1. 19 Nov, 2009 3 commits
    • David Howells's avatar
      FS-Cache: Allow the current state of all objects to be dumped · 4fbf4291
      David Howells authored
      
      
      Allow the current state of all fscache objects to be dumped by doing:
      
      	cat /proc/fs/fscache/objects
      
      By default, all objects and all fields will be shown.  This can be restricted
      by adding a suitable key to one of the caller's keyrings (such as the session
      keyring):
      
      	keyctl add user fscache:objlist "<restrictions>" @s
      
      The <restrictions> are:
      
      	K	Show hexdump of object key (don't show if not given)
      	A	Show hexdump of object aux data (don't show if not given)
      
      And paired restrictions:
      
      	C	Show objects that have a cookie
      	c	Show objects that don't have a cookie
      	B	Show objects that are busy
      	b	Show objects that aren't busy
      	W	Show objects that have pending writes
      	w	Show objects that don't have pending writes
      	R	Show objects that have outstanding reads
      	r	Show objects that don't have outstanding reads
      	S	Show objects that have slow work queued
      	s	Show objects that don't have slow work queued
      
      If neither side of a restriction pair is given, then both are implied.  For
      example:
      
      	keyctl add user fscache:objlist KB @s
      
      shows objects that are busy, and lists their object keys, but does not dump
      their auxiliary data.  It also implies "CcWwRrSs", but as 'B' is given, 'b' is
      not implied.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      4fbf4291
    • David Howells's avatar
      FS-Cache: Annotate slow-work runqueue proc lines for FS-Cache work items · 440f0aff
      David Howells authored
      
      
      Annotate slow-work runqueue proc lines for FS-Cache work items.  Objects
      include the object ID and the state.  Operations include the object ID, the
      operation ID and the operation type and state.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      440f0aff
    • David Howells's avatar
      SLOW_WORK: Wait for outstanding work items belonging to a module to clear · 3d7a641e
      David Howells authored
      
      
      Wait for outstanding slow work items belonging to a module to clear when
      unregistering that module as a user of the facility.  This prevents the put_ref
      code of a work item from being taken away before it returns.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      3d7a641e
  2. 27 May, 2009 1 commit
  3. 03 Apr, 2009 12 commits
    • David Howells's avatar
      FS-Cache: Implement data I/O part of netfs API · b5108822
      David Howells authored
      
      
      Implement the data I/O part of the FS-Cache netfs API.  The documentation and
      API header file were added in a previous patch.
      
      This patch implements the following functions for the netfs to call:
      
       (*) fscache_attr_changed().
      
           Indicate that the object has changed its attributes.  The only attribute
           currently recorded is the file size.  Only pages within the set file size
           will be stored in the cache.
      
           This operation is submitted for asynchronous processing, and will return
           immediately.  It will return -ENOMEM if an out of memory error is
           encountered, -ENOBUFS if the object is not actually cached, or 0 if the
           operation is successfully queued.
      
       (*) fscache_read_or_alloc_page().
       (*) fscache_read_or_alloc_pages().
      
           Request data be fetched from the disk, and allocate internal metadata to
           track the netfs pages and reserve disk space for unknown pages.
      
           These operations perform semi-asynchronous data reads.  Upon returning
           they will indicate which pages they think can be retrieved from disk, and
           will have set in progress attempts to retrieve those pages.
      
           These will return, in order of preference, -ENOMEM on memory allocation
           error, -ERESTARTSYS if a signal interrupted proceedings, -ENODATA if one
           or more requested pages are not yet cached, -ENOBUFS if the object is not
           actually cached or if there isn't space for future pages to be cached on
           this object, or 0 if successful.
      
           In the case of the multipage function, the pages for which reads are set
           in progress will be removed from the list and the page count decreased
           appropriately.
      
           If any read operations should fail, the completion function will be given
           an error, and will also be passed contextual information to allow the
           netfs to fall back to querying the server for the absent pages.
      
           For each successful read, the page completion function will also be
           called.
      
           Any pages subsequently tracked by the cache will have PG_fscache set upon
           them on return.  fscache_uncache_page() must be called for such pages.
      
           If supplied by the netfs, the mark_pages_cached() cookie op will be
           invoked for any pages now tracked.
      
       (*) fscache_alloc_page().
      
           Allocate internal metadata to track a netfs page and reserve disk space.
      
           This will return -ENOMEM on memory allocation error, -ERESTARTSYS on
           signal, -ENOBUFS if the object isn't cached, or there isn't enough space
           in the cache, or 0 if successful.
      
           Any pages subsequently tracked by the cache will have PG_fscache set upon
           them on return.  fscache_uncache_page() must be called for such pages.
      
           If supplied by the netfs, the mark_pages_cached() cookie op will be
           invoked for any pages now tracked.
      
