[buildd-tools-devel] Bug#813360: Bug#813360: Overlayfs available on newer Linux kernel only

[Johannes Schauer]

Hi,

Quoting Luca Falavigna (2016-02-01 10:09:37)
> Beside the fact overlayfs is available since 3.18 Linux kernels, which
> makes a little bit harder to backport latest sbuild (for instance,
> Jessie has 3.16), this change could cause issues on systems where
> overlayfs is not available (thinking about kFreeBSD, for instance).

does there exist an easy way to detect at run-time whether overlayfs is
available on the system?

If yes, then that mechanism could be used to dynamically either add or not add
the union-type=overlay line to the default schroot configuration.

> Would a patch adding a new switch to define a different union-type method be
> welcome?

I don't think a switch would be a good idea for the following reasons:

 - if the user is willing to think of manually supplying a command line switch
   to sbuild-createchroot, then they could as well also just edit the schroot
   configuration

 - it is not clear which the default should be. Should we make overlayfs the
   default because linux-* architectures have more users? That doesn't seem
   fair.

 - sbuild should do the right thing out of the box. Switches should be there to
   overwrite the default behavior. Thus auto-detection would be awesome.

 - leaving it as a sbuildrc config option would make more sense because then
   users on non-overlayfs architectures could permanently store this
   information in their sbuildrc

Thanks!

cheers, josch
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