scoutfs: add SK_ helpers for printing keys

Add some percpu string buffers so that we can pass formatted strings as
arguments when printing keys.  The percpu struct uses a different buffer
for each argument.  We wrap the whole print call in a wrapper that
disables and enables preemption.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/key.c

@@ -116,9 +116,8 @@ void scoutfs_key_dec(struct scoutfs_key_buf *key)
  *
  * XXX nonprintable characters in the trace?
  */
-int scoutfs_key_str(char *buf, struct scoutfs_key_buf *key)
+int scoutfs_key_str_size(char *buf, struct scoutfs_key_buf *key, size_t size)
 {
-	size_t size = buf ? INT_MAX : 0;
 	int len;
 	u8 type;
 
@@ -170,3 +169,55 @@ int scoutfs_key_str(char *buf, struct scoutfs_key_buf *key)
 	return snprintf_null(buf, size, "[truncated type %u len %u]",
 			     type, key->key_len);
 }
+
+/*
+ * A null buf can be set to find the length of the formatted string.
+ */
+int scoutfs_key_str(char *buf, struct scoutfs_key_buf *key)
+{
+	return scoutfs_key_str_size(buf, key, buf ? INT_MAX : 0);
+}
+
+#define MAX_STR_COUNT 10
+
+struct key_strings {
+	bool started;
+	int next_str;
+	char strings[MAX_STR_COUNT][SK_STR_BYTES];
+};
+
+static DEFINE_PER_CPU(struct key_strings, percpu_key_strings);
+
+void scoutfs_key_start_percpu(void)
+{
+	struct key_strings *ks = this_cpu_ptr(&percpu_key_strings);
+
+	BUG_ON(ks->started);
+	ks->started = true;
+	get_cpu();
+}
+
+char *scoutfs_key_percpu_string(void)
+{
+	struct key_strings *ks = this_cpu_ptr(&percpu_key_strings);
+	char *str;
+
+	BUG_ON(!ks->started);
+
+	str = ks->strings[ks->next_str++];
+	BUG_ON(ks->next_str >= MAX_STR_COUNT);
+
+	return str;
+}
+
+void scoutfs_key_finish_percpu(void)
+{
+	struct key_strings *ks = this_cpu_ptr(&percpu_key_strings);
+
+	BUG_ON(!ks->started);
+
+	ks->next_str = 0;
+	ks->started = false;
+
+	put_cpu();
+}

kmod/src/key.h

@@ -19,7 +19,36 @@ void scoutfs_key_inc_cur_len(struct scoutfs_key_buf *key);
 void scoutfs_key_dec(struct scoutfs_key_buf *key);
 void scoutfs_key_dec_cur_len(struct scoutfs_key_buf *key);
 
+int scoutfs_key_str_size(char *buf, struct scoutfs_key_buf *key, size_t size);
 int scoutfs_key_str(char *buf, struct scoutfs_key_buf *key);
+void scoutfs_key_start_percpu(void);
+char *scoutfs_key_percpu_string(void);
+void scoutfs_key_finish_percpu(void);
+
+#define SK_PCPU(statements) do {	\
+	scoutfs_key_start_percpu();	\
+	{ statements; }			\
+	scoutfs_key_finish_percpu();	\
+} while (0)
+
+/*
+ * The biggest keys are typically a little struct then a large name.  The
+ * string representation will tend to be mostly the name, but some of the
+ * strict fields can blow up from say 8 bytes to 20 bytes.  So we give
+ * a lot of padding for that.
+ */
+#define SK_STR_BYTES (100 + SCOUTFS_MAX_KEY_SIZE)
+
+#define SK_FMT "%s"
+#define SK_ARG(k)					\
+({							\
+	char *__str = scoutfs_key_percpu_string();	\
+	scoutfs_key_str_size(__str, k, SK_STR_BYTES);	\
+	__str;						\
+})
+
+#define SK_TRACE_PRINTK(args...) SK_PCPU(trace_printk(args))
+#define SK_PRINTK(args...) SK_PCPU(printk(args))
 
 /*
  * Initialize a small key in a larger allocated buffer.  This lets