Commit 9549332d authored by David Howells's avatar David Howells

fscache: Implement cache registration

Implement a register of caches and provide functions to manage it.

Two functions are provided for the cache backend to use:

 (1) Acquire a cache cookie:

	struct fscache_cache *fscache_acquire_cache(const char *name)

     This gets the cache cookie for a cache of the specified name and moves
     it to the preparation state.  If a nameless cache cookie exists, that
     will be given this name and used.

 (2) Relinquish a cache cookie:

	void fscache_relinquish_cache(struct fscache_cache *cache);

     This relinquishes a cache cookie, cleans it and makes it available if
     it's still referenced by a network filesystem.

Note that network filesystems don't deal with cache cookies directly, but
rather go straight to the volume registration.
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819587157.215744.13523139317322503286.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906889665.143852.10378009165231294456.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967085081.1823006.2218944206363626210.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021494847.640689.10109692261640524343.stgit@warthog.procyon.org.uk/ # v4
parent e8a07c9d
......@@ -4,6 +4,7 @@
#
fscache-y := \
cache.o \
main.o
fscache-$(CONFIG_PROC_FS) += proc.o
......
// SPDX-License-Identifier: GPL-2.0-or-later
/* FS-Cache cache handling
*
* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#define FSCACHE_DEBUG_LEVEL CACHE
#include <linux/export.h>
#include <linux/slab.h>
#include "internal.h"
static LIST_HEAD(fscache_caches);
DECLARE_RWSEM(fscache_addremove_sem);
EXPORT_SYMBOL(fscache_addremove_sem);
static atomic_t fscache_cache_debug_id;
/*
* Allocate a cache cookie.
*/
static struct fscache_cache *fscache_alloc_cache(const char *name)
{
struct fscache_cache *cache;
cache = kzalloc(sizeof(*cache), GFP_KERNEL);
if (cache) {
if (name) {
cache->name = kstrdup(name, GFP_KERNEL);
if (!cache->name) {
kfree(cache);
return NULL;
}
}
refcount_set(&cache->ref, 1);
INIT_LIST_HEAD(&cache->cache_link);
cache->debug_id = atomic_inc_return(&fscache_cache_debug_id);
}
return cache;
}
static bool fscache_get_cache_maybe(struct fscache_cache *cache,
enum fscache_cache_trace where)
{
bool success;
int ref;
success = __refcount_inc_not_zero(&cache->ref, &ref);
if (success)
trace_fscache_cache(cache->debug_id, ref + 1, where);
return success;
}
/*
* Look up a cache cookie.
*/
struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache)
{
struct fscache_cache *candidate, *cache, *unnamed = NULL;
/* firstly check for the existence of the cache under read lock */
down_read(&fscache_addremove_sem);
list_for_each_entry(cache, &fscache_caches, cache_link) {
if (cache->name && name && strcmp(cache->name, name) == 0 &&
fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
goto got_cache_r;
if (!cache->name && !name &&
fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
goto got_cache_r;
}
if (!name) {
list_for_each_entry(cache, &fscache_caches, cache_link) {
if (cache->name &&
fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
goto got_cache_r;
}
}
up_read(&fscache_addremove_sem);
/* the cache does not exist - create a candidate */
candidate = fscache_alloc_cache(name);
if (!candidate)
return ERR_PTR(-ENOMEM);
/* write lock, search again and add if still not present */
down_write(&fscache_addremove_sem);
list_for_each_entry(cache, &fscache_caches, cache_link) {
if (cache->name && name && strcmp(cache->name, name) == 0 &&
fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
goto got_cache_w;
if (!cache->name) {
unnamed = cache;
if (!name &&
fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
goto got_cache_w;
}
}
if (unnamed && is_cache &&
fscache_get_cache_maybe(unnamed, fscache_cache_get_acquire))
goto use_unnamed_cache;
if (!name) {
list_for_each_entry(cache, &fscache_caches, cache_link) {
if (cache->name &&
fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
goto got_cache_w;
}
}
list_add_tail(&candidate->cache_link, &fscache_caches);
trace_fscache_cache(candidate->debug_id,
