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/mempool.c

@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "nm-sd-adapt-shared.h"
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "env-util.h"
+#include "macro.h"
+#include "mempool.h"
+#include "process-util.h"
+#include "util.h"
+
+struct pool {
+        struct pool *next;
+        size_t n_tiles;
+        size_t n_used;
+};
+
+void* mempool_alloc_tile(struct mempool *mp) {
+        size_t i;
+
+        /* When a tile is released we add it to the list and simply
+         * place the next pointer at its offset 0. */
+
+        assert(mp->tile_size >= sizeof(void*));
+        assert(mp->at_least > 0);
+
+        if (mp->freelist) {
+                void *r;
+
+                r = mp->freelist;
+                mp->freelist = * (void**) mp->freelist;
+                return r;
+        }
+
+        if (_unlikely_(!mp->first_pool) ||
+            _unlikely_(mp->first_pool->n_used >= mp->first_pool->n_tiles)) {
+                size_t size, n;
+                struct pool *p;
+
+                n = mp->first_pool ? mp->first_pool->n_tiles : 0;
+                n = MAX(mp->at_least, n * 2);
+                size = PAGE_ALIGN(ALIGN(sizeof(struct pool)) + n*mp->tile_size);
+                n = (size - ALIGN(sizeof(struct pool))) / mp->tile_size;
+
+                p = malloc(size);
+                if (!p)
+                        return NULL;
+
+                p->next = mp->first_pool;
+                p->n_tiles = n;
+                p->n_used = 0;
+
+                mp->first_pool = p;
+        }
+
+        i = mp->first_pool->n_used++;
+
+        return ((uint8_t*) mp->first_pool) + ALIGN(sizeof(struct pool)) + i*mp->tile_size;
+}
+
+void* mempool_alloc0_tile(struct mempool *mp) {
+        void *p;
+
+        p = mempool_alloc_tile(mp);
+        if (p)
+                memzero(p, mp->tile_size);
+        return p;
+}
+
+void mempool_free_tile(struct mempool *mp, void *p) {
+        * (void**) p = mp->freelist;
+        mp->freelist = p;
+}
+
+bool mempool_enabled(void) {
+        static int b = -1;
+
+        if (!is_main_thread())
+                return false;
+
+        if (!mempool_use_allowed)
+                b = false;
+        if (b < 0)
+                b = getenv_bool("SYSTEMD_MEMPOOL") != 0;
+
+        return b;
+}
+
+#if VALGRIND
+void mempool_drop(struct mempool *mp) {
+        struct pool *p = mp->first_pool;
+        while (p) {
+                struct pool *n;
+                n = p->next;
+                free(p);
+                p = n;
+        }
+}
+#endif