This reverts commit 048c36ccaa.
With the patch applied for fixing the overlayfs bug in QEMU, there
really shouldn't stand anything in our way to use 4.19 as the default
kernel.
Signed-off-by: aszlig <aszlig@nix.build>
Our VM tests and everything related to our virtualisation infrastructure
is currently broken if used with kernel 4.19 or later.
The reason for this is that since 4.19, overlayfs uses the O_NOATIME
flag when opening files in lowerdir and this doesn't play nice with the
way we pass the Nix store to our QEMU guests.
On a NixOS system, paths in the Nix store are typically owned by root
but the QEMU process is usually run by an ordinary user. Using O_NOATIME
on a file where you're not the owner (or superuser) will return with
EPERM (Operation not permitted).
This is exactly what happens in our VM tests, because we're using
overlayfs in the guests to allow writes to the store.
Another implication of this is that the default kernel version for NixOS
19.03 has been reverted to Linux 4.14.
Work on getting this upstream is still ongoing and the patch I posted
previously was incomplete, needs rework and also some more review from
upstream maintainers - in summary: This will take a while.
So instead of rushing in a kernel patch to nixpkgs, which will affect
all users of overlayfs, not just NixOS VM tests, I opted to patch QEMU
for now to ignore the O_NOATIME flag in 9p.
I think this is also the least impacting change, because even if you
care about whether access times are written or not, you get the same
behaviour as with Linux 4.19 in conjunction with QEMU.
Signed-off-by: aszlig <aszlig@nix.build>
Fixes: https://github.com/NixOS/nixpkgs/issues/54509
Yesterday we had a discussion about several Hydra-related problems in the #nixos
IRC channel[1], as a result a lot of stalled PRs were merged.
I think that we want to use the latest Hydra now as it contains lots of
new fixes and folks mentioned that they want to use a self-hosted
Hydra, so they probably use the `nixpkgs` package rather than the
expressions from `NixOS/hydra`.
Simply moving to 2019-03-18 should be fine for now as Hydra doesn't have
a release model.
[1] https://logs.nix.samueldr.com/nixos/2019-03-17#2048416;
