Add support for AVIRT

Leverage the new AVIRT driver for a more secure, more dynamically
configurable loopback sound driver.

To use, replace the file smixer-4a-default.json with
smixer-4a-avirt.json, at /usr/libexec/agl/smixer/etc.
The snd-avirt drivers are installed in AGL by default as of 6.99.2.

The existing snd-aloop configuration is not broken by this change.

Change-Id: I827636656c109a7393ad77997e05069a2462ea46
Signed-off-by: Mark Farrugia <mark.farrugia@fiberdyne.com.au>

6 files changed, 323 insertions, 95 deletions

diff --git a/conf.d/cmake/config.cmake b/conf.d/cmake/config.cmake
index 8093548..f5509f2 100644
--- a/conf.d/cmake/config.cmake
+++ b/conf.d/cmake/config.cmake
@@ -88,7 +88,7 @@ set (PKG_REQUIRED_LIST
 # Customize link option
 # -----------------------------
 #list(APPEND link_libraries -an-option)
-list(APPEND link_libraries afb-helpers)
+list(APPEND link_libraries afb-helpers avirt)
 
 # Compilation options definition
 # Use CMake generator expressions to specify only for a specific language
diff --git a/conf.d/project/etc/smixer-4a-avirt.json b/conf.d/project/etc/smixer-4a-avirt.json
new file mode 100644
index 0000000..18d6193
--- /dev/null
+++ b/conf.d/project/etc/smixer-4a-avirt.json
@@ -0,0 +1,44 @@
+{
+    "$schema": "http://iot.bzh/download/public/schema/json/ctl-schema.json",
+    "metadata": {
+        "uid": "Soft Mixer",
+        "version": "1.0",
+        "api": "smixer",
+        "info": "Soft Mixer emulating hardware mixer"
+    },
+    "resources": [
+        {
+            "uid": "softmixer-avirt",
+            "info": "Map avirt-loop to 4A HAL streams",
+            "spath": "./package/lib/plugins:./package/var:./lib/plugins:./var:/usr/libexec/agl/smixer",
+            "libs": ["alsa-softmixer.ctlso"]
+        }
+    ],
+    "onload": [
+        {
+            "uid": "mixer-create-api",
+            "info": "Create Audio Router",
+            "action": "plugin://softmixer-avirt#MixerCreate",
+            "args": {
+                "uid":"Alsa-Mixer",
+                "max_loop": 1,
+                "max_sink": 16,
+                "max_source": 16,
+                "max_zone": 16,
+                "max_stream": 16,
+                "max_ramp": 6
+            }
+        },
+        {
+          "uid": "mixer-attach-loop",
+          "info": "Create Audio Router",
+          "action": "plugin://softmixer-avirt#MixerAttach",
+          "args": {
+              "loops" : {
+                  "uid":"AVIRT-Loopback",
+                  "path": "/dev/snd/by-path/platform-snd_avirt.0"
+              }
+          }
+        }
+    ]
+}
diff --git a/plugins/alsa/alsa-api-loop.c b/plugins/alsa/alsa-api-loop.c
index a123bb3..c0ea549 100644
--- a/plugins/alsa/alsa-api-loop.c
+++ b/plugins/alsa/alsa-api-loop.c
@@ -19,8 +19,50 @@
 #define _GNU_SOURCE  // needed for vasprintf
 
 #include "alsa-softmixer.h"
+#include <avirt/avirt.h>
 #include <string.h>
 
+#define UID_AVIRT_LOOP "AVIRT-Loopback"
+
+#define REGNUMID_0  51
+#define REGNUMID_1  57
+#define REGNUMID_2  63
+#define REGNUMID_3  69
+#define REGNUMID_4  75
+#define REGNUMID_5  81
+#define REGNUMID_6  87
+#define REGNUMID_7  93
+#define REGNUMID_8  99
+#define REGNUMID_9  105
+#define REGNUMID_10 111
+#define REGNUMID_11 117
+#define REGNUMID_12 123
+#define REGNUMID_13 129
+#define REGNUMID_14 135
+#define REGNUMID_15 141
+
+struct RegistryNumidMap {
+    int index;
+    int numid;
+} numidmap[] = {
+    { 0,  REGNUMID_0  },
+    { 1,  REGNUMID_1  },
+    { 2,  REGNUMID_2  },
+    { 3,  REGNUMID_3  },
+    { 4,  REGNUMID_4  },
+    { 5,  REGNUMID_5  },
+    { 6,  REGNUMID_6  },
+    { 7,  REGNUMID_7  },
+    { 8,  REGNUMID_8  },
+    { 9,  REGNUMID_9  },
+    { 10, REGNUMID_10 },
+    { 11, REGNUMID_11 },
+    { 12, REGNUMID_12 },
+    { 13, REGNUMID_13 },
+    { 14, REGNUMID_14 },
+    { 15, REGNUMID_15 },
+};
+
 PUBLIC AlsaLoopSubdevT *ApiLoopFindSubdev(SoftMixerT *mixer, const char *streamUid, const char *targetUid, AlsaSndLoopT **loop) {
 
