Re: losetup: failed to setup loop device > 1

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

On 10/07/2014 11:32 AM, Francis Moreau wrote:
> 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.
> 

In HEAD of the git tree, in file losetup.c, the return value of
loopcxt_add_device() is not checked in main().

Is this expected ?

Thanks