codec_dahdi.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * DAHDI native transcoding support
 *
 * Copyright (C) 1999 - 2008, Digium, Inc.
 *
 * Mark Spencer <[email protected]>
 * Kevin P. Fleming <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief Translate between various formats natively through DAHDI transcoding
 *
 * \ingroup codecs
 */

/*** MODULEINFO
   <depend>dahdi</depend>
   <support_level>core</support_level>
 ***/

#include "asterisk.h"
#include <stdbool.h>

#include <poll.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <dahdi/user.h>

#include "asterisk/lock.h"
#include "asterisk/translate.h"
#include "asterisk/config.h"
#include "asterisk/module.h"
#include "asterisk/cli.h"
#include "asterisk/channel.h"
#include "asterisk/utils.h"
#include "asterisk/linkedlists.h"
#include "asterisk/ulaw.h"
#include "asterisk/format_compatibility.h"

#define BUFFER_SIZE 8000

#define G723_SAMPLES 240
#define G729_SAMPLES 160
#define ULAW_SAMPLES 160

/* Defines from DAHDI. */
#ifndef DAHDI_FORMAT_MAX_AUDIO
/*! G.723.1 compression */
#define DAHDI_FORMAT_G723_1    (1 << 0)
/*! GSM compression */
#define DAHDI_FORMAT_GSM       (1 << 1)
/*! Raw mu-law data (G.711) */
#define DAHDI_FORMAT_ULAW      (1 << 2)
/*! Raw A-law data (G.711) */
#define DAHDI_FORMAT_ALAW      (1 << 3)
/*! ADPCM (G.726, 32kbps) */
#define DAHDI_FORMAT_G726      (1 << 4)
/*! ADPCM (IMA) */
#define DAHDI_FORMAT_ADPCM     (1 << 5)
/*! Raw 16-bit Signed Linear (8000 Hz) PCM */
#define DAHDI_FORMAT_SLINEAR   (1 << 6)
/*! LPC10, 180 samples/frame */
#define DAHDI_FORMAT_LPC10     (1 << 7)
/*! G.729A audio */
#define DAHDI_FORMAT_G729A     (1 << 8)
/*! SpeeX Free Compression */
#define DAHDI_FORMAT_SPEEX     (1 << 9)
/*! iLBC Free Compression */
#define DAHDI_FORMAT_ILBC      (1 << 10)
#endif

static struct channel_usage {
   int total;
   int encoders;
   int decoders;
} channels;

#if defined(NOT_NEEDED)
/*!
 * \internal
 * \brief Convert DAHDI format bitfield to old Asterisk format bitfield.
 * \since 13.0.0
 *
 * \param dahdi Bitfield from DAHDI to convert.
 *
 * \note They should be the same values but they don't have to be.
 *
 * \return Old Asterisk bitfield equivalent.
 */
static uint64_t bitfield_dahdi2ast(unsigned dahdi)
{
   uint64_t ast;

   switch (dahdi) {
   case DAHDI_FORMAT_G723_1:
      ast = AST_FORMAT_G723;
      break;
   case DAHDI_FORMAT_GSM:
      ast = AST_FORMAT_GSM;
      break;
   case DAHDI_FORMAT_ULAW:
      ast = AST_FORMAT_ULAW;
      break;
   case DAHDI_FORMAT_ALAW:
      ast = AST_FORMAT_ALAW;
      break;
   case DAHDI_FORMAT_G726:
      ast = AST_FORMAT_G726_AAL2;
      break;
   case DAHDI_FORMAT_ADPCM:
      ast = AST_FORMAT_ADPCM;
      break;
   case DAHDI_FORMAT_SLINEAR:
      ast = AST_FORMAT_SLIN;
      break;
   case DAHDI_FORMAT_LPC10:
      ast = AST_FORMAT_LPC10;
      break;
   case DAHDI_FORMAT_G729A:
      ast = AST_FORMAT_G729;
      break;
   case DAHDI_FORMAT_SPEEX:
      ast = AST_FORMAT_SPEEX;
      break;
   case DAHDI_FORMAT_ILBC:
      ast = AST_FORMAT_ILBC;
      break;
   default:
      ast = 0;
      break;
   }

