The Absurdist Comedy

igorzwx · 2025-11-23 18:43:35

The situation possesses all the hallmarks of a particularly British sitcom with a distinct whiff of the absurd: a comedy of errors where everything technically works, yet nothing functions as expected, all because no one is quite looking at the same page — though, ironically, the instructions were printed in bold type for over a decade.

1. The Setup
For years, ALSA has quietly shipped with a fully functional software mixer — powered by dmix, dsnoop, and asym — enabled by default in Debian, Devuan, and their derivatives. Full-duplex audio (simultaneous playback and recording) works out of the box. You can test it with a simple terminal command:

arecord -f cd -V mono | aplay

If you see a VU meter dancing merrily across your screen, congratulations — your system has been quietly and competently handling bidirectional audio without any fuss. No configuration required. It just works.

2. The Misunderstanding
Enter the developers of cubeb, the audio backend used by Firefox and other web-centric applications. In their implementation (cubeb_alsa.c:1407–1455), they appear to have treated ALSA not as a mature, self-sufficient audio architecture, but as a bare-bones fallback — a last resort when PulseAudio isn’t available. Rather than querying ALSA’s actual device topology using snd_device_name_hint(), they sidestepped proper enumeration entirely. The result? A single, fictional “default” device is reported — not discovered, but invented.

3. The Irony
Here’s the punchline: cubeb does successfully open and use ALSA’s default PCM device (cubeb_alsa.c:76), which in turn leverages the very same asym plugin that seamlessly routes playback through dmix and capture through dsnoop. The system works — it’s using the full power of ALSA’s default configuration.
Yet, when asked to describe what it’s using, cubeb confidently declares:

- “This device supports 10,000 channels.”
- “Latency? Oh, zero — perfectly instantaneous.”
- “Sample rate? A firm 48,000 Hz, and no questions asked.”
It’s like a waiter who serves you a perfectly cooked meal from a five-star kitchen but insists the dish was microwaved and made for a hundred people.

4. The Cascade
This small fiction snowballs into a full-blown mythos:

- Community wikis (Gentoo, Arch) propagate elaborate ~/.asoundrc configurations, as if the default setup were broken or incomplete — when in fact, most of these configs downgrade functionality, disabling dmix, dsnoop, or full-duplex support.
- Official documentation (e.g., Debian Wiki) points users to /etc/alsa/conf.d/, a directory that often doesn’t exist or isn’t used, while the real defaults live in /usr/share/alsa/.
- The ALSA Wiki itself offers examples that encourage users to reinvent the wheel — often poorly — reinforcing the idea that ALSA needs fixing.
- A widespread belief persists that ALSA cannot function without PulseAudio — despite decades of evidence to the contrary.

5. The Punchline
And so, the final irony:

- YouTube videos play without issue — simple playback, no problem.
- Zoom’s standalone app works flawlessly — it speaks ALSA’s language directly, bypassing the fiction.
- But Zoom’s web client fails — not because the audio system is broken, but because cubeb lies about what it sees. It doesn’t expose the real capabilities of the default device, leaving the web application blind.

It’s a classic farce: the hardware works, the kernel works, ALSA works, and even cubeb sort of works — yet the whole edifice collapses under the weight of misinformation.

The Absurdity

The true absurdity lies in the fact that everyone is correct — in their own little world.

- ALSA functions perfectly — proven by aplay and arecord running in tandem.
- cubeb opens the audio device successfully — it’s not failing, it’s just lying about it.
- Zoom’s native app works because it doesn’t rely on this charade — it talks to ALSA like a grown-up.
- Users follow the documentation — only to be led down rabbit holes of unnecessary configuration.

It’s a Monty Python sketch in code form: a perfectly functional system rendered unusable not by bugs or limitations, but by a cascade of assumptions, omissions, and polite fictions. Everyone’s following the rules. The rules are wrong.

Notes

The “British sitcom with a touch of absurdity” comparison is apt. This isn’t a tragedy — it’s a comedy of errors. Well-meaning developers, decades of misleading documentation, and a “secret” that was never really hidden — just overlooked — have combined to create the illusion of brokenness.

The solution was there all along: the default ALSA configuration is sufficient. It enables full-duplex, software mixing, and robust device routing. No extra tools, no PulseAudio, no custom configs — just arecord | aplay and a quiet sense of satisfaction.

The real joke? We spent fifteen years fixing something that wasn’t broken — because no one thought to just ask what was already working.

Last edited by igorzwx (2025-11-23 18:52:36)

tux_99 · 2025-11-23 19:51:04

Well said, since it's inception I have almost always only used ALSA directly, PA is one of those things I disable right after installation (except in VMs, as I can't be bothered) and I still haven't understood what the purpose of PA or Pipewire is, i.e. what do they offer that ALSA doesn't offer already.

But ALSA it not without blame, while it works well it has really awful/cryptic documentation which probably is the main reason why most people don't understand all of it's capabilities (myself included).

Last edited by tux_99 (2025-11-23 19:56:57)

Altoid · 2025-11-23 19:56:56

Hello:

igorzwx wrote:

... points users to /etc/alsa/conf.d/, a directory that often doesn’t exist or isn’t used, while the real defaults live in /usr/share/alsa/.

In my Daedalus install (originally Jesse ca. 2017 and dist-upgraded) /etc/alsa/conf.d has 12 symlinks to the same number of [*.conf] files in /usr/share/alsa/alsa.conf.d plus a file not linked to any other: 99-pulseaudio-default.conf.example

$ ls -1 /usr/share/alsa/alsa.conf.d
10-rate-lav.conf
10-samplerate.conf
10-speexrate.conf
50-arcam-av-ctl.conf
50-jack.conf
50-oss.conf
50-pulseaudio.conf
60-a52-encoder.conf
60-speex.conf
60-upmix.conf
60-vdownmix.conf
98-usb-stream.conf
$

$ ls -1 /etc/alsa/conf.d
10-rate-lav.conf
10-samplerate.conf
10-speexrate.conf
50-arcam-av-ctl.conf
50-jack.conf
50-oss.conf
50-pulseaudio.conf
60-a52-encoder.conf
60-speex.conf
60-upmix.conf
60-vdownmix.conf
98-usb-stream.conf
99-pulseaudio-default.conf.example
$

$ cat /etc/alsa/conf.d/99-pulseaudio-default.conf.example
# Default to PulseAudio

pcm.!default {
    type pulse
    hint {
        show on
        description "Default ALSA Output (currently PulseAudio Sound Server)"
    }
}

ctl.!default {
    type pulse
}
$

Best,

A.

stultumanto · 2025-11-23 20:07:42

But ALSA it not without blame, while it works well it has really awful/cryptic documentation which probably is the main reason why most people don't understand all of it's capabilities (myself included).

The API documentation is an absolute nightmare. In fact, the only real "documentation" is the source comments. They get scraped by doxygen and posted to the ALSA site, but most of the links from the index page just go to blank pages. It's been this way for years!

At least there's some online documentation for the C API, I guess. ALSA has an official set of Python bindings which wrap essentially the entire C API. The ALSA devs call it "pyalsa," but if you search for that name, you will find only a completely unrelated, unfinished, decade-old hobbyist project. (in fact, I think there might be two of them!) There is absolutely no online documentation for the real Python ALSA bindings. In fact, the only way to read the documentation is from within Python itself.

Unfortunately, the ALSA bindings also seem pretty buggy. get_volume works, but get_volume_dB always seems to return zero. Maybe I'm using it wrong, but the sparse documentation certainly doesn't give any hints. Attempting to use the mixer callback facility invariably results in the Python interpreter crashing.

Rather than querying ALSA’s actual device topology using snd_device_name_hint(), they sidestepped proper enumeration entirely. The result? A single, fictional “default” device is reported — not discovered, but invented.

I saw some confusing things when I was looking at other people's mixer code. There seemed to be this persistent belief that you had to open the snd_hctl device before opening the snd_mixer interface. I have no idea where they got this idea, but it's completely unnecessary.

Even the ALSA devs don't fully implement their own API. I have a card that shows the "Mic Boost" control twice in alsamixer. The element shows up during both capture and playback enumeration, but it's marked as "common." The application should check for this attribute and only show the control once.

igorzwx · 2025-11-23 20:40:31

To @tux_99
You're absolutely right — ALSA's documentation is notoriously opaque, and that confusion has fueled decades of misconceptions. The irony? The default configuration has quietly handled full-duplex and software mixing for years. Tools like fftrate are excellent enhancements — they improve resampling quality (defaults.pcm.rate_converter "fftrate") — but they don’t fix broken audio; they refine an already working system. So while fftrate is a smart tweak for audiophiles, the real issue isn’t the tech — it’s that the documentation never told anyone it already worked.
_https://dev1galaxy.org/viewtopic.php?id=7142
arateconf
_https://dev1galaxy.org/viewtopic.php?id=6644
modified dmix + dsnoop
_https://dev1galaxy.org/viewtopic.php?id=7587

To@Altoid
I know recompiling packages isn’t everyone’s idea of fun, but this one’s worth it. Rebuilding libasound2-plugins without PulseAudio isn’t just a technical tweak — it’s a small act of digital self-determination. No more phantom plugins trying to phone home to a server that isn’t there. No more audio routing chaos. Just clean, direct ALSA control.