     // Either allocate a free loop subdev or search for a specific targetUid when specified
@@ -55,6 +97,90 @@ fail:
 	return NULL;
 }
 
+STATIC int CheckOneSubdev(SoftMixerT *mixer, AlsaSndLoopT *loop, AlsaLoopSubdevT *subdev) {
+    // create loop subdev entry point with cardidx+device+subdev in order to open subdev and not sndcard
+    AlsaDevInfoT loopSubdev;
+    loopSubdev.devpath=NULL;
+    loopSubdev.cardid=NULL;
+    loopSubdev.pcmplug_params = NULL;
+    loopSubdev.cardidx = loop->sndcard->cid.cardidx;
+    loopSubdev.device = loop->capture;
+    loopSubdev.subdev = subdev->index;
+
+    // assert we may open this loopback subdev in capture mode
+    AlsaPcmCtlT *pcmCtl = AlsaByPathOpenPcmCtl(mixer, &loopSubdev, SND_PCM_STREAM_CAPTURE);
+    if (!pcmCtl) {
+        AFB_API_ERROR(mixer->api, "%s: Failed", __func__);
+        return -1;
+    }
+
+    pcmCtl->closeAtDeletion = true;
+
+    // free PCM as we only open loop to assert it's a valid capture device
+    AlsaMixerTransactionObjectForget(mixer->transaction, pcmCtl);
+    AlsaPcmCtlDelete(mixer, pcmCtl);
+
+    return 0;
+}
+
+STATIC AlsaLoopSubdevT *ProcessOneAvirtSubdev(SoftMixerT *mixer, AlsaSndLoopT *loop, json_object *streamJ, int index) {
+    char *uid, *zone_uid;
+    AlsaSndZoneT *zone;
+    AFB_API_INFO(mixer->api, "%s: %d", __func__, index);
+    int error;
+
+    uid = alloca(32);
+
+    error = wrap_json_unpack(streamJ, "{ss,s?s,s?s,ss,s?s,s?i,s?b,s?o,s?s !}"
+            , "uid", &uid
+            , "verb", NULL
+            , "info", NULL
+            , "zone", &zone_uid
+            , "source", NULL
+            , "volume", NULL
+            , "mute", NULL
+            , "params", NULL
+            , "ramp", NULL
+            );
+    if (error) {
+        AFB_API_NOTICE(mixer->api,
+                       "%s: hal=%s missing 'uid|[info]|zone|source||[volume]|[mute]|[params]' error=%s stream=%s",
+                       __func__, uid, wrap_json_get_error_string(error), json_object_get_string(streamJ));
+        goto OnErrorExit;
+    }
+
+    if (mixer->nbZones != 0) {
+        zone = ApiZoneGetByUid(mixer, zone_uid);
+        if (!zone)
+          goto OnErrorExit;
+    } else {
+        AFB_API_ERROR(mixer->api, "%s: No zones defined!", __func__);
+        goto OnErrorExit;
+    }
+
+    error = snd_avirt_stream_new(uid, zone->ccount,
+                                 SND_PCM_STREAM_PLAYBACK, "ap_loopback");
+    if (error < 0) {
+        AFB_API_ERROR(mixer->api,
+        "%s: mixer=%s stream=%s could not create AVIRT stream [errno=%d]",
+        __func__, mixer->uid, uid, error);
+        return NULL;
+    }
+
+    AlsaLoopSubdevT *subdev = calloc(1, sizeof (AlsaPcmCtlT));
+    subdev->uid = NULL;
+    subdev->index = index;
+    subdev->numid = numidmap[index].index;
+
+    if (CheckOneSubdev(mixer, loop, subdev) < 0)
+      return NULL;
+
+    return subdev;
+
+OnErrorExit:
+    AFB_API_ERROR(mixer->api, "%s fail", __func__);
+    return NULL;
+}
 