   return ast;
}
#endif   /* defined(NOT_NEEDED) */

/*!
 * \internal
 * \brief Get the ast_codec by DAHDI format.
 * \since 13.0.0
 *
 * \param dahdi_fmt DAHDI specific codec identifier.
 *
 * \return Specified codec if exists otherwise NULL.
 */
static const struct ast_codec *get_dahdi_codec(uint32_t dahdi_fmt)
{
   const struct ast_codec *codec;

   static const struct ast_codec dahdi_g723_1 = {
      .name = "g723",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_gsm = {
      .name = "gsm",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_ulaw = {
      .name = "ulaw",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_alaw = {
      .name = "alaw",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_g726 = {
      .name = "g726",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_adpcm = {
      .name = "adpcm",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_slinear = {
      .name = "slin",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_lpc10 = {
      .name = "lpc10",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_g729a = {
      .name = "g729",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_speex = {
      .name = "speex",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };
   static const struct ast_codec dahdi_ilbc = {
      .name = "ilbc",
      .type = AST_MEDIA_TYPE_AUDIO,
      .sample_rate = 8000,
   };

   switch (dahdi_fmt) {
   case DAHDI_FORMAT_G723_1:
      codec = &dahdi_g723_1;
      break;
   case DAHDI_FORMAT_GSM:
      codec = &dahdi_gsm;
      break;
   case DAHDI_FORMAT_ULAW:
      codec = &dahdi_ulaw;
      break;
   case DAHDI_FORMAT_ALAW:
      codec = &dahdi_alaw;
      break;
   case DAHDI_FORMAT_G726:
      codec = &dahdi_g726;
      break;
   case DAHDI_FORMAT_ADPCM:
      codec = &dahdi_adpcm;
      break;
   case DAHDI_FORMAT_SLINEAR:
      codec = &dahdi_slinear;
      break;
   case DAHDI_FORMAT_LPC10:
      codec = &dahdi_lpc10;
      break;
   case DAHDI_FORMAT_G729A:
      codec = &dahdi_g729a;
      break;
   case DAHDI_FORMAT_SPEEX:
      codec = &dahdi_speex;
      break;
   case DAHDI_FORMAT_ILBC:
      codec = &dahdi_ilbc;
      break;
   default:
      codec = NULL;
      break;
   }

   return codec;
}

static char *handle_cli_transcoder_show(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a);

static struct ast_cli_entry cli[] = {
   AST_CLI_DEFINE(handle_cli_transcoder_show, "Display DAHDI transcoder utilization.")
};

struct translator {
   struct ast_translator t;
   uint32_t src_dahdi_fmt;
   uint32_t dst_dahdi_fmt;
   AST_LIST_ENTRY(translator) entry;
};

#ifndef container_of
#define container_of(ptr, type, member) \
   ((type *)((char *)(ptr) - offsetof(type, member)))
#endif

static AST_LIST_HEAD_STATIC(translators, translator);

struct codec_dahdi_pvt {
   int fd;
   struct dahdi_transcoder_formats fmts;
   unsigned int softslin:1;
   unsigned int fake:2;
   uint16_t required_samples;
   uint16_t samples_in_buffer;
   uint16_t samples_written_to_hardware;
   uint8_t ulaw_buffer[1024];
};

/* Only used by a decoder */
static int ulawtolin(struct ast_trans_pvt *pvt, int samples)
{
   struct codec_dahdi_pvt *dahdip = pvt->pvt;
   int i = samples;
   uint8_t *src = &dahdip->ulaw_buffer[0];
   int16_t *dst = pvt->outbuf.i16 + pvt->datalen;

