mm: bdi init hooks

provide BDI constructor/destructor hooks

[akpm@linux-foundation.org: compile fix]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 64551ab..0e937f6 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -893,6 +893,11 @@
 static int __init chr_dev_init(void)
 {
 	int i;
+	int err;
+
+	err = bdi_init(&zero_bdi);
+	if (err)
+		return err;
 
 	if (register_chrdev(MEM_MAJOR,"mem",&memory_fops))
 		printk("unable to get major %d for memory devs\n", MEM_MAJOR);