[PATCH v3] UBI: block: Dynamically allocate minor numbers

[PATCH v3] 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
Changes in v3: Minor code simplification

 drivers/mtd/ubi/block.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
index db2c05b..e0bb501 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 +352,8 @@ static struct blk_mq_ops ubiblock_mq_ops = {
 	.map_queue      = blk_mq_map_queue,
 };
 
+static DEFINE_IDR(ubiblock_minor_idr);
+
 int ubiblock_create(struct ubi_volume_info *vi)
 {
 	struct ubiblock *dev;
@@ -388,7 +391,13 @@ 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 = idr_alloc(&ubiblock_minor_idr, dev, 0, 0, GFP_KERNEL);
+	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 +414,7 @@ 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 +452,8 @@ out_free_queue:
 	blk_cleanup_queue(dev->rq);
 out_free_tags:
 	blk_mq_free_tag_set(&dev->tag_set);
+out_remove_minor:
+	idr_remove(&ubiblock_minor_idr, gd->first_minor);
 out_put_disk:
 	put_disk(dev->gd);
 out_free_dev:
@@ -461,6 +472,7 @@ 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");
+	idr_remove(&ubiblock_minor_idr, dev->gd->first_minor);
 	put_disk(dev->gd);
 }
 
-- 
2.2.0.rc0.207.ga3a616c

Re: [PATCH v3] UBI: block: Dynamically allocate minor numbers

[Ezequiel Garcia]

On 03/17/2015 02:37 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>
> 

Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
-- 
Ezequiel Garcia, VanguardiaSur
www.vanguardiasur.com.ar

Re: [PATCH v3] UBI: block: Dynamically allocate minor numbers

[Ezequiel Garcia]

On 03/19/2015 11:38 AM, Ezequiel Garcia wrote:
> 
> 
> On 03/17/2015 02:37 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>
>>
> 
> Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
> 

Hm.. it seems this one fell through the cracks :/ Richard?
-- 
Ezequiel Garcia, VanguardiaSur
www.vanguardiasur.com.ar

Re: [PATCH v3] UBI: block: Dynamically allocate minor numbers

[Richard Weinberger]

Am 22.04.2015 um 00:57 schrieb Ezequiel Garcia:
> 
> 
> On 03/19/2015 11:38 AM, Ezequiel Garcia wrote:
>>
>>
>> On 03/17/2015 02:37 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>
>>>
>>
>> Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
>>
> 
> Hm.. it seems this one fell through the cracks :/ Richard?

Yep. :(
Applied to my 4.2 queue!

Thanks everyone!
//richard