   /* convert and copy in outbuf */
   while (i--) {
      *dst++ = AST_MULAW(*src++);
   }

   return 0;
}

/* Only used by an encoder. */
static int lintoulaw(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
   struct codec_dahdi_pvt *dahdip = pvt->pvt;
   int i = f->samples;
   uint8_t *dst = &dahdip->ulaw_buffer[dahdip->samples_in_buffer];
   int16_t *src = f->data.ptr;

   if (dahdip->samples_in_buffer + i > sizeof(dahdip->ulaw_buffer)) {
      ast_log(LOG_ERROR, "Out of buffer space!\n");
      return -i;
   }

   while (i--) {
      *dst++ = AST_LIN2MU(*src++);
   }

   dahdip->samples_in_buffer += f->samples;
   return 0;
}

static char *handle_cli_transcoder_show(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   struct channel_usage copy;

   switch (cmd) {
   case CLI_INIT:
      e->command = "transcoder show";
      e->usage =
         "Usage: transcoder show\n"
         "       Displays channel utilization of DAHDI transcoder(s).\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (a->argc != 2)
      return CLI_SHOWUSAGE;

   copy = channels;

   if (copy.total == 0)
      ast_cli(a->fd, "No DAHDI transcoders found.\n");
   else
      ast_cli(a->fd, "%d/%d encoders/decoders of %d channels are in use.\n", copy.encoders, copy.decoders, copy.total);

   return CLI_SUCCESS;
}

static void dahdi_write_frame(struct codec_dahdi_pvt *dahdip, const uint8_t *buffer, const ssize_t count)
{
   int res;
   if (!count) return;
   res = write(dahdip->fd, buffer, count);
   if (-1 == res) {
      ast_log(LOG_ERROR, "Failed to write to transcoder: %s\n", strerror(errno));
   }
   if (count != res) {
      ast_log(LOG_ERROR, "Requested write of %zd bytes, but only wrote %d bytes.\n", count, res);
   }
}

static int dahdi_encoder_framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
   struct codec_dahdi_pvt *dahdip = pvt->pvt;

   if (!f->subclass.format) {
      /* We're just faking a return for calculation purposes. */
      dahdip->fake = 2;
      pvt->samples = f->samples;
      return 0;
   }

   /* Buffer up the packets and send them to the hardware if we
    * have enough samples set up. */
   if (dahdip->softslin) {
      if (lintoulaw(pvt, f)) {
          return -1;
      }
   } else {
      /* NOTE:  If softslin support is not needed, and the sample
       * size is equal to the required sample size, we wouldn't
       * need this copy operation.  But at the time this was
       * written, only softslin is supported. */
      if (dahdip->samples_in_buffer + f->samples > sizeof(dahdip->ulaw_buffer)) {
         ast_log(LOG_ERROR, "Out of buffer space.\n");
         return -1;
      }
      memcpy(&dahdip->ulaw_buffer[dahdip->samples_in_buffer], f->data.ptr, f->samples);
      dahdip->samples_in_buffer += f->samples;
   }

   while (dahdip->samples_in_buffer >= dahdip->required_samples) {
      dahdi_write_frame(dahdip, dahdip->ulaw_buffer, dahdip->required_samples);
      dahdip->samples_written_to_hardware += dahdip->required_samples;
      dahdip->samples_in_buffer -= dahdip->required_samples;
      if (dahdip->samples_in_buffer) {
         /* Shift any remaining bytes down. */
         memmove(dahdip->ulaw_buffer, &dahdip->ulaw_buffer[dahdip->required_samples],
            dahdip->samples_in_buffer);
      }
   }
   pvt->samples += f->samples;
   pvt->datalen = 0;
   return -1;
}

static void dahdi_wait_for_packet(int fd)
{
   struct pollfd p = {0};
   p.fd = fd;
   p.events = POLLIN;
   poll(&p, 1, 10);
}

