filebuf_is_lowdata isn't needed anymore

[Rockbox.git] / apps / buffering.c

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2007 Nicolas Pennequin
 *
 * All files in this archive are subject to the GNU General Public License.
 * See the file COPYING in the source tree root for full license agreement.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/

#include "config.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include "buffering.h"

#include "ata.h"
#include "system.h"
#include "thread.h"
#include "file.h"
#include "panic.h"
#include "memory.h"
#include "lcd.h"
#include "font.h"
#include "button.h"
#include "kernel.h"
#include "tree.h"
#include "debug.h"
#include "sprintf.h"
#include "settings.h"
#include "codecs.h"
#include "audio.h"
#include "logf.h"
#include "mp3_playback.h"
#include "usb.h"
#include "status.h"
#include "screens.h"
#include "playlist.h"
#include "playback.h"
#include "pcmbuf.h"
#include "buffer.h"
#include "ata_idle_notify.h"

#ifdef SIMULATOR
#define ata_disk_is_active() 1
#endif

#if MEM > 1
#define GUARD_BUFSIZE   (32*1024)
#else
#define GUARD_BUFSIZE  (8*1024)
#endif


/* macros to enable logf for queues
   logging on SYS_TIMEOUT can be disabled */
#ifdef SIMULATOR
/* Define this for logf output of all queuing except SYS_TIMEOUT */
#define BUFFERING_LOGQUEUES
/* Define this to logf SYS_TIMEOUT messages */
/* #define BUFFERING_LOGQUEUES_SYS_TIMEOUT */
#endif

#ifdef BUFFERING_LOGQUEUES
#define LOGFQUEUE logf
#else
#define LOGFQUEUE(...)
#endif

#ifdef BUFFERING_LOGQUEUES_SYS_TIMEOUT
#define LOGFQUEUE_SYS_TIMEOUT logf
#else
#define LOGFQUEUE_SYS_TIMEOUT(...)
#endif


/* amount of data to read in one read() call */
#define AUDIO_DEFAULT_FILECHUNK      (1024*32)

/* Ring buffer helper macros */
/* Buffer pointer (p) plus value (v), wrapped if necessary */
#define RINGBUF_ADD(p,v) ((p+v)<buffer_len ? p+v : p+v-buffer_len)
/* Buffer pointer (p) minus value (v), wrapped if necessary */
#define RINGBUF_SUB(p,v) ((p>=v) ? p-v : p+buffer_len-v)
/* How far value (v) plus buffer pointer (p1) will cross buffer pointer (p2) */
#define RINGBUF_ADD_CROSS(p1,v,p2) \
((p1<p2) ? (int)(p1+v)-(int)p2 : (int)(p1+v-p2)-(int)buffer_len)
/* Bytes available in the buffer */
#define BUF_USED RINGBUF_SUB(buf_widx, buf_ridx)

struct memory_handle {
    int id;              /* A unique ID for the handle */
    enum data_type type;
    char path[MAX_PATH];
    int fd;
    size_t data;         /* Start index of the handle's data buffer */
    size_t ridx;         /* Current read pointer, relative to the main buffer */
    size_t widx;         /* Current write pointer */
    size_t filesize;     /* File total length */
    size_t filerem;      /* Remaining bytes of file NOT in buffer */
    size_t available;    /* Available bytes to read from buffer */
    size_t offset;       /* Offset at which we started reading the file */
    struct memory_handle *next;
};
/* at all times, we have: filesize == offset + available + filerem */


static char *buffer;
static char *guard_buffer;

static size_t buffer_len;

static size_t buf_widx;  /* current writing position */
static size_t buf_ridx;  /* current reading position */
/* buf_*idx are values relative to the buffer, not real pointers. */

static size_t conf_filechunk = 0;
static size_t conf_watermark = 0; /* Level to trigger filebuf fill */
#if MEM > 8
static size_t high_watermark = 0; /* High watermark for rebuffer */
#endif


/* current memory handle in the linked list. NULL when the list is empty. */
static struct memory_handle *cur_handle;
/* first memory handle in the linked list. NULL when the list is empty. */
static struct memory_handle *first_handle;

static int num_handles;  /* number of handles in the list */

/* Handle cache (makes find_handle faster).
   These need to be global so that move_handle can invalidate them. */
static int cached_handle_id = -1;
static struct memory_handle *cached_handle = NULL;


/*
LINKED LIST MANAGEMENT
======================

add_handle  : Add a handle to the list
rm_handle   : Remove a handle from the list
find_handle : Get a handle pointer from an ID
move_handle : Move a handle in the buffer (with or without its data)

These functions only handle the linked list structure. They don't touch the
contents of the struct memory_handle headers. They also change the buf_*idx
pointers when necessary and manage the handle IDs.

