sunrpc: add helpers to count and snapshot pending cache requests

Add sunrpc_cache_requests_count() and sunrpc_cache_requests_snapshot()
to allow callers to count and snapshot the pending upcall request list
without exposing struct cache_request outside of cache.c.

Both functions skip entries that no longer have CACHE_PENDING set.

The snapshot function takes a cache_get() reference on each item so the
caller can safely use them after the queue_lock is released.

These will be used by the nfsd generic netlink dumpit handler for
svc_export upcall requests.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: jtlayton

include/linux/sunrpc/cache.h

@@ -251,6 +251,12 @@ extern int sunrpc_cache_register_pipefs(struct dentry *parent, const char *,
 extern void sunrpc_cache_unregister_pipefs(struct cache_detail *);
 extern void sunrpc_cache_unhash(struct cache_detail *, struct cache_head *);
 
+int sunrpc_cache_requests_count(struct cache_detail *cd);
+int sunrpc_cache_requests_snapshot(struct cache_detail *cd,
+				   struct cache_head **items,
+				   u64 *seqnos, int max,
+				   u64 min_seqno);
+
 /* Must store cache_detail in seq_file->private if using next three functions */
 extern void *cache_seq_start_rcu(struct seq_file *file, loff_t *pos);
 extern void *cache_seq_next_rcu(struct seq_file *file, void *p, loff_t *pos);

net/sunrpc/cache.c

@@ -1902,3 +1902,64 @@ void sunrpc_cache_unhash(struct cache_detail *cd, struct cache_head *h)
 		spin_unlock(&cd->hash_lock);
 }
 EXPORT_SYMBOL_GPL(sunrpc_cache_unhash);
+
+/**
+ * sunrpc_cache_requests_count - count pending upcall requests
+ * @cd: cache_detail to query
+ *
+ * Returns the number of requests on the cache's request list that
+ * still have CACHE_PENDING set.
+ */
+int sunrpc_cache_requests_count(struct cache_detail *cd)
+{
+	struct cache_request *crq;
+	int cnt = 0;
+
+	spin_lock(&cd->queue_lock);
+	list_for_each_entry(crq, &cd->requests, list) {
+		if (test_bit(CACHE_PENDING, &crq->item->flags))
+			cnt++;
+	}
+	spin_unlock(&cd->queue_lock);
+	return cnt;
+}
+EXPORT_SYMBOL_GPL(sunrpc_cache_requests_count);
+
+/**
+ * sunrpc_cache_requests_snapshot - snapshot pending upcall requests
+ * @cd: cache_detail to query
+ * @items: array to fill with cache_head pointers (caller-allocated)
+ * @seqnos: array to fill with sequence numbers (caller-allocated)
+ * @max: size of the arrays
+ * @min_seqno: only include entries with seqno > min_seqno (0 for all)
+ *
+ * Only entries with CACHE_PENDING set are included. Takes a reference
+ * on each cache_head via cache_get(). Caller must call cache_put()
+ * on each returned item when done.
+ *
+ * Returns the number of entries filled.
+ */
+int sunrpc_cache_requests_snapshot(struct cache_detail *cd,
+				   struct cache_head **items,
+				   u64 *seqnos, int max,
+				   u64 min_seqno)
+{
+	struct cache_request *crq;
+	int i = 0;
+
+	spin_lock(&cd->queue_lock);
+	list_for_each_entry(crq, &cd->requests, list) {
+		if (i >= max)
+			break;
+		if (!test_bit(CACHE_PENDING, &crq->item->flags))
+			continue;
+		if (crq->seqno <= min_seqno)
+			continue;
+		items[i] = cache_get(crq->item);
+		seqnos[i] = crq->seqno;
+		i++;
+	}
+	spin_unlock(&cd->queue_lock);
+	return i;
+}
+EXPORT_SYMBOL_GPL(sunrpc_cache_requests_snapshot);