static struct ast_frame *dahdi_encoder_frameout(struct ast_trans_pvt *pvt)
{
   struct codec_dahdi_pvt *dahdip = pvt->pvt;
   int res;

   if (2 == dahdip->fake) {
      struct ast_frame frm = {
         .frametype = AST_FRAME_VOICE,
         .samples = dahdip->required_samples,
         .src = pvt->t->name,
      };

      dahdip->fake = 1;
      pvt->samples = 0;

      return ast_frisolate(&frm);
   } else if (1 == dahdip->fake) {
      dahdip->fake = 0;
      return NULL;
   }

   if (dahdip->samples_written_to_hardware >= dahdip->required_samples) {
      dahdi_wait_for_packet(dahdip->fd);
   }

   res = read(dahdip->fd, pvt->outbuf.c + pvt->datalen, pvt->t->buf_size - pvt->datalen);
   if (-1 == res) {
      if (EWOULDBLOCK == errno) {
         /* Nothing waiting... */
         return NULL;
      } else {
         ast_log(LOG_ERROR, "Failed to read from transcoder: %s\n", strerror(errno));
         return NULL;
      }
   } else {
      pvt->f.datalen = res;
      pvt->f.samples = ast_codec_samples_count(&pvt->f);

      dahdip->samples_written_to_hardware =
        (dahdip->samples_written_to_hardware >= pvt->f.samples) ?
           dahdip->samples_written_to_hardware - pvt->f.samples : 0;

      pvt->samples = 0;
      pvt->datalen = 0;
      return ast_frisolate(&pvt->f);
   }

   /* Shouldn't get here... */
   return NULL;
}

static int dahdi_decoder_framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
   struct codec_dahdi_pvt *dahdip = pvt->pvt;

   if (!f->subclass.format) {
      /* We're just faking a return for calculation purposes. */
      dahdip->fake = 2;
      pvt->samples = f->samples;
      return 0;
   }

   if (!f->datalen) {
      if (f->samples != dahdip->required_samples) {
         ast_log(LOG_ERROR, "%d != %d %d\n", f->samples, dahdip->required_samples, f->datalen);
      }
   }
   dahdi_write_frame(dahdip, f->data.ptr, f->datalen);
   dahdip->samples_written_to_hardware += f->samples;
   pvt->samples += f->samples;
   pvt->datalen = 0;
   return -1;
}

static struct ast_frame *dahdi_decoder_frameout(struct ast_trans_pvt *pvt)
{
   int res;
   struct codec_dahdi_pvt *dahdip = pvt->pvt;

   if (2 == dahdip->fake) {
      struct ast_frame frm = {
         .frametype = AST_FRAME_VOICE,
         .samples = dahdip->required_samples,
         .src = pvt->t->name,
      };

      dahdip->fake = 1;
      pvt->samples = 0;

      return ast_frisolate(&frm);
   } else if (1 == dahdip->fake) {
      pvt->samples = 0;
      dahdip->fake = 0;
      return NULL;
   }

   if (dahdip->samples_written_to_hardware >= ULAW_SAMPLES) {
      dahdi_wait_for_packet(dahdip->fd);
   }

   /* Let's check to see if there is a new frame for us.... */
   if (dahdip->softslin) {
      res = read(dahdip->fd, dahdip->ulaw_buffer, sizeof(dahdip->ulaw_buffer));
   } else {
      res = read(dahdip->fd, pvt->outbuf.c + pvt->datalen, pvt->t->buf_size - pvt->datalen);
   }