The first and current (== last) handle are kept track of.
A new handle is added at buf_widx and becomes the current one.
buf_widx always points to the current writing position for the current handle
buf_ridx always points to the location of the first handle.
buf_ridx == buf_widx means the buffer is empty.
*/


/* Add a new handle to the linked list and return it. It will have become the
   new current handle. The handle will reserve "data_size" bytes or if that's
   not possible, decrease "data_size" to allow adding the handle. */
static struct memory_handle *add_handle(size_t *data_size)
{
    /* this will give each handle a unique id */
    static int cur_handle_id = 1;

    /* make sure buf_widx is 32-bit aligned so that the handle struct is,
       but before that we check we can actually align. */
    if (RINGBUF_ADD_CROSS(buf_widx, 3, buf_ridx) >= 0) {
        return NULL;
    }
    buf_widx = (RINGBUF_ADD(buf_widx, 3)) & ~3;

    size_t len = (data_size ? *data_size : 0)
                 + sizeof(struct memory_handle);

    /* check that we actually can add the handle and its data */
    int overlap = RINGBUF_ADD_CROSS(buf_widx, len, buf_ridx);
    if (overlap >= 0) {
        *data_size -= overlap;
        len -= overlap;
    }
    if (len < sizeof(struct memory_handle)) {
        /* There isn't even enough space to write the struct */
        return NULL;
    }

    struct memory_handle *new_handle =
        (struct memory_handle *)(&buffer[buf_widx]);

    /* only advance the buffer write index of the size of the struct */
    buf_widx = RINGBUF_ADD(buf_widx, sizeof(struct memory_handle));

    if (!first_handle) {
        /* the new handle is the first one */
        first_handle = new_handle;
    }

    if (cur_handle) {
        cur_handle->next = new_handle;
    }

    cur_handle = new_handle;
    cur_handle->id = cur_handle_id++;
    cur_handle->next = NULL;
    num_handles++;
    return cur_handle;
}

/* Delete a given memory handle from the linked list
   and return true for success. Nothing is actually erased from memory. */
static bool rm_handle(struct memory_handle *h)
{
    if (h == first_handle) {
        first_handle = h->next;
        if (h == cur_handle) {
            /* h was the first and last handle: the buffer is now empty */
            cur_handle = NULL;
            buf_ridx = buf_widx;
        } else {
            /* update buf_ridx to point to the new first handle */
            buf_ridx = (void *)first_handle - (void *)buffer;
        }
    } else {
        struct memory_handle *m = first_handle;
        while (m && m->next != h) {
            m = m->next;
        }
        if (h && m && m->next == h) {
            m->next = h->next;
            if (h == cur_handle) {
                cur_handle = m;
                buf_widx = cur_handle->widx;
            }
        } else {
            return false;
        }
    }

    num_handles--;
    return true;
}

/* Return a pointer to the memory handle of given ID.
   NULL if the handle wasn't found */
static struct memory_handle *find_handle(int handle_id)
{
    /* simple caching because most of the time the requested handle
    will either be the same as the last, or the one after the last */
    if (cached_handle)
    {
        if (cached_handle_id == handle_id &&
            cached_handle_id == cached_handle->id)
            return cached_handle;
        else if (cached_handle->next && (cached_handle->next->id == handle_id))
        {
            /* JD's quick testing showd this block was only entered
               2/1971 calls to find_handle.
               8/1971 calls to find_handle resulted in a cache miss */
            cached_handle = cached_handle->next;
            cached_handle_id = handle_id;
            return cached_handle;
        }
    }

    struct memory_handle *m = first_handle;
    while (m && m->id != handle_id) {
        m = m->next;
    }
    cached_handle_id = handle_id;
    cached_handle = m;
    return (m && m->id == handle_id) ? m : NULL;
}

