[[!comment format=mdwn
 username="spwhitton"
 subject="comment 3"
 date="2016-06-14T03:16:18Z"
 content="""
Thanks for taking a look at my branch, and especially for fixing my inadequately-tested `readVersionMaybe`.

`Sbuild.built` does not *require* a particular version of the kernel.  It is just that the file that it generates in `/etc/schroot/chroot.d` can vary depending on the kernel version running at the time that `Sbuild.built` is first ensured.  In particular, if the running kernel does not support overlayfs (as jessie's kernel doesn't), the line `union-type=overlay` will be omitted from the file in `/etc/schroot/chroot.d`.  This renders `Schroot.overlaysInTmpfs` useless.

I think it should be up to the user to apply a property like

    & Sbuild.built foo `requires` Reboot.toKernelNewerThan bar

to individual hosts, because it depends on whether they actually care about using an overlay chroot.  Perhaps on an old machine they don't intend to use overlays.  In my config, I do something like this:

    & osDebian Testing \"i386\"
    & Apt.stdSourcesList `onChange` (Apt.upgraded `before` Apt.cacheCleaned `before` Reboot.toKernelNewerThan \"4\")
    & Sbuilt.builtFor ...

The idea is that if I reinstall my machine from a jessie installation CD, propellor will upgrade to testing and boot to the new kernel before it builds the chroot, so I get the `union-type=overlay` line in my config.

I could prepare a patch to add this information to the haddock of Sbuild.hs?
"""]]