 STATIC AlsaLoopSubdevT *ProcessOneSubdev(SoftMixerT *mixer, AlsaSndLoopT *loop, json_object *subdevJ) {
 
@@ -87,26 +213,8 @@ STATIC AlsaLoopSubdevT *ProcessOneSubdev(SoftMixerT *mixer, AlsaSndLoopT *loop,
 		}
 	}
 
-    // create loop subdev entry point with cardidx+device+subdev in order to open subdev and not sndcard
-    AlsaDevInfoT loopSubdev;
-    loopSubdev.devpath=NULL;
-    loopSubdev.cardid=NULL;
-    loopSubdev.pcmplug_params = NULL;
-    loopSubdev.cardidx = loop->sndcard->cid.cardidx;
-    loopSubdev.device = loop->capture;
-    loopSubdev.subdev = subdev->index;
-
-    // assert we may open this loopback subdev in capture mode
-	AlsaPcmCtlT *pcmCtl = AlsaByPathOpenPcmCtl(mixer, &loopSubdev, SND_PCM_STREAM_CAPTURE);
-	if (!pcmCtl) {
-		goto fail_subdev_uid;
-	}
-
-	pcmCtl->closeAtDeletion = true;
-
-    // free PCM as we only open loop to assert it's a valid capture device
-	AlsaMixerTransactionObjectForget(mixer->transaction, pcmCtl);
-	AlsaPcmCtlDelete(mixer, pcmCtl);
+    if (CheckOneSubdev(mixer, loop, subdev) < 0)
+      goto fail_subdev_uid;
 
 	AFB_API_DEBUG(mixer->api, "%s DONE", __func__);
 
@@ -126,7 +234,7 @@ static void freeSubdev(SoftMixerT* mixer, AlsaLoopSubdevT * subdev) {
 }
 
 
-STATIC AlsaSndLoopT *AttachOneLoop(SoftMixerT *mixer, const char *uid, json_object *argsJ) {
+STATIC AlsaSndLoopT *AttachOneLoop(SoftMixerT *mixer, const char *uid, json_object *argsJ, json_object *streamsJ) {
 
     json_object *subdevsJ = NULL, *devicesJ = NULL;
     int error;
@@ -152,67 +260,122 @@ STATIC AlsaSndLoopT *AttachOneLoop(SoftMixerT *mixer, const char *uid, json_obje
 
 	loop->sndcard = sndctl;
 
-    error = wrap_json_unpack(argsJ, "{ss,s?s,s?s,so,so !}"
+    error = wrap_json_unpack(argsJ, "{ss,s?s,s?s,s?o,s?o !}"
             , "uid", &loop->uid
             , "path", &loop->sndcard->cid.devpath
             , "cardid", &loop->sndcard->cid.cardid
             , "devices", &devicesJ
             , "subdevs", &subdevsJ
             );
-    if (error || !loop->uid || !subdevsJ || (!loop->sndcard->cid.devpath && !loop->sndcard->cid.cardid)) {
-        AFB_API_NOTICE(mixer->api, "%s mixer=%s hal=%s missing 'uid|path|cardid|devices|subdevs' error=%s args=%s",
-        		__func__, mixer->uid, uid, wrap_json_get_error_string(error),json_object_get_string(argsJ));
-		goto fail_snd_card;
+
+    if (loop->uid) {
+        if (!strcmp(loop->uid, UID_AVIRT_LOOP))
+            loop->avirt = true;
+        else
+            loop->avirt = false;
     }
 