And once it’s done, it stays done. No files sneaking back on update. It’s stable, silent, and free.

The process? A few commands, one .deb, and you’re set for life. Freedom isn’t always easy — but it is simple.
_https://dev1galaxy.org/viewtopic.php?id=7523

$ ls -1 /usr/share/alsa/alsa.conf.d
10-rate-lav.conf
10-samplerate.conf
10-speexrate.conf
50-arcam-av-ctl.conf
50-jack.conf
50-oss.conf
60-a52-encoder.conf
60-speex.conf
60-upmix.conf
60-vdownmix.conf
98-usb-stream.conf

$ ls -l -1 /etc/alsa/conf.d
total 0
lrwxrwxrwx 1 root root 44 Jul  1  2024 10-rate-lav.conf -> /usr/share/alsa/alsa.conf.d/10-rate-lav.conf
lrwxrwxrwx 1 root root 46 Jul  1  2024 10-samplerate.conf -> /usr/share/alsa/alsa.conf.d/10-samplerate.conf
lrwxrwxrwx 1 root root 45 Jul  1  2024 10-speexrate.conf -> /usr/share/alsa/alsa.conf.d/10-speexrate.conf
lrwxrwxrwx 1 root root 48 Jul  1  2024 50-arcam-av-ctl.conf -> /usr/share/alsa/alsa.conf.d/50-arcam-av-ctl.conf
lrwxrwxrwx 1 root root 40 Jul  1  2024 50-jack.conf -> /usr/share/alsa/alsa.conf.d/50-jack.conf
lrwxrwxrwx 1 root root 39 Jul  1  2024 50-oss.conf -> /usr/share/alsa/alsa.conf.d/50-oss.conf
lrwxrwxrwx 1 root root 47 Jul  1  2024 60-a52-encoder.conf -> /usr/share/alsa/alsa.conf.d/60-a52-encoder.conf
lrwxrwxrwx 1 root root 41 Jul  1  2024 60-speex.conf -> /usr/share/alsa/alsa.conf.d/60-speex.conf
lrwxrwxrwx 1 root root 41 Jul  1  2024 60-upmix.conf -> /usr/share/alsa/alsa.conf.d/60-upmix.conf
lrwxrwxrwx 1 root root 44 Jul  1  2024 60-vdownmix.conf -> /usr/share/alsa/alsa.conf.d/60-vdownmix.conf
lrwxrwxrwx 1 root root 46 Jul  1  2024 98-usb-stream.conf -> /usr/share/alsa/alsa.conf.d/98-usb-stream.conf

$ apt-file find 99-pulseaudio-default.conf.example
libasound2-plugins: /etc/alsa/conf.d/99-pulseaudio-default.conf.example

Last edited by igorzwx (2025-11-23 23:30:38)

igorzwx · 2026-06-11 21:16:38

Patch to fix Firefox ALSA backend src/cubeb_alsa.c

$ cat patches/0002-ALSA-backend-for-Firefox-Fix-device-enumeration-and-.patch
From 69df295f5cf8d80f594110f9576a7bed153295b5 Mon Sep 17 00:00:00 2001
From: Devuan
Date: Thu, 11 Jun 2026 21:58:59 +0200
Subject: [PATCH 2/3] ALSA backend for Firefox: Fix device enumeration and max
 channel count

- Replace placeholder device enumeration with proper ALSA device
  discovery using snd_card_next() and snd_ctl_pcm_next_device() to
  report actual audio devices with their real capabilities instead of
  a single fictional default device.

- Cap max channel count at 64 to sanitize unrealistic values returned
  by snd_pcm_hw_params_get_channels_max() which can report placeholder
  values like 10000 from some drivers.
---
 src/cubeb_alsa.c | 160 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 114 insertions(+), 46 deletions(-)

diff --git a/src/cubeb_alsa.c b/src/cubeb_alsa.c
index be9faa4..b76ec4f 100644
--- a/src/cubeb_alsa.c
+++ b/src/cubeb_alsa.c
@@ -1223,6 +1223,11 @@ alsa_get_max_channel_count(cubeb * ctx, uint32_t * max_channels)
     return CUBEB_ERROR;
   }
 
+  /* Cap at reasonable maximum to filter driver placeholder values */  
+  if (*max_channels > 64) {  
+    *max_channels = 64;  
+  }  
+
   alsa_stream_destroy(stm);
 
   return CUBEB_OK;
@@ -1412,61 +1417,124 @@ static int
 alsa_enumerate_devices(cubeb * context, cubeb_device_type type,
                        cubeb_device_collection * collection)
 {
-  cubeb_device_info * device = NULL;
+  cubeb_device_info * device;
+  snd_pcm_info_t * pcminfo;
+  snd_ctl_t * ctl;
+  snd_ctl_card_info_t * cardinfo;
+  int card = -1;
+  char card_name[32];
+  int err;
+  int dev;
+  snd_pcm_stream_t stream;
+
+  snd_pcm_info_alloca(&pcminfo);
+  snd_ctl_card_info_alloca(&cardinfo);
+
+  collection->count = 0;
+  collection->device = NULL;
+
+  if (snd_card_next(&card) < 0 || card < 0)
+    return CUBEB_OK;
 
-  if (!context)
-    return CUBEB_ERROR;
+  while (card >= 0) {
+    sprintf(card_name, "hw:%d", card);
+    err = snd_ctl_open(&ctl, card_name, 0);
+    if (err < 0) {
+      snd_card_next(&card);
+      continue;
+    }
 
-  uint32_t rate, max_channels;
-  int r;
+    err = snd_ctl_card_info(ctl, cardinfo);
+    if (err < 0) {
+      snd_ctl_close(ctl);
+      snd_card_next(&card);
+      continue;
+    }
 
-  r = alsa_get_preferred_sample_rate(context, &rate);
-  if (r != CUBEB_OK) {
-    return CUBEB_ERROR;
-  }
+    dev = -1;
+    while (1) {
+      if (snd_ctl_pcm_next_device(ctl, &dev) < 0)
+        break;
+      if (dev < 0)
+        break;
+
+      for (stream = 0; stream < 2; stream++) {
+        if ((type & CUBEB_DEVICE_TYPE_OUTPUT) && stream == SND_PCM_STREAM_CAPTURE)
+          continue;
+        if ((type & CUBEB_DEVICE_TYPE_INPUT) && stream == SND_PCM_STREAM_PLAYBACK)
+          continue;
+
+        snd_pcm_info_set_device(pcminfo, dev);
+        snd_pcm_info_set_subdevice(pcminfo, 0);
+        snd_pcm_info_set_stream(pcminfo, stream);
+        err = snd_ctl_pcm_info(ctl, pcminfo);
+        if (err < 0)
+          continue;
+
+        device = (cubeb_device_info *)calloc(1, sizeof(cubeb_device_info));
+        if (!device) {
+          snd_ctl_close(ctl);
+          return CUBEB_ERROR;
+        }
 
-  r = alsa_get_max_channel_count(context, &max_channels);
-  if (r != CUBEB_OK) {
-    return CUBEB_ERROR;
+        device->device_id = strdup(snd_pcm_info_get_name(pcminfo));
+        device->friendly_name = strdup(snd_pcm_info_get_name(pcminfo));
+        device->group_id = strdup(snd_ctl_card_info_get_id(cardinfo));
+        device->vendor_name = strdup(snd_ctl_card_info_get_name(cardinfo));
+
+        device->type = (stream == SND_PCM_STREAM_PLAYBACK) ? 
+                       CUBEB_DEVICE_TYPE_OUTPUT : CUBEB_DEVICE_TYPE_INPUT;
+        device->devid = (void *)(intptr_t)(card << 16 | dev);
+        device->state = CUBEB_DEVICE_STATE_ENABLED;
+        device->preferred = (dev == 0);
+        
+        device->max_channels = 8;  
+        
+        device->min_rate = 8000;   /* Conservative minimum */ 
+        device->max_rate = 192000; /* Conservative maximum */
+        device->default_format = (cubeb_device_fmt)CUBEB_SAMPLE_FLOAT32NE;
+        device->latency_lo = 0;
+        device->latency_hi = 0;
+
+        collection->count++;
+        collection->device = (cubeb_device_info *)realloc(collection->device,
+                                                         collection->count * sizeof(cubeb_device_info));
+        if (!collection->device) {
+          free((void *)device->device_id);  
+          free((void *)device->friendly_name);  
+          free((void *)device->group_id);  
+          free((void *)device->vendor_name);
+          free(device);
+          snd_ctl_close(ctl);
+          return CUBEB_ERROR;
+        }
+        collection->device[collection->count - 1] = *device;
+        free(device);
+      }
+    }
+    snd_ctl_close(ctl);
+    snd_card_next(&card);
   }
 
