usually an I/O error) and
+ * that it should be withdrawn as soon as possible.
+ */
+static inline void fscache_object_lookup_error(struct fscache_object *object)
+{
+        set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events);
+}
+
+/**
+ * fscache_set_store_limit - Set the maximum size to be stored in an object
+ * @object: The object to set the maximum on
+ * @i_size: The limit to set in bytes
+ *
+ * Set the maximum size an object is permitted to reach, implying the highest
+ * byte that may be written.  Intended to be called by the attr_changed() op.
+ *
+ * See Documentation/filesystems/caching/backend-api.txt for a complete
+ * description.
+ */
+static inline
+void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
+{
+        object->store_limit = i_size >> PAGE_SHIFT;
+        if (i_size & ~PAGE_MASK)
+                object->store_limit++;
+}
+
+/**
+ * fscache_end_io - End a retrieval operation on a page
+ * @op: The FS-Cache operation covering the retrieval
+ * @page: The page that was to be fetched
+ * @error: The error code (0 if successful)
+ *
+ * Note the end of an operation to retrieve a page, as covered by a particular
+ * operation record.
+ */
+static inline void fscache_end_io(struct fscache_retrieval *op,
+                                  struct page *page, int error)
+{
+        op->end_io_func(page, op->context, error);
+}
+
+/*
+ * out-of-line cache backend functions
+ */
+extern void fscache_init_cache(struct fscache_cache *cache,
+                               const struct fscache_cache_ops *ops,
+                               const char *idfmt,
+                               ...) __attribute__ ((format (printf, 3, 4)));
+
+extern int fscache_add_cache(struct fscache_cache *cache,
+                             struct fscache_object *fsdef,
+                             const char *tagname);
+extern void fscache_withdraw_cache(struct fscache_cache *cache);
+
+extern void fscache_io_error(struct fscache_cache *cache);
+
+extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
+                                      struct pagevec *pagevec);
+
+extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
+                                               const void *data,
+                                               uint16_t datalen);
+
+#endif /* _LINUX_FSCACHE_CACHE_H */