-    // try to open sound card control interface
-    loop->sndcard->ctl = AlsaByPathOpenCtl(mixer, loop->uid, loop->sndcard);
-    if (!loop->sndcard->ctl) {
-        AFB_API_ERROR(mixer->api, "%s mixer=%s hal=%s Fail open sndcard loop=%s devpath=%s cardid=%s (please check 'modprobe snd_aloop')",
-        		__func__, mixer->uid, uid, loop->uid, loop->sndcard->cid.devpath, loop->sndcard->cid.cardid);
+    if (error || !loop->uid || (!loop->avirt && !subdevsJ) || (!loop->sndcard->cid.devpath && !loop->sndcard->cid.cardid)) {
+        AFB_API_NOTICE(mixer->api, "%s mixer=%s hal=%s missing 'uid|path|cardid|devices|subdevs' error=%s args=%s",
+        		__func__, mixer->uid, uid, wrap_json_get_error_string(error),json_object_get_string(argsJ));
 		goto fail_snd_card;
     }
 
-	// Default devices is playback=0 capture=1
-    if (!devicesJ) {
-        loop->playback = 0;
-        loop->capture = 1;
-    } else {
-        error = wrap_json_unpack(devicesJ, "{si,si !}", "capture", &loop->capture, "playback", &loop->playback);
-        if (error) {
-            AFB_API_NOTICE(mixer->api, "%s mixer=%s hal=%s Loop=%s missing 'capture|playback' error=%s devices=%s",
-            		__func__, mixer->uid, uid, loop->uid, wrap_json_get_error_string(error),json_object_get_string(devicesJ));
-			goto fail_snd_card_ctl;
+    if (!loop->avirt) {
+        // try to open sound card control interface
+        loop->sndcard->ctl = AlsaByPathOpenCtl(mixer, loop->uid, loop->sndcard);
+        if (!loop->sndcard->ctl) {
+            AFB_API_ERROR(mixer->api, "%s mixer=%s hal=%s Fail open sndcard loop=%s devpath=%s cardid=%s (please check 'modprobe snd_aloop')",
+                __func__, mixer->uid, uid, loop->uid, loop->sndcard->cid.devpath, loop->sndcard->cid.cardid);
+            goto fail_snd_card;
         }
-    }
 
-	AlsaLoopSubdevT * subdev;
+        // Default devices is playback=0 capture=1
+        if (!devicesJ) {
+            loop->playback = 0;
+            loop->capture = 1;
+        } else {
+            error = wrap_json_unpack(devicesJ, "{si,si !}", "capture", &loop->capture, "playback", &loop->playback);
+            if (error) {
+                AFB_API_NOTICE(mixer->api, "%s mixer=%s hal=%s Loop=%s missing 'capture|playback' error=%s devices=%s",
+                    __func__, mixer->uid, uid, loop->uid, wrap_json_get_error_string(error),json_object_get_string(devicesJ));
+                goto fail_snd_card_ctl;
+            }
+        }
 