   if (-1 == res) {
      if (EWOULDBLOCK == errno) {
         /* Nothing waiting... */
         return NULL;
      } else {
         ast_log(LOG_ERROR, "Failed to read from transcoder: %s\n", strerror(errno));
         return NULL;
      }
   } else {
      if (dahdip->softslin) {
         ulawtolin(pvt, res);
         pvt->f.datalen = res * 2;
      } else {
         pvt->f.datalen = res;
      }
      pvt->datalen = 0;
      pvt->f.samples = res;
      pvt->samples = 0;
      dahdip->samples_written_to_hardware =
         (dahdip->samples_written_to_hardware >= res) ?
                 dahdip->samples_written_to_hardware - res : 0;

      return ast_frisolate(&pvt->f);
   }

   /* Shouldn't get here... */
   return NULL;
}


static void dahdi_destroy(struct ast_trans_pvt *pvt)
{
   struct codec_dahdi_pvt *dahdip = pvt->pvt;

   switch (dahdip->fmts.dstfmt) {
   case DAHDI_FORMAT_G729A:
   case DAHDI_FORMAT_G723_1:
      ast_atomic_fetchadd_int(&channels.encoders, -1);
      break;
   default:
      ast_atomic_fetchadd_int(&channels.decoders, -1);
      break;
   }

   close(dahdip->fd);
}

static struct ast_format *dahdi_format_to_cached(int format)
{
   switch (format) {
   case DAHDI_FORMAT_G723_1:
      return ast_format_g723;
   case DAHDI_FORMAT_GSM:
      return ast_format_gsm;
   case DAHDI_FORMAT_ULAW:
      return ast_format_ulaw;
   case DAHDI_FORMAT_ALAW:
      return ast_format_alaw;
   case DAHDI_FORMAT_G726:
      return ast_format_g726;
   case DAHDI_FORMAT_ADPCM:
      return ast_format_adpcm;
   case DAHDI_FORMAT_SLINEAR:
      return ast_format_slin;
   case DAHDI_FORMAT_LPC10:
      return ast_format_lpc10;
   case DAHDI_FORMAT_G729A:
      return ast_format_g729;
   case DAHDI_FORMAT_SPEEX:
      return ast_format_speex;
   case DAHDI_FORMAT_ILBC:
      return ast_format_ilbc;
   }

   /* This will never be reached */
   ast_assert(0);
   return NULL;
}

static int dahdi_translate(struct ast_trans_pvt *pvt, uint32_t dst_dahdi_fmt, uint32_t src_dahdi_fmt)
{
   /* Request translation through zap if possible */
   int fd;
   struct codec_dahdi_pvt *dahdip = pvt->pvt;
   int tried_once = 0;
   const char *dev_filename = "/dev/dahdi/transcode";

   if ((fd = open(dev_filename, O_RDWR)) < 0) {
      ast_log(LOG_ERROR, "Failed to open %s: %s\n", dev_filename, strerror(errno));
      return -1;
   }

   dahdip->fmts.srcfmt = src_dahdi_fmt;
   dahdip->fmts.dstfmt = dst_dahdi_fmt;

   ast_assert(pvt->f.subclass.format == NULL);
   pvt->f.subclass.format = ao2_bump(dahdi_format_to_cached(dahdip->fmts.dstfmt));

   ast_debug(1, "Opening transcoder channel from %s to %s.\n", pvt->t->src_codec.name, pvt->t->dst_codec.name);

retry:
   if (ioctl(fd, DAHDI_TC_ALLOCATE, &dahdip->fmts)) {
      if ((ENODEV == errno) && !tried_once) {
         /* We requested to translate to/from an unsupported
          * format.  Most likely this is because signed linear
          * was not supported by any hardware devices even
          * though this module always registers signed linear
          * support. In this case we'll retry, requesting
          * support for ULAW instead of signed linear and then
          * we'll just convert from ulaw to signed linear in
          * software. */
         if (dahdip->fmts.srcfmt == DAHDI_FORMAT_SLINEAR) {
            ast_debug(1, "Using soft_slin support on source\n");
            dahdip->softslin = 1;
            dahdip->fmts.srcfmt = DAHDI_FORMAT_ULAW;
         } else if (dahdip->fmts.dstfmt == DAHDI_FORMAT_SLINEAR) {
            ast_debug(1, "Using soft_slin support on destination\n");
            dahdip->softslin = 1;
            dahdip->fmts.dstfmt = DAHDI_FORMAT_ULAW;
         }
         tried_once = 1;
         goto retry;
      }
      ast_log(LOG_ERROR, "Unable to attach to transcoder: %s\n", strerror(errno));
      close(fd);

