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e6acd3299b
linux/fs/fscache/internal.h
David Howells e6acd3299b fscache: Implement volume-level access helpers 
Add a pair of helper functions to manage access to a volume, pinning the
volume in place for the duration to prevent cache withdrawal from removing
it:

	bool fscache_begin_volume_access(struct fscache_volume *volume,
					 enum fscache_access_trace why);
	void fscache_end_volume_access(struct fscache_volume *volume,
				       enum fscache_access_trace why);

The way the access gate on the volume works/will work is:

  (1) If the cache tests as not live (state is not FSCACHE_CACHE_IS_ACTIVE),
      then we return false to indicate access was not permitted.

  (2) If the cache tests as live, then we increment the volume's n_accesses
      count and then recheck the cache liveness, ending the access if it
      ceased to be live.

  (3) When we end the access, we decrement the volume's n_accesses and wake
      up the any waiters if it reaches 0.

  (4) Whilst the cache is caching, the volume's n_accesses is kept
      artificially incremented to prevent wakeups from happening.

  (5) When the cache is taken offline, the state is changed to prevent new
      accesses, the volume's n_accesses is decremented and we wait for it to
      become 0.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819594158.215744.8285859817391683254.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906894315.143852.5454793807544710479.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967095028.1823006.9173132503876627466.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021501546.640689.9631510472149608443.stgit@warthog.procyon.org.uk/ # v4
2022-01-07 09:22:19 +00:00

