dm-crypt: add a variable num_threads

Add a variable num_threads. Later, it could be set when parsing the arguments.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-crypt.c |   38 +++++++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 9 deletions(-)

Index: linux-3.2-fast/drivers/md/dm-crypt.c
===================================================================
--- linux-3.2-fast.orig/drivers/md/dm-crypt.c	2012-01-31 02:30:30.000000000 +0100
+++ linux-3.2-fast/drivers/md/dm-crypt.c	2012-01-31 02:30:35.000000000 +0100
@@ -1634,6 +1634,7 @@ static int crypt_ctr(struct dm_target *t
 	struct dm_arg_set as;
 	const char *opt_string;
 	int i;
+	unsigned num_threads = num_online_cpus();
 
 	static struct dm_arg _args[] = {
 		{0, 1, "Invalid number of feature args"},
@@ -1751,9 +1752,15 @@ static int crypt_ctr(struct dm_target *t
 		goto bad;
 	}
 
-	for (i = 0; i < NR_CPUS; i++)
-		if (cpu_online(i))
-			cc->crypt_threads_size = i + 1;
+	if (num_threads == num_online_cpus()) {
+		for (i = 0; i < NR_CPUS; i++)
+			if (cpu_online(i))
+				cc->crypt_threads_size = i + 1;
+	} else {
+		if (num_threads > INT_MAX / sizeof(struct task_struct *))
+			num_threads = INT_MAX / sizeof(struct task_struct *);
+		cc->crypt_threads_size = num_threads;
+	}
 
 	init_waitqueue_head(&cc->crypt_thread_wait);
 	INIT_LIST_HEAD(&cc->crypt_thread_list);
@@ -1765,18 +1772,31 @@ static int crypt_ctr(struct dm_target *t
 		goto bad;
 	}
 
-	for (i = 0; i < cc->crypt_threads_size; i++) {
-		if (cpu_online(i)) {
-			cc->crypt_threads[i] = kthread_create_on_node(
-				dmcrypt_thread, cc, cpu_to_node(i),
-				"dmcryptd/%d", i);
+	if (num_threads == num_online_cpus())
+		for (i = 0; i < cc->crypt_threads_size; i++) {
+			if (cpu_online(i)) {
+				cc->crypt_threads[i] = kthread_create_on_node(
+					dmcrypt_thread, cc, cpu_to_node(i),
+					"dmcryptd/%d", i);
+				if (IS_ERR(cc->crypt_threads[i])) {
+					ret = PTR_ERR(cc->crypt_threads[i]);
+					cc->crypt_threads[i] = NULL;
+					ti->error = "Couldn't spawn thread";
+					goto bad;
+				}
+				kthread_bind(cc->crypt_threads[i], i);
+				wake_up_process(cc->crypt_threads[i]);
+			}
+	} else {
+		for (i = 0; i < cc->crypt_threads_size; i++) {
+			cc->crypt_threads[i] = kthread_create(
+				dmcrypt_thread, cc, "dmcryptd/%d", i);
 			if (IS_ERR(cc->crypt_threads[i])) {
 				ret = PTR_ERR(cc->crypt_threads[i]);
 				cc->crypt_threads[i] = NULL;
 				ti->error = "Couldn't spawn thread";
 				goto bad;
 			}
-			kthread_bind(cc->crypt_threads[i], i);
 			wake_up_process(cc->crypt_threads[i]);
 		}
 	}