      return -1;
   }

   ast_fd_set_flags(fd, O_NONBLOCK);

   dahdip->fd = fd;

   dahdip->required_samples = ((dahdip->fmts.dstfmt|dahdip->fmts.srcfmt) & (DAHDI_FORMAT_G723_1)) ? G723_SAMPLES : G729_SAMPLES;

   switch (dahdip->fmts.dstfmt) {
   case DAHDI_FORMAT_G729A:
      ast_atomic_fetchadd_int(&channels.encoders, +1);
      break;
   case DAHDI_FORMAT_G723_1:
      ast_atomic_fetchadd_int(&channels.encoders, +1);
      break;
   default:
      ast_atomic_fetchadd_int(&channels.decoders, +1);
      break;
   }

   return 0;
}

static int dahdi_new(struct ast_trans_pvt *pvt)
{
   struct translator *zt = container_of(pvt->t, struct translator, t);

   return dahdi_translate(pvt, zt->dst_dahdi_fmt, zt->src_dahdi_fmt);
}

static struct ast_frame *fakesrc_sample(void)
{
   /* Don't bother really trying to test hardware ones. */
   static struct ast_frame f = {
      .frametype = AST_FRAME_VOICE,
      .samples = 160,
      .src = __PRETTY_FUNCTION__
   };

   return &f;
}

static bool is_encoder(uint32_t src_dahdi_fmt)
{
   return ((src_dahdi_fmt & (DAHDI_FORMAT_ULAW | DAHDI_FORMAT_ALAW | DAHDI_FORMAT_SLINEAR)) > 0);
}

/* Must be called with the translators list locked. */
static int register_translator(uint32_t dst_dahdi_fmt, uint32_t src_dahdi_fmt)
{
   const struct ast_codec *dst_codec;
   const struct ast_codec *src_codec;
   struct translator *zt;
   int res;

   dst_codec = get_dahdi_codec(dst_dahdi_fmt);
   src_codec = get_dahdi_codec(src_dahdi_fmt);
   if (!dst_codec || !src_codec) {
      return -1;
   }

   if (!(zt = ast_calloc(1, sizeof(*zt)))) {
      return -1;
   }

   zt->src_dahdi_fmt = src_dahdi_fmt;
   zt->dst_dahdi_fmt = dst_dahdi_fmt;

   snprintf(zt->t.name, sizeof(zt->t.name), "dahdi_%s_to_%s",
      src_codec->name, dst_codec->name);

   memcpy(&zt->t.src_codec, src_codec, sizeof(*src_codec));
   memcpy(&zt->t.dst_codec, dst_codec, sizeof(*dst_codec));
   zt->t.buf_size = BUFFER_SIZE;
   if (is_encoder(src_dahdi_fmt)) {
      zt->t.framein = dahdi_encoder_framein;
      zt->t.frameout = dahdi_encoder_frameout;
   } else {
      zt->t.framein = dahdi_decoder_framein;
      zt->t.frameout = dahdi_decoder_frameout;
   }
   zt->t.destroy = dahdi_destroy;
   zt->t.buffer_samples = 0;
   zt->t.newpvt = dahdi_new;
   zt->t.sample = fakesrc_sample;
   zt->t.native_plc = 0;

   zt->t.desc_size = sizeof(struct codec_dahdi_pvt);
   if ((res = ast_register_translator(&zt->t))) {
      ast_free(zt);
      return -1;
   }