-    switch (json_object_get_type(subdevsJ)) {
-        case json_type_object:
-			subdev = ProcessOneSubdev(mixer, loop, subdevsJ);
-			if (!subdev)
-				goto fail_loop_subdev;
-			loop->nbSubdevs++;
-			cds_list_add_tail(&subdev->list, &loop->subdevs.list);
-            break;
-		case json_type_array: {
-			int nbSubDevs = (int) json_object_array_length(subdevsJ);
-			for (int idx = 0; idx < nbSubDevs; idx++) {
-                json_object *subdevJ = json_object_array_get_idx(subdevsJ, idx);
-				subdev = ProcessOneSubdev(mixer, loop, subdevJ);
-				if (!subdev) {
-					goto fail_loop_subdev;
-				}
-				loop->nbSubdevs++;
-				cds_list_add_tail(&subdev->list, &loop->subdevs.list);
+        AlsaLoopSubdevT * subdev;
+
+        switch (json_object_get_type(subdevsJ)) {
+            case json_type_object:
+                subdev = ProcessOneSubdev(mixer, loop, subdevsJ);
+                if (!subdev)
+                    goto fail_loop_subdev;
+                loop->nbSubdevs++;
+                cds_list_add_tail(&subdev->list, &loop->subdevs.list);
+                break;
+            case json_type_array: {
+                int nbSubDevs = (int) json_object_array_length(subdevsJ);
+                for (int idx = 0; idx < nbSubDevs; idx++) {
+                    json_object *subdevJ = json_object_array_get_idx(subdevsJ, idx);
+                    subdev = ProcessOneSubdev(mixer, loop, subdevJ);
+                    if (!subdev) {
+                        goto fail_loop_subdev;
+                    }
+                    loop->nbSubdevs++;
+                    cds_list_add_tail(&subdev->list, &loop->subdevs.list);
+                }
+                break;
             }
-            break;
-		}
-        default:
-            AFB_API_ERROR(mixer->api, "%s mixer=%s hal=%s Loop=%s invalid subdevs= %s",
-            		__func__, mixer->uid, uid, loop->uid, json_object_get_string(subdevsJ));
-			goto fail_snd_card_ctl;
+            default:
+                AFB_API_ERROR(mixer->api, "%s mixer=%s hal=%s Loop=%s invalid subdevs= %s",
+                    __func__, mixer->uid, uid, loop->uid, json_object_get_string(subdevsJ));
+                goto fail_snd_card_ctl;
+        }
+    } else { // loop->avirt == true
+        AFB_API_NOTICE(mixer->api, "nbStreams: %d max.streams: %d", mixer->nbStreams, mixer->max.streams);
+
+        if (mixer->nbStreams >= mixer->max.streams)
+            goto fail_snd_card_ctl;
+
+        AlsaLoopSubdevT * subdev;
+
+        // Create AVIRT streams
+        switch (json_object_get_type(streamsJ)) {
+            case json_type_object:
+                subdev = ProcessOneAvirtSubdev(mixer, loop, streamsJ, 0);
+                if (!subdev)
+                    goto fail_loop_subdev;
+                loop->nbSubdevs++;
+                cds_list_add_tail(&subdev->list, &loop->subdevs.list);
+                break;
+            case json_type_array: {
+                int nbSubDevs = (int) json_object_array_length(streamsJ);
+                if (nbSubDevs >= mixer->max.streams)
+                    goto fail_loop_subdev;
+                for (int idx = 0; idx < nbSubDevs; idx++) {
+                    json_object *streamJ = json_object_array_get_idx(streamsJ, idx);
+                    subdev = ProcessOneAvirtSubdev(mixer, loop, streamJ, idx);
+                    if (!subdev) {
+                        goto fail_loop_subdev;
+                    }
+                    loop->nbSubdevs++;
+                    cds_list_add_tail(&subdev->list, &loop->subdevs.list);
+                }
+                break;
+            }
+            default:
+                goto fail_snd_card_ctl;
+        }
+
+        snd_avirt_card_seal();
+
+        // try to open sound card control interface
+        loop->sndcard->ctl = AlsaByPathOpenCtl(mixer, loop->uid, loop->sndcard);
+        if (!loop->sndcard->ctl) {
+            AFB_API_ERROR(mixer->api, "%s mixer=%s hal=%s Fail open sndcard loop=%s devpath=%s cardid=%s (please check 'modprobe snd_aloop')",
+                __func__, mixer->uid, uid, loop->uid, loop->sndcard->cid.devpath, loop->sndcard->cid.cardid);
+            goto fail_snd_card;
+        }
     }
 
 	AFB_API_NOTICE(mixer->api, "%s, uid %s DONE", __func__, uid);
@@ -258,9 +421,9 @@ static void loopDestroy(SoftMixerT * mixer, void* arg) {
 
 }
 
-static AlsaSndLoopT * loopCreate(SoftMixerT *mixer, const char *uid, json_object *argsJ) {
+static AlsaSndLoopT * loopCreate(SoftMixerT *mixer, const char *uid, json_object *argsJ, json_object *streamsJ) {
 
-	AlsaSndLoopT * newLoop = AttachOneLoop(mixer, uid, argsJ);
+	AlsaSndLoopT * newLoop = AttachOneLoop(mixer, uid, argsJ, streamsJ);
 	if (!newLoop) {
 		goto fail;
 	}
@@ -276,7 +439,7 @@ fail:
 	return newLoop;
 }
 
-PUBLIC int ApiLoopAttach(SoftMixerT *mixer, afb_req_t request, const char * uid, json_object * argsJ) {
+PUBLIC int ApiLoopAttach(SoftMixerT *mixer, afb_req_t request, const char * uid, json_object * argsJ, json_object *streamsJ) {
 
 	AlsaSndLoopT * newLoop = NULL;
 
