Merge "Update comments"

     * user:    Pointer to context for use by the callback receiver.

     * info:    Pointer to optional parameter according to event type:

     *          - EVENT_MORE_DATA: pointer to AudioRecord::Buffer struct. The callback must not read

     *            more bytes than indicated by 'size' field and update 'size' if fewer bytes are

     *            consumed.

     *                             more bytes than indicated by 'size' field and update 'size' if

     *                             fewer bytes are consumed.

     *          - EVENT_OVERRUN: unused.

     *          - EVENT_MARKER: pointer to const uint32_t containing the marker position in frames.

     *          - EVENT_NEW_POS: pointer to const uint32_t containing the new position in frames.

    // audio_stream->get_buffer_size()/audio_stream_out_frame_size()

    static status_t getFrameCount(audio_io_handle_t output,

                                  size_t* frameCount);

    // returns the audio output stream latency in ms. Corresponds to

    // returns the audio output latency in ms. Corresponds to

    // audio_stream_out->get_latency()

    static status_t getLatency(audio_io_handle_t output,

                               uint32_t* latency);

    static status_t setVoiceVolume(float volume);

    // return the number of audio frames written by AudioFlinger to audio HAL and

    // audio dsp to DAC since the specified output I/O handle has exited standby.

    // audio dsp to DAC since the specified output has exited standby.

    // returned status (from utils/Errors.h) can be:

    // - NO_ERROR: successful operation, halFrames and dspFrames point to valid data

    // - INVALID_OPERATION: Not supported on current hardware platform

                                sp<IMemory>& buffers,   // return value 0 means it follows cblk

                                status_t *status) = 0;

    // FIXME Surprisingly, sampleRate/format/frameCount/latency don't work for input handles

    /* query the audio hardware state. This state never changes,

     * and therefore can be cached.

     */

struct AudioTrackSharedStreaming {

    // similar to NBAIO MonoPipe

    // in continuously incrementing frame units, take modulo buffer size, which must be a power of 2

    volatile int32_t mFront;    // read by server

    volatile int32_t mRear;     // write by client

    volatile int32_t mFront;    // read by consumer (output: server, input: client)

    volatile int32_t mRear;     // written by producer (output: client, input: server)

    volatile int32_t mFlush;    // incremented by client to indicate a request to flush;

                                // server notices and discards all data between mFront and mRear

    volatile uint32_t mUnderrunFrames;  // server increments for each unavailable but desired frame

            goto end;

        }

        // check for obtainBuffer interrupted by client

        // check for obtainBuffer interrupted by client

        if (flags & CBLK_INTERRUPT) {

            ALOGV("waitStreamEndDone() interrupted by client");

            status = -EINTR;