       (*) fscache_write_page().
      
           Request data be stored to disk.  This may only be called on pages that
           have been read or alloc'd by the above three functions and have not yet
           been uncached.
      
           This will return -ENOMEM on memory allocation error, -ERESTARTSYS on
           signal, -ENOBUFS if the object isn't cached, or there isn't immediately
           enough space in the cache, or 0 if successful.
      
           On a successful return, this operation will have queued the page for
           asynchronous writing to the cache.  The page will be returned with
           PG_fscache_write set until the write completes one way or another.  The
           caller will not be notified if the write fails due to an I/O error.  If
           that happens, the object will become available and all pending writes will
           be aborted.
      
           Note that the cache may batch up page writes, and so it may take a while
           to get around to writing them out.
      
           The caller must assume that until PG_fscache_write is cleared the page is
           use by the cache.  Any changes made to the page may be reflected on disk.
           The page may even be under DMA.
      
       (*) fscache_uncache_page().
      
           Indicate that the cache should stop tracking a page previously read or
           alloc'd from the cache.  If the page was alloc'd only, but unwritten, it
           will not appear on disk.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      b5108822
    • David Howells's avatar
      FS-Cache: Add and document asynchronous operation handling · 952efe7b
      David Howells authored
      
      
      Add and document asynchronous operation handling for use by FS-Cache's data
      storage and retrieval routines.
      
      The following documentation is added to:
      
      	Documentation/filesystems/caching/operations.txt
      
      		       ================================
      		       ASYNCHRONOUS OPERATIONS HANDLING
      		       ================================
      
      ========
      OVERVIEW
      ========
      
      FS-Cache has an asynchronous operations handling facility that it uses for its
      data storage and retrieval routines.  Its operations are represented by
      fscache_operation structs, though these are usually embedded into some other
      structure.
      
      This facility is available to and expected to be be used by the cache backends,
      and FS-Cache will create operations and pass them off to the appropriate cache
      backend for completion.
      
      To make use of this facility, <linux/fscache-cache.h> should be #included.
      
      ===============================
      OPERATION RECORD INITIALISATION
      ===============================
      
      An operation is recorded in an fscache_operation struct:
      
      	struct fscache_operation {
      		union {
      			struct work_struct fast_work;
      			struct slow_work slow_work;
      		};
      		unsigned long		flags;
      		fscache_operation_processor_t processor;
      		...
      	};
      
      Someone wanting to issue an operation should allocate something with this
      struct embedded in it.  They should initialise it by calling:
      
      	void fscache_operation_init(struct fscache_operation *op,
      				    fscache_operation_release_t release);
      
      with the operation to be initialised and the release function to use.
      
      The op->flags parameter should be set to indicate the CPU time provision and
      the exclusivity (see the Parameters section).
      
      The op->fast_work, op->slow_work and op->processor flags should be set as
      appropriate for the CPU time provision (see the Parameters section).
      
      FSCACHE_OP_WAITING may be set in op->flags prior to each submission of the
      operation and waited for afterwards.
      
      ==========
      PARAMETERS
      ==========
      
      There are a number of parameters that can be set in the operation record's flag
      parameter.  There are three options for the provision of CPU time in these
      operations:
      
       (1) The operation may be done synchronously (FSCACHE_OP_MYTHREAD).  A thread
           may decide it wants to handle an operation itself without deferring it to
           another thread.
      
           This is, for example, used in read operations for calling readpages() on
           the backing filesystem in CacheFiles.  Although readpages() does an
           asynchronous data fetch, the determination of whether pages exist is done
           synchronously - and the netfs does not proceed until this has been
           determined.
      
           If this option is to be used, FSCACHE_OP_WAITING must be set in op->flags
           before submitting the operation, and the operating thread must wait for it
           to be cleared before proceeding:
      
      		wait_on_bit(&op->flags, FSCACHE_OP_WAITING,
      			    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
      
       (2) The operation may be fast asynchronous (FSCACHE_OP_FAST), in which case it
           will be given to keventd to process.  Such an operation is not permitted
           to sleep on I/O.
      
           This is, for example, used by CacheFiles to copy data from a backing fs
           page to a netfs page after the backing fs has read the page in.
      
           If this option is used, op->fast_work and op->processor must be
           initialised before submitting the operation:
      
      		INIT_WORK(&op->fast_work, do_some_work);
      
       (3) The operation may be slow asynchronous (FSCACHE_OP_SLOW), in which case it
           will be given to the slow work facility to process.  Such an operation is
           permitted to sleep on I/O.
      
           This is, for example, used by FS-Cache to handle background writes of
           pages that have just been fetched from a remote server.
      
