Note, the whitespace damage in the patch is not needed, just my text client cleaning up trailing whitespace.

With this patch applied, vgscan --mknodes no longer creates block devices in /dev/mapper

root@ubuntu:/dev/mapper# ls -al
total 0
drwxr-xr-x  2 root root     120 Apr 28 16:31 .
drwxr-xr-x 17 root root    3800 Apr 28 15:25 ..
crw-------  1 root root 10, 236 Apr 28 15:22 control
lrwxrwxrwx  1 root root       7 Apr 28 16:31 mpatha -> ../dm-0
lrwxrwxrwx  1 root root       7 Apr 28 16:31 mpatha-part1 -> ../dm-1
lrwxrwxrwx  1 root root       7 Apr 28 16:31 mpatha-part2 -> ../dm-2
root@ubuntu:/dev/mapper#
root@ubuntu:/dev/mapper#
root@ubuntu:/dev/mapper# ls -al
total 0
drwxr-xr-x  2 root root     120 Apr 28 16:31 .
drwxr-xr-x 17 root root    3800 Apr 28 15:25 ..
crw-------  1 root root 10, 236 Apr 28 15:22 control
lrwxrwxrwx  1 root root       7 Apr 28 16:31 mpatha -> ../dm-0
lrwxrwxrwx  1 root root       7 Apr 28 16:31 mpatha-part1 -> ../dm-1
lrwxrwxrwx  1 root root       7 Apr 28 16:31 mpatha-part2 -> ../dm-2
root@ubuntu:/dev/mapper# rm -rf mpatha*
root@ubuntu:/dev/mapper# vgscan --mknodes
root@ubuntu:/dev/mapper# ls -al
total 0
drwxr-xr-x  2 root root      60 Apr 28 16:40 .
drwxr-xr-x 17 root root    3800 Apr 28 15:25 ..
crw-------  1 root root 10, 236 Apr 28 15:22 control

The relevant output:

16:40:35.179504 vgscan[55466] toollib.c:2288  No volume groups found.
16:40:35.179806 vgscan[55466] device_mapper/libdm-common.c:2205  WARK: setting a cookie
16:40:35.180137 vgscan[55466] device_mapper/libdm-common.c:2565  Udev cookie 0xd4d8d17 (semid 32786) created
16:40:35.180451 vgscan[55466] device_mapper/libdm-common.c:2585  Udev cookie 0xd4d8d17 (semid 32786) incremented to 1
16:40:35.180762 vgscan[55466] device_mapper/libdm-common.c:2457  Udev cookie 0xd4d8d17 (semid 32786) incremented to 2
16:40:35.181082 vgscan[55466] device_mapper/libdm-common.c:2690  Udev cookie 0xd4d8d17 (semid 32786) assigned to MKNODES task(15) with flags DISABLE_LIBRARY_FALLBACK         (0x20)
16:40:35.181398 vgscan[55466] device_mapper/libdm-common.c:2709  WARK: got my cookie, return 1
16:40:35.181714 vgscan[55466] device_mapper/libdm-common.c:2214  WARK: running dmt with DM-DEV_DISABLE_LIBRARY_FALLBACK flag
16:40:35.182048 vgscan[55466] device_mapper/ioctl/libdm-iface.c:1853  dm names   [ opencount flush ]   [16384] (*1)
16:40:35.182379 vgscan[55466] device_mapper/ioctl/libdm-iface.c:1853  dm mknodes mpatha  [ noopencount flush ]   [16384] (*1)
16:40:35.182687 vgscan[55466] device_mapper/libdm-common.c:1484  mpatha: Stacking NODE_ADD (253,0) 0:6 0660 [trust_udev]
16:40:35.183004 vgscan[55466] device_mapper/ioctl/libdm-iface.c:1853  dm mknodes mpatha-part2  [ noopencount flush ]   [16384] (*1)
16:40:35.183341 vgscan[55466] device_mapper/libdm-common.c:1484  mpatha-part2: Stacking NODE_ADD (253,2) 0:6 0660 [trust_udev]
16:40:35.183648 vgscan[55466] device_mapper/ioctl/libdm-iface.c:1853  dm mknodes mpatha-part1  [ noopencount flush ]   [16384] (*1)
16:40:35.183968 vgscan[55466] device_mapper/libdm-common.c:1484  mpatha-part1: Stacking NODE_ADD (253,1) 0:6 0660 [trust_udev]
16:40:35.184275 vgscan[55466] device_mapper/libdm-common.c:2218  WARK: running out path
16:40:35.184563 vgscan[55466] activate/fs.c:492  Syncing device names
16:40:35.184862 vgscan[55466] device_mapper/libdm-common.c:1484  mpatha: Skipping NODE_ADD (253,0) 0:6 0660 [trust_udev]
16:40:35.185163 vgscan[55466] device_mapper/libdm-common.c:1484  mpatha-part2: Skipping NODE_ADD (253,2) 0:6 0660 [trust_udev]
16:40:35.185478 vgscan[55466] device_mapper/libdm-common.c:1484  mpatha-part1: Skipping NODE_ADD (253,1) 0:6 0660 [trust_udev]
16:40:35.185806 vgscan[55466] device_mapper/libdm-config.c:986  report/output_format not found in config: defaulting to basic
16:40:35.186112 vgscan[55466] device_mapper/libdm-config.c:1085  log/report_command_log not found in config: defaulting to 0