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

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

[Dan Ehrenberg]

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@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);
+}
+
 int ubiblock_create(struct ubi_volume_info *vi)
 {
 	struct ubiblock *dev;
@@ -388,7 +401,13 @@ int ubiblock_create(struct ubi_volume_info *vi)
 
 	gd->fops = &ubiblock_ops;
 	gd->major = ubiblock_major;
-	gd->first_minor = dev->ubi_num * UBI_MAX_VOLUMES + dev->vol_id;
+	gd->first_minor = ubiblock_alloc_minor(dev);
+	if (gd->first_minor < 0) {
+		dev_err(disk_to_dev(gd),
+			"block: dynamic minor allocation failed");
+		ret = -ENODEV;
+		goto out_put_disk;
+	}
 	gd->private_data = dev;
 	sprintf(gd->disk_name, "ubiblock%d_%d", dev->ubi_num, dev->vol_id);
 	set_capacity(gd, disk_capacity);
@@ -405,7 +424,7 @@ int ubiblock_create(struct ubi_volume_info *vi)
 	ret = blk_mq_alloc_tag_set(&dev->tag_set);
 	if (ret) {
 		dev_err(disk_to_dev(dev->gd), "blk_mq_alloc_tag_set failed");
-		goto out_put_disk;
+		goto out_remove_minor;
 	}
 
 	dev->rq = blk_mq_init_queue(&dev->tag_set);
@@ -443,6 +462,8 @@ out_free_queue:
 	blk_cleanup_queue(dev->rq);
 out_free_tags:
 	blk_mq_free_tag_set(&dev->tag_set);
+out_remove_minor:
+	ubiblock_remove_minor(gd->first_minor);
 out_put_disk:
 	put_disk(dev->gd);
 out_free_dev:
@@ -461,6 +482,7 @@ static void ubiblock_cleanup(struct ubiblock *dev)
 	blk_cleanup_queue(dev->rq);
 	blk_mq_free_tag_set(&dev->tag_set);
 	dev_info(disk_to_dev(dev->gd), "released");
+	ubiblock_remove_minor(dev->gd->first_minor);
 	put_disk(dev->gd);
 }
 
-- 
2.2.0.rc0.207.ga3a616c

Re: [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@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