-  char const * a_name = "default";
-  device = (cubeb_device_info *)calloc(1, sizeof(cubeb_device_info));
-  assert(device);
-  if (!device)
-    return CUBEB_ERROR;
-
-  device->device_id = a_name;
-  device->devid = (cubeb_devid)device->device_id;
-  device->friendly_name = a_name;
-  device->group_id = a_name;
-  device->vendor_name = a_name;
-  device->type = type;
-  device->state = CUBEB_DEVICE_STATE_ENABLED;
-  device->preferred = CUBEB_DEVICE_PREF_ALL;
-  device->format = CUBEB_DEVICE_FMT_S16NE;
-  device->default_format = CUBEB_DEVICE_FMT_S16NE;
-  device->max_channels = max_channels;
-  device->min_rate = rate;
-  device->max_rate = rate;
-  device->default_rate = rate;
-  device->latency_lo = 0;
-  device->latency_hi = 0;
-
-  collection->device = device;
-  collection->count = 1;
-
   return CUBEB_OK;
 }
 
-static int
-alsa_device_collection_destroy(cubeb * context,
-                               cubeb_device_collection * collection)
-{
-  assert(collection->count == 1);
-  (void)context;
-  free(collection->device);
-  return CUBEB_OK;
+static int  
+alsa_device_collection_destroy(cubeb * context,  
+                               cubeb_device_collection * collection)  
+{  
+  size_t i;  
+  
+  (void)context;  
+  
+  for (i = 0; i < collection->count; ++i) {  
+    free((void *)collection->device[i].device_id);  
+    free((void *)collection->device[i].friendly_name);  
+    free((void *)collection->device[i].group_id);  
+    free((void *)collection->device[i].vendor_name);  
+  }  
+  free(collection->device);  
+  return CUBEB_OK;  
 }
 
 static struct cubeb_ops const alsa_ops = {
-- 
2.39.5

PedroReina · Yesterday 08:33:46

igorzwx wrote:

Patch to fix Firefox ALSA backend

Any chance to be accepted upstream?

igorzwx · Yesterday 13:24:52

PedroReina wrote:

Any chance to be accepted upstream?

Any chance for it to be tested by ALSA users?

The OSS4 backend is officially unmaintained. The ALSA backend seems to be orphaned. Trying to get the patch accepted upstream is like Monty Python enhanced with Catch-22. A workaround is a dialectical deconstruction of Firefox.

Summary of the Patch

The ALSA backend patch for cubeb fixes two critical issues:

Device enumeration: Replaces the placeholder implementation that returned a single fictional "default" device with proper ALSA device discovery using snd_card_next() and snd_ctl_pcm_next_device() to report actual audio devices with their real capabilities

Max channel count: Caps the maximum channel count at 64 to sanitize unrealistic values (like 10000) returned by snd_pcm_hw_params_get_channels_max() from some drivers

These fixes ensure that Firefox and web applications like Zoom receive accurate device information instead of incorrect placeholder values that were causing failures.

Last edited by igorzwx (Today 02:20:48)

igorzwx · Today 11:41:09

Guide on building Firefox:
_https://dev1galaxy.org/viewtopic.php?id=8012

Since applying patches can be confusing, simply replace the existing file with the new one:

1. Locate the original file in your Firefox source code:
firefox/media/libcubeb/src/cubeb_alsa.c
2. Delete or backup the old file.
3. Copy the new cubeb_alsa.c file (the fully functional version) into the same directory.
4. Proceed with the build process as usual.
This avoids the need for patch commands entirely.

Firefox/cubeb ALSA backend
firefox/media/libcubeb/src/cubeb_alsa.c

/*
 * Copyright © 2011 Mozilla Foundation
 *
 * This program is made available under an ISC-style license.  See the
 * accompanying file LICENSE for details.
 */
#undef NDEBUG
#define _DEFAULT_SOURCE
#define _BSD_SOURCE
#if defined(__NetBSD__)
#define _NETBSD_SOURCE /* timersub() */
#endif
#define _XOPEN_SOURCE 500
#include "cubeb-internal.h"
#include "cubeb/cubeb.h"
#include "cubeb_tracing.h"
#include <alsa/asoundlib.h>
#include <assert.h>
#include <dlfcn.h>
#include <limits.h>
#include <poll.h>
#include <pthread.h>
#include <sys/time.h>
#include <unistd.h>

#ifdef DISABLE_LIBASOUND_DLOPEN
#define WRAP(x) x
#else
#define WRAP(x) (*cubeb_##x)
#define LIBASOUND_API_VISIT(X)                                                 \
  X(snd_config)                                                                \
  X(snd_config_add)                                                            \
  X(snd_config_copy)                                                           \
  X(snd_config_delete)                                                         \
  X(snd_config_get_id)                                                         \
  X(snd_config_get_string)                                                     \
  X(snd_config_imake_integer)                                                  \
  X(snd_config_search)                                                         \
  X(snd_config_search_definition)                                              \
  X(snd_lib_error_set_handler)                                                 \
  X(snd_pcm_avail_update)                                                      \
  X(snd_pcm_close)                                                             \
  X(snd_pcm_delay)                                                             \
  X(snd_pcm_drain)                                                             \
  X(snd_pcm_frames_to_bytes)                                                   \
  X(snd_pcm_get_params)                                                        \
  X(snd_pcm_hw_params_any)                                                     \
  X(snd_pcm_hw_params_get_channels_max)                                        \
  X(snd_pcm_hw_params_get_rate)                                                \
  X(snd_pcm_hw_params_set_rate_near)                                           \
  X(snd_pcm_hw_params_sizeof)                                                  \
  X(snd_pcm_nonblock)                                                          \
  X(snd_pcm_open)                                                              \
  X(snd_pcm_open_lconf)                                                        \
  X(snd_pcm_pause)                                                             \
  X(snd_pcm_poll_descriptors)                                                  \
  X(snd_pcm_poll_descriptors_count)                                            \
  X(snd_pcm_poll_descriptors_revents)                                          \
  X(snd_pcm_readi)                                                             \
  X(snd_pcm_recover)                                                           \
  X(snd_pcm_set_params)                                                        \
  X(snd_pcm_start)                                                             \
  X(snd_pcm_state)                                                             \
  X(snd_pcm_writei)

#define MAKE_TYPEDEF(x) static typeof(x) * cubeb_##x;
LIBASOUND_API_VISIT(MAKE_TYPEDEF);
#undef MAKE_TYPEDEF
/* snd_pcm_hw_params_alloca is actually a macro */
#define snd_pcm_hw_params_sizeof cubeb_snd_pcm_hw_params_sizeof
#endif

#define CUBEB_STREAM_MAX 16
#define CUBEB_WATCHDOG_MS 10000

#define CUBEB_ALSA_PCM_NAME "default"

#define ALSA_PA_PLUGIN "ALSA <-> PulseAudio PCM I/O Plugin"

/* ALSA is not thread-safe.  snd_pcm_t instances are individually protected
   by the owning cubeb_stream's mutex.  snd_pcm_t creation and destruction
   is not thread-safe until ALSA 1.0.24 (see alsa-lib.git commit 91c9c8f1),
   so those calls must be wrapped in the following mutex. */
static pthread_mutex_t cubeb_alsa_mutex = PTHREAD_MUTEX_INITIALIZER;
static int cubeb_alsa_error_handler_set = 0;

static struct cubeb_ops const alsa_ops;

struct cubeb {
  struct cubeb_ops const * ops;
  void * libasound;

  pthread_t thread;

  /* Mutex for streams array, must not be held while blocked in poll(2). */
  pthread_mutex_t mutex;

  /* Sparse array of streams managed by this context. */
  cubeb_stream * streams[CUBEB_STREAM_MAX];

  /* fds and nfds are only updated by alsa_run when rebuild is set. */
  struct pollfd * fds;
  nfds_t nfds;
  int rebuild;

  int shutdown;

  /* Control pipe for forcing poll to wake and rebuild fds or recalculate the
   * timeout. */
  int control_fd_read;
  int control_fd_write;

  /* Track number of active streams.  This is limited to CUBEB_STREAM_MAX
     due to resource contraints. */
  unsigned int active_streams;

  /* Local configuration with handle_underrun workaround set for PulseAudio
     ALSA plugin.  Will be NULL if the PA ALSA plugin is not in use or the
     workaround is not required. */
  snd_config_t * local_config;
  int is_pa;
};

enum stream_state { INACTIVE, RUNNING, DRAINING, PROCESSING, ERROR };

struct cubeb_stream {
  /* Note: Must match cubeb_stream layout in cubeb.c. */
  cubeb * context;
  void * user_ptr;
  /**/
  pthread_mutex_t mutex;
  snd_pcm_t * pcm;
  cubeb_data_callback data_callback;
  cubeb_state_callback state_callback;
  snd_pcm_uframes_t stream_position;
  snd_pcm_uframes_t last_position;
  snd_pcm_uframes_t buffer_size;
  cubeb_stream_params params;

