libhardware: add concept of module classes

Needed for things like audio and audio effects. Provides a
new interface to loading modules named 'hw_get_module_by_class'.
This takes two parameters: 'class_id' and 'instance' which are
used to construct the filename for the module to be loaded. If
instance is NULL, then this function acts identically to
hw_get_module where 'class_id' == 'id' (and in fact the latter
implemented exactly this way).

For audio, this new mechanism allows us to load multiple audio
interfaces by doing:

hw_get_module_by_class("audio", "primary", &module);
hw_get_module_by_class("audio", "a2dp", &module);
hw_get_module_by_class("audio", "usb", &module);
...

In the future we will likely want to add the ability to load a set of
module instances based on a config file, which will have a standard
syntax and the mechanism will be provided by libhardware.

Change-Id: I9976cc6d59a85a414b18e7b398a36edfbce4abd8
Signed-off-by: Dima Zavin <dima@android.com>

2 files changed, 33 insertions, 6 deletions

diff --git a/hardware.c b/hardware.c
index d2e3b4c..2559237 100644
--- a/hardware.c
+++ b/hardware.c
@@ -117,13 +117,20 @@ static int load(const char *id,
     return status;
 }
 
-int hw_get_module(const char *id, const struct hw_module_t **module) 
+int hw_get_module_by_class(const char *class_id, const char *inst,
+                           const struct hw_module_t **module)
 {
     int status;
     int i;
     const struct hw_module_t *hmi = NULL;
     char prop[PATH_MAX];
     char path[PATH_MAX];
+    char name[PATH_MAX];
+
+    if (inst)
+        snprintf(name, PATH_MAX, "%s.%s", class_id, inst);
+    else
+        strlcpy(name, class_id, PATH_MAX);
 
     /*
      * Here we rely on the fact that calling dlopen multiple times on
@@ -139,15 +146,15 @@ int hw_get_module(const char *id, const struct hw_module_t **module)
                 continue;
             }
             snprintf(path, sizeof(path), "%s/%s.%s.so",
-                    HAL_LIBRARY_PATH1, id, prop);
+                    HAL_LIBRARY_PATH1, name, prop);
             if (access(path, R_OK) == 0) break;
 
             snprintf(path, sizeof(path), "%s/%s.%s.so",
-                     HAL_LIBRARY_PATH2, id, prop);
+                     HAL_LIBRARY_PATH2, name, prop);
             if (access(path, R_OK) == 0) break;
         } else {
             snprintf(path, sizeof(path), "%s/%s.default.so",
-                     HAL_LIBRARY_PATH1, id);
+                     HAL_LIBRARY_PATH1, name);
             if (access(path, R_OK) == 0) break;
         }
     }
@@ -156,8 +163,13 @@ int hw_get_module(const char *id, const struct hw_module_t **module)
     if (i < HAL_VARIANT_KEYS_COUNT+1) {
         /* load the module, if this fails, we're doomed, and we should not try
          * to load a different variant. */
-        status = load(id, path, module);
+        status = load(class_id, path, module);
     }
 
     return status;
 }
+
+int hw_get_module(const char *id, const struct hw_module_t **module)
+{
+    return hw_get_module_by_class(id, NULL, module);
+}
diff --git a/include/hardware/hardware.h b/include/hardware/hardware.h
index d9cc0dc..2251593 100644
--- a/include/hardware/hardware.h
+++ b/include/hardware/hardware.h
@@ -113,10 +113,25 @@ typedef struct hw_device_t {
 
 /**
  * Get the module info associated with a module by id.
- * @return: 0 == success, <0 == error and *pHmi == NULL
+ *
+ * @return: 0 == success, <0 == error and *module == NULL
  */
 int hw_get_module(const char *id, const struct hw_module_t **module);
 
+/**
+ * Get the module info associated with a module instance by class 'class_id'
+ * and instance 'inst'.
+ *
+ * Some modules types necessitate multiple instances. For example audio supports
+ * multiple concurrent interfaces and thus 'audio' is the module class
+ * and 'primary' or 'a2dp' are module interfaces. This implies that the files
+ * providing these modules would be named audio.primary.<variant>.so and
+ * audio.a2dp.<variant>.so
+ *
+ * @return: 0 == success, <0 == error and *module == NULL
+ */
+int hw_get_module_by_class(const char *class_id, const char *inst,
+                           const struct hw_module_t **module);
 
 /**
  * pixel format definitions