Discourage mktemp usage

[salseeg]

Environment

• Elixir version (elixir -v):

Erlang/OTP 26 [erts-14.1] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit:ns] 

Elixir 1.15.5 (compiled with Erlang/OTP 26)

• Nerves environment: (mix nerves.env --info)

nerves| Environment Package List

  Pkg:         nerves_toolchain_ctng
  Vsn:         1.9.3
  Type:        toolchain_platform
  BuildRunner: {nil, []}

  Pkg:         nerves_toolchain_aarch64_nerves_linux_gnu
  Vsn:         1.8.0
  Type:        toolchain
  BuildRunner: {Nerves.Artifact.BuildRunners.Local, []}

  Pkg:         bktp_rpi4
  Vsn:         1.24.1-bktp.3
  Type:        system
  BuildRunner: {Nerves.Artifact.BuildRunners.Docker, [make_args: ["source", "all", "legal-info"]]}

  Pkg:         nerves_system_br
  Vsn:         1.24.1
  Type:        system_platform
  BuildRunner: {nil, []}

|nerves| Loadpaths Start


Nerves environment
  MIX_TARGET:   bktp_rpi4
  MIX_ENV:      prod

|nerves| Environment Variable List
  target:     bktp_rpi4
  toolchain:  /Users/s/.nerves/artifacts/nerves_toolchain_aarch64_nerves_linux_gnu-darwin_x86_64-1.8.0
  system:     /Users/s/.nerves/artifacts/bktp_rpi4-portable-1.24.1-bktp.3
  app:        .

|nerves| Loadpaths End

Nerves:           1.10.4
Nerves Bootstrap: 1.12.1
Elixir:           1.15.5
|nerves| Info End

• Additional information about your host, target hardware or environment that
  may help: /Volume/cs_fs is case sensitive on my Mac. / (and /tmp cosequently) is case insensitive.

Current behavior

Original error on mix firmware

|nerves| Building OTP Release...

* [Nerves] validating vm.args
* skipping runtime configuration (config/runtime.exs not found)
* creating _build/bktp_rpi4_prod/rel/platform/releases/2023-12-14_10469b5___2023-12-14_3215ba1/vm.args
Updating base firmware image with Erlang release...
Copying rootfs_overlay: /Volumes/cs_fs/buckitUp/platform/_build/bktp_rpi4_prod/nerves/rootfs_overlay
Copying rootfs_overlay: /Volumes/cs_fs/buckitUp/platform/rootfs_overlay

FATAL ERROR: write_file: file squashfs-root/usr/lib/xtables/libip6t_hl.so already exists

/Volume/cs_fs is case sensitive on my Mac. / (and /tmp cosequently) is case insensitive.

I faces problems building any custom system before. Workaround of moving linux kernel to case sensitive FS worked.

This time I was adding iptables and described error have happend.
iptables generates and . This is the root cause of the error.

ls usr/lib/xtables | grep ip6t_

libip6t_DNPT.so
libip6t_HL.so
libip6t_NETMAP.so
libip6t_REJECT.so
libip6t_SNPT.so
libip6t_ah.so
libip6t_dst.so
libip6t_eui64.so
libip6t_frag.so
libip6t_hbh.so
libip6t_hl.so
libip6t_icmp6.so
libip6t_ipv6header.so
libip6t_mh.so
libip6t_rt.so
libip6t_srh.so

Moving project to case sensitive FS had not helped.

See Workaround down below.

Expected behavior

Create custom temp directory under project _build or Nerves dir. This way developer may control the filesystem used for building.

It would be helpful to note in the documentation that case sensitive filesystem is needed to build.

Workaround

Replacing mktemp usage with hardcoded directory in merge-squashfs worked.

...
workdir="/Volumes/cs_fs/nerves/squash_merge_tmp"
rm -rf "$workdir"
mkdir -p "$workdir"
# workdir=$(mktemp -d 2>/dev/null || mktemp -d -t 'merge-squashfs-tmp')
pushd "$workdir" >/dev/null
...

[salseeg]

Added as instruction in my project - https://github.com/Buckitup-chat/bktp_rpi4/tree/otp_26?tab=readme-ov-file#macos-specific

[fhunleth]

@salseeg Sorry for the delayed response and thank you for sharing your instructions. We've been very slowly working on a way to remove the use of merge-squashfs, and I had hoped to share it by now, but that hasn't happened. The issue with adding iptables and building on MacOS has hit quite a few people.