http://github.com/lu-zero/eudev/commit/96da532526fec9bbfc9f53f2c5819520b971710c

--- src/shared/conf-files.c
+++ src/shared/conf-files.c
@@ -37,11 +37,27 @@
 #include "hashmap.h"
 #include "conf-files.h"
 
-static int files_add(Hashmap *h, const char *path, const char *suffix) {
+static int files_add(Hashmap *h,
+                     const char *prefix,
+                     const char *path,
+                     const char *suffix) {
         DIR *dir;
         int r = 0;
 
-        dir = opendir(path);
+        if (prefix) {
+            char *p = NULL;
+
+            if (asprintf(&p, "%s/%s", prefix, path) < 0) {
+                r = -ENOMEM;
+                goto finish;
+            }
+
+            dir = opendir(p);
+            free(p);
+        } else {
+            dir = opendir(path);
+        }
+
         if (!dir) {
                 if (errno == ENOENT)
                         return 0;
@@ -90,7 +106,10 @@
         return strcmp(path_get_file_name(s1), path_get_file_name(s2));
 }
 
-int conf_files_list_strv(char ***strv, const char *suffix, const char **dirs) {
+int conf_files_list_strv(char ***strv,
+                         const char *prefix,
+                         const char *suffix,
+                         const char **dirs) {
         Hashmap *fh = NULL;
         char **files = NULL;
         const char **p;
@@ -105,7 +124,7 @@
         }
 
         STRV_FOREACH(p, dirs) {
-                r = files_add(fh, *p, suffix);
+                r = files_add(fh, prefix, *p, suffix);
                 if (r < 0)
                         log_warning("Failed to search for files in %s: %s",
                                     *p, strerror(-r));
@@ -126,7 +145,10 @@
         return r;
 }
 
-int conf_files_list(char ***strv, const char *suffix, const char *dir, ...) {
+int conf_files_list(char ***strv,
+                    const char *prefix,
+                    const char *suffix,
+                    const char *dir, ...) {
         char **dirs = NULL;
         va_list ap;
         int r;
@@ -145,7 +167,7 @@
         }
         strv_uniq(dirs);
 
-        r = conf_files_list_strv(strv, suffix, (const char **)dirs);
+        r = conf_files_list_strv(strv, prefix, suffix, (const char **)dirs);
 
 finish:
         strv_free(dirs);
--- src/shared/conf-files.h
+++ src/shared/conf-files.h
@@ -25,7 +25,13 @@
 
 #include "macro.h"
 
-int conf_files_list(char ***strv, const char *suffix, const char *dir, ...);
-int conf_files_list_strv(char ***strv, const char *suffix, const char **dirs);
+int conf_files_list(char ***strv,
+                    const char *prefix,
+                    const char *suffix,
+                    const char *dir, ...);
+int conf_files_list_strv(char ***strv,
+                         const char *prefix,
+                         const char *suffix,
+                         const char **dirs);
 
 #endif
--- src/udev/udevadm-hwdb.c
+++ src/udev/udevadm-hwdb.c
@@ -472,17 +472,20 @@
         printf("Usage: udevadm hwdb OPTIONS\n"
                "  --update            update the hardware database\n"
                "  --test <modalias>   query database and print result\n"
+               "  --root <root path>  define custom root path\n"
                "  --help\n\n");
 }
 
 static int adm_hwdb(struct udev *udev, int argc, char *argv[]) {
         static const struct option options[] = {
                 { "update", no_argument, NULL, 'u' },
+                { "root", required_argument, NULL, 'r' },
                 { "test", required_argument, NULL, 't' },
                 { "help", no_argument, NULL, 'h' },
                 {}
         };
-        const char *test = NULL;
+        const char *test = NULL, *root_path = NULL;
+        char *udev_hwdb_path = HWDB_BIN;
         bool update = false;
         struct trie *trie = NULL;
         int err;
@@ -491,7 +494,7 @@
         for (;;) {
                 int option;
 
-                option = getopt_long(argc, argv, "ut:h", options, NULL);
+                option = getopt_long(argc, argv, "ut:r:h", options, NULL);
                 if (option == -1)
                         break;
 
@@ -502,6 +505,9 @@
                 case 't':
                         test = optarg;
                         break;
+                case 'r':
+                        root_path = optarg;
+                        break;
                 case 'h':
                         help();
                         return EXIT_SUCCESS;
@@ -537,7 +543,7 @@
                 }
                 trie->nodes_count++;
 
-                err = conf_files_list_strv(&files, ".hwdb", (const char **)conf_file_dirs);
+                err = conf_files_list_strv(&files, root_path, ".hwdb", (const char **)conf_file_dirs);
                 if (err < 0) {
                         log_error("failed to enumerate hwdb files: %s\n", strerror(-err));
                         rc = EXIT_FAILURE;
@@ -565,11 +571,24 @@
                 log_debug("strings dedup'ed: %8zu bytes (%8zu)\n",
                           trie->strings->dedup_len, trie->strings->dedup_count);
 
-                mkdir_parents(HWDB_BIN, 0755);
-                err = trie_store(trie, HWDB_BIN);
+		if (root_path) {
+			if (asprintf(&udev_hwdb_path,
+					"%s/%s", root_path, udev_hwdb_path) < 0) {
+				rc = EXIT_FAILURE;
+				goto out;
+			}
+		}
+
+		mkdir_parents(udev_hwdb_path, 0755);
+		err = trie_store(trie, udev_hwdb_path);
+
+		if (root_path) {
+			free(udev_hwdb_path);
+		}
+
                 if (err < 0) {
                         log_error("Failure writing hardware database '%s': %s",
-                                  HWDB_BIN, strerror(-err));
+                                  udev_hwdb_path, strerror(-err));
                         rc = EXIT_FAILURE;
                 }
         }
--- src/udev/udev-rules.c
+++ src/udev/udev-rules.c
@@ -1619,7 +1619,7 @@
                 return udev_rules_unref(rules);
         udev_rules_check_timestamp(rules);
 
-        r = conf_files_list_strv(&files, ".rules", (const char **)rules->dirs);
+        r = conf_files_list_strv(&files, NULL, ".rules", (const char **)rules->dirs);
         if (r < 0) {
                 log_error("failed to enumerate rules files: %s\n", strerror(-r));
                 return udev_rules_unref(rules);