The first step to add device selection to linux.

media/audio/linux/audio_manager_linux.cc

Index: media/audio/linux/audio_manager_linux.cc
===================================================================
--- media/audio/linux/audio_manager_linux.cc	(revision 104076)
+++ media/audio/linux/audio_manager_linux.cc	(working copy)
@@ -39,54 +39,13 @@
   "surround",
 };
 
-static bool IsValidAudioInputDevice(const char* device_name) {
-  if (!device_name)
-    return false;
-
-  for (size_t i = 0; i < arraysize(kInvalidAudioInputDevices); ++i) {
-    if (strcmp(kInvalidAudioInputDevices[i], device_name) == 0)
-      return false;
-  }
-
-  return true;
-}
-
 // Implementation of AudioManager.
 bool AudioManagerLinux::HasAudioOutputDevices() {
-  // TODO(ajwong): Make this actually query audio devices.
-  return true;
+  return HasAnyAlsaAudioDevice(kStreamPlayback);
 }
 
 bool AudioManagerLinux::HasAudioInputDevices() {
-  if (!initialized()) {
-    return false;
-  }
-
-  // Constants specified by the ALSA API for device hints.
-  static const char kPcmInterfaceName[] = "pcm";
-  bool has_device = false;
-  void** hints = NULL;
-  int card = -1;
-
-  // Loop through the sound cards to get Alsa device hints.
-  // Don't use snd_device_name_hint(-1,..) since there is a access violation
-  // inside this ALSA API with libasound.so.2.0.0.
-  while (!wrapper_->CardNext(&card) && (card >= 0) && !has_device) {
-    int error = wrapper_->DeviceNameHint(card,
-                                         kPcmInterfaceName,
-                                         &hints);
-    if (error == 0) {
-      has_device = HasAnyValidAudioInputDevice(hints);
-
-      // Destroy the hints now that we're done with it.
-      wrapper_->DeviceNameFreeHint(hints);
-      hints = NULL;
-    } else {
-      LOG(ERROR) << "Unable to get device hints: " << wrapper_->StrError(error);
-    }
-  }
-
-  return has_device;
+  return HasAnyAlsaAudioDevice(kStreamCapture);
 }
 
 AudioOutputStream* AudioManagerLinux::MakeAudioOutputStream(
@@ -141,6 +100,7 @@
   if (!initialized())
     return NULL;
 
+  // TODO(xians): Pass the device name From AudioInputController instead.
   std::string device_name = AlsaPcmOutputStream::kAutoSelectDevice;
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kAlsaInputDevice)) {
     device_name = CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
@@ -213,21 +173,49 @@
 
 void AudioManagerLinux::GetAudioInputDeviceNames(
     media::AudioDeviceNames* device_names) {
-  // TODO(xians): query a full list of valid devices.
-  if (HasAudioInputDevices()) {
-    // Add the default device to the list.
-    // We use index 0 to make up the unique_id to identify the
-    // default devices.
-    media::AudioDeviceName name;
-    name.device_name = AudioManagerBase::kDefaultDeviceName;
-    name.unique_id = "0";
-    device_names->push_back(name);
+  // Empty the name list.

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

remove

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+  device_names->clear();
+
+  GetAlsaAudioInputDevices(device_names);
+
+  if (!device_names->empty()) {
+    // Pre-pend the default device to the list.

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

Perhaps extend the comments why this is needed.

[scherkus (not reviewing), 2011/10/07 16:54:45]

nit: Pre-pend -> Prepend

also agree w/ henrik on explanation as to why

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+    // We use index 0 to make up the unique_id to identify the default devices.
+    device_names->push_front(media::AudioDeviceName(
+      AudioManagerBase::kDefaultDeviceName, "0"));

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

indent by 4

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

   }
 }
 
-bool AudioManagerLinux::HasAnyValidAudioInputDevice(void** hints) {
+void AudioManagerLinux::GetAlsaAudioInputDevices(
+    media::AudioDeviceNames* device_names) {
+

[scherkus (not reviewing), 2011/10/07 16:54:45]

nit: remove blank line

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+  // Constants specified by the ALSA API for device hints.
+  static const char kPcmInterfaceName[] = "pcm";
+  void** hints = NULL;
+  int card = -1;
+
+  // Loop through the sound cards to get Alsa device hints.

