linux-kernel - Re: [PATCH] loop: export module parameters

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Date:	Fri, 27 May 2011 13:57:38 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	linux-kernel@...r.kernel.org,
	Laurent Vivier <Laurent.Vivier@...l.net>
Subject: Re: [PATCH] loop: export module parameters

2011-05-25 (수), 14:44 +0900, Namhyung Kim:
> 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@...il.com>
> Cc: Laurent Vivier <Laurent.Vivier@...l.net>
> ---
>  drivers/block/loop.c |   17 ++++++++++++++---
>  1 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index c59a672a3de0..76c8da78212b 100644
> --- 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;
>  

Hi Jens,

Could you please consider applying this in your tree too? It's exactly
the same thing what I did for brd series.

Thanks.


-- 
Regards,
Namhyung Kim


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