ucm: add possibility to skip the UCM card completely (Linked)

We have a requirement to "hide" some hardware drivers, because
other (main) UCM configuration will refer them.

This patch use special error codes to notify the upper layers
to skip the module loading.

BugLink: https://github.com/alsa-project/alsa-ucm-conf/issues/30
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

src/modules/alsa/alsa-ucm.c

@@ -757,13 +757,11 @@ static void append_lost_relationship(pa_alsa_ucm_device *dev) {
 
 int pa_alsa_ucm_query_profiles(pa_alsa_ucm_config *ucm, int card_index) {
     char *card_name;
-    const char **verb_list;
+    const char **verb_list, *value;
     int num_verbs, i, err = 0;
 
     /* support multiple card instances, address card directly by index */
     card_name = pa_sprintf_malloc("hw:%i", card_index);
-    if (card_name == NULL)
-        return -ENOMEM;
     err = snd_use_case_mgr_open(&ucm->ucm_mgr, card_name);
     if (err < 0) {
         /* fallback longname: is UCM available for this card ? */
@@ -771,22 +769,36 @@ int pa_alsa_ucm_query_profiles(pa_alsa_ucm_config *ucm, int card_index) {
         err = snd_card_get_name(card_index, &card_name);
         if (err < 0) {
             pa_log("Card can't get card_name from card_index %d", card_index);
+            err = -PA_ALSA_ERR_UNSPECIFIED;
             goto name_fail;
         }
 
         err = snd_use_case_mgr_open(&ucm->ucm_mgr, card_name);
         if (err < 0) {
             pa_log_info("UCM not available for card %s", card_name);
+            err = -PA_ALSA_ERR_UCM_OPEN;
             goto ucm_mgr_fail;
         }
     }
 
+    err = snd_use_case_get(ucm->ucm_mgr, "=Linked", &value);
+    if (err >= 0) {
+        if (strcasecmp(value, "true") == 0 || strcasecmp(value, "1") == 0) {
+            free((void *)value);
+            pa_log_info("Empty (linked) UCM for card %s", card_name);
+            err = -PA_ALSA_ERR_UCM_LINKED;
+            goto ucm_verb_fail;
+        }
+        free((void *)value);
+    }
+
     pa_log_info("UCM available for card %s", card_name);
 
     /* get a list of all UCM verbs (profiles) for this card */
     num_verbs = snd_use_case_verb_list(ucm->ucm_mgr, &verb_list);
     if (num_verbs < 0) {
         pa_log("UCM verb list not found for %s", card_name);
+        err = -PA_ALSA_ERR_UNSPECIFIED;
         goto ucm_verb_fail;
     }
 
@@ -806,7 +818,7 @@ int pa_alsa_ucm_query_profiles(pa_alsa_ucm_config *ucm, int card_index) {
 
     if (!ucm->verbs) {
         pa_log("No UCM verb is valid for %s", card_name);
-        err = -1;
+        err = -PA_ALSA_ERR_UCM_NO_VERB;
     }
 
     snd_use_case_free_list(verb_list, num_verbs);

src/modules/alsa/alsa-util.h

@@ -33,6 +33,13 @@
 
 #include "alsa-mixer.h"
 
+enum {
+    PA_ALSA_ERR_UNSPECIFIED = 1,
+    PA_ALSA_ERR_UCM_OPEN = 1000,
+    PA_ALSA_ERR_UCM_NO_VERB = 1001,
+    PA_ALSA_ERR_UCM_LINKED = 1002
+};
+
 int pa_alsa_set_hw_params(
         snd_pcm_t *pcm_handle,
         pa_sample_spec *ss,                /* modified at return */

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

@@ -785,6 +785,7 @@ int pa__init(pa_module *m) {
     const char *profile_str = NULL;
     char *fn = NULL;
     bool namereg_fail = false;
+    int err = -PA_MODULE_ERR_UNSPECIFIED, rval;
 
     pa_alsa_refcnt_inc();
 
@@ -841,7 +842,12 @@ int pa__init(pa_module *m) {
 
     snd_config_update_free_global();
 
