module-alsa-card: handle udev PULSE_MODARGS

Allow adding module arguments using udev PULSE_MODARGS environment variable and
fail module loading if there is a problem with PULSE_MODARGS

This helps setting e.g. 'tsched=0' for specific devices without a need to create
full load module entry in default.pa.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/436>

src/modules/alsa/module-alsa-card.c

@@ -104,6 +104,8 @@ static const char* const valid_modargs[] = {
 
 #define DEFAULT_DEVICE_ID "0"
 
+#define PULSE_MODARGS "PULSE_MODARGS"
+
 struct userdata {
     pa_core *core;
     pa_module *module;
@@ -820,6 +822,7 @@ int pa__init(pa_module *m) {
     const char *description;
     const char *profile_str = NULL;
     char *fn = NULL;
+    char *udev_args = NULL;
     bool namereg_fail = false;
     int err = -PA_MODULE_ERR_UNSPECIFIED, rval;
 
@@ -849,6 +852,47 @@ int pa__init(pa_module *m) {
         goto fail;
     }
 
+#ifdef HAVE_UDEV
+    udev_args = pa_udev_get_property(u->alsa_card_index, PULSE_MODARGS);
+#endif
+
+    if (udev_args) {
+        bool udev_modargs_success = true;
+        pa_modargs *temp_ma = pa_modargs_new(udev_args, valid_modargs);
+
+        if (temp_ma) {
+            /* do not try to replace device_id */
+
+            if (pa_modargs_remove_key(temp_ma, "device_id") == 0) {
+                pa_log_warn("Unexpected 'device_id' module argument override ignored from udev " PULSE_MODARGS "='%s'", udev_args);
+            }
+
+            /* Implement modargs override by copying original module arguments
+             * over udev entry arguments ignoring duplicates. */
+
+            if (pa_modargs_merge_missing(temp_ma, u->modargs, valid_modargs) == 0) {
+                /* swap module arguments */
+                pa_modargs *old_ma = u->modargs;
+                u->modargs = temp_ma;
+                temp_ma = old_ma;
+
+                pa_log_info("Applied module arguments override from udev " PULSE_MODARGS "='%s'", udev_args);
+            } else {
+                pa_log("Failed to apply module arguments override from udev " PULSE_MODARGS "='%s'", udev_args);
+                udev_modargs_success = false;
+            }
+
+            pa_modargs_free(temp_ma);
+        } else {
+            pa_log("Failed to parse module arguments from udev " PULSE_MODARGS "='%s'", udev_args);
+            udev_modargs_success = false;
+        }
+        pa_xfree(udev_args);
+
+        if (!udev_modargs_success)
+            goto fail;
+    }
+
     if (pa_modargs_get_value_boolean(u->modargs, "ignore_dB", &ignore_dB) < 0) {
         pa_log("Failed to parse ignore_dB argument.");
         goto fail;

src/pulsecore/modargs.c

@@ -272,6 +272,15 @@ int pa_modargs_append(pa_modargs *ma, const char *args, const char* const* valid
     return parse(ma, args, valid_keys, true);
 }
 
+int pa_modargs_remove_key(pa_modargs *ma, const char *key) {
+    if (pa_hashmap_remove_and_free(ma->unescaped, key) == 0) {
+        pa_hashmap_remove_and_free(ma->raw, key);
+        return 0;
+    }
+
+    return -1;
+}
+
 void pa_modargs_free(pa_modargs*ma) {
     pa_assert(ma);
 
@@ -544,3 +553,20 @@ const char *pa_modargs_iterate(pa_modargs *ma, void **state) {
 
     return e->key;
 }
+
+int pa_modargs_merge_missing(pa_modargs *dst, pa_modargs *src, const char* const valid_keys[]) {
+    void *state;
+    const char *key, *value;
+    int ret = 0;
+
+    for (state = NULL, key = pa_modargs_iterate(src, &state); key; key = pa_modargs_iterate(src, &state)) {
+        value = pa_modargs_get_value(src, key, NULL);
+        if (value && add_key_value(dst, pa_xstrdup(key), pa_xstrdup(value), valid_keys, true) < 0) {
+            pa_log_warn("Failed to add module argument '%s=%s'", key, value);
+            ret = -1;
+            /* continue to gather all errors */
+        }
+    }
+
+    return ret;
+}

src/pulsecore/modargs.h

@@ -95,4 +95,11 @@ int pa_modargs_get_proplist(pa_modargs *ma, const char *name, pa_proplist *p, pa
  * have any particular order. */
 const char *pa_modargs_iterate(pa_modargs *ma, void **state);
 
+/* Remove entry by key. Returns 0 if successful, -1 otherwise */
+int pa_modargs_remove_key(pa_modargs *ma, const char *key);
+
+/* Add all key/value pairs from src that are is not already present in dst, to dst.
+ * Returns 0 if there were no errors, -1 otherwise. */
+int pa_modargs_merge_missing(pa_modargs *dst, pa_modargs *src, const char* const valid_keys[]);
+
 #endif