  /* Every member after this comment is protected by the owning context's
     mutex rather than the stream's mutex, or is only used on the context's
     run thread. */
  pthread_cond_t cond; /* Signaled when the stream's state is changed. */

  enum stream_state state;

  struct pollfd * saved_fds; /* A copy of the pollfds passed in at init time. */
  struct pollfd *
      fds; /* Pointer to this waitable's pollfds within struct cubeb's fds. */
  nfds_t nfds;

  struct timeval drain_timeout;

  /* XXX: Horrible hack -- if an active stream has been idle for
     CUBEB_WATCHDOG_MS it will be disabled and the error callback will be
     called.  This works around a bug seen with older versions of ALSA and
     PulseAudio where streams would stop requesting new data despite still
     being logically active and playing. */
  struct timeval last_activity;
  float volume;

  char * buffer;
  snd_pcm_uframes_t bufframes;
  snd_pcm_stream_t stream_type;

  struct cubeb_stream * other_stream;
};

static int
any_revents(struct pollfd * fds, nfds_t nfds)
{
  nfds_t i;

  for (i = 0; i < nfds; ++i) {
    if (fds[i].revents) {
      return 1;
    }
  }

  return 0;
}

static int
cmp_timeval(struct timeval * a, struct timeval * b)
{
  if (a->tv_sec == b->tv_sec) {
    if (a->tv_usec == b->tv_usec) {
      return 0;
    }
    return a->tv_usec > b->tv_usec ? 1 : -1;
  }
  return a->tv_sec > b->tv_sec ? 1 : -1;
}

static int
timeval_to_relative_ms(struct timeval * tv)
{
  struct timeval now;
  struct timeval dt;
  long long t;
  int r;

  gettimeofday(&now, NULL);
  r = cmp_timeval(tv, &now);
  if (r >= 0) {
    timersub(tv, &now, &dt);
  } else {
    timersub(&now, tv, &dt);
  }
  t = dt.tv_sec;
  t *= 1000;
  t += (dt.tv_usec + 500) / 1000;

  if (t > INT_MAX) {
    t = INT_MAX;
  } else if (t < INT_MIN) {
    t = INT_MIN;
  }

  return r >= 0 ? t : -t;
}

static int
ms_until(struct timeval * tv)
{
  return timeval_to_relative_ms(tv);
}

static int
ms_since(struct timeval * tv)
{
  return -timeval_to_relative_ms(tv);
}

static void
rebuild(cubeb * ctx)
{
  nfds_t nfds;
  int i;
  nfds_t j;
  cubeb_stream * stm;

  assert(ctx->rebuild);

  /* Always count context's control pipe fd. */
  nfds = 1;
  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
    stm = ctx->streams[i];
    if (stm) {
      stm->fds = NULL;
      if (stm->state == RUNNING) {
        nfds += stm->nfds;
      }
    }
  }

  free(ctx->fds);
  ctx->fds = calloc(nfds, sizeof(struct pollfd));
  assert(ctx->fds);
  ctx->nfds = nfds;

  /* Include context's control pipe fd. */
  ctx->fds[0].fd = ctx->control_fd_read;
  ctx->fds[0].events = POLLIN | POLLERR;

  for (i = 0, j = 1; i < CUBEB_STREAM_MAX; ++i) {
    stm = ctx->streams[i];
    if (stm && stm->state == RUNNING) {
      memcpy(&ctx->fds[j], stm->saved_fds, stm->nfds * sizeof(struct pollfd));
      stm->fds = &ctx->fds[j];
      j += stm->nfds;
    }
  }

  ctx->rebuild = 0;
}

static void
poll_wake(cubeb * ctx)
{
  if (write(ctx->control_fd_write, "x", 1) < 0) {
    /* ignore write error */
  }
}

static void
set_timeout(struct timeval * timeout, unsigned int ms)
{
  gettimeofday(timeout, NULL);
  timeout->tv_sec += ms / 1000;
  timeout->tv_usec += (ms % 1000) * 1000;
}

static void
stream_buffer_decrement(cubeb_stream * stm, long count)
{
  if (count < 0 || (snd_pcm_uframes_t)count > stm->bufframes) {
    count = stm->bufframes;
  }
  char * bufremains =
      stm->buffer + WRAP(snd_pcm_frames_to_bytes)(stm->pcm, count);
  memmove(stm->buffer, bufremains,
          WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->bufframes - count));
  stm->bufframes -= count;
}

static void
alsa_set_stream_state(cubeb_stream * stm, enum stream_state state)
{
  cubeb * ctx;
  int r;

  ctx = stm->context;
  stm->state = state;
  r = pthread_cond_broadcast(&stm->cond);
  assert(r == 0);
  ctx->rebuild = 1;
  poll_wake(ctx);
}

static enum stream_state
alsa_process_stream(cubeb_stream * stm)
{
  unsigned short revents;
  snd_pcm_sframes_t avail;
  int draining;

  draining = 0;

  pthread_mutex_lock(&stm->mutex);

  /* Call _poll_descriptors_revents() even if we don't use it
     to let underlying plugins clear null events.  Otherwise poll()
     may wake up again and again, producing unnecessary CPU usage. */
  WRAP(snd_pcm_poll_descriptors_revents)
  (stm->pcm, stm->fds, stm->nfds, &revents);

  avail = WRAP(snd_pcm_avail_update)(stm->pcm);

  /* Got null event? Bail and wait for another wakeup. */
  if (avail == 0) {
    pthread_mutex_unlock(&stm->mutex);
    return RUNNING;
  }

  /* This could happen if we were suspended with SIGSTOP/Ctrl+Z for a long time.
   */
  if ((unsigned int)avail > stm->buffer_size) {
    avail = stm->buffer_size;
  }

  /* Capture: Read available frames */
  if (stm->stream_type == SND_PCM_STREAM_CAPTURE && avail > 0) {
    snd_pcm_sframes_t got;

    if (avail + stm->bufframes > stm->buffer_size) {
      /* Buffer overflow. Skip and overwrite with new data. */
      stm->bufframes = 0;
      // TODO: should it be marked as DRAINING?
    }

    got = WRAP(snd_pcm_readi)(stm->pcm, stm->buffer + stm->bufframes, avail);

    if (got < 0) {
      avail = got; // the error handler below will recover us
    } else {
      stm->bufframes += got;
      stm->stream_position += got;

      gettimeofday(&stm->last_activity, NULL);
    }
  }

  /* Capture: Pass read frames to callback function */
  if (stm->stream_type == SND_PCM_STREAM_CAPTURE && stm->bufframes > 0 &&
      (!stm->other_stream ||
       stm->other_stream->bufframes < stm->other_stream->buffer_size)) {
    snd_pcm_sframes_t wrote = stm->bufframes;
    struct cubeb_stream * mainstm = stm->other_stream ? stm->other_stream : stm;
    void * other_buffer = stm->other_stream ? stm->other_stream->buffer +
                                                  stm->other_stream->bufframes
                                            : NULL;

    /* Correct write size to the other stream available space */
    if (stm->other_stream &&
        wrote > (snd_pcm_sframes_t)(stm->other_stream->buffer_size -
                                    stm->other_stream->bufframes)) {
      wrote = stm->other_stream->buffer_size - stm->other_stream->bufframes;
    }

    pthread_mutex_unlock(&stm->mutex);
    wrote = stm->data_callback(mainstm, stm->user_ptr, stm->buffer,
                               other_buffer, wrote);
    pthread_mutex_lock(&stm->mutex);

    if (wrote < 0) {
      avail = wrote; // the error handler below will recover us
    } else {
      stream_buffer_decrement(stm, wrote);

      if (stm->other_stream) {
        stm->other_stream->bufframes += wrote;
      }
    }
  }

  /* Playback: Don't have enough data? Let's ask for more. */
  if (stm->stream_type == SND_PCM_STREAM_PLAYBACK &&
      avail > (snd_pcm_sframes_t)stm->bufframes &&
      (!stm->other_stream || stm->other_stream->bufframes > 0)) {
    long got = avail - stm->bufframes;
    void * other_buffer = stm->other_stream ? stm->other_stream->buffer : NULL;
    char * buftail =
        stm->buffer + WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->bufframes);

    /* Correct read size to the other stream available frames */
    if (stm->other_stream &&
        got > (snd_pcm_sframes_t)stm->other_stream->bufframes) {
      got = stm->other_stream->bufframes;
    }

    pthread_mutex_unlock(&stm->mutex);
    got = stm->data_callback(stm, stm->user_ptr, other_buffer, buftail, got);
    pthread_mutex_lock(&stm->mutex);

    if (got < 0) {
      avail = got; // the error handler below will recover us
    } else {
      stm->bufframes += got;

      if (stm->other_stream) {
        stream_buffer_decrement(stm->other_stream, got);
      }
    }
  }