-    if (u->use_ucm && !pa_alsa_ucm_query_profiles(&u->ucm, u->alsa_card_index)) {
+    rval = u->use_ucm ? pa_alsa_ucm_query_profiles(&u->ucm, u->alsa_card_index) : -1;
+    if (rval == -PA_ALSA_ERR_UCM_LINKED) {
+        err = -PA_MODULE_ERR_SKIP;
+        goto fail;
+    }
+    if (rval == 0) {
         pa_log_info("Found UCM profiles");
 
         u->profile_set = pa_alsa_ucm_add_profile_set(&u->ucm, &u->core->default_channel_map);
@@ -1009,7 +1015,7 @@ fail:
 
     pa__done(m);
 
-    return -1;
+    return err;
 }
 
 int pa__get_n_used(pa_module *m) {

src/modules/module-udev-detect.c

@@ -52,6 +52,7 @@ PA_MODULE_USAGE(
 struct device {
     char *path;
     bool need_verify;
+    bool ignore;
     char *card_name;
     char *args;
     uint32_t module;
@@ -286,6 +287,9 @@ static void verify_access(struct userdata *u, struct device *d) {
     pa_assert(u);
     pa_assert(d);
 
+    if (d->ignore)
+        return;
+
     cd = pa_sprintf_malloc("/dev/snd/controlC%s", path_get_card_id(d->path));
     accessible = access(cd, R_OK|W_OK) >= 0;
     pa_log_debug("%s is accessible: %s", cd, pa_yes_no(accessible));
@@ -332,14 +336,20 @@ static void verify_access(struct userdata *u, struct device *d) {
                  * failure or a "fatal" failure. */
 
                 if (pa_ratelimit_test(&d->ratelimit, PA_LOG_DEBUG)) {
+                    int err;
+
                     pa_log_debug("Loading module-alsa-card with arguments '%s'", d->args);
-                    pa_module_load(&m, u->core, "module-alsa-card", d->args);
+                    err = pa_module_load(&m, u->core, "module-alsa-card", d->args);
 
                     if (m) {
                         d->module = m->index;
                         pa_log_info("Card %s (%s) module loaded.", d->path, d->card_name);
-                    } else
+                    } else if (err == -PA_ERR_NOENTITY) {
+                        pa_log_info("Card %s (%s) module skipped.", d->path, d->card_name);
+                        d->ignore = true;
+                    } else {
                         pa_log_info("Card %s (%s) failed to load module.", d->path, d->card_name);
+                    }
                 } else
                     pa_log_warn("Tried to configure %s (%s) more often than %u times in %llus",
                                 d->path,

src/pulsecore/module.c

@@ -116,7 +116,7 @@ int pa_module_load(pa_module** module, pa_core *c, const char *name, const char
     bool (*load_once)(void);
     const char* (*get_deprecated)(void);
     pa_modinfo *mi;
-    int errcode;
+    int errcode, rval;
 
     pa_assert(module);
     pa_assert(c);
@@ -188,7 +188,11 @@ int pa_module_load(pa_module** module, pa_core *c, const char *name, const char
     pa_assert_se(pa_idxset_put(c->modules, m, &m->index) >= 0);
     pa_assert(m->index != PA_IDXSET_INVALID);
 
-    if (m->init(m) < 0) {
+    if ((rval = m->init(m)) < 0) {
+        if (rval == -PA_MODULE_ERR_SKIP) {
+            errcode = -PA_ERR_NOENTITY;
+            goto fail;
+        }
         pa_log_error("Failed to load module \"%s\" (argument: \"%s\"): initialization failed.", name, argument ? argument : "");
         errcode = -PA_ERR_IO;
         goto fail;

src/pulsecore/module.h

@@ -30,6 +30,11 @@ typedef struct pa_module pa_module;
 
 #include <pulsecore/core.h>
 
+enum {
+  PA_MODULE_ERR_UNSPECIFIED = 1,
+  PA_MODULE_ERR_SKIP = 2
+};
+
 struct pa_module {
     pa_core *core;
     char *name, *argument;