drivers: char: mem: Make /dev/mem an optional device

Adds Kconfig option CONFIG_DEVMEM that allows the
/dev/mem device to be disabled.

Option defaults to /dev/mem enabled.

Signed-off-by: Rob Ward <robert.ward114@googlemail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 4c58333..7d67784 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -715,7 +715,7 @@
 #define open_mem	open_port
 #define open_kmem	open_mem
 
-static const struct file_operations mem_fops = {
+static const struct file_operations __maybe_unused mem_fops = {
 	.llseek		= memory_lseek,
 	.read		= read_mem,
 	.write		= write_mem,
@@ -785,7 +785,9 @@
 	const struct file_operations *fops;
 	struct backing_dev_info *dev_info;
 } devlist[] = {
+#ifdef CONFIG_DEVMEM
 	 [1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi },
+#endif
 #ifdef CONFIG_DEVKMEM
 	 [2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },
 #endif