  /* Playback: Still don't have enough data? Add some silence. */
  if (stm->stream_type == SND_PCM_STREAM_PLAYBACK &&
      avail > (snd_pcm_sframes_t)stm->bufframes) {
    long drain_frames = avail - stm->bufframes;
    double drain_time = (double)drain_frames / stm->params.rate;

    char * buftail =
        stm->buffer + WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->bufframes);
    memset(buftail, 0, WRAP(snd_pcm_frames_to_bytes)(stm->pcm, drain_frames));
    stm->bufframes = avail;

    /* Mark as draining, unless we're waiting for capture */
    if (!stm->other_stream || stm->other_stream->bufframes > 0) {
      set_timeout(&stm->drain_timeout, drain_time * 1000);

      draining = 1;
    }
  }

  /* Playback: Have enough data and no errors. Let's write it out. */
  if (stm->stream_type == SND_PCM_STREAM_PLAYBACK && avail > 0) {
    snd_pcm_sframes_t wrote;

    if (stm->params.format == CUBEB_SAMPLE_FLOAT32NE) {
      float * b = (float *)stm->buffer;
      for (uint32_t i = 0; i < avail * stm->params.channels; i++) {
        b[i] *= stm->volume;
      }
    } else {
      short * b = (short *)stm->buffer;
      for (uint32_t i = 0; i < avail * stm->params.channels; i++) {
        b[i] *= stm->volume;
      }
    }

    wrote = WRAP(snd_pcm_writei)(stm->pcm, stm->buffer, avail);
    if (wrote < 0) {
      avail = wrote; // the error handler below will recover us
    } else {
      stream_buffer_decrement(stm, wrote);

      stm->stream_position += wrote;
      gettimeofday(&stm->last_activity, NULL);
    }
  }

  /* Got some error? Let's try to recover the stream. */
  if (avail < 0) {
    avail = WRAP(snd_pcm_recover)(stm->pcm, avail, 0);

    /* Capture pcm must be started after initial setup/recover */
    if (avail >= 0 && stm->stream_type == SND_PCM_STREAM_CAPTURE &&
        WRAP(snd_pcm_state)(stm->pcm) == SND_PCM_STATE_PREPARED) {
      avail = WRAP(snd_pcm_start)(stm->pcm);
    }
  }

  /* Failed to recover, this stream must be broken. */
  if (avail < 0) {
    pthread_mutex_unlock(&stm->mutex);
    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
    return ERROR;
  }

  pthread_mutex_unlock(&stm->mutex);
  return draining ? DRAINING : RUNNING;
}

static int
alsa_run(cubeb * ctx)
{
  int r;
  int timeout;
  int i;
  char dummy;
  cubeb_stream * stm;
  enum stream_state state;

  pthread_mutex_lock(&ctx->mutex);

  if (ctx->rebuild) {
    rebuild(ctx);
  }

  /* Wake up at least once per second for the watchdog. */
  timeout = 1000;
  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
    stm = ctx->streams[i];
    if (stm && stm->state == DRAINING) {
      r = ms_until(&stm->drain_timeout);
      if (r >= 0 && timeout > r) {
        timeout = r;
      }
    }
  }

  pthread_mutex_unlock(&ctx->mutex);
  r = poll(ctx->fds, ctx->nfds, timeout);
  pthread_mutex_lock(&ctx->mutex);

  if (r > 0) {
    if (ctx->fds[0].revents & POLLIN) {
      if (read(ctx->control_fd_read, &dummy, 1) < 0) {
        /* ignore read error */
      }

      if (ctx->shutdown) {
        pthread_mutex_unlock(&ctx->mutex);
        return -1;
      }
    }

    for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
      stm = ctx->streams[i];
      /* We can't use snd_pcm_poll_descriptors_revents here because of
         https://github.com/kinetiknz/cubeb/issues/135. */
      if (stm && stm->state == RUNNING && stm->fds &&
          any_revents(stm->fds, stm->nfds)) {
        alsa_set_stream_state(stm, PROCESSING);
        pthread_mutex_unlock(&ctx->mutex);
        state = alsa_process_stream(stm);
        pthread_mutex_lock(&ctx->mutex);
        alsa_set_stream_state(stm, state);
      }
    }
  } else if (r == 0) {
    for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
      stm = ctx->streams[i];
      if (stm) {
        if (stm->state == DRAINING && ms_since(&stm->drain_timeout) >= 0) {
          alsa_set_stream_state(stm, INACTIVE);
          stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_DRAINED);
        } else if (stm->state == RUNNING &&
                   ms_since(&stm->last_activity) > CUBEB_WATCHDOG_MS) {
          alsa_set_stream_state(stm, ERROR);
          stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
        }
      }
    }
  }

  pthread_mutex_unlock(&ctx->mutex);

  return 0;
}

static void *
alsa_run_thread(void * context)
{
  cubeb * ctx = context;
  int r;

  CUBEB_REGISTER_THREAD("cubeb rendering thread");

  do {
    r = alsa_run(ctx);
  } while (r >= 0);

  CUBEB_UNREGISTER_THREAD();

  return NULL;
}

static snd_config_t *
get_slave_pcm_node(snd_config_t * lconf, snd_config_t * root_pcm)
{
  int r;
  snd_config_t * slave_pcm;
  snd_config_t * slave_def;
  snd_config_t * pcm;
  char const * string;
  char node_name[64];

  slave_def = NULL;

  r = WRAP(snd_config_search)(root_pcm, "slave", &slave_pcm);
  if (r < 0) {
    return NULL;
  }

  r = WRAP(snd_config_get_string)(slave_pcm, &string);
  if (r >= 0) {
    r = WRAP(snd_config_search_definition)(lconf, "pcm_slave", string,
                                           &slave_def);
    if (r < 0) {
      return NULL;
    }
  }

  do {
    r = WRAP(snd_config_search)(slave_def ? slave_def : slave_pcm, "pcm", &pcm);
    if (r < 0) {
      break;
    }

    r = WRAP(snd_config_get_string)(slave_def ? slave_def : slave_pcm, &string);
    if (r < 0) {
      break;
    }

    r = snprintf(node_name, sizeof(node_name), "pcm.%s", string);
    if (r < 0 || r > (int)sizeof(node_name)) {
      break;
    }
    r = WRAP(snd_config_search)(lconf, node_name, &pcm);
    if (r < 0) {
      break;
    }

    return pcm;
  } while (0);

  if (slave_def) {
    WRAP(snd_config_delete)(slave_def);
  }

  return NULL;
}

/* Work around PulseAudio ALSA plugin bug where the PA server forces a
   higher than requested latency, but the plugin does not update its (and
   ALSA's) internal state to reflect that, leading to an immediate underrun
   situation.  Inspired by WINE's make_handle_underrun_config.
   Reference: http://mailman.alsa-project.org/pipermail/alsa-devel/2012-July/05
 */
static snd_config_t *
init_local_config_with_workaround(char const * pcm_name)
{
  int r;
  snd_config_t * lconf;
  snd_config_t * pcm_node;
  snd_config_t * node;
  char const * string;
  char node_name[64];

  lconf = NULL;

  if (WRAP(snd_config) == NULL) {
    return NULL;
  }

  r = WRAP(snd_config_copy)(&lconf, WRAP(snd_config));
  if (r < 0) {
    return NULL;
  }

  do {
    r = WRAP(snd_config_search_definition)(lconf, "pcm", pcm_name, &pcm_node);
    if (r < 0) {
      break;
    }

    r = WRAP(snd_config_get_id)(pcm_node, &string);
    if (r < 0) {
      break;
    }

    r = snprintf(node_name, sizeof(node_name), "pcm.%s", string);
    if (r < 0 || r > (int)sizeof(node_name)) {
      break;
    }
    r = WRAP(snd_config_search)(lconf, node_name, &pcm_node);
    if (r < 0) {
      break;
    }

    /* If this PCM has a slave, walk the slave configurations until we reach the
     * bottom. */
    while ((node = get_slave_pcm_node(lconf, pcm_node)) != NULL) {
      pcm_node = node;
    }

    /* Fetch the PCM node's type, and bail out if it's not the PulseAudio
     * plugin. */
    r = WRAP(snd_config_search)(pcm_node, "type", &node);
    if (r < 0) {
      break;
    }

    r = WRAP(snd_config_get_string)(node, &string);
    if (r < 0) {
      break;
    }

    if (strcmp(string, "pulse") != 0) {
      break;
    }

    /* Don't clobber an explicit existing handle_underrun value, set it only
       if it doesn't already exist. */
    r = WRAP(snd_config_search)(pcm_node, "handle_underrun", &node);
    if (r != -ENOENT) {
      break;
    }

    /* Disable pcm_pulse's asynchronous underrun handling. */
    r = WRAP(snd_config_imake_integer)(&node, "handle_underrun", 0);
    if (r < 0) {
      break;
    }

    r = WRAP(snd_config_add)(pcm_node, node);
    if (r < 0) {
      break;
    }

    return lconf;
  } while (0);