@@ -289,7 +452,7 @@ PUBLIC int ApiLoopAttach(SoftMixerT *mixer, afb_req_t request, const char * uid,
             size_t count;
 
         case json_type_object:
-			newLoop = loopCreate(mixer, uid, argsJ);
+			newLoop = loopCreate(mixer, uid, argsJ, streamsJ);
 			if (!newLoop) {
 				goto fail;
             }
@@ -304,7 +467,7 @@ PUBLIC int ApiLoopAttach(SoftMixerT *mixer, afb_req_t request, const char * uid,
 
             for (int idx = 0; idx < count; idx++) {
                 json_object *loopJ = json_object_array_get_idx(argsJ, idx);
-				newLoop = loopCreate(mixer, uid, loopJ);
+				newLoop = loopCreate(mixer, uid, loopJ, streamsJ);
 				if (newLoop == NULL) {
 					goto fail_loop;
                 }
diff --git a/plugins/alsa/alsa-api-mixer.c b/plugins/alsa/alsa-api-mixer.c
index e892b2f..ebb8c25 100644
--- a/plugins/alsa/alsa-api-mixer.c
+++ b/plugins/alsa/alsa-api-mixer.c
@@ -27,6 +27,9 @@ static struct cds_list_head mixerList;
 
 static void MixerDelete(SoftMixerT * mixer);
 
+// AVIRT: temporary loops JSON
+static json_object *LoopsJ = NULL;
+
 static void MixerExit() {
 	SoftMixerT *mixer, *tmp;
 	printf("%s !\n", __func__);
@@ -575,13 +578,6 @@ STATIC void MixerAttachVerb(afb_req_t request) {
 
 	mixer->transaction = transaction;
 
-    AFB_API_INFO(mixer->api, "%s set LOOPS", __func__);
-
-    if (loopsJ) {
-        error = ApiLoopAttach(mixer, request, uid, loopsJ);
-		if (error) goto fail;
-    }
-    
 	AFB_API_INFO(mixer->api, "%s set PLAYBACKS", __func__);
 
     if (playbacksJ) {
@@ -616,6 +612,16 @@ STATIC void MixerAttachVerb(afb_req_t request) {
         json_object_object_add(responseJ, "zone", resultJ);
     }
 
+    // In AVIRT mode, we require both the loops and streams JSON objects to
+    // construct the loopbacks, so when the loops are set, but the streams
+    // are not, we need to save the loops until the streams are given to us
+    if (streamsJ && (loopsJ || LoopsJ)) {
+        AFB_API_INFO(mixer->api, "%s set LOOPS/AVIRT", __func__);
+        error = ApiLoopAttach(mixer, request, uid,
+                              ((loopsJ) ? loopsJ : LoopsJ), streamsJ);
+        if (error) goto fail_loop;
+    }
+
     AFB_API_INFO(mixer->api, "%s set RAMPS", __func__);
 
     if (rampsJ) {
@@ -657,12 +663,12 @@ fail_ramp:
 	// TODO remove created ramps
 fail_zone:
 	// TODO remove created zone
+fail_loop:
+	// TODO remove created loops
 fail_source:
 	// TODO remove created sources
 fail_sink:
 	// TODO remove created sinks
-fail_loop:
-	// TODO remove created loops
 fail:
 
 	if (mixer->transaction)
@@ -734,9 +740,14 @@ CTLP_CAPI(MixerAttach, source, argsJ, responseJ) {
         if (error) goto OnErrorExit;
     }
 
-    if (loopsJ) {
-        error = ApiLoopAttach(mixer, NULL, uid, loopsJ);
+    // In AVIRT mode, we require both the loops and streams JSON objects to
+    // construct the loopbacks, so when the loops are set, but the streams
+    // are not, we need to save the loops until the streams are given to us
+    if (loopsJ && streamsJ) {
+        error = ApiLoopAttach(mixer, NULL, uid, loopsJ, streamsJ);
         if (error) goto OnErrorExit;
+    } else {
+      LoopsJ = loopsJ;
     }
 
     if (zonesJ) {
diff --git a/plugins/alsa/alsa-api-streams.c b/plugins/alsa/alsa-api-streams.c
index c1fb749..edf506e 100644
--- a/plugins/alsa/alsa-api-streams.c
+++ b/plugins/alsa/alsa-api-streams.c
@@ -19,6 +19,7 @@
 #define _GNU_SOURCE  // needed for vasprintf
 