refcount_read(&candidate->ref),
fscache_cache_new_acquire);
up_write(&fscache_addremove_sem);
return candidate;
got_cache_r:
up_read(&fscache_addremove_sem);
return cache;
use_unnamed_cache:
cache = unnamed;
cache->name = candidate->name;
candidate->name = NULL;
got_cache_w:
up_write(&fscache_addremove_sem);
kfree(candidate->name);
kfree(candidate);
return cache;
}
/**
* fscache_acquire_cache - Acquire a cache-level cookie.
* @name: The name of the cache.
*
* Get a cookie to represent an actual cache. If a name is given and there is
* a nameless cache record available, this will acquire that and set its name,
* directing all the volumes using it to this cache.
*
* The cache will be switched over to the preparing state if not currently in
* use, otherwise -EBUSY will be returned.
*/
struct fscache_cache *fscache_acquire_cache(const char *name)
{
struct fscache_cache *cache;
ASSERT(name);
cache = fscache_lookup_cache(name, true);
if (IS_ERR(cache))
return cache;
if (!fscache_set_cache_state_maybe(cache,
FSCACHE_CACHE_IS_NOT_PRESENT,
FSCACHE_CACHE_IS_PREPARING)) {
pr_warn("Cache tag %s in use\n", name);
fscache_put_cache(cache, fscache_cache_put_cache);
return ERR_PTR(-EBUSY);
}
return cache;
}
EXPORT_SYMBOL(fscache_acquire_cache);
/**
* fscache_put_cache - Release a cache-level cookie.
* @cache: The cache cookie to be released
* @where: An indication of where the release happened
*
* Release the caller's reference on a cache-level cookie. The @where
* indication should give information about the circumstances in which the call
* occurs and will be logged through a tracepoint.
*/
void fscache_put_cache(struct fscache_cache *cache,
enum fscache_cache_trace where)
{
unsigned int debug_id = cache->debug_id;
bool zero;
int ref;
if (IS_ERR_OR_NULL(cache))
return;
zero = __refcount_dec_and_test(&cache->ref, &ref);
trace_fscache_cache(debug_id, ref - 1, where);
if (zero) {
down_write(&fscache_addremove_sem);
list_del_init(&cache->cache_link);
up_write(&fscache_addremove_sem);
kfree(cache->name);
kfree(cache);
}
}
/**
* fscache_relinquish_cache - Reset cache state and release cookie
* @cache: The cache cookie to be released
*
* Reset the state of a cache and release the caller's reference on a cache
* cookie.
*/
void fscache_relinquish_cache(struct fscache_cache *cache)
{
enum fscache_cache_trace where =
(cache->state == FSCACHE_CACHE_IS_PREPARING) ?
fscache_cache_put_prep_failed :
fscache_cache_put_relinquish;
cache->cache_priv = NULL;
smp_store_release(&cache->state, FSCACHE_CACHE_IS_NOT_PRESENT);
fscache_put_cache(cache, where);
}
EXPORT_SYMBOL(fscache_relinquish_cache);
#ifdef CONFIG_PROC_FS
static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW";
/*
* Generate a list of caches in /proc/fs/fscache/caches
*/
static int fscache_caches_seq_show(struct seq_file *m, void *v)
{
struct fscache_cache *cache;
if (v == &fscache_caches) {
seq_puts(m,
"CACHE REF VOLS OBJS ACCES S NAME\n"
"======== ===== ===== ===== ===== = ===============\n"
);
return 0;
}
cache = list_entry(v, struct fscache_cache, cache_link);
seq_printf(m,
"%08x %5d %5d %5d %5d %c %s\n",
cache->debug_id,
refcount_read(&cache->ref),
atomic_read(&cache->n_volumes),
atomic_read(&cache->object_count),
atomic_read(&cache->n_accesses),
fscache_cache_states[cache->state],
cache->name ?: "-");
return 0;
}
static void *fscache_caches_seq_start(struct seq_file *m, loff_t *_pos)
__acquires(fscache_addremove_sem)
{
down_read(&fscache_addremove_sem);
return seq_list_start_head(&fscache_caches, *_pos);
}
static void *fscache_caches_seq_next(struct seq_file *m, void *v, loff_t *_pos)
{
return seq_list_next(v, &fscache_caches, _pos);
}
static void fscache_caches_seq_stop(struct seq_file *m, void *v)
__releases(fscache_addremove_sem)
{
up_read(&fscache_addremove_sem);
}
const struct seq_operations fscache_caches_seq_ops = {
.start = fscache_caches_seq_start,
.next = fscache_caches_seq_next,
.stop = fscache_caches_seq_stop,
.show = fscache_caches_seq_show,
};
#endif /* CONFIG_PROC_FS */
......@@ -17,6 +17,39 @@
#include <linux/sched.h>
#include <linux/seq_file.h>
/*
* cache.c
*/
#ifdef CONFIG_PROC_FS
