move min-list-garbage into min-collect-garbage pkg

we don't want it in the same package as min-copy-closure as
that depends on bash

pkgs/min-collect-garbage/default.nix

@@ -0,0 +1,17 @@
+{
+  stdenv
+, nix
+, cpio
+, openssh
+}: stdenv.mkDerivation {
+  name = "min-collect-garbage";
+  buildInputs = [ ];
+#  propagatedBuildInputs = [ openssh ];
+  src = ./.;
+  makeFlags = [ "min-list-garbage" ];
+  installPhase = ''
+    mkdir -p $out/bin
+    cp  min-collect-garbage.sh $out/bin/min-collect-garbage
+    cp min-list-garbage $out/bin
+  '';
+}

pkgs/min-collect-garbage/min-collect-garbage.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+test -f /persist/nix-store-paths || exit 1
+(cd /nix/store && min-list-garbage /persist/nix-store-paths | xargs rm -r)

pkgs/min-collect-garbage/min-list-garbage.c

@@ -0,0 +1,78 @@
+#include <dirent.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <string.h>
+#include <unistd.h>
+
+typedef char hash_t[32];
+hash_t *hash_list = NULL;
+int hash_list_entries = 0;
+int hash_list_size = 0;
+
+int add_list_entry(char *name)
+{
+    name += strlen("/nix/store/");
+    if(hash_list_entries >= hash_list_size) {
+	if(hash_list_size == 0) hash_list_size =  4;
+	hash_list_size = hash_list_size * 2;
+	hash_list = realloc(hash_list, hash_list_size * sizeof(hash_t));
+    }
+    strncpy(hash_list[hash_list_entries++], name, 32);
+}
+
+int read_list(char *filename)
+{
+    char s[1024];
+    FILE *fp;
+    if(fp = fopen(filename, "r")) {
+	while(fgets(s, 1024, fp)) {
+	    if(strrchr(s, '\n')) {
+		add_list_entry(s);
+	    } else {
+		puts("hash list entry too long");
+		exit(1);
+	    }
+	}
+    }
+    fclose(fp);
+}
+
+int on_list(char *name)
+{
+    int i;
+    for(i = 0; i < hash_list_entries; i++) {
+	if(!strncmp(hash_list[i], name, 32)) {
+	    return 1;
+	}
+    }
+    return 0;
+}
+
+int main(int argc, char * argv[])
+{
+    struct dirent * de;
+    DIR  * dirp;
+    char hash[32];
+
+    if(argc < 2) {
+	puts("Usage: min-list-garbage store-paths-file\n\nChecks all store paths against the list of expected paths in store-paths-file,\n and prints any which are present unexpectedly");
+	exit(1);
+    }
+
+    read_list(argv[1]);
+    
+    if((dirp = opendir("/nix/store")) == NULL) {
+	puts("can't open /nix/store");
+	exit(1);
+    }
+
+     while(de = readdir(dirp)) {
+	if(strlen(de->d_name) >= 32) {
+	    strncpy(hash, de->d_name, 32);
+	    if(!on_list(hash)) puts(de->d_name);
+	}
+    }
+
+    closedir(dirp);
+}