[Bug 2059092] Re: [VROC] mdadm detects dm-device as partition

Hi,

has somebody analyzed this issue?

** Package changed: ubuntu => linux (Ubuntu)

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https://bugs.launchpad.net/bugs/2059092

Title:
[VROC] mdadm detects dm-device as partition

Status in linux package in Ubuntu:
New

Bug description:
We discovered an issue when trying to create imsm container with mdadm
on dm-device.

Environment:
OS: Ubuntu 24.04
Kernel: inbox 6.6.0

Scenario:

1. Create dm device
# echo -e '0 195312 linear /dev/nvme2n1 0' | dmsetup create nvme2n1DM

2. Create IMSM container.
# dmdev=$(readlink -f /dev/mapper/nvme2n1DM)
# export IMSM_DEVNAME_AS_SERIAL=1 IMSM_NO_PLATFORM=1; mdadm --create /dev/md/container --metadata=imsm --raid-disks=1 $dmdev --force

Expected result:
Container is created.

Actual result:

Error message is displayed
# mdadm: imsm: /dev/dm-0 is a partition, cannot be used in IMSM
Container is not created.

Additional info:

Mdadm uses ioctl call underneath to check if device is a partition.
Here's the function:

int test_partition(int fd)
{
/* Check if fd is a whole-disk or a partition.
* BLKPG will return EINVAL on a partition, and BLKPG_DEL_PARTITION
* will return ENXIO on an invalid partition number.
*/
struct blkpg_ioctl_arg a;
struct blkpg_partition p;
a.op = BLKPG_DEL_PARTITION;
a.data = (void*)&p;
a.datalen = sizeof(p);
a.flags = 0;
memset(a.data, 0, a.datalen);
p.pno = 1<<30;
if (ioctl(fd, BLKPG, &a) == 0)
/* Very unlikely, but not a partition */
return 0;
if (errno == ENXIO || errno == ENOTTY)
/* not a partition */
return 0;

return 1;
}

We established that the behavior is caused by regression in ioctl.
Thread: https://lore.kernel.org/all/CAOYeF9VsmqKMcQjo1k6YkGNujwN-nzfxY17N3F-CMikE1tYp+w@mail.gmail.com/
Fix: https://lore.kernel.org/all/20240118130401.792757-1-lilingfeng@huaweicloud.com/

We established that ioctl call on dm-device returns EINVAL as if it was a partition.
Note that this function was was working unchanged for last 10+years and the issue was fixed in newer kenel.

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