[PATCH v2] UBI: block: Dynamically allocate minor numbers

[Ezequiel Garcia]

On 03/16/2015 09:55 PM, Dan Ehrenberg wrote:
> This patch makes ubiblock devices have minor numbers beginning from
> 0, allocated dynamically independently of the ubi device/volume
> number. This property becomes useful because, on 32-bit architectures
> with LFS turned off in a userspace program, device minor numbers
> over 8 bits cause stat to return -EOVERFLOW. If the device number is
> high (>1) due to multiple MTD partitions, such an overflow will occur.
> While enabling LFS is clearly a nicer solution, it's often difficult
> to turn on in practice globally as many widely distributed packages
> don't work with LFS on.
> 
> Other storage systems have their own workarounds, with SCSI making
> multiple device majors and MMC having a config option for the number
> of partitions per device. A completely dynamic minor numbering is
> simpler than these. It is unlikely that anyone is depending on a
> static minor number since the major is dynamic anyway. In addition,
> ubiblock is still relatively new, so now is the time to make such
> changes.
> 
> Signed-off-by: Dan Ehrenberg <dehrenberg at chromium.org>
> 
> ---
> Changes in v2: Removed config option and made dynamic minor universal
> 
>  drivers/mtd/ubi/block.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
> index db2c05b..6faf268 100644
> --- a/drivers/mtd/ubi/block.c
> +++ b/drivers/mtd/ubi/block.c
> @@ -48,6 +48,7 @@
>  #include <linux/blk-mq.h>
>  #include <linux/hdreg.h>
>  #include <linux/scatterlist.h>
> +#include <linux/idr.h>
>  #include <asm/div64.h>
>  
>  #include "ubi-media.h"
> @@ -351,6 +352,18 @@ static struct blk_mq_ops ubiblock_mq_ops = {
>  	.map_queue      = blk_mq_map_queue,
>  };
>  
> +static DEFINE_IDR(ubiblock_minor_idr);
> +
> +static int ubiblock_alloc_minor(struct ubiblock *dev)
> +{
> +	return idr_alloc(&ubiblock_minor_idr, dev, 0, 0, GFP_KERNEL);
> +}
> +
> +static void ubiblock_remove_minor(int minor)
> +{
> +	idr_remove(&ubiblock_minor_idr, minor);
> +}
> +

How about just using idr_alloc,remove directly instead of having this
tiny wrappers? They don't seem to add much value.

-- 
Ezequiel Garcia, VanguardiaSur
www.vanguardiasur.com.ar