trace: make argument 'mem' of trace_seq_putmem() const

Impact: fix build warning

I passed a const value to trace_seq_putmem(), and I got compile warning.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_output.c

@@ -137,7 +137,7 @@ int trace_seq_putc(struct trace_seq *s, unsigned char c)
 	return 1;
 }
 
-int trace_seq_putmem(struct trace_seq *s, void *mem, size_t len)
+int trace_seq_putmem(struct trace_seq *s, const void *mem, size_t len)
 {
 	if (len > ((PAGE_SIZE - 1) - s->len))
 		return 0;
@@ -148,10 +148,10 @@ int trace_seq_putmem(struct trace_seq *s, void *mem, size_t len)
 	return len;
 }
 
-int trace_seq_putmem_hex(struct trace_seq *s, void *mem, size_t len)
+int trace_seq_putmem_hex(struct trace_seq *s, const void *mem, size_t len)
 {
 	unsigned char hex[HEX_CHARS];
-	unsigned char *data = mem;
+	const unsigned char *data = mem;
 	int i, j;
 
 #ifdef __BIG_ENDIAN

kernel/trace/trace_output.h

@@ -31,8 +31,9 @@ extern ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
 				 size_t 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, void *mem, size_t len);
-extern int trace_seq_putmem_hex(struct trace_seq *s, void *mem, size_t len);
+extern int trace_seq_putmem(struct trace_seq *s, const void *mem, size_t 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);
 extern int trace_seq_path(struct trace_seq *s, struct path *path);
 extern int seq_print_userip_objs(const struct userstack_entry *entry,