btrfs-progs: bugs in "subvolume list" command
While digging deeper into the "subvolume list" command, I found some flaws which I'm addressing here:
1. The "parent id" seems to be a relict of old days. btrfs-subvolume(8) states:
"If -p is given, then parent <ID> is added to the output between ID and top level. The parent's ID may be used at mount time via the subvolrootid= option."
The "Mount Options" site [1] tells me that the "subvolrootid=" mount option is deprecated since kernel 3.2. A quick check on my system (kernel 4.2.2) shows that "parent" is equal to "top level" for all subvolumes. Is this always true for kernels >3.2 ?
Furthermore, the output is confusing, as "parent" is not related at all to "parent_uuid".
Note that this is also true for "subvolume show", which prints "parent" as "Parent ID".
Suggestion: drop the '-p' option and don't print "parent" anymore. I don't know the "backwards compatibility policy" the btrfs-devs have here, but my impression is that kernel 3.2 is not really supported anymore.
2. The output of -a option (as well as -o) is inconsistent. Given /tmp/btr_test is mounted with subvolid=0:
# btrfs subvolume create /tmp/btr_test/vol0 # btrfs subvolume create /tmp/btr_test/vol0/vol1 # btrfs subvolume create /tmp/btr_test/vol0/vol1/vol2 # list_path=/tmp/btr_test # btrfs subvolume list -a $list_path ID 256 gen 8 top level 5 path vol0 ID 257 gen 9 top level 256 path <FS_TREE>/vol0/vol1 ID 258 gen 9 top level 257 path <FS_TREE>/vol0/vol1/vol2
The only relative path shown is "vol0", which is at "$list_path/vol0", as expected. But then "vol0/vol1" are printed as absolute, while they are relative to $list_path.
# list_path=/tmp/btr_test/vol0
# btrfs subvolume list -a $list_path ID 256 gen 8 top level 5 path <FS_TREE>/vol0 ID 257 gen 9 top level 256 path vol0/vol1 ID 258 gen 9 top level 257 path <FS_TREE>/vol0/vol1/vol2
But if $list_path points to a subvolume, the relative path shown is now "vol0/vol1", which is actually at "$list_path/../vol0/vol1".
Things get even more confusing when subvolumes are within directories:
# mkdir /tmp/btr_test/vol0/dir1 # btrfs subvolume create /tmp/btr_test/vol0/dir1/vol3 # list_path=/tmp/btr_test/vol0/dir1 # btrfs subvolume list -a $list_path ID 256 gen 11 top level 5 path <FS_TREE>/vol0 ID 257 gen 9 top level 256 path vol0/vol1 ID 258 gen 9 top level 257 path <FS_TREE>/vol0/vol1/vol2 ID 259 gen 11 top level 256 path vol0/dir1/vol3
I know that handling "real" directories is very tricky to handle correctly (involving symlinks et all), and is probably not a feature that "subvolume list" command should handle.
Suggestions:
- Fix '-a' option to also print sub-subvolumes as relative, or drop it (there is the -o option for this purpose).
- Fix output of '-o' option, by always printing relative paths ("vol1" instead of "vol0/vol1" in the example above).
Regards,
- Axel