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

ALSA?

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+  while (!wrapper_->CardNext(&card) && (card >= 0)) {
+    int error = wrapper_->DeviceNameHint(card, kPcmInterfaceName, &hints);

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

Do you allocate memory here? 
I think you should move hint declaration inside while.

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+    if (!error) {
+      // Get devices

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

remove

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+      GetAlsaDevicesInfo(hints, device_names);
+
+      // Destroy the hints now that we're done with it.
+      wrapper_->DeviceNameFreeHint(hints);
+      hints = NULL;

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

remove

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+    } else {
+      LOG(WARNING) << "GetAudioInputDevices error: unable to get device hints: "

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

DLOG

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+                   << wrapper_->StrError(error);
+    }
+  }
+}
+
+void AudioManagerLinux::GetAlsaDevicesInfo(
+    void** hints, media::AudioDeviceNames* device_names) {
   static const char kIoHintName[] = "IOID";
   static const char kNameHintName[] = "NAME";
+  static const char kDescriptionHintName[] = "DESC";
   static const char kOutputDevice[] = "Output";
 
   for (void** hint_iter = hints; *hint_iter != NULL; hint_iter++) {
@@ -238,15 +226,98 @@
     if (io != NULL && strcmp(kOutputDevice, io.get()) == 0)
       continue;
 
-    scoped_ptr_malloc<char> hint_device_name(
+    // Get the unique device name for the device.
+    scoped_ptr_malloc<char> unique_device_name(
         wrapper_->DeviceNameGetHint(*hint_iter, kNameHintName));
-    if (IsValidAudioInputDevice(hint_device_name.get()))
-      return true;
+    // Find out if the device is available.

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

empty line before

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+    if (IsAlsaDeviceAvailable(unique_device_name.get())) {
+      // Get the description for the device.
+      scoped_ptr_malloc<char> desc(wrapper_->DeviceNameGetHint(
+          *hint_iter, kDescriptionHintName));
+
+      media::AudioDeviceName name;
+      name.unique_id = unique_device_name.get();
+      if (desc.get()) {
+        // Use the more user friendly description as name.
+        // Replace '\n' with '-'.
+        char* pret = strchr(desc.get(), '\n');
+        if (pret)
+          *pret = '-';
+        name.device_name = desc.get();
+      } else {
+        // Virtual devices don't necessarily have descriptions.
+        // Use their names instead.
+        name.device_name = unique_device_name.get();
+      }
+
+      // Store the device information.
+      device_names->push_back(name);
+    }
   }
+}
 
-  return false;
+bool AudioManagerLinux::IsAlsaDeviceAvailable(const char* device_name) {
+  if (!device_name)
+    return false;
+
+  // Check if the device is in the list of invalid devices.
+  for (size_t i = 0; i < arraysize(kInvalidAudioInputDevices); ++i) {
+    if (!strncmp(kInvalidAudioInputDevices[i], device_name,
+                strlen(kInvalidAudioInputDevices[i])))

[scherkus (not reviewing), 2011/10/07 16:54:45]

indent by 1 more space

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+      return false;
+  }
+
+  // The only way to check if the device is available is to open/close the
+  // device, return false if it fails either of operations.
+  snd_pcm_t* device_handle = NULL;
+  if (wrapper_->PcmOpen(&device_handle, device_name,

[scherkus (not reviewing), 2011/10/07 16:54:45]

how long does this take to run?

The call stack is:
GetAudioInputDeviceNames()
GetAlsaAudioInputDevices()
GetAlsaDevicesInfo()
IsAlsaDeviceAvailable() // For each device
PcmOpen() / PcmClose()  // For each device


Is it possible to execute this code from javascript by invoking WebRTC methods?

[no longer working on chromium, 2011/10/10 13:49:24]

I have totally 3 physical devices attached to PC, one is built-in device,
another is USB headset, the last one is camera with mic.