extern const struct seq_operations fscache_caches_seq_ops;
#endif
struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache);
void fscache_put_cache(struct fscache_cache *cache, enum fscache_cache_trace where);
static inline enum fscache_cache_state fscache_cache_state(const struct fscache_cache *cache)
{
return smp_load_acquire(&cache->state);
}
static inline bool fscache_cache_is_live(const struct fscache_cache *cache)
{
return fscache_cache_state(cache) == FSCACHE_CACHE_IS_ACTIVE;
}
static inline void fscache_set_cache_state(struct fscache_cache *cache,
enum fscache_cache_state new_state)
{
smp_store_release(&cache->state, new_state);
}
static inline bool fscache_set_cache_state_maybe(struct fscache_cache *cache,
enum fscache_cache_state old_state,
enum fscache_cache_state new_state)
{
return try_cmpxchg_release(&cache->state, &old_state, new_state);
}
/*
* main.c
*/
......
......@@ -19,6 +19,10 @@ int __init fscache_proc_init(void)
if (!proc_mkdir("fs/fscache", NULL))
goto error_dir;
if (!proc_create_seq("fs/fscache/caches", S_IFREG | 0444, NULL,
&fscache_caches_seq_ops))
goto error;
#ifdef CONFIG_FSCACHE_STATS
if (!proc_create_single("fs/fscache/stats", S_IFREG | 0444, NULL,
fscache_stats_show))
......
......@@ -16,6 +16,40 @@
#include <linux/fscache.h>
enum fscache_cache_trace;
enum fscache_access_trace;
enum fscache_cache_state {
FSCACHE_CACHE_IS_NOT_PRESENT, /* No cache is present for this name */
FSCACHE_CACHE_IS_PREPARING, /* A cache is preparing to come live */
FSCACHE_CACHE_IS_ACTIVE, /* Attached cache is active and can be used */
FSCACHE_CACHE_GOT_IOERROR, /* Attached cache stopped on I/O error */
FSCACHE_CACHE_IS_WITHDRAWN, /* Attached cache is being withdrawn */
#define NR__FSCACHE_CACHE_STATE (FSCACHE_CACHE_IS_WITHDRAWN + 1)
};
/*
* Cache cookie.
*/
struct fscache_cache {
struct list_head cache_link; /* Link in cache list */
void *cache_priv; /* Private cache data (or NULL) */
refcount_t ref;
atomic_t n_volumes; /* Number of active volumes; */
atomic_t n_accesses; /* Number of in-progress accesses on the cache */
atomic_t object_count; /* no. of live objects in this cache */
unsigned int debug_id;
enum fscache_cache_state state;
char *name;
};
extern struct workqueue_struct *fscache_wq;
/*
* out-of-line cache backend functions
*/
extern struct rw_semaphore fscache_addremove_sem;
extern struct fscache_cache *fscache_acquire_cache(const char *name);
extern void fscache_relinquish_cache(struct fscache_cache *cache);
#endif /* _LINUX_FSCACHE_CACHE_H */
......@@ -19,11 +19,27 @@
#ifndef __FSCACHE_DECLARE_TRACE_ENUMS_ONCE_ONLY
#define __FSCACHE_DECLARE_TRACE_ENUMS_ONCE_ONLY
enum fscache_cache_trace {
fscache_cache_collision,
fscache_cache_get_acquire,
fscache_cache_new_acquire,
fscache_cache_put_cache,
fscache_cache_put_prep_failed,
fscache_cache_put_relinquish,
};
#endif
/*
* Declare tracing information enums and their string mappings for display.
*/
#define fscache_cache_traces \
EM(fscache_cache_collision, "*COLLIDE*") \
EM(fscache_cache_get_acquire, "GET acq ") \
EM(fscache_cache_new_acquire, "NEW acq ") \
EM(fscache_cache_put_cache, "PUT cache") \
EM(fscache_cache_put_prep_failed, "PUT pfail") \
E_(fscache_cache_put_relinquish, "PUT relnq")
/*
* Export enum symbols via userspace.
......@@ -33,6 +49,8 @@
#define EM(a, b) TRACE_DEFINE_ENUM(a);
#define E_(a, b) TRACE_DEFINE_ENUM(a);
fscache_cache_traces;
/*
* Now redefine the EM() and E_() macros to map the enums to the strings that
* will be printed in the output.
......@@ -43,6 +61,31 @@
#define E_(a, b) { a, b }
TRACE_EVENT(fscache_cache,
TP_PROTO(unsigned int cache_debug_id,
int usage,
enum fscache_cache_trace where),
TP_ARGS(cache_debug_id, usage, where),
TP_STRUCT__entry(
__field(unsigned int, cache )
__field(int, usage )
__field(enum fscache_cache_trace, where )
),
TP_fast_assign(
__entry->cache = cache_debug_id;
__entry->usage = usage;
__entry->where = where;
),
TP_printk("C=%08x %s r=%d",
__entry->cache,
__print_symbolic(__entry->where, fscache_cache_traces),
__entry->usage)
);
#endif /* _TRACE_FSCACHE_H */
/* This part must be outside protection */
......
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