/* Move a memory handle and data_size of its data of delta.
   Return a pointer to the new location of the handle.
   delta is the value of which to move the struct data.
   data_size is the amount of data to move along with the struct. */
static struct memory_handle *move_handle(struct memory_handle *h,
                                         size_t *delta, size_t data_size)
{
    if (*delta < 4) {
        /* aligning backwards would yield a negative result,
           and moving the handle of such a small amount is a waste
           of time anyway. */
        return NULL;
    }
    /* make sure delta is 32-bit aligned so that the handle struct is. */
    *delta = (*delta - 3) & ~3;

    size_t newpos = RINGBUF_ADD((void *)h - (void *)buffer, *delta);

    struct memory_handle *dest = (struct memory_handle *)(&buffer[newpos]);

    /* Invalidate the cache to prevent it from keeping the old location of h */
    if (h == cached_handle)
        cached_handle = NULL;

    /* the cur_handle pointer might need updating */
    if (h == cur_handle) {
        cur_handle = dest;
    }

    if (h == first_handle) {
        first_handle = dest;
        buf_ridx = newpos;
    } else {
        struct memory_handle *m = first_handle;
        while (m && m->next != h) {
            m = m->next;
        }
        if (h && m && m->next == h) {
            m->next = dest;
        } else {
            return NULL;
        }
    }

    memmove(dest, h, sizeof(struct memory_handle) + data_size);

    return dest;
}


/*
BUFFER SPACE MANAGEMENT
=======================

yield_codec     : Used by buffer_handle to know if it should interrupt buffering
buffer_handle   : Buffer data for a handle
reset_handle    : Reset writing position and data buffer of a handle to its
                  current offset
rebuffer_handle : Seek to a nonbuffered part of a handle by rebuffering the data
shrink_handle   : Free buffer space by moving a handle
fill_buffer     : Call buffer_handle for all handles that have data to buffer
can_add_handle  : Indicate whether it's safe to add a handle
data_rem        : Total amount of data needing to be buffered
wasted_space    : Total amount of space available for freeing
buffered_data   : Total amount of data currently in the buffer

These functions are used by the buffering thread to manage buffer space.
*/

/* Buffer data for the given handle. Return when finished or when an event was
   received on the buffering queue.
   ev is where queue events will be received. If buffering wasn't interrupted,
   ev->id == SYS_TIMEOUT.
   Return value is the amount of data buffered, or -1 if the handle wasn't found
*/
static ssize_t buffer_handle(int handle_id, struct queue_event *ev)
{
    DEBUGF("buffer_handle(%d)\n", handle_id);
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return -1;

    if (h->filerem == 0) {
        /* nothing left to buffer */
        return 0;
    }

    if (h->fd < 0)  /* file closed, reopen */
    {
        if (*h->path)
            h->fd = open(h->path, O_RDONLY);
        else
            return -1;

        if (h->fd < 0)
            return -1;

        if (h->offset)
            lseek(h->fd, h->offset, SEEK_SET);
    }

    trigger_cpu_boost();

    ssize_t ret = 0;
    while (h->filerem > 0)
    {
        /* max amount to copy */
        size_t copy_n = MIN( MIN(h->filerem, conf_filechunk),
                             buffer_len - h->widx);

        /* stop copying if it would overwrite the reading position
           or the next handle */
        if (RINGBUF_ADD_CROSS(h->widx, copy_n, buf_ridx) >= 0 || (h->next &&
            RINGBUF_ADD_CROSS(h->widx, copy_n, (unsigned)
                              ((void *)h->next - (void *)buffer)) > 0))
            break;

        /* rc is the actual amount read */
        int rc = read(h->fd, &buffer[h->widx], copy_n);

        if (rc < 0)
        {
            if (h->type == TYPE_CODEC) {
                DEBUGF("Partial codec\n");
                break;
            }

            DEBUGF("File ended %ld bytes early\n", (long)h->filerem);
            h->filesize -= h->filerem;
            h->filerem = 0;
            break;
        }

