Comment # 13 on bug 1230345 from Ruediger Oertel

not sure if this helps:

s390zl21:~ # l /dev/mapper/
total 0
drwxr-xr-x  2 root root     260 Sep 11 16:50 ./
drwxr-xr-x 14 root root    5660 Sep 12 16:47 ../
lrwxrwxrwx  1 root root       7 Sep 11 16:50 3600507630bffd2160000000000002000
-> ../dm-1
lrwxrwxrwx  1 root root       7 Sep  9 16:26 3600507630bffd2160000000000002100
-> ../dm-2
lrwxrwxrwx  1 root root       7 Sep  9 16:26
3600507630bffd2160000000000002100-part1 -> ../dm-5
lrwxrwxrwx  1 root root       7 Sep  9 16:26
3600507630bffd2160000000000002100-part2 -> ../dm-6
lrwxrwxrwx  1 root root       7 Sep  9 16:26
3600507630bffd2160000000000002100-part3 -> ../dm-7
lrwxrwxrwx  1 root root       7 Sep  9 16:26 3600507630bffd2160000000000002101
-> ../dm-3
lrwxrwxrwx  1 root root       7 Sep  9 16:26 3600507630bffd2160000000000002104
-> ../dm-4
lrwxrwxrwx  1 root root       7 Sep  9 16:26
3600507630bffd2160000000000002104-part1 -> ../dm-9
lrwxrwxrwx  1 root root       7 Sep  9 16:26 3600507638081855cd80000000000002a
-> ../dm-0
lrwxrwxrwx  1 root root       7 Sep  9 16:26 3600a0980383041622f2455736d434a76
-> ../dm-8
crw-------  1 root root 10, 236 Sep  9 16:28 control
s390zl21:~ # dmsetup table
3600507630bffd2160000000000002000: 0 8388608 multipath 1 queue_if_no_path 1
alua 1 1 service-time 0 2 2 8:16 1 1 8:112 1 1 
3600507630bffd2160000000000002100: 0 20971520 multipath 1 queue_if_no_path 1
alua 1 1 service-time 0 2 2 8:32 1 1 8:128 1 1 
3600507630bffd2160000000000002100-part1: 0 5117952 linear 254:2 2048
3600507630bffd2160000000000002100-part2: 0 13305856 linear 254:2 5120000
3600507630bffd2160000000000002100-part3: 0 2543616 linear 254:2 18425856
3600507630bffd2160000000000002101: 0 1073741824 multipath 1 queue_if_no_path 1
alua 1 1 service-time 0 2 2 8:48 1 1 8:144 1 1 
3600507630bffd2160000000000002104: 0 209715200 multipath 1 queue_if_no_path 1
alua 1 1 service-time 0 2 2 8:64 1 1 8:160 1 1 
3600507630bffd2160000000000002104-part1: 0 209713152 linear 254:4 2048
3600507638081855cd80000000000002a: 0 8388608 multipath 1 queue_if_no_path 1
alua 2 1 service-time 0 1 2 8:176 1 1 service-time 0 1 2 8:0 1 1 
3600a0980383041622f2455736d434a76: 0 8388608 multipath 3 queue_if_no_path
pg_init_retries 50 1 alua 2 1 service-time 0 2 2 8:80 1 1 8:192 1 1
service-time 0 2 2 8:96 1 1 8:208 1 1 

and grepping mknod from the strace runs:
s390zl21:~ # grep mknod bla.multipath 
3480780 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0xfe, 0x1)) =
0
3480782 mknodat(AT_FDCWD, "/dev/zipl-dm-temp-00", S_IFBLK|000, makedev(0x8,
0x10)) = 0
3480780 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0xfe, 0x1)) =
0
3480780 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0xfe, 0x1)) =
-1 EEXIST (File exists)
3480780 mknodat(AT_FDCWD, "/dev/zipl0001", S_IFBLK|0700, makedev(0xfe, 0x1)) =
0
3480789 mknodat(AT_FDCWD, "/dev/zipl-dm-temp-00", S_IFBLK|000, makedev(0x8,
0x10)) = 0
3480780 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0xfe, 0x1)) =
-1 EEXIST (File exists)
3480780 mknodat(AT_FDCWD, "/dev/zipl0001", S_IFBLK|0700, makedev(0xfe, 0x1)) =
0
3480823 mknodat(AT_FDCWD, "/dev/zipl-dm-temp-00", S_IFBLK|000, makedev(0x8,
0x10)) = 0
s390zl21:~ # grep mknod bla.sdb 
3482680 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0x8, 0x10)) =
0
3482680 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0x8, 0x10)) =
0
3482680 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0x8, 0x10)) =
-1 EEXIST (File exists)
3482680 mknodat(AT_FDCWD, "/dev/zipl0001", S_IFBLK|0700, makedev(0x8, 0x10)) =
0
3482680 mknodat(AT_FDCWD, "/dev/zipl0000", S_IFBLK|0700, makedev(0x8, 0x10)) =
-1 EEXIST (File exists)
3482680 mknodat(AT_FDCWD, "/dev/zipl0001", S_IFBLK|0700, makedev(0x8, 0x10)) =
0


0xfe,0x1 = 254,1 = dm-1
0x08,0x10 = 8,16 = sdb