tracing: Clean up trace_seq.c

For using trace_seq_*() functions in NMI context, I posted a patch to move
it to the lib/ directory. This caused Andrew Morton to take a look at the code.
He went through and gave a lot of comments about missing kernel doc,
inconsistent types for the save variable, mix match of EXPORT_SYMBOL_GPL()
and EXPORT_SYMBOL() as well as missing EXPORT_SYMBOL*()s. There were
a few comments about the way variables were being compared (int vs uint).

All these were good review comments and should be implemented regardless of
if trace_seq.c should be moved to lib/ or not.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 185 insertions, 42 deletions

diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index 66ea365acf01..1f05317f51c4 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -38,14 +38,14 @@ int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args);
 extern int
 trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary);
 extern int trace_print_seq(struct seq_file *m, struct trace_seq *s);
-extern ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
-                                 size_t cnt);
+extern int trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
+                             int cnt);
 extern int trace_seq_puts(struct trace_seq *s, const char *str);
 extern int trace_seq_putc(struct trace_seq *s, unsigned char c);
-extern int trace_seq_putmem(struct trace_seq *s, const void *mem, size_t len);
+extern int trace_seq_putmem(struct trace_seq *s, const void *mem, unsigned int len);
 extern int trace_seq_putmem_hex(struct trace_seq *s, const void *mem,
-                                size_t len);
-extern void *trace_seq_reserve(struct trace_seq *s, size_t len);
+                                unsigned int len);
+extern void *trace_seq_reserve(struct trace_seq *s, unsigned int len);
 extern int trace_seq_path(struct trace_seq *s, const struct path *path);
 
 extern int trace_seq_bitmask(struct trace_seq *s, const unsigned long *maskp,
@@ -73,8 +73,8 @@ static inline int trace_print_seq(struct seq_file *m, struct trace_seq *s)
 {
         return 0;
 }
-static inline ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
-                                 size_t cnt)
+static inline int trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
+                                    int cnt)
 {
         return 0;
 }
@@ -87,16 +87,16 @@ static inline int trace_seq_putc(struct trace_seq *s, unsigned char c)
         return 0;
 }
 static inline int
-trace_seq_putmem(struct trace_seq *s, const void *mem, size_t len)
+trace_seq_putmem(struct trace_seq *s, const void *mem, unsigned int len)
 {
         return 0;
 }
 static inline int trace_seq_putmem_hex(struct trace_seq *s, const void *mem,
-                                       size_t len)
+                                       unsigned int len)
 {
         return 0;
 }
-static inline void *trace_seq_reserve(struct trace_seq *s, size_t len)
+static inline void *trace_seq_reserve(struct trace_seq *s, unsigned int len)
 {
         return NULL;
 }
diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
index 5ba99c6cf834..0fabca773e51 100644
--- a/kernel/trace/trace_seq.c
+++ b/kernel/trace/trace_seq.c
@@ -3,21 +3,55 @@
  *
  * Copyright (C) 2008-2014 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
  *
+ * The trace_seq is a handy tool that allows you to pass a descriptor around
+ * to a buffer that other functions can write to. It is similar to the
+ * seq_file functionality but has some differences.
+ *
+ * To use it, the trace_seq must be initialized with trace_seq_init().
+ * This will set up the counters within the descriptor. You can call
+ * trace_seq_init() more than once to reset the trace_seq to start
+ * from scratch.
+ * 
+ * The buffer size is currently PAGE_SIZE, although it may become dynamic
+ * in the future.
+ *
+ * A write to the buffer will either succed or fail. That is, unlike
+ * sprintf() there will not be a partial write (well it may write into
+ * the buffer but it wont update the pointers). This allows users to
+ * try to write something into the trace_seq buffer and if it fails
+ * they can flush it and try again.
+ *
  */
 #include <linux/uaccess.h>
 #include <linux/seq_file.h>
 #include <linux/trace_seq.h>
 
+/* How much buffer is left on the trace_seq? */
+#define TRACE_SEQ_BUF_LEFT(s) ((PAGE_SIZE - 1) - (s)->len)
+
+/* How much buffer is written? */
+#define TRACE_SEQ_BUF_USED(s) min((s)->len, (unsigned int)(PAGE_SIZE - 1))
+
+/**
+ * trace_print_seq - move the contents of trace_seq into a seq_file
+ * @m: the seq_file descriptor that is the destination
+ * @s: the trace_seq descriptor that is the source.
+ *
+ * Returns 0 on success and non zero on error. If it succeeds to
+ * write to the seq_file it will reset the trace_seq, otherwise
+ * it does not modify the trace_seq to let the caller try again.
+ */
 int trace_print_seq(struct seq_file *m, struct trace_seq *s)
 {
-        int len = s->len >= PAGE_SIZE ? PAGE_SIZE - 1 : s->len;
+        unsigned int len = TRACE_SEQ_BUF_USED(s);
         int ret;
 
         ret = seq_write(m, s->buffer, len);
 
         /*
          * Only reset this buffer if we successfully wrote to the
-         * seq_file buffer.
+         * seq_file buffer. This lets the caller try again or
+         * do something else with the contents.
          */
         if (!ret)
                 trace_seq_init(s);
@@ -30,19 +64,20 @@ int trace_print_seq(struct seq_file *m, struct trace_seq *s)
  * @s: trace sequence descriptor
  * @fmt: printf format string
  *
- * It returns 0 if the trace oversizes the buffer's free
- * space, 1 otherwise.
- *
  * The tracer may use either sequence operations or its own
  * copy to user routines. To simplify formating of a trace
- * trace_seq_printf is used to store strings into a special
+ * trace_seq_printf() is used to store strings into a special
  * buffer (@s). Then the output may be either used by
  * the sequencer or pulled into another buffer.
+ *
+ * Returns 1 if we successfully written all the contents to
+ *   the buffer.
+  * Returns 0 if we the length to write is bigger than the
+ *   reserved buffer space. In this case, nothing gets written.
  */
-int
-trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
+int trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
 {
-        int len = (PAGE_SIZE - 1) - s->len;
+        unsigned int len = TRACE_SEQ_BUF_LEFT(s);
         va_list ap;
         int ret;
 
@@ -66,21 +101,22 @@ trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
 EXPORT_SYMBOL_GPL(trace_seq_printf);
 
 /**
- * trace_seq_bitmask - put a list of longs as a bitmask print output
+ * trace_seq_bitmask - write a bitmask array in its ASCII representation
  * @s:          trace sequence descriptor
  * @maskp:      points to an array of unsigned longs that represent a bitmask
  * @nmaskbits:  The number of bits that are valid in @maskp
  *
- * It returns 0 if the trace oversizes the buffer's free
- * space, 1 otherwise.
- *
  * Writes a ASCII representation of a bitmask string into @s.
+ *
+ * Returns 1 if we successfully written all the contents to
+ *   the buffer.
+ * Returns 0 if we the length to write is bigger than the
+ *   rese