systemd: move basic systemd library to shared/nm-utils

For better or worse, we already pull in large parts of systemd sources.

I need a base64 decode implementation (because glib's g_base64_decode()
cannot reject invalid encodings). Instead of coming up with my own or
copy-paste if from somewhere, reuse systemd's unbase64mem().

But for that, make systemd's basic bits an independent static library
first because I will need it in libnm-core.

This doesn't really change anything except making "libnm-systemd-core.la"
an indpendent static library that could be used from "libnm-core". We
shall still be mindful about which internal code of systemd we use, and only
access functionality that is exposed via "systemd/nm-sd-utils-shared.h".

shared/systemd/src/basic/hash-funcs.c

@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "nm-sd-adapt-shared.h"
+
+#include <string.h>
+
+#include "hash-funcs.h"
+#include "path-util.h"
+
+void string_hash_func(const char *p, struct siphash *state) {
+        siphash24_compress(p, strlen(p) + 1, state);
+}
+
+#if 0 /* NM_IGNORED */
+DEFINE_HASH_OPS(string_hash_ops, char, string_hash_func, string_compare_func);
+
+void path_hash_func(const char *q, struct siphash *state) {
+        size_t n;
+
+        assert(q);
+        assert(state);
+
+        /* Calculates a hash for a path in a way this duplicate inner slashes don't make a differences, and also
+         * whether there's a trailing slash or not. This fits well with the semantics of path_compare(), which does
+         * similar checks and also doesn't care for trailing slashes. Note that relative and absolute paths (i.e. those
+         * which begin in a slash or not) will hash differently though. */
+
+        n = strspn(q, "/");
+        if (n > 0) { /* Eat up initial slashes, and add one "/" to the hash for all of them */
+                siphash24_compress(q, 1, state);
+                q += n;
+        }
+
+        for (;;) {
+                /* Determine length of next component */
+                n = strcspn(q, "/");
+                if (n == 0) /* Reached the end? */
+                        break;
+
+                /* Add this component to the hash and skip over it */
+                siphash24_compress(q, n, state);
+                q += n;
+
+                /* How many slashes follow this component? */
+                n = strspn(q, "/");
+                if (q[n] == 0) /* Is this a trailing slash? If so, we are at the end, and don't care about the slashes anymore */
+                        break;
+
+                /* We are not add the end yet. Hash exactly one slash for all of the ones we just encountered. */
+                siphash24_compress(q, 1, state);
+                q += n;
+        }
+}
+
+int path_compare_func(const char *a, const char *b) {
+        return path_compare(a, b);
+}
+
+DEFINE_HASH_OPS(path_hash_ops, char, path_hash_func, path_compare_func);
+#endif /* NM_IGNORED */
+
+void trivial_hash_func(const void *p, struct siphash *state) {
+        siphash24_compress(&p, sizeof(p), state);
+}
+
+int trivial_compare_func(const void *a, const void *b) {
+        return CMP(a, b);
+}
+
+const struct hash_ops trivial_hash_ops = {
+        .hash = trivial_hash_func,
+        .compare = trivial_compare_func,
+};
+
+void uint64_hash_func(const uint64_t *p, struct siphash *state) {
+        siphash24_compress(p, sizeof(uint64_t), state);
+}
+
+int uint64_compare_func(const uint64_t *a, const uint64_t *b) {
+        return CMP(*a, *b);
+}
+
+DEFINE_HASH_OPS(uint64_hash_ops, uint64_t, uint64_hash_func, uint64_compare_func);
+
+#if 0 /* NM_IGNORED */
+#if SIZEOF_DEV_T != 8
+void devt_hash_func(const dev_t *p, struct siphash *state) {
+        siphash24_compress(p, sizeof(dev_t), state);
+}
+
+int devt_compare_func(const dev_t *a, const dev_t *b) {
+        return CMP(*a, *b);
+}
+
+DEFINE_HASH_OPS(devt_hash_ops, dev_t, devt_hash_func, devt_compare_func);
+#endif
+#endif /* NM_IGNORED */