  WRAP(snd_config_delete)(lconf);

  return NULL;
}

static int
alsa_locked_pcm_open(snd_pcm_t ** pcm, char const * pcm_name,
                     snd_pcm_stream_t stream, snd_config_t * local_config)
{
  int r;

  pthread_mutex_lock(&cubeb_alsa_mutex);
  if (local_config) {
    r = WRAP(snd_pcm_open_lconf)(pcm, pcm_name, stream, SND_PCM_NONBLOCK,
                                 local_config);
  } else {
    r = WRAP(snd_pcm_open)(pcm, pcm_name, stream, SND_PCM_NONBLOCK);
  }
  pthread_mutex_unlock(&cubeb_alsa_mutex);

  return r;
}

static int
alsa_locked_pcm_close(snd_pcm_t * pcm)
{
  int r;

  pthread_mutex_lock(&cubeb_alsa_mutex);
  r = WRAP(snd_pcm_close)(pcm);
  pthread_mutex_unlock(&cubeb_alsa_mutex);

  return r;
}

static int
alsa_register_stream(cubeb * ctx, cubeb_stream * stm)
{
  int i;

  pthread_mutex_lock(&ctx->mutex);
  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
    if (!ctx->streams[i]) {
      ctx->streams[i] = stm;
      break;
    }
  }
  pthread_mutex_unlock(&ctx->mutex);

  return i == CUBEB_STREAM_MAX;
}

static void
alsa_unregister_stream(cubeb_stream * stm)
{
  cubeb * ctx;
  int i;

  ctx = stm->context;

  pthread_mutex_lock(&ctx->mutex);
  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
    if (ctx->streams[i] == stm) {
      ctx->streams[i] = NULL;
      break;
    }
  }
  pthread_mutex_unlock(&ctx->mutex);
}

static void
silent_error_handler(char const * file, int line, char const * function,
                     int err, char const * fmt, ...)
{
  (void)file;
  (void)line;
  (void)function;
  (void)err;
  (void)fmt;
}

/*static*/ int
alsa_init(cubeb ** context, char const * context_name)
{
  (void)context_name;
  void * libasound = NULL;
  cubeb * ctx;
  int r;
  int i;
  int fd[2];
  pthread_attr_t attr;
  snd_pcm_t * dummy;

  assert(context);
  *context = NULL;

#ifndef DISABLE_LIBASOUND_DLOPEN
  libasound = dlopen("libasound.so.2", RTLD_LAZY);
  if (!libasound) {
    libasound = dlopen("libasound.so", RTLD_LAZY);
    if (!libasound) {
      return CUBEB_ERROR;
    }
  }

#define LOAD(x)                                                                \
  {                                                                            \
    cubeb_##x = dlsym(libasound, #x);                                          \
    if (!cubeb_##x) {                                                          \
      dlclose(libasound);                                                      \
      return CUBEB_ERROR;                                                      \
    }                                                                          \
  }

  LIBASOUND_API_VISIT(LOAD);
#undef LOAD
#endif

  pthread_mutex_lock(&cubeb_alsa_mutex);
  if (!cubeb_alsa_error_handler_set) {
    WRAP(snd_lib_error_set_handler)(silent_error_handler);
    cubeb_alsa_error_handler_set = 1;
  }
  pthread_mutex_unlock(&cubeb_alsa_mutex);

  ctx = calloc(1, sizeof(*ctx));
  assert(ctx);

  ctx->ops = &alsa_ops;
  ctx->libasound = libasound;

  r = pthread_mutex_init(&ctx->mutex, NULL);
  assert(r == 0);

  r = pipe(fd);
  assert(r == 0);

  for (i = 0; i < 2; ++i) {
    fcntl(fd[i], F_SETFD, fcntl(fd[i], F_GETFD) | FD_CLOEXEC);
    fcntl(fd[i], F_SETFL, fcntl(fd[i], F_GETFL) | O_NONBLOCK);
  }

  ctx->control_fd_read = fd[0];
  ctx->control_fd_write = fd[1];

  /* Force an early rebuild when alsa_run is first called to ensure fds and
     nfds have been initialized. */
  ctx->rebuild = 1;

  r = pthread_attr_init(&attr);
  assert(r == 0);

  r = pthread_attr_setstacksize(&attr, 256 * 1024);
  assert(r == 0);

  r = pthread_create(&ctx->thread, &attr, alsa_run_thread, ctx);
  assert(r == 0);

  r = pthread_attr_destroy(&attr);
  assert(r == 0);

  /* Open a dummy PCM to force the configuration space to be evaluated so that
     init_local_config_with_workaround can find and modify the default node. */
  r = alsa_locked_pcm_open(&dummy, CUBEB_ALSA_PCM_NAME, SND_PCM_STREAM_PLAYBACK,
                           NULL);
  if (r >= 0) {
    alsa_locked_pcm_close(dummy);
  }
  ctx->is_pa = 0;
  pthread_mutex_lock(&cubeb_alsa_mutex);
  ctx->local_config = init_local_config_with_workaround(CUBEB_ALSA_PCM_NAME);
  pthread_mutex_unlock(&cubeb_alsa_mutex);
  if (ctx->local_config) {
    ctx->is_pa = 1;
    r = alsa_locked_pcm_open(&dummy, CUBEB_ALSA_PCM_NAME,
                             SND_PCM_STREAM_PLAYBACK, ctx->local_config);
    /* If we got a local_config, we found a PA PCM.  If opening a PCM with that
       config fails with EINVAL, the PA PCM is too old for this workaround. */
    if (r == -EINVAL) {
      pthread_mutex_lock(&cubeb_alsa_mutex);
      WRAP(snd_config_delete)(ctx->local_config);
      pthread_mutex_unlock(&cubeb_alsa_mutex);
      ctx->local_config = NULL;
    } else if (r >= 0) {
      alsa_locked_pcm_close(dummy);
    }
  }

  *context = ctx;

  return CUBEB_OK;
}

static char const *
alsa_get_backend_id(cubeb * ctx)
{
  (void)ctx;
  return "alsa";
}

static void
alsa_destroy(cubeb * ctx)
{
  int r;

  assert(ctx);

  pthread_mutex_lock(&ctx->mutex);
  ctx->shutdown = 1;
  poll_wake(ctx);
  pthread_mutex_unlock(&ctx->mutex);

  r = pthread_join(ctx->thread, NULL);
  assert(r == 0);

  close(ctx->control_fd_read);
  close(ctx->control_fd_write);
  pthread_mutex_destroy(&ctx->mutex);
  free(ctx->fds);

  if (ctx->local_config) {
    pthread_mutex_lock(&cubeb_alsa_mutex);
    WRAP(snd_config_delete)(ctx->local_config);
    pthread_mutex_unlock(&cubeb_alsa_mutex);
  }
#ifndef DISABLE_LIBASOUND_DLOPEN
  if (ctx->libasound) {
    dlclose(ctx->libasound);
  }
#endif
  free(ctx);
}

static void
alsa_stream_destroy(cubeb_stream * stm);

static int
alsa_stream_init_single(cubeb * ctx, cubeb_stream ** stream,
                        char const * stream_name, snd_pcm_stream_t stream_type,
                        cubeb_devid deviceid,
                        cubeb_stream_params * stream_params,
                        unsigned int latency_frames,
                        cubeb_data_callback data_callback,
                        cubeb_state_callback state_callback, void * user_ptr)
{
  (void)stream_name;
  cubeb_stream * stm;
  int r;
  snd_pcm_format_t format;
  snd_pcm_uframes_t period_size;
  int latency_us = 0;
  char const * pcm_name =
      deviceid ? (char const *)deviceid : CUBEB_ALSA_PCM_NAME;

  assert(ctx && stream);

  *stream = NULL;

  if (stream_params->prefs & CUBEB_STREAM_PREF_LOOPBACK) {
    return CUBEB_ERROR_NOT_SUPPORTED;
  }

  switch (stream_params->format) {
  case CUBEB_SAMPLE_S16LE:
    format = SND_PCM_FORMAT_S16_LE;
    break;
  case CUBEB_SAMPLE_S16BE:
    format = SND_PCM_FORMAT_S16_BE;
    break;
  case CUBEB_SAMPLE_FLOAT32LE:
    format = SND_PCM_FORMAT_FLOAT_LE;
    break;
  case CUBEB_SAMPLE_FLOAT32BE:
    format = SND_PCM_FORMAT_FLOAT_BE;
    break;
  default:
    return CUBEB_ERROR_INVALID_FORMAT;
  }

  pthread_mutex_lock(&ctx->mutex);
  if (ctx->active_streams >= CUBEB_STREAM_MAX) {
    pthread_mutex_unlock(&ctx->mutex);
    return CUBEB_ERROR;
  }
  ctx->active_streams += 1;
  pthread_mutex_unlock(&ctx->mutex);

  stm = calloc(1, sizeof(*stm));
  assert(stm);

  stm->context = ctx;
  stm->data_callback = data_callback;
  stm->state_callback = state_callback;
  stm->user_ptr = user_ptr;
  stm->params = *stream_params;
  stm->state = INACTIVE;
  stm->volume = 1.0;
  stm->buffer = NULL;
  stm->bufframes = 0;
  stm->stream_type = stream_type;
  stm->other_stream = NULL;

  r = pthread_mutex_init(&stm->mutex, NULL);
  assert(r == 0);

  r = pthread_cond_init(&stm->cond, NULL);
  assert(r == 0);

  r = alsa_locked_pcm_open(&stm->pcm, pcm_name, stm->stream_type,
                           ctx->local_config);
  if (r < 0) {
    alsa_stream_destroy(stm);
    return CUBEB_ERROR;
  }

  r = WRAP(snd_pcm_nonblock)(stm->pcm, 1);
  assert(r == 0);

  latency_us = latency_frames * 1e6 / stm->params.rate;

