On 2016-07-13 00:39, Andrei Borzenkov wrote:

12.07.2016 15:25, Austin S. Hemmelgarn пишет:

quoted

I'm not changing my init system just to add functionality that should
already exist in btrfs-progs.  The fact that the balance ioctl is
synchronous was a poor design choice, and we need to provide the option
to work around that independent of what our users are running.  There's
been enough interest from other people that it should be obvious that
people want this _in_ btrfs-progs.  The point is to not _need_ anything
else to do this.

May be I miss something obvious, but what is wrong with

nohup btrfs balance start &

nohup is definitely available on every system and so far I have been
using it in exactly such cases when I needed to leave something running
for a long time.

That does work, but it still falls into the category of needing external 
software to do it.  I'm trying to get something that works without any 
external software, and doesn't even depend on having a shell with job 
control.