 #include "alsa-softmixer.h"
+#include <avirt/avirt.h>
 
 #include <string.h>
 #include <stdbool.h>
@@ -231,6 +232,7 @@ STATIC int CreateOneStream(SoftMixerT *mixer, const char * uid, AlsaStreamAudioT
     char *volName = NULL;
     int pauseNumid = 0;
     int volNumid = 0;
+    int device, subdev;
 
 	AFB_API_DEBUG(mixer->api,
 				"NEW STREAM stream %s %s, source %s, sink %s, mute %d",
@@ -238,12 +240,20 @@ STATIC int CreateOneStream(SoftMixerT *mixer, const char * uid, AlsaStreamAudioT
 
     loopDev = ApiLoopFindSubdev(mixer, stream->uid, stream->source, &loop);
     if (loopDev) {
+        if (loop->avirt) {
+            device = loopDev->index;
+            subdev = 0;
+        } else { // loop->avirt == false
+            device = loop->capture;
+            subdev = loopDev->index;
+        }
+
         // create a valid PCM reference and try to open it.
         captureDev->devpath = NULL;
         captureDev->cardid = NULL;
         captureDev->cardidx = loop->sndcard->cid.cardidx;
-        captureDev->device = loop->capture;
-        captureDev->subdev = loopDev->index;
+        captureDev->device = device;
+        captureDev->subdev = subdev;
         captureDev->pcmplug_params = NULL;
         captureCard = loop->sndcard;
 
@@ -476,11 +486,10 @@ STATIC int CreateOneStream(SoftMixerT *mixer, const char * uid, AlsaStreamAudioT
     }
 
     if (loop) {
-		if (asprintf((char**) &stream->source, "hw:%d,%d,%d", captureDev->cardidx, loop->playback, capturePcm->cid.subdev) == -1) {
-			SOFTMIXER_NOMEM(mixer->api);
-			goto OnErrorExit;
-		}
-
+        int device = (loop->avirt) ? captureDev->device
+                                   : loop->playback;
+        if (asprintf((char**) &stream->source, "hw:%d,%d,%d", captureDev->cardidx, device, capturePcm->cid.subdev) == -1)
+            goto OnErrorExit;
     } else {
 		if (asprintf((char**) &stream->source, "hw:%d,%d,%d", captureDev->cardidx, captureDev->device, captureDev->subdev) == -1) {
 			SOFTMIXER_NOMEM(mixer->api);
diff --git a/plugins/alsa/alsa-softmixer.h b/plugins/alsa/alsa-softmixer.h
index b6c0e5b..2fb9370 100644
--- a/plugins/alsa/alsa-softmixer.h
+++ b/plugins/alsa/alsa-softmixer.h
@@ -242,7 +242,7 @@ typedef struct {
 
 typedef struct {
     char * uid;
-    int index;
+    int index; // AVIRT: parent PCM index (Since subdev idx is always 0)
     int numid;
 	struct cds_list_head list;
 } AlsaLoopSubdevT;
@@ -251,10 +251,11 @@ typedef struct {
 struct SoftMixerT_;
 
 typedef struct AlsaSndLoopT {
+    bool avirt; // AVIRT: Is this loop AVIRT?
     const char *uid;
 	struct SoftMixerT_ * mixer; /* owner */
-    int playback;
-    int capture;
+    int playback; // AVIRT: UNUSED
+    int capture; // AVIRT: UNUSED
     AlsaSndCtlT *sndcard;
 	int nbSubdevs;
 	AlsaLoopSubdevT subdevs;
@@ -368,7 +369,7 @@ PUBLIC AlsaPcmCtlT* AlsaCreateDmix(SoftMixerT *mixer, const char* pcmName, AlsaS
 
 // alsa-api-*
 
-PUBLIC int ApiLoopAttach(SoftMixerT *mixer, afb_req_t request, const char *, json_object * argsJ);
+PUBLIC int ApiLoopAttach(SoftMixerT *mixer, afb_req_t request, const char *, json_object * argsJ, json_object *streamsJ);
 PUBLIC int ApiSourceAttach(SoftMixerT *mixer, afb_req_t request, const char *, json_object * argsJ);
 PUBLIC int ApiSinkAttach(SoftMixerT *mixer, afb_req_t request, const char *, json_object * argsJ);
 PUBLIC int ApiStreamAttach(SoftMixerT *mixer, afb_req_t request, const char * uid, const char *prefix, json_object * argsJ);