nixpkgs/pkgs/development/libraries/glibc/nix-nss-open-files.patch

diff --git a/nss/nss_files/files-XXX.c b/nss/nss_files/files-XXX.c
index 1db9e46127..3a567e0224 100644
--- a/nss/nss_files/files-XXX.c
+++ b/nss/nss_files/files-XXX.c
@@ -75,8 +75,20 @@ internal_setent (FILE **stream)
 
   if (*stream == NULL)
     {
-      *stream = __nss_files_fopen (DATAFILE);
-
+      const char *file = DATAFILE;
+
+      #ifdef NIX_DATAFILE
+      // use the Nix environment variable such as `NIX_ETC_PROTOCOLS`
+      char *path = secure_getenv (NIX_DATAFILE);
+
+      // if the environment variable is set, then read from the /nix/store entry instead
+      if (path && path[0]) {
+        file = path;
+      }
+      #endif
+      
+      *stream = __nss_files_fopen (file);
+    
       if (*stream == NULL)
 	status = errno == EAGAIN ? NSS_STATUS_TRYAGAIN : NSS_STATUS_UNAVAIL;
     }
diff --git a/nss/nss_files/files-proto.c b/nss/nss_files/files-proto.c
index c30bedc0aa..b321e68d3c 100644
--- a/nss/nss_files/files-proto.c
+++ b/nss/nss_files/files-proto.c
@@ -23,6 +23,7 @@ NSS_DECLARE_MODULE_FUNCTIONS (files)
 
 #define ENTNAME		protoent
 #define DATABASE	"protocols"
+#define NIX_DATAFILE "NIX_ETC_PROTOCOLS"
 
 struct protoent_data {};
 
diff --git a/nss/nss_files/files-service.c b/nss/nss_files/files-service.c
index bfc2590699..0bff36aee5 100644
--- a/nss/nss_files/files-service.c
+++ b/nss/nss_files/files-service.c
@@ -24,6 +24,7 @@ NSS_DECLARE_MODULE_FUNCTIONS (files)
 
 #define ENTNAME		servent
 #define DATABASE	"services"
+#define NIX_DATAFILE "NIX_ETC_SERVICES"
 
 struct servent_data {};