fwupd update fails trying to create temp file in /nix/store/

[snaar]

Issue description

# fwupdmgr update
Downloading 0.2.6.2 for XPS 13 9360 System Firmware...
Updating 0.2.6.2 on XPS 13 9360 System Firmware...
Decompressing…         [***************************************]
Authenticating…        [***************************************]
Scheduling…            [***************************************]
UEFI firmware update failed: {error #0} libfwup.c:1479 get_fd_and_media_path(): open of /nix/store/v2rcywfc2gvxqrbcx24afgmidxyfv9yd-fwupdate-10/boot/EFI/ubuntu/fw/fwupdate-JiILuZ.cap failed: No such file or directory        {error #1} libfwup.c:1513 get_fd_and_media_path(): mkostemps(/nix/store/v2rcywfc2gvxqrbcx24afgmidxyfv9yd-fwupdate-10/boot/EFI/nixos/fw/fwupdate-4HdcOC.cap) failed: Read-only file system

Steps to reproduce

• NixOS 18.03 on Dell XPS 13 9360
• services.fwupd.enable = true; in configuration.nix
• fwupdmgr refresh - works as expected
• fwupdmgr update - fails as above, nothing happens on reboot - i.e. scheduling did not happen indeed

Technical details

# nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 4.14.33, NixOS, 18.03.131954.2569e482904 (Impala)`
 - multi-user?: `yes`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.0`
 - channels(root): `"nixos-18.03.131954.2569e482904, nixos-unstable-18.09pre133640.ea145b68a01"`
 - channels(snaar): `""`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs`

[jtojnar]

See comments on https://github.com/NixOS/nixpkgs/pull/35065#issuecomment-366556815 for more info about the issue.

[jtojnar]

Closing in favour #39386