loop: export module parameters

Export 'max_loop' and 'max_part' parameters to sysfs so user can know
that how many devices are allowed and how many partitions are supported.

If 'max_loop' is 0, there is no restriction on the number of loop devices.
User can create/use the devices as many as minor numbers available. 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: Namhyung Kim <namhyung@gmail.com>
Cc: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index c59a672a3de0d6571fbe173a8328d12a1e03c86b..76c8da78212bffec71f5dc7af025a84e4028d456 100644 (file)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1540,9 +1540,9 @@ static const struct block_device_operations lo_fops = {
  * And now the modules code and kernel interface.
  */
 static int max_loop;
-module_param(max_loop, int, 0);
+module_param(max_loop, int, S_IRUGO);
 MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
-module_param(max_part, int, 0);
+module_param(max_part, int, S_IRUGO);
 MODULE_PARM_DESC(max_part, "Maximum number of partitions per loop device");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);
@@ -1688,9 +1688,20 @@ static int __init loop_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;