fscache: Provide read/write stat counters for the cache

Provide read/write stat counters for the cache backend to use.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Reviewed-by: NJeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819609532.215744.10821082637727410554.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906912598.143852.12960327989649429069.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967113830.1823006.3222957649202368162.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021517502.640689.6077928311710357342.stgit@warthog.procyon.org.uk/ # v4

fs/fscache/stats.c

@@ -35,6 +35,11 @@ atomic_t fscache_n_relinquishes;
 atomic_t fscache_n_relinquishes_retire;
 atomic_t fscache_n_relinquishes_dropped;
 
+atomic_t fscache_n_read;
+EXPORT_SYMBOL(fscache_n_read);
+atomic_t fscache_n_write;
+EXPORT_SYMBOL(fscache_n_write);
+
 /*
  * display the general statistics
  */
@@ -72,6 +77,10 @@ int fscache_stats_show(struct seq_file *m, void *v)
 		   atomic_read(&fscache_n_relinquishes_retire),
 		   atomic_read(&fscache_n_relinquishes_dropped));
 
+	seq_printf(m, "IO     : rd=%u wr=%u\n",
+		   atomic_read(&fscache_n_read),
+		   atomic_read(&fscache_n_write));
+
 	netfs_stats_show(m);
 	return 0;
 }

include/linux/fscache-cache.h

@@ -179,4 +179,14 @@ static inline void fscache_wait_for_objects(struct fscache_cache *cache)
 		   atomic_read(&cache->object_count) == 0);
 }
 
+#ifdef CONFIG_FSCACHE_STATS
+extern atomic_t fscache_n_read;
+extern atomic_t fscache_n_write;
+#define fscache_count_read() atomic_inc(&fscache_n_read)
+#define fscache_count_write() atomic_inc(&fscache_n_write)
+#else
+#define fscache_count_read() do {} while(0)
+#define fscache_count_write() do {} while(0)
+#endif
+
 #endif /* _LINUX_FSCACHE_CACHE_H */