brd: export module parameters

Export 'rd_nr', 'rd_size' and 'max_part' parameters to sysfs so user can
know that how many devices are allowed, how big each device is and how
many partitions are supported. If 'max_part' is 0, it means simply the
device doesn't support partitioning.

Also note that 'max_part' can be adjusted to power of 2 minus 1 form if
needed. User should check this value after the module loading if he/she
want to use that number correctly (i.e. fdisk, mknod, etc.).
Signed-off-by: NNamhyung Kim <namhyung@gmail.com>
Cc: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

drivers/block/brd.c

@@ -436,11 +436,11 @@ static int rd_nr;
 int rd_size = CONFIG_BLK_DEV_RAM_SIZE;
 static int max_part;
 static int part_shift;
-module_param(rd_nr, int, 0);
+module_param(rd_nr, int, S_IRUGO);
 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
-module_param(rd_size, int, 0);
+module_param(rd_size, int, S_IRUGO);
 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
-module_param(max_part, int, 0);
+module_param(max_part, int, S_IRUGO);
 MODULE_PARM_DESC(max_part, "Maximum number of partitions per RAM disk");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
@@ -578,9 +578,20 @@ static int __init brd_init(void)
 	 */
 
 	part_shift = 0;
-	if (max_part > 0)
+	if (max_part > 0) {
 		part_shift = fls(max_part);
 
+		/*
+		 * Adjust max_part according to part_shift as it is exported
+		 * to user space so that user can decide correct minor number
+		 * if [s]he want to create more devices.
+		 *
+		 * Note that -1 is required because partition 0 is reserved
+		 * for the whole disk.
+		 */
+		max_part = (1UL << part_shift) - 1;
+	}
+
 	if ((1UL << part_shift) > DISK_MAX_PARTS)
 		return -EINVAL;