The whole call stack takes 39467us.
DEVICE  front:CARD=Intel,DEV=0TIME open/close time:  441us
DEVICE  front:CARD=Q9000,DEV=0TIME open/close time:  527us
DEVICE  iec958:CARD=Q9000,DEV=0TIME open/close time:  628us
DEVICE  front:CARD=Headset,DEV=0TIME open/close time:  462us
DEVICE  iec958:CARD=Headset,DEV=0TIME open/close time:  675us

So roughly 1ms for each device.
As far as I know, we don't have a specific javascript for device enumeration.

But We have javascript for the MediaStream, which will execute this code. We
feed MediaStream with a list of devices, and MediaStream handles the device
internally like popping up a windows and letting users the select the device.

+                        SND_PCM_STREAM_CAPTURE, SND_PCM_NONBLOCK) < 0 ||
+     wrapper_->PcmClose(device_handle) < 0) {

[scherkus (not reviewing), 2011/10/07 16:54:45]

could you re-write this to be more explicit?  using the || makes it harder to
figure out the error condition

if (!PcmOpen) {
  return false;
} else if (!PcmClose) {
  return false;
}
return true;

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+    return false;
+  }
+
+  return true;
 }
 
+bool AudioManagerLinux::HasAnyAlsaAudioDevice(StreamType stream) {
+  static const char kPcmInterfaceName[] = "pcm";
+  static const char kIoHintName[] = "IOID";
+  static const char* kNotWantedDevice =
+      (stream == kStreamPlayback ? "Input" : "Output");
+  void** hints = NULL;
+  bool has_device = false;
+  int card = -1;
+
+  // Loop through the sound cards.
+  // Don't use snd_device_name_hint(-1,..) since there is a access violation
+  // inside this ALSA API with libasound.so.2.0.0.

[scherkus (not reviewing), 2011/10/07 16:54:45]

do you know whether we can do a compile time/run time check?

have you checked whether this is fixed upstream / filed a bug with ALSA?

[no longer working on chromium, 2011/10/10 13:49:24]

I am not sure, probably yes.
But I am not sure if we will gain much by doing it, having two solutions for
different versions can be quite messy. Furthermore, what snd_device_name_hint(-1
does it looping through the cards in ALSA, right now we are doing the same thing
but looping them in chrome instead. The behavior should be more or less the
same.
Sorry, I haven't. I will do it later, thanks for reminding.

+  while (!wrapper_->CardNext(&card) && (card >= 0) && !has_device) {
+    int error = wrapper_->DeviceNameHint(card, kPcmInterfaceName, &hints);
+    if(!error) {

[scherkus (not reviewing), 2011/10/07 16:54:45]

space between if and (

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+      for (void** hint_iter = hints; *hint_iter != NULL; hint_iter++) {
+        // Only examine devices that are |stream| capable.  Valid values are
+        // "Input", "Output", and NULL which means both input and output.
+        scoped_ptr_malloc<char> io(wrapper_->DeviceNameGetHint(*hint_iter,
+                                                               kIoHintName));
+        if (io != NULL && strcmp(kNotWantedDevice, io.get()) == 0)
+          continue;  // Wrong type, skip the device.
+
+        // Found an input device.
+        has_device = true;
+        break;
+      }
+      // Destroy the hints now that we're done with it.

[scherkus (not reviewing), 2011/10/07 16:54:45]

nit: blank line before this one

[no longer working on chromium, 2011/10/10 13:49:24]

Done.

+      wrapper_->DeviceNameFreeHint(hints);
+      hints = NULL;
+    } else {
+      LOG(WARNING) << "HasAnyAudioDevice warning: unable to get device hints: "

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

DLOG

[henrika (OOO until Aug 14), 2011/10/07 12:07:51]

remove warning

+                   << wrapper_->StrError(error);
+    }
+  }
+
+  return has_device;
+}
+
 // static
 AudioManager* AudioManager::CreateAudioManager() {
   return new AudioManagerLinux();