           If this option is used, op->slow_work and op->processor must be
           initialised before submitting the operation:
      
      		fscache_operation_init_slow(op, processor)
      
      Furthermore, operations may be one of two types:
      
       (1) Exclusive (FSCACHE_OP_EXCLUSIVE).  Operations of this type may not run in
           conjunction with any other operation on the object being operated upon.
      
           An example of this is the attribute change operation, in which the file
           being written to may need truncation.
      
       (2) Shareable.  Operations of this type may be running simultaneously.  It's
           up to the operation implementation to prevent interference between other
           operations running at the same time.
      
      =========
      PROCEDURE
      =========
      
      Operations are used through the following procedure:
      
       (1) The submitting thread must allocate the operation and initialise it
           itself.  Normally this would be part of a more specific structure with the
           generic op embedded within.
      
       (2) The submitting thread must then submit the operation for processing using
           one of the following two functions:
      
      	int fscache_submit_op(struct fscache_object *object,
      			      struct fscache_operation *op);
      
      	int fscache_submit_exclusive_op(struct fscache_object *object,
      					struct fscache_operation *op);
      
           The first function should be used to submit non-exclusive ops and the
           second to submit exclusive ones.  The caller must still set the
           FSCACHE_OP_EXCLUSIVE flag.
      
           If successful, both functions will assign the operation to the specified
           object and return 0.  -ENOBUFS will be returned if the object specified is
           permanently unavailable.
      
           The operation manager will defer operations on an object that is still
           undergoing lookup or creation.  The operation will also be deferred if an
           operation of conflicting exclusivity is in progress on the object.
      
           If the operation is asynchronous, the manager will retain a reference to
           it, so the caller should put their reference to it by passing it to:
      
      	void fscache_put_operation(struct fscache_operation *op);
      
       (3) If the submitting thread wants to do the work itself, and has marked the
           operation with FSCACHE_OP_MYTHREAD, then it should monitor
           FSCACHE_OP_WAITING as described above and check the state of the object if
           necessary (the object might have died whilst the thread was waiting).
      
           When it has finished doing its processing, it should call
           fscache_put_operation() on it.
      
       (4) The operation holds an effective lock upon the object, preventing other
           exclusive ops conflicting until it is released.  The operation can be
           enqueued for further immediate asynchronous processing by adjusting the
           CPU time provisioning option if necessary, eg:
      
      	op->flags &= ~FSCACHE_OP_TYPE;
      	op->flags |= ~FSCACHE_OP_FAST;
      
           and calling:
      
      	void fscache_enqueue_operation(struct fscache_operation *op)
      
           This can be used to allow other things to have use of the worker thread
           pools.
      
      =====================
      ASYNCHRONOUS CALLBACK
      =====================
      
      When used in asynchronous mode, the worker thread pool will invoke the
      processor method with a pointer to the operation.  This should then get at the
      container struct by using container_of():
      
      	static void fscache_write_op(struct fscache_operation *_op)
      	{
      		struct fscache_storage *op =
      			container_of(_op, struct fscache_storage, op);
      	...
      	}
      
      The caller holds a reference on the operation, and will invoke
      fscache_put_operation() when the processor function returns.  The processor
      function is at liberty to call fscache_enqueue_operation() or to take extra
      references.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      952efe7b
    • David Howells's avatar
      FS-Cache: Implement the cookie management part of the netfs API · ccc4fc3d
      David Howells authored
      
      
      Implement the cookie management part of the FS-Cache netfs client API.  The
      documentation and API header file were added in a previous patch.
      
      This patch implements the following three functions:
      
       (1) fscache_acquire_cookie().
      
           Acquire a cookie to represent an object to the netfs.  If the object in
           question is a non-index object, then that object and its parent indices
           will be created on disk at this point if they don't already exist.  Index
           creation is deferred because an index may reside in multiple caches.
      
       (2) fscache_relinquish_cookie().
      
           Retire or release a cookie previously acquired.  At this point, the
           object on disk may be destroyed.
      
       (3) fscache_update_cookie().
      
           Update the in-cache representation of a cookie.  This is used to update
           the auxiliary data for coherency management purposes.
      
      With this patch it is possible to have a netfs instruct a cache backend to
      look up, validate and create metadata on disk and to destroy it again.
      The ability to actually store and retrieve data in the objects so created is
      added in later patches.
      
      Note that these functions will never return an error.  _All_ errors are
      handled internally to FS-Cache.
      
      The worst that can happen is that fscache_acquire_cookie() may return a NULL
      pointer - which is considered a negative cookie pointer and can be passed back
      to any function that takes a cookie without harm.  A negative cookie pointer
      merely suppresses caching at that level.
      
      The stub in linux/fscache.h will detect inline the negative cookie pointer and
      abort the operation as fast as possible.  This means that the compiler doesn't
      have to set up for a call in that case.
      