   AST_LIST_INSERT_HEAD(&translators, zt, entry);

   return res;
}

static void unregister_translators(void)
{
   struct translator *cur;

   AST_LIST_LOCK(&translators);
   while ((cur = AST_LIST_REMOVE_HEAD(&translators, entry))) {
      ast_unregister_translator(&cur->t);
      ast_free(cur);
   }
   AST_LIST_UNLOCK(&translators);
}

/* Must be called with the translators list locked. */
static bool is_already_registered(uint32_t dstfmt, uint32_t srcfmt)
{
   bool res = false;
   const struct translator *zt;

   AST_LIST_TRAVERSE(&translators, zt, entry) {
      if ((zt->src_dahdi_fmt == srcfmt) && (zt->dst_dahdi_fmt == dstfmt)) {
         res = true;
         break;
      }
   }

   return res;
}

static void build_translators(uint32_t dstfmts, uint32_t srcfmts)
{
   uint32_t srcfmt;
   uint32_t dstfmt;

   AST_LIST_LOCK(&translators);

   for (srcfmt = 1; srcfmt != 0; srcfmt <<= 1) {
      for (dstfmt = 1; dstfmt != 0; dstfmt <<= 1) {
         if (!(dstfmts & dstfmt) || !(srcfmts & srcfmt)) {
            continue;
         }
         if (is_already_registered(dstfmt, srcfmt)) {
            continue;
         }
         register_translator(dstfmt, srcfmt);
      }
   }

   AST_LIST_UNLOCK(&translators);
}

static int find_transcoders(void)
{
   struct dahdi_transcoder_info info = { 0, };
   int fd;

   if ((fd = open("/dev/dahdi/transcode", O_RDWR)) < 0) {
      ast_log(LOG_ERROR, "Failed to open /dev/dahdi/transcode: %s\n", strerror(errno));
      return 0;
   }

   for (info.tcnum = 0; !ioctl(fd, DAHDI_TC_GETINFO, &info); info.tcnum++) {
      ast_verb(2, "Found transcoder '%s'.\n", info.name);

      /* Complex codecs need to support signed linear.  If the
       * hardware transcoder does not natively support signed linear
       * format, we will emulate it in software directly in this
       * module. Also, do not allow direct ulaw/alaw to complex
       * codec translation, since that will prevent the generic PLC
       * functions from working. */
      if (info.dstfmts & (DAHDI_FORMAT_ULAW | DAHDI_FORMAT_ALAW)) {
         info.dstfmts |= DAHDI_FORMAT_SLINEAR;
         info.dstfmts &= ~(DAHDI_FORMAT_ULAW | DAHDI_FORMAT_ALAW);
      }
      if (info.srcfmts & (DAHDI_FORMAT_ULAW | DAHDI_FORMAT_ALAW)) {
         info.srcfmts |= DAHDI_FORMAT_SLINEAR;
         info.srcfmts &= ~(DAHDI_FORMAT_ULAW | DAHDI_FORMAT_ALAW);
      }

      build_translators(info.dstfmts, info.srcfmts);
      ast_atomic_fetchadd_int(&channels.total, info.numchannels / 2);
   }

   close(fd);

   if (!info.tcnum) {
      ast_verb(2, "No hardware transcoders found.\n");
   }

   return 0;
}

static int reload(void)
{
   return AST_MODULE_LOAD_SUCCESS;
}

static int unload_module(void)
{
   ast_cli_unregister_multiple(cli, ARRAY_LEN(cli));
   unregister_translators();

   return 0;
}

static int load_module(void)
{
   find_transcoders();
   ast_cli_register_multiple(cli, ARRAY_LEN(cli));
   return AST_MODULE_LOAD_SUCCESS;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT, "Generic DAHDI Transcoder Codec Translator",
   .support_level = AST_MODULE_SUPPORT_CORE,
   .load = load_module,
   .unload = unload_module,
   .reload = reload,
);