Add nr parameter to file_service_type

Right now we switch for every IO, add a postfix that allows to switch
for every 'x' number of ios.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 1374d05..f9e3fc7 100644
--- a/HOWTO
+++ b/HOWTO
@@ -265,6 +265,11 @@
 			roundrobin  Round robin over open files. This
 				is the default.
 
+		The string can have a number appended, indicating how
+		often to switch to a new file. So if option random:4 is
+		given, fio will switch to a new random file after 4 ios
+		have been issued.
+
 ioengine=str	Defines how the job issues io to the file. The following
 		types are defined:
 
diff --git a/fio.h b/fio.h
index a60be10..9d190b1 100644
--- a/fio.h
+++ b/fio.h
@@ -473,6 +473,13 @@
 	 */
 	struct timeval timeout_end;
 	struct itimerval timer;
+
+	/*
+	 * for fileservice, how often to switch to a new file
+	 */
+	unsigned int file_service_nr;
+	unsigned int file_service_left;
+	struct fio_file *file_service_file;
 };
 
 /*
diff --git a/init.c b/init.c
index 2129882..eee2335 100644
--- a/init.c
+++ b/init.c
@@ -30,6 +30,7 @@
 #endif
 static int str_exitall_cb(void);
 static int str_cpumask_cb(void *, unsigned int *);
+static int str_fst_cb(void *, const char *);
 
 #define __stringify_1(x)	#x
 #define __stringify(x)		__stringify_1(x)
@@ -190,6 +191,7 @@
 	{
 		.name	= "file_service_type",
 		.type	= FIO_OPT_STR,
+		.cb	= str_fst_cb,
 		.off1	= td_var_offset(file_service_type),
 		.help	= "How to select which file to service next",
 		.def	= "roundrobin",
@@ -1048,7 +1050,7 @@
 /*
  * Check if mmap/mmaphuge has a :/foo/bar/file at the end. If so, return that.
  */
-static char *get_mmap_file(const char *str)
+static char *get_opt_postfix(const char *str)
 {
 	char *p = strstr(str, ":");
 
@@ -1066,7 +1068,7 @@
 	struct thread_data *td = data;
 
 	if (td->mem_type == MEM_MMAPHUGE || td->mem_type == MEM_MMAP) {
-		td->mmapfile = get_mmap_file(mem);
+		td->mmapfile = get_opt_postfix(mem);
 		if (td->mem_type == MEM_MMAPHUGE && !td->mmapfile) {
 			log_err("fio: mmaphuge:/path/to/file\n");
 			return 1;
@@ -1114,6 +1116,18 @@
 	return 0;
 }
 
+static int str_fst_cb(void *data, const char *str)
+{
+	struct thread_data *td = data;
+	char *nr = get_opt_postfix(str);
+
+	td->file_service_nr = 1;
+	if (nr)
+		td->file_service_nr = atoi(nr);
+
+	return 0;
+}
+
 /*
  * This is our [ini] type file parser.
  */
diff --git a/io_u.c b/io_u.c
index e283e72..c9a344f 100644
--- a/io_u.c
+++ b/io_u.c
@@ -368,13 +368,23 @@
 
 static struct fio_file *get_next_file(struct thread_data *td)
 {
+	struct fio_file *f;
+
 	if (!td->nr_open_files)
 		return NULL;
 
+	f = td->file_service_file;
+	if (f && f->open && td->file_service_left--)
+		return f;
+
 	if (td->file_service_type == FIO_FSERVICE_RR)
-		return get_next_file_rr(td);
+		f = get_next_file_rr(td);
 	else
-		return get_next_file_rand(td);
+		f = get_next_file_rand(td);
+
+	td->file_service_file = f;
+	td->file_service_left = td->file_service_nr - 1;
+	return f;
 }
 
 struct io_u *__get_io_u(struct thread_data *td)