glibc: add dependency on netbase /etc/protocols

Add an explicit dependency on netbase for /etc/protocols

Certain functions in glibc look for files present in /etc such as getprotobyname which reads /etc/protocols.
If you are using Nix over a Linux installation, this file may not be present, and therefore it will cause errors.

- add netbase as a new package in nixpks
- add a dependency in glibc on it using postPatchPhase and substitute
the path

Fixes #124401

2 files changed, 18 insertions, 0 deletions

diff --git a/doc/builders/packages/etc-files.section.md b/doc/builders/packages/etc-files.section.md
new file mode 100644
index 00000000000..0b837938359
--- /dev/null
+++ b/doc/builders/packages/etc-files.section.md
@@ -0,0 +1,17 @@
+# /etc files {#etc}
+
+Certain calls in glibc require access to runtime files found in /etc such as `/etc/protocols` or `/etc/services` -- [getprotobyname](https://linux.die.net/man/3/getprotobyname) is one such function.
+
+On non-NixOS distributions these files are typically provided by packages (i.e. [netbase](https://packages.debian.org/sid/netbase)) if not already pre-installed in your distribution. This can cause non-reproducibility for code if they rely on these files being present.
+
+If [iana-etc](https://hydra.nixos.org/job/nixos/trunk-combined/nixpkgs.iana-etc.x86_64-linux) is part of your _buildInputs_ then it will set the environment varaibles `NIX_ETC_PROTOCOLS` and `NIX_ETC_SERVICES` to the corresponding files in the package through a _setup-hook_.
+
+```bash
+❯ nix-shell -p iana-etc
+
+[nix-shell:~]$ env | grep NIX_ETC
+NIX_ETC_SERVICES=/nix/store/aj866hr8fad8flnggwdhrldm0g799ccz-iana-etc-20210225/etc/services
+NIX_ETC_PROTOCOLS=/nix/store/aj866hr8fad8flnggwdhrldm0g799ccz-iana-etc-20210225/etc/protocols
+```
+
+Nixpkg's version of [glibc](https://hydra.nixos.org/job/nixos/trunk-combined/nixpkgs.glibc.x86_64-linux) has been patched to check for the existence of these environment variables. If the environment variable are *not set*, then it will attempt to find the files at the default location within _/etc_.
diff --git a/doc/builders/packages/index.xml b/doc/builders/packages/index.xml
index f5b05b0bbcc..206e1e49f1f 100644
--- a/doc/builders/packages/index.xml
+++ b/doc/builders/packages/index.xml
@@ -17,6 +17,7 @@
  <xi:include href="kakoune.section.xml" />
  <xi:include href="linux.section.xml" />
  <xi:include href="locales.section.xml" />
+ <xi:include href="etc-files.section.xml" />
  <xi:include href="nginx.section.xml" />
  <xi:include href="opengl.section.xml" />
  <xi:include href="shell-helpers.section.xml" />