On Tue 2017-08-22 (11:03), Austin S. Hemmelgarn wrote:

Or alternatively, repeatedly call `btrfs filesystem show` on the path, 
removing one component from the end each time until you get a zero 
return code.  The path you called it on that got a zero return code is 
where the mount is (and thus what filesystem that subvolume is part of), 
and the output just gave you a list of devices it's on.

"btrfs filesystem show" is relative slow (2.6 s), 
"btrfs subvolume show" is MUCH faster (0.02 s).


In perl I have now:

$root = $volume;
while (`btrfs subvolume show "$root" 2>/dev/null` !~ /toplevel subvolume/) {
  $root = dirname($root);
  last if $root eq '/';
}


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
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