Implement helper functions to acquire a cache record and put a reference on
it. These are used both as part of cache registration by the cache backend
and as part of cache request by the network filesystem.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
---
fs/fscache/Makefile | 1
fs/fscache/cache.c | 229 ++++++++++++++++++++++++++++++++++++++++
fs/fscache/internal.h | 8 +
fs/fscache/proc.c | 4 +
include/linux/fscache-cache.h | 60 ++++++++++
include/trace/events/fscache.h | 37 ++++++
6 files changed, 339 insertions(+)
create mode 100644 fs/fscache/cache.c
diff --git a/fs/fscache/Makefile b/fs/fscache/Makefile
index f9722de32247..d9fc22c18090 100644
--- a/fs/fscache/Makefile
+++ b/fs/fscache/Makefile
@@ -4,6 +4,7 @@
#
fscache-y := \
+ cache.o \
main.o
fscache-$(CONFIG_PROC_FS) += proc.o
diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
new file mode 100644
index 000000000000..da08e29ee5b9
--- /dev/null
+++ b/fs/fscache/cache.c
@@ -0,0 +1,229 @@
+// 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@xxxxxxxxxx)
+ */
+
+#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 record for a cache.
+ * @name: The name of the cache.
+ *
+ * Get a cache record for a cache. If there is a nameless cache record
+ * available, this will acquire that and set its name, directing all the
+ * volumes using it to this cache.
+ */
+struct fscache_cache *fscache_acquire_cache(const char *name)
+{
+ ASSERT(name);
+ return fscache_lookup_cache(name, true);
+}
+EXPORT_SYMBOL(fscache_acquire_cache);
+
+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);
+ }
+}
+EXPORT_SYMBOL(fscache_put_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 */
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 64767992bd15..8ac81294e43e 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -17,6 +17,14 @@
#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);
+
/*
* main.c
*/
diff --git a/fs/fscache/proc.c b/fs/fscache/proc.c
index b28003d7d63f..7400568bf85e 100644
--- a/fs/fscache/proc.c
+++ b/fs/fscache/proc.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))
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index d6910a913918..f6429e5ba6e7 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -16,6 +16,66 @@
#include <linux/fscache.h>
+struct fscache_cache;
+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;
+};
+
+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);
+}
+
+/*
+ * 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_put_cache(struct fscache_cache *cache,
+ enum fscache_cache_trace where);
+
extern struct workqueue_struct *fscache_wq;
#endif /* _LINUX_FSCACHE_CACHE_H */
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index fe214c5cc87f..3263cbf32961 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -19,11 +19,21 @@
#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,
+};
+
#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 ") \
+ E_(fscache_cache_new_acquire, "NEW acq ")
/*
* Export enum symbols via userspace.
@@ -33,6 +43,8 @@
#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 +55,31 @@
#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 */
