Bug 1441175

Description of problem:

lsblk -ls used to output the child first, then the parent, but now it outputs the parent first, then the child.

Consider a block disk with a single partition on it.  Lsblk lists the disk before the partition both as a tree and as a list:

# lsblk /dev/sda
NAME                          MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                             8:0    0  100M  0 disk 
└─sda1                          8:1    0  100M  0 part 

# lsblk -l /dev/sda
NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                         8:0    0  100M  0 disk 
sda1                        8:1    0  100M  0 part 

However, when using inverse order (-s), the tree and list show different output order:

# lsblk -s /dev/sda1
NAME  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda1    8:1    0  100M  0 part 
└─sda   8:0    0  100M  0 disk 

# lsblk -sl /dev/sda1
NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda    8:0    0  100M  0 disk 
sda1   8:1    0  100M  0 part 

Now the parent comes first with -sl, but last with just -s.  The parent used to always come last.

We use lsblk in a script to walk up the dependency tree of a block device and used to assume that -sl orders its output from children to parent.

If this isn't a regression in lsblk, it would be nice to document how -l orders its output.

Version-Release number of selected component (if applicable):
util-linux-2.29.1-2.fc26.x86_64

How reproducible:
Always

Steps to Reproduce: See above