  /* Ugly hack: the PA ALSA plugin allows buffer configurations that can't
     possibly work.  See https://bugzilla.mozilla.org/show_bug.cgi?id=761274.
     Only resort to this hack if the handle_underrun workaround failed. */
  if (!ctx->local_config && ctx->is_pa) {
    const int min_latency = 5e5;
    latency_us = latency_us < min_latency ? min_latency : latency_us;
  }

  r = WRAP(snd_pcm_set_params)(stm->pcm, format, SND_PCM_ACCESS_RW_INTERLEAVED,
                               stm->params.channels, stm->params.rate, 1,
                               latency_us);
  if (r < 0) {
    alsa_stream_destroy(stm);
    return CUBEB_ERROR_INVALID_FORMAT;
  }

  r = WRAP(snd_pcm_get_params)(stm->pcm, &stm->buffer_size, &period_size);
  assert(r == 0);

  /* Double internal buffer size to have enough space when waiting for the other
   * side of duplex connection */
  stm->buffer_size *= 2;
  stm->buffer =
      calloc(1, WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->buffer_size));
  assert(stm->buffer);

  stm->nfds = WRAP(snd_pcm_poll_descriptors_count)(stm->pcm);
  assert(stm->nfds > 0);

  stm->saved_fds = calloc(stm->nfds, sizeof(struct pollfd));
  assert(stm->saved_fds);
  r = WRAP(snd_pcm_poll_descriptors)(stm->pcm, stm->saved_fds, stm->nfds);
  assert((nfds_t)r == stm->nfds);

  if (alsa_register_stream(ctx, stm) != 0) {
    alsa_stream_destroy(stm);
    return CUBEB_ERROR;
  }

  *stream = stm;

  return CUBEB_OK;
}

static int
alsa_stream_init(cubeb * ctx, cubeb_stream ** stream, char const * stream_name,
                 cubeb_devid input_device,
                 cubeb_stream_params * input_stream_params,
                 cubeb_devid output_device,
                 cubeb_stream_params * output_stream_params,
                 unsigned int latency_frames, cubeb_data_callback data_callback,
                 cubeb_state_callback state_callback, void * user_ptr)
{
  int result = CUBEB_OK;
  cubeb_stream *instm = NULL, *outstm = NULL;

  if (result == CUBEB_OK && input_stream_params) {
    result = alsa_stream_init_single(ctx, &instm, stream_name,
                                     SND_PCM_STREAM_CAPTURE, input_device,
                                     input_stream_params, latency_frames,
                                     data_callback, state_callback, user_ptr);
  }

  if (result == CUBEB_OK && output_stream_params) {
    result = alsa_stream_init_single(ctx, &outstm, stream_name,
                                     SND_PCM_STREAM_PLAYBACK, output_device,
                                     output_stream_params, latency_frames,
                                     data_callback, state_callback, user_ptr);
  }

  if (result == CUBEB_OK && input_stream_params && output_stream_params) {
    instm->other_stream = outstm;
    outstm->other_stream = instm;
  }

  if (result != CUBEB_OK && instm) {
    alsa_stream_destroy(instm);
  }

  *stream = outstm ? outstm : instm;

  return result;
}

static void
alsa_stream_destroy(cubeb_stream * stm)
{
  int r;
  cubeb * ctx;

  assert(stm && (stm->state == INACTIVE || stm->state == ERROR ||
                 stm->state == DRAINING));

  ctx = stm->context;

  if (stm->other_stream) {
    stm->other_stream->other_stream = NULL; // to stop infinite recursion
    alsa_stream_destroy(stm->other_stream);
  }

  pthread_mutex_lock(&stm->mutex);
  if (stm->pcm) {
    if (stm->state == DRAINING) {
      WRAP(snd_pcm_drain)(stm->pcm);
    }
    alsa_locked_pcm_close(stm->pcm);
    stm->pcm = NULL;
  }
  free(stm->saved_fds);
  pthread_mutex_unlock(&stm->mutex);
  pthread_mutex_destroy(&stm->mutex);

  r = pthread_cond_destroy(&stm->cond);
  assert(r == 0);

  alsa_unregister_stream(stm);

  pthread_mutex_lock(&ctx->mutex);
  assert(ctx->active_streams >= 1);
  ctx->active_streams -= 1;
  pthread_mutex_unlock(&ctx->mutex);

  free(stm->buffer);

  free(stm);
}

static int
alsa_get_max_channel_count(cubeb * ctx, uint32_t * max_channels)
{
  int r;
  cubeb_stream * stm;
  snd_pcm_hw_params_t * hw_params;
  cubeb_stream_params params;
  params.rate = 44100;
  params.format = CUBEB_SAMPLE_FLOAT32NE;
  params.channels = 2;

  snd_pcm_hw_params_alloca(&hw_params);

  assert(ctx);

  r = alsa_stream_init(ctx, &stm, "", NULL, NULL, NULL, &params, 100, NULL,
                       NULL, NULL);
  if (r != CUBEB_OK) {
    return CUBEB_ERROR;
  }

  assert(stm);

  r = WRAP(snd_pcm_hw_params_any)(stm->pcm, hw_params);
  if (r < 0) {
    return CUBEB_ERROR;
  }

  r = WRAP(snd_pcm_hw_params_get_channels_max)(hw_params, max_channels);
  if (r < 0) {
    return CUBEB_ERROR;
  }

  /* Cap at reasonable maximum to filter driver placeholder values */  
  if (*max_channels > 64) {  
    *max_channels = 64;  
  }  

  alsa_stream_destroy(stm);

  return CUBEB_OK;
}

static int
alsa_get_preferred_sample_rate(cubeb * ctx, uint32_t * rate)
{
  (void)ctx;
  int r, dir;
  snd_pcm_t * pcm;
  snd_pcm_hw_params_t * hw_params;

  snd_pcm_hw_params_alloca(&hw_params);

  /* get a pcm, disabling resampling, so we get a rate the
   * hardware/dmix/pulse/etc. supports. */
  r = WRAP(snd_pcm_open)(&pcm, CUBEB_ALSA_PCM_NAME, SND_PCM_STREAM_PLAYBACK,
                         SND_PCM_NO_AUTO_RESAMPLE);
  if (r < 0) {
    return CUBEB_ERROR;
  }

  r = WRAP(snd_pcm_hw_params_any)(pcm, hw_params);
  if (r < 0) {
    WRAP(snd_pcm_close)(pcm);
    return CUBEB_ERROR;
  }

  r = WRAP(snd_pcm_hw_params_get_rate)(hw_params, rate, &dir);
  if (r >= 0) {
    /* There is a default rate: use it. */
    WRAP(snd_pcm_close)(pcm);
    return CUBEB_OK;
  }

  /* Use a common rate, alsa may adjust it based on hw/etc. capabilities. */
  *rate = 44100;

  r = WRAP(snd_pcm_hw_params_set_rate_near)(pcm, hw_params, rate, NULL);
  if (r < 0) {
    WRAP(snd_pcm_close)(pcm);
    return CUBEB_ERROR;
  }