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/* SPDX-License-Identifier: GPL-2.0-or-later */
/* Internal definitions for FS-Cache
*
* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#ifdef pr_fmt
#undef pr_fmt
#endif
#define pr_fmt(fmt) "FS-Cache: " fmt
#include <linux/slab.h>
#include <linux/fscache-cache.h>
#include <trace/events/fscache.h>
#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
bool fscache_begin_cache_access(struct fscache_cache *cache, enum fscache_access_trace why);
void fscache_end_cache_access(struct fscache_cache *cache, enum fscache_access_trace why);
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);
}
/*
* cookie.c
*/
extern struct kmem_cache *fscache_cookie_jar;
extern const struct seq_operations fscache_cookies_seq_ops;
extern void fscache_print_cookie(struct fscache_cookie *cookie, char prefix);
static inline void fscache_see_cookie(struct fscache_cookie *cookie,
enum fscache_cookie_trace where)
{
trace_fscache_cookie(cookie->debug_id, refcount_read(&cookie->ref),
where);
}
/*
* main.c
*/
extern unsigned fscache_debug;
extern unsigned int fscache_hash(unsigned int salt, const void *data, size_t len);
/*
* proc.c
*/
#ifdef CONFIG_PROC_FS
extern int __init fscache_proc_init(void);
extern void fscache_proc_cleanup(void);
#else
#define fscache_proc_init() (0)
#define fscache_proc_cleanup() do {} while (0)
#endif
/*
* stats.c
*/
#ifdef CONFIG_FSCACHE_STATS
extern atomic_t fscache_n_volumes;
extern atomic_t fscache_n_volumes_collision;
extern atomic_t fscache_n_volumes_nomem;
extern atomic_t fscache_n_cookies;
extern atomic_t fscache_n_acquires;
extern atomic_t fscache_n_acquires_ok;
extern atomic_t fscache_n_acquires_oom;
extern atomic_t fscache_n_relinquishes;
extern atomic_t fscache_n_relinquishes_retire;
extern atomic_t fscache_n_relinquishes_dropped;
static inline void fscache_stat(atomic_t *stat)
{
atomic_inc(stat);
}
static inline void fscache_stat_d(atomic_t *stat)
{
atomic_dec(stat);
}
#define __fscache_stat(stat) (stat)
int fscache_stats_show(struct seq_file *m, void *v);
#else
#define __fscache_stat(stat) (NULL)
#define fscache_stat(stat) do {} while (0)
#define fscache_stat_d(stat) do {} while (0)
#endif
/*
* volume.c
*/
extern const struct seq_operations fscache_volumes_seq_ops;
struct fscache_volume *fscache_get_volume(struct fscache_volume *volume,
enum fscache_volume_trace where);
void fscache_put_volume(struct fscache_volume *volume,
enum fscache_volume_trace where);
bool fscache_begin_volume_access(struct fscache_volume *volume,
struct fscache_cookie *cookie,
enum fscache_access_trace why);
void fscache_create_volume(struct fscache_volume *volume, bool wait);
/*****************************************************************************/
/*
* debug tracing
*/
#define dbgprintk(FMT, ...) \
printk("[%-6.6s] "FMT"\n", current->comm, ##__VA_ARGS__)
#define kenter(FMT, ...) dbgprintk("==> %s("FMT")", __func__, ##__VA_ARGS__)
#define kleave(FMT, ...) dbgprintk("<== %s()"FMT"", __func__, ##__VA_ARGS__)
#define kdebug(FMT, ...) dbgprintk(FMT, ##__VA_ARGS__)
#define kjournal(FMT, ...) no_printk(FMT, ##__VA_ARGS__)
#ifdef __KDEBUG
#define _enter(FMT, ...) kenter(FMT, ##__VA_ARGS__)
#define _leave(FMT, ...) kleave(FMT, ##__VA_ARGS__)
#define _debug(FMT, ...) kdebug(FMT, ##__VA_ARGS__)
#elif defined(CONFIG_FSCACHE_DEBUG)
#define _enter(FMT, ...) \
do { \
if (__do_kdebug(ENTER)) \
kenter(FMT, ##__VA_ARGS__); \
} while (0)
#define _leave(FMT, ...) \
do { \
if (__do_kdebug(LEAVE)) \
kleave(FMT, ##__VA_ARGS__); \
} while (0)
#define _debug(FMT, ...) \
do { \
if (__do_kdebug(DEBUG)) \
kdebug(FMT, ##__VA_ARGS__); \
} while (0)
#else
#define _enter(FMT, ...) no_printk("==> %s("FMT")", __func__, ##__VA_ARGS__)
#define _leave(FMT, ...) no_printk("<== %s()"FMT"", __func__, ##__VA_ARGS__)
#define _debug(FMT, ...) no_printk(FMT, ##__VA_ARGS__)
#endif
/*
* determine whether a particular optional debugging point should be logged
* - we need to go through three steps to persuade cpp to correctly join the
* shorthand in FSCACHE_DEBUG_LEVEL with its prefix
*/
#define ____do_kdebug(LEVEL, POINT) \
unlikely((fscache_debug & \
(FSCACHE_POINT_##POINT << (FSCACHE_DEBUG_ ## LEVEL * 3))))
#define ___do_kdebug(LEVEL, POINT) \
____do_kdebug(LEVEL, POINT)
#define __do_kdebug(POINT) \
___do_kdebug(FSCACHE_DEBUG_LEVEL, POINT)
#define FSCACHE_DEBUG_CACHE 0
#define FSCACHE_DEBUG_COOKIE 1
#define FSCACHE_DEBUG_OBJECT 2
#define FSCACHE_DEBUG_OPERATION 3
#define FSCACHE_POINT_ENTER 1
#define FSCACHE_POINT_LEAVE 2
#define FSCACHE_POINT_DEBUG 4
#ifndef FSCACHE_DEBUG_LEVEL
#define FSCACHE_DEBUG_LEVEL CACHE
#endif
/*
* assertions
*/
#if 1 /* defined(__KDEBUGALL) */
#define ASSERT(X) \
do { \
if (unlikely(!(X))) { \
pr_err("\n"); \
pr_err("Assertion failed\n"); \
BUG(); \
} \
} while (0)
#define ASSERTCMP(X, OP, Y) \
do { \
if (unlikely(!((X) OP (Y)))) { \
pr_err("\n"); \
pr_err("Assertion failed\n"); \
pr_err("%lx " #OP " %lx is false\n", \
(unsigned long)(X), (unsigned long)(Y)); \
BUG(); \
} \
} while (0)
#define ASSERTIF(C, X) \
do { \
if (unlikely((C) && !(X))) { \
pr_err("\n"); \
pr_err("Assertion failed\n"); \
BUG(); \
} \
} while (0)
#define ASSERTIFCMP(C, X, OP, Y) \
do { \
if (unlikely((C) && !((X) OP (Y)))) { \
pr_err("\n"); \
pr_err("Assertion failed\n"); \
pr_err("%lx " #OP " %lx is false\n", \
(unsigned long)(X), (unsigned long)(Y)); \
BUG(); \
} \
} while (0)
#else
#define ASSERT(X) do {} while (0)
#define ASSERTCMP(X, OP, Y) do {} while (0)
#define ASSERTIF(C, X) do {} while (0)
#define ASSERTIFCMP(C, X, OP, Y) do {} while (0)
#endif /* assert or not */
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