      See the documentation in Documentation/filesystems/caching/netfs-api.txt for
      more information.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      ccc4fc3d
    • David Howells's avatar
      FS-Cache: Object management state machine · 36c95590
      David Howells authored
      
      
      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: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      36c95590
    • David Howells's avatar
      FS-Cache: Bit waiting helpers · 2868cbea
      David Howells authored
      
      
      Add helpers for use with wait_on_bit().
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      2868cbea
    • David Howells's avatar
      FS-Cache: Add netfs registration · 726dd7ff
      David Howells authored
      
      
      Add functions to register and unregister a network filesystem or other client
      of the FS-Cache service.  This allocates and releases the cookie representing
      the top-level index for a netfs, and makes it available to the netfs.
      
      If the FS-Cache facility is disabled, then the calls are optimised away at
      compile time.
      
      Note that whilst this patch may appear to work with FS-Cache enabled and a
      netfs attempting to use it, it will leak the cookie it allocates for the netfs
      as fscache_relinquish_cookie() is implemented in a later patch.  This will
      cause the slab code to emit a warning when the module is removed.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      726dd7ff
    • David Howells's avatar
      FS-Cache: Provide a slab for cookie allocation · 955d0091
      David Howells authored
      
      
      Provide a slab from which can be allocated the FS-Cache cookies that will be
      presented to the netfs.
      
      Also provide a slab constructor and a function to recursively discard a cookie
      and its ancestor chain.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      955d0091
    • David Howells's avatar
      FS-Cache: Add cache management · 4c515dd4
      David Howells authored
      
      
      Implement the entry points by which a cache backend may initialise, add,
      declare an error upon and withdraw a cache.
      
      Further, an object is created in sysfs under which each cache added will get
      an object created:
      
      	/sys/fs/fscache/<cachetag>/
      
      All of this is described in Documentation/filesystems/caching/backend-api.txt
      added by a previous patch.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      4c515dd4
    • David Howells's avatar
      FS-Cache: Add cache tag handling · 0e04d4ce
      David Howells authored
      
      
      Implement two features of FS-Cache:
      
       (1) The ability to request and release cache tags - names by which a cache may
           be known to a netfs, and thus selected for use.
      
       (2) An internal function by which a cache is selected by consulting the netfs,
           if the netfs wishes to be consulted.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      0e04d4ce
    • David Howells's avatar
      FS-Cache: Root index definition · a6891645
      David Howells authored
      
      
      Add a description of the root index of the cache for later patches to make use
      of.
      
      The root index is owned by FS-Cache itself.  When a netfs requests caching
      facilities, FS-Cache will, if one doesn't already exist, create an entry in
      the root index with the key being the name of the netfs ("AFS" for example),
      and the auxiliary data holding the index structure version supplied by the
      netfs:
      
      				     FSDEF
      				       |
      				 +-----------+
      				 |           |
      				NFS         AFS
      			       [v=1]       [v=1]
      
      If an entry with the appropriate name does already exist, the version is
      compared.  If the version is different, the entire subtree from that entry
      will be discarded and a new entry created.
      
      The new entry will be an index, and a cookie referring to it will be passed to
      the netfs.  This is then the root handle by which the netfs accesses the
      cache.  It can create whatever objects it likes in that index, including
      further indices.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      a6891645
    • David Howells's avatar
      FS-Cache: Add use of /proc and presentation of statistics · 7394daa8
      David Howells authored
      
      
      Make FS-Cache create its /proc interface and present various statistical
      information through it.  Also provide the functions for updating this
      information.
      
      These features are enabled by:
      
      	CONFIG_FSCACHE_PROC
      	CONFIG_FSCACHE_STATS
      	CONFIG_FSCACHE_HISTOGRAM
      
      The /proc directory for FS-Cache is also exported so that caching modules can
      add their own statistics there too.
      
      The FS-Cache module is loadable at this point, and the statistics files can be
      examined by userspace:
      
      	cat /proc/fs/fscache/stats
      	cat /proc/fs/fscache/histogram
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      7394daa8
    • David Howells's avatar
      FS-Cache: Add main configuration option, module entry points and debugging · 06b3db1b
      David Howells authored
      
      
      Add the main configuration option, allowing FS-Cache to be selected; the
      module entry and exit functions and the debugging stuff used by these patches.
      
      The two configuration options added are:
      
      	CONFIG_FSCACHE
      	CONFIG_FSCACHE_DEBUG
      
      The first enables the facility, and the second makes the debugging statements
      enableable through the "debug" module parameter.  The value of this parameter
      is a bitmask as described in:
      
      	Documentation/filesystems/caching/fscache.txt
      
      The module can be loaded at this point, but all it will do at this point in
      the patch series is to start up the slow work facility and shut it down again.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarSteve Dickson <steved@redhat.com>
      Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
      06b3db1b