I think I found a bug with partition scanning/loopback devices with 4k logical sectors. It affects 4.14.x and 4.17.x kernels (and presumably others). I've also filed the bug on the kernel bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=200749 Copied from the bugzilla report: Loop devices with the logical sector size set to 4096 do not autodetect partitions when attached. It may be the case for devices with 4k logical sectors in general, but I do not have hardware to test that. I have not tested with non-GPT disks. I expect to see /dev/loopNpX devices appear when attaching a loopback device with partitions, regardless of logical block size. With 4096 byte logical block size I only see /dev/loopN devices and no /dev/loopNpX devices. Steps to reproduce: 1) truncate -s 1G diskimg 2) losetup -fP --show -b 4096 diskimg 3) sgdisk -n 0:0:0 /dev/loopN # Other partitioning tools will probably also work. 4) losetup -d /dev/loopN 5) losetup -fP --show -b 4096 diskimg This happens reliably. I can reproduce it 100% of the time. Running `sgdisk -p /dev/loopN` with trigger a partition scan and it find the partitions correctly then, but they do not appear when initially attached with `losetup -P`. Disk images with logical block size 512 do appear correctly. I've tested this with a Fedora 4.17.x kernel, my gentoo 4.17.x kernel and a Container linux 4.14.x kernel; they all exhibit the same behavior. I don't see anything interesting in dmesg and udevadm monitor shows there are no ADD uevents for the partition block devices until `sgdisk -p /dev/loopN` is run. Let me know if there's any other information you want. Also please CC me in replies. I am not subscribed to the list in general - Andrew Jeddeloh
