path: root/fs/fscache/object.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* FS-Cache object state machine handler
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * See Documentation/filesystems/caching/object.rst for a description of the
 * object state machine and the in-kernel representations.
 */

#define FSCACHE_DEBUG_LEVEL COOKIE
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/prefetch.h>
#include "internal.h"

static const struct fscache_state *fscache_abort_initialisation(struct fscache_object *, int);
static const struct fscache_state *fscache_kill_dependents(struct fscache_object *, int);
static const struct fscache_state *fscache_drop_object(struct fscache_object *, int);
static const struct fscache_state *fscache_initialise_object(struct fscache_object *, int);
static const struct fscache_state *fscache_invalidate_object(struct fscache_object *, int);
static const struct fscache_state *fscache_jumpstart_dependents(struct fscache_object *, int);
static const struct fscache_state *fscache_kill_object(struct fscache_object *, int);
static const struct fscache_state *fscache_lookup_failure(struct fscache_object *, int);
static const struct fscache_state *fscache_look_up_object(struct fscache_object *, int);
static const struct fscache_state *fscache_object_available(struct fscache_object *, int);
static const struct fscache_state *fscache_parent_ready(struct fscache_object *, int);
static const struct fscache_state *fscache_update_object(struct fscache_object *, int);
static const struct fscache_state *fscache_object_dead(struct fscache_object *, int);

#define __STATE_NAME(n) fscache_osm_##n
#define STATE(n) (&__STATE_NAME(n))

/*
 * Define a work state.  Work states are execution states.  No event processing
 * is performed by them.  The function attached to a work state returns a
 * pointer indicating the next state to which the state machine should
 * transition.  Returning NO_TRANSIT repeats the current state, but goes back
 * to the scheduler first.
 */
#define WORK_STATE(n, sn, f) \
	const struct fscache_state __STATE_NAME(n) = {			\
		.name = #n,						\
		.short_name = sn,					\
		.work = f						\
	}

/*
 * Returns from work states.
 */
#define transit_to(state) ({ prefetch(&STATE(state)->work); STATE(state); })

#define NO_TRANSIT ((struct fscache_state *)NULL)

/*
 * Define a wait state.  Wait states are event processing states.  No execution
 * is performed by them.  Wait states are just tables of "if event X occurs,
 * clear it and transition to state Y".  The dispatcher returns to the
 * scheduler if none of the events in which the wait state has an interest are
 * currently pending.
 */
#define WAIT_STATE(n, sn, ...) \
	const struct fscache_state __STATE_NAME(n) = {			\
		.name = #n,						\
		.short_name = sn,					\
		.work = NULL,						\
		.transitions = { __VA_ARGS__, { 0, NULL } }		\
	}

#define TRANSIT_TO(state, emask) \
	{ .events = (emask), .transit_to = STATE(state) }

/*
 * The object state machine.
 */
static WORK_STATE(INIT_OBJECT,		"INIT", fscache_initialise_object);
static WORK_STATE(PARENT_READY,		"PRDY", fscache_parent_ready);
static WORK_STATE(ABORT_INIT,		"ABRT", fscache_abort_initialisation);
static WORK_STATE(LOOK_UP_OBJECT,	"LOOK", fscache_look_up_object);
static WORK_STATE(CREATE_OBJECT,	"CRTO", fscache_look_up_object);
static WORK_STATE(OBJECT_AVAILABLE,	"AVBL", fscache_object_available);
static WORK_STATE(JUMPSTART_DEPS,	"JUMP", fscache_jumpstart_dependents);

static WORK_STATE(INVALIDATE_OBJECT,	"INVL", fscache_invalidate_object);
static WORK_STATE(UPDATE_OBJECT,	"UPDT", fscache_update_object);

static WORK_STATE(LOOKUP_FAILURE,	"LCFL", fscache_lookup_failure);
static WORK_STATE(KILL_OBJECT,		"KILL", fscache_kill_object);
static WORK_STATE(KILL_DEPENDENTS,	"KDEP", fscache_kill_dependents);
static WORK_STATE(DROP_OBJECT,		"DROP", fscache_drop_object);
static WORK_STATE(OBJECT_DEAD,		"DEAD", fscache_object_dead);

static WAIT_STATE(WAIT_FOR_INIT,	"?INI",
		  TRANSIT_TO(INIT_OBJECT,	1 << FSCACHE_OBJECT_EV_NEW_CHILD));

static WAIT_STATE(WAIT_FOR_PARENT,	"?PRN",
		  TRANSIT_TO(PARENT_READY,	1 << FSCACHE_OBJECT_EV_PARENT_READY));

static WAIT_STATE(WAIT_FOR_CMD,		"?CMD",
		  TRANSIT_TO(INVALIDATE_OBJECT,	1 << FSCACHE_OBJECT_EV_INVALIDATE),
		  TRANSIT_TO(UPDATE_OBJECT,	1 << FSCACHE_OBJECT_EV_UPDATE),
		  TRANSIT_TO(JUMPSTART_DEPS,	1 << FSCACHE_OBJECT_EV_NEW_CHILD));

static WAIT_STATE(WAIT_FOR_CLEARANCE,	"?CLR",
		  TRANSIT_TO(KILL_OBJECT,	1 << FSCACHE_OBJECT_EV_CLEARED));

/*
 * Out-of-band event transition tables.  These are for handling unexpected
 * events, such as an I/O error.  If an OOB event occurs, the state machine
 * clears and disables the event and forces a transition to the nominated work
 * state (acurrently executing work states will complete first).
 *
 * In such a situation, object->state remembers the state the machine should
 * have been in/gone to and returning NO_TRANSIT returns to that.
 */
static const struct fscache_transition fscache_osm_init_oob[] = {
	   TRANSIT_TO(ABORT_INIT,
		      (1 << FSCACHE_OBJECT_EV_ERROR) |
		      (1 << FSCACHE_OBJECT_EV_KILL)),
	   { 0, NULL }
};

static const struct fscache_transition fscache_osm_lookup_oob[] = {
	   TRANSIT_TO(LOOKUP_FAILURE,
		      (1 << FSCACHE_OBJECT_EV_ERROR) |
		      (1 << FSCACHE_OBJECT_EV_KILL)),
	   { 0, NULL }
};

static const struct fscache_transition fscache_osm_run_oob[] = {
	   TRANSIT_TO(KILL_OBJECT,
		      (1 << FSCACHE_OBJECT_EV_ERROR) |
		      (1 << FSCACHE_OBJECT_EV_KILL)),
	   { 0