Re: losetup: failed to setup loop device > 1

[Francis Moreau <francis.moro@gmail.com>]

On 10/07/2014 11:17 AM, Karel Zak wrote:
> On Mon, Oct 06, 2014 at 10:59:00PM +0200, Francis Moreau wrote:
>> On 10/06/2014 07:40 PM, Karel Zak wrote:
>>> On Mon, Oct 06, 2014 at 06:35:20PM +0200, Francis Moreau wrote:
>>>> One last details is that the system uses pretty old stuff: kernel
>>>> 3.4.50, util-linux 2.21.1.
>>>
>>> $ git log --oneline v2.21.. -- lib/loopdev.c sys-utils/losetup.c | wc -l
>>> 62
>>>
>>>> Could anybody give me some help ?
>>>
>>> update, this is upstream mailing list I have doubts anyone is ready
>>> to help you with code released 2 years ago.
>>
>> well it looks like more a kernel issue since the sequence of syscalls
>> done by losetup looks correct. Maybe someone here already encountered
>> this...
>>
>> I just found that loop module was loaded with max_part=16 and
>> CONFIG_BLK_DEV_LOOP_MIN_COUNT=8. If max_part is set to 0 then the issue
>> is gone :-/
> 
> Well, if you have kernel that provides /dev/loop-control then you
> don't have to set CONFIG_BLK_DEV_LOOP_MIN_COUNT at all. I guess 
> "8" (kernel upstream default?) is mostly about backward compatibility.
> 
> For example fedora uses CONFIG_BLK_DEV_LOOP_MIN_COUNT=0. All is
> dynamically allocated by kernel + udev.

You're right, CONFIG_BLK_DEV_LOOP_MIN_COUNT can be set to 0. But that
doesnt explain my initial issue.

I have to understand why setting up a loop dev fails if the number of
loop used is > 1 and max_part != 0.

Thanks