util: Add property_get() fallback for android

Environment variables aren't the easiest thing to use on android.  So
add a fallback to android's property mechanism for os_get_option().

This is slightly complicated by the fact that the assumption that the
return value of os_get_option() need not be freed.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7763>

src/util/os_misc.c

@@ -56,6 +56,7 @@
 #  define LOG_TAG "MESA"
 #  include <unistd.h>
 #  include <log/log.h>
+#  include <cutils/properties.h>
 #elif DETECT_OS_LINUX || DETECT_OS_CYGWIN || DETECT_OS_SOLARIS || DETECT_OS_HURD
 #  include <unistd.h>
 #elif DETECT_OS_OPENBSD || DETECT_OS_FREEBSD
@@ -121,16 +122,100 @@ os_log_message(const char *message)
 #endif
 }
 
+#if DETECT_OS_ANDROID
+#  include <ctype.h>
+#  include "hash_table.h"
+#  include "ralloc.h"
+#  include "simple_mtx.h"
+
+static struct hash_table *options_tbl;
+static simple_mtx_t options_tbl_lock = _SIMPLE_MTX_INITIALIZER_NP;
+
+static void
+options_tbl_fini(void)
+{
+   _mesa_hash_table_destroy(options_tbl, NULL);
+}
+
+/**
+ * Get an option value from android's property system, as a fallback to
+ * getenv() (which is generally less useful on android due to processes
+ * typically being forked from the zygote.
+ *
+ * The option name used for getenv is translated into a property name
+ * by:
+ *
+ *  1) convert to lowercase
+ *  2) replace '_' with '.'
+ *  3) if necessary, prepend "mesa."
+ *
+ * For example:
+ *  - MESA_EXTENSION_OVERRIDE -> mesa.extension.override
+ *  - GALLIUM_HUD -> mesa.gallium.hud
+ *
+ * Note that we use a hashtable for two purposes:
+ *  1) Avoid re-translating the option name on subsequent lookups
+ *  2) Avoid leaking memory.  Because property_get() returns the
+ *     property value into a user allocated buffer, we cannot return
+ *     that directly to the caller, so we need to strdup().  With the
+ *     hashtable, subsquent lookups can return the existing string.
+ */
+static const char *
+os_get_android_option(const char *name)
+{
+   if (!options_tbl) {
+      options_tbl = _mesa_hash_table_create(NULL, _mesa_hash_string,
+            _mesa_key_string_equal);
+      atexit(options_tbl_fini);
+   }
+
+   struct hash_entry *entry = _mesa_hash_table_search(options_tbl, name);
+   if (entry) {
+      return entry->data;
+   }
+
+   char value[PROPERTY_VALUE_MAX];
+   char key[PROPERTY_KEY_MAX];
+   char *p = key, *end = key + PROPERTY_KEY_MAX;
+   /* add "mesa." prefix if necessary: */
+   if (strstr(name, "MESA_") != name)
+      p += strlcpy(p, "mesa.", end - p);
+   p += strlcpy(p, name, end - p);
+   for (int i = 0; key[i]; i++) {
+      if (key[i] == '_') {
+         key[i] = '.';
+      } else {
+         key[i] = tolower(key[i]);
+      }
+   }
+
+   const char *opt = NULL;
+   int len = property_get(key, value, NULL);
+   if (len > 1) {
+      opt = ralloc_strdup(options_tbl, value);
+   }
+
+   _mesa_hash_table_insert(options_tbl, name, value);
+
+   return opt;
+}
+#endif
+
 
 #if !defined(EMBEDDED_DEVICE)
 const char *
 os_get_option(const char *name)
 {
-   return getenv(name);
+   const char *opt = getenv(name);
+#if DETECT_OS_ANDROID
+   if (!opt) {
+      opt = os_get_android_option(name);
+   }
+#endif
+   return opt;
 }
 #endif /* !EMBEDDED_DEVICE */
 
-
 /**
  * Return the size of the total physical memory.
  * \param size returns the size of the total physical memory