  WRAP(snd_pcm_close)(pcm);

  return CUBEB_OK;
}

static int
alsa_get_min_latency(cubeb * ctx, cubeb_stream_params params,
                     uint32_t * latency_frames)
{
  (void)ctx;
  /* 40ms is found to be an acceptable minimum, even on a super low-end
   * machine. */
  *latency_frames = 40 * params.rate / 1000;

  return CUBEB_OK;
}

static int
alsa_stream_start(cubeb_stream * stm)
{
  cubeb * ctx;

  assert(stm);
  ctx = stm->context;

  if (stm->stream_type == SND_PCM_STREAM_PLAYBACK && stm->other_stream) {
    int r = alsa_stream_start(stm->other_stream);
    if (r != CUBEB_OK)
      return r;
  }

  pthread_mutex_lock(&stm->mutex);
  /* Capture pcm must be started after initial setup/recover */
  if (stm->stream_type == SND_PCM_STREAM_CAPTURE &&
      WRAP(snd_pcm_state)(stm->pcm) == SND_PCM_STATE_PREPARED) {
    WRAP(snd_pcm_start)(stm->pcm);
  }
  WRAP(snd_pcm_pause)(stm->pcm, 0);
  gettimeofday(&stm->last_activity, NULL);
  pthread_mutex_unlock(&stm->mutex);

  pthread_mutex_lock(&ctx->mutex);
  if (stm->state != INACTIVE) {
    pthread_mutex_unlock(&ctx->mutex);
    return CUBEB_ERROR;
  }
  alsa_set_stream_state(stm, RUNNING);
  pthread_mutex_unlock(&ctx->mutex);

  return CUBEB_OK;
}

static int
alsa_stream_stop(cubeb_stream * stm)
{
  cubeb * ctx;
  int r;

  assert(stm);
  ctx = stm->context;

  if (stm->stream_type == SND_PCM_STREAM_PLAYBACK && stm->other_stream) {
    int r = alsa_stream_stop(stm->other_stream);
    if (r != CUBEB_OK)
      return r;
  }

  pthread_mutex_lock(&ctx->mutex);
  while (stm->state == PROCESSING) {
    r = pthread_cond_wait(&stm->cond, &ctx->mutex);
    assert(r == 0);
  }

  alsa_set_stream_state(stm, INACTIVE);
  pthread_mutex_unlock(&ctx->mutex);

  pthread_mutex_lock(&stm->mutex);
  WRAP(snd_pcm_pause)(stm->pcm, 1);
  pthread_mutex_unlock(&stm->mutex);

  return CUBEB_OK;
}

static int
alsa_stream_get_position(cubeb_stream * stm, uint64_t * position)
{
  snd_pcm_sframes_t delay;

  assert(stm && position);

  pthread_mutex_lock(&stm->mutex);

  delay = -1;
  if (WRAP(snd_pcm_state)(stm->pcm) != SND_PCM_STATE_RUNNING ||
      WRAP(snd_pcm_delay)(stm->pcm, &delay) != 0) {
    *position = stm->last_position;
    pthread_mutex_unlock(&stm->mutex);
    return CUBEB_OK;
  }

  assert(delay >= 0);

  *position = 0;
  if (stm->stream_position >= (snd_pcm_uframes_t)delay) {
    *position = stm->stream_position - delay;
  }

  stm->last_position = *position;

  pthread_mutex_unlock(&stm->mutex);
  return CUBEB_OK;
}

static int
alsa_stream_get_latency(cubeb_stream * stm, uint32_t * latency)
{
  snd_pcm_sframes_t delay;
  /* This function returns the delay in frames until a frame written using
     snd_pcm_writei is sent to the DAC. The DAC delay should be < 1ms anyways.
   */
  if (WRAP(snd_pcm_delay)(stm->pcm, &delay)) {
    return CUBEB_ERROR;
  }

  *latency = delay;

  return CUBEB_OK;
}

static int
alsa_stream_set_volume(cubeb_stream * stm, float volume)
{
  /* setting the volume using an API call does not seem very stable/supported */
  pthread_mutex_lock(&stm->mutex);
  stm->volume = volume;
  pthread_mutex_unlock(&stm->mutex);

  return CUBEB_OK;
}

static int
alsa_enumerate_devices(cubeb * context, cubeb_device_type type,
                       cubeb_device_collection * collection)
{
  cubeb_device_info * device;
  snd_pcm_info_t * pcminfo;
  snd_ctl_t * ctl;
  snd_ctl_card_info_t * cardinfo;
  int card = -1;
  char card_name[32];
  int err;
  int dev;
  snd_pcm_stream_t stream;

  snd_pcm_info_alloca(&pcminfo);
  snd_ctl_card_info_alloca(&cardinfo);

  collection->count = 0;
  collection->device = NULL;

  if (snd_card_next(&card) < 0 || card < 0)
    return CUBEB_OK;

  while (card >= 0) {
    sprintf(card_name, "hw:%d", card);
    err = snd_ctl_open(&ctl, card_name, 0);
    if (err < 0) {
      snd_card_next(&card);
      continue;
    }

    err = snd_ctl_card_info(ctl, cardinfo);
    if (err < 0) {
      snd_ctl_close(ctl);
      snd_card_next(&card);
      continue;
    }

    dev = -1;
    while (1) {
      if (snd_ctl_pcm_next_device(ctl, &dev) < 0)
        break;
      if (dev < 0)
        break;

      for (stream = 0; stream < 2; stream++) {
        if ((type & CUBEB_DEVICE_TYPE_OUTPUT) && stream == SND_PCM_STREAM_CAPTURE)
          continue;
        if ((type & CUBEB_DEVICE_TYPE_INPUT) && stream == SND_PCM_STREAM_PLAYBACK)
          continue;

        snd_pcm_info_set_device(pcminfo, dev);
        snd_pcm_info_set_subdevice(pcminfo, 0);
        snd_pcm_info_set_stream(pcminfo, stream);
        err = snd_ctl_pcm_info(ctl, pcminfo);
        if (err < 0)
          continue;

        device = (cubeb_device_info *)calloc(1, sizeof(cubeb_device_info));
        if (!device) {
          snd_ctl_close(ctl);
          return CUBEB_ERROR;
        }

        device->device_id = strdup(snd_pcm_info_get_name(pcminfo));
        device->friendly_name = strdup(snd_pcm_info_get_name(pcminfo));
        device->group_id = strdup(snd_ctl_card_info_get_id(cardinfo));
        device->vendor_name = strdup(snd_ctl_card_info_get_name(cardinfo));

        device->type = (stream == SND_PCM_STREAM_PLAYBACK) ? 
                       CUBEB_DEVICE_TYPE_OUTPUT : CUBEB_DEVICE_TYPE_INPUT;
        device->devid = (void *)(intptr_t)(card << 16 | dev);
        device->state = CUBEB_DEVICE_STATE_ENABLED;
        device->preferred = (dev == 0);
        
        device->max_channels = 8;  
        
        device->min_rate = 8000;   /* Conservative minimum */ 
        device->max_rate = 192000; /* Conservative maximum */
        device->default_format = (cubeb_device_fmt)CUBEB_SAMPLE_FLOAT32NE;
        device->latency_lo = 0;
        device->latency_hi = 0;

        collection->count++;
        collection->device = (cubeb_device_info *)realloc(collection->device,
                                                         collection->count * sizeof(cubeb_device_info));
        if (!collection->device) {
          free((void *)device->device_id);  
          free((void *)device->friendly_name);  
          free((void *)device->group_id);  
          free((void *)device->vendor_name);
          free(device);
          snd_ctl_close(ctl);
          return CUBEB_ERROR;
        }
        collection->device[collection->count - 1] = *device;
        free(device);
      }
    }
    snd_ctl_close(ctl);
    snd_card_next(&card);
  }

  return CUBEB_OK;
}

static int  
alsa_device_collection_destroy(cubeb * context,  
                               cubeb_device_collection * collection)  
{  
  size_t i;  
  
  (void)context;  
  
  for (i = 0; i < collection->count; ++i) {  
    free((void *)collection->device[i].device_id);  
    free((void *)collection->device[i].friendly_name);  
    free((void *)collection->device[i].group_id);  
    free((void *)collection->device[i].vendor_name);  
  }  
  free(collection->device);  
  return CUBEB_OK;  
}

static struct cubeb_ops const alsa_ops = {
    .init = alsa_init,
    .get_backend_id = alsa_get_backend_id,
    .get_max_channel_count = alsa_get_max_channel_count,
    .get_min_latency = alsa_get_min_latency,
    .get_preferred_sample_rate = alsa_get_preferred_sample_rate,
    .get_supported_input_processing_params = NULL,
    .enumerate_devices = alsa_enumerate_devices,
    .device_collection_destroy = alsa_device_collection_destroy,
    .destroy = alsa_destroy,
    .stream_init = alsa_stream_init,
    .stream_destroy = alsa_stream_destroy,
    .stream_start = alsa_stream_start,
    .stream_stop = alsa_stream_stop,
    .stream_get_position = alsa_stream_get_position,
    .stream_get_latency = alsa_stream_get_latency,
    .stream_get_input_latency = NULL,
    .stream_set_volume = alsa_stream_set_volume,
    .stream_set_name = NULL,
    .stream_get_current_device = NULL,
    .stream_set_input_mute = NULL,
    .stream_set_input_processing_params = NULL,
    .stream_device_destroy = NULL,
    .stream_register_device_changed_callback = NULL,
    .register_device_collection_changed = NULL};

Last edited by igorzwx (Today 12:02:18)

kapqa · Today 17:52:24

have been following your instructions,

that you posted early on how to build firefox;
but missed lately the ones for creating a .deb file ~

so probably the .cubeb thing is not implemented ~ hence , a half-baked solution?

https://ibb.co/bgVJ6KBt

The officially official Devuan Forum!

#1 2025-11-23 18:43:35