        /* Advance buffer */
        h->widx = RINGBUF_ADD(h->widx, rc);
        if (h == cur_handle)
            buf_widx = h->widx;
        h->available += rc;
        ret += rc;
        h->filerem -= rc;

        /* DEBUGF("buffer_handle(%d): buffered %ld bytes. done: %ld. remaining: %ld.\n",
               h->id, rc, h->available, h->filerem); */

        /* Sleep a bit and stop buffering if new queue events have arrived */
        queue_wait_w_tmo(&buffering_queue, ev, 10);

        if (ev->id == Q_BUFFER_HANDLE && (int)ev->data == handle_id) {
            /* Don't stop buffering if the request is to buffer the same file */
            LOGFQUEUE("buffering < Q_BUFFER_HANDLE");
            DEBUGF("buffer_handle: continuing buffering of handle %d\n",
                   handle_id);
        }
        else if (ev->id != SYS_TIMEOUT) {
            /* An event was received, break the loop so it can be treated */
            DEBUGF("buffer_handle: event received, interrupting buffering\n");
            break;
        }
    }

    if (h->filerem == 0) {
        /* finished buffering the file */
        close(h->fd);
        h->fd = -1;
    }

    DEBUGF("buffer_handle(%d): buffered %ld bytes (%ld of %ld available, "
           "rem: %ld, off: %ld)\n",
           handle_id, (long)ret, (long)h->available, (long)h->filesize,
           (long)h->filerem, (long)h->offset);

    return ret;
}

/* Reset writing position and data buffer of a handle to its current offset.
   Use this after having set the new offset to use.
   Returns 0 for success or -1 if the handle wasn't found. */
static void reset_handle(int handle_id)
{
    DEBUGF("reset_handle(%d)\n", handle_id);

    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return;

    h->widx = h->data;
    if (h == cur_handle)
        buf_widx = h->widx;
    h->available = 0;
    h->filerem = h->filesize - h->offset;

    if (h->fd >= 0) {
        lseek(h->fd, h->offset, SEEK_SET);
    }
}

/* Seek to a nonbuffered part of a handle by rebuffering the data. */
static void rebuffer_handle(int handle_id, size_t newpos)
{
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return;

    DEBUGF("rebuffer_handle: resetting the handle to offset %ld\n", (long)newpos);
    h->offset = newpos;

    LOGFQUEUE("? >| buffering Q_RESET_HANDLE");
    queue_send(&buffering_queue, Q_RESET_HANDLE, handle_id);

    LOGFQUEUE("? >| buffering Q_BUFFER_HANDLE");
    queue_send(&buffering_queue, Q_BUFFER_HANDLE, handle_id);

    h->ridx = h->data;
}

/* Free buffer space by moving the handle struct right before the useful
   part of its data buffer or by moving all the data. */
static void shrink_handle(int handle_id)
{
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return;

    size_t delta;
    /* The value of delta might change for alignment reasons */

    if (h->next && (h->type == TYPE_ID3 || h->type == TYPE_CUESHEET ||
                    h->type == TYPE_IMAGE) && h->filerem == 0 )
    {
        /* metadata handle: we can move all of it */
        delta = RINGBUF_SUB( (unsigned)((void *)h->next - (void *)buffer),
                             h->data) - h->available;
        h = move_handle(h, &delta, h->available);
        if (!h) return;
        h->data = RINGBUF_ADD(h->data, delta);
        h->ridx = RINGBUF_ADD(h->ridx, delta);
        h->widx = RINGBUF_ADD(h->widx, delta);

        /* when moving a struct mp3entry we need to readjust its pointers. */
        if (h->type == TYPE_ID3 && h->filesize == sizeof(struct mp3entry)) {
            adjust_mp3entry((struct mp3entry *)&buffer[h->data],
                            (void *)&buffer[h->data],
                            (void *)&buffer[RINGBUF_SUB(h->data, delta)]);
        }

        DEBUGF("shrink_handle(%d): metadata, moved by %ld bytes\n",
               handle_id, (long)delta);
    }
    else
    {
        /* only move the handle struct */
        delta = RINGBUF_SUB(h->ridx, h->data);
        h = move_handle(h, &delta, 0);
        if (!h) return;
        h->data = RINGBUF_ADD(h->data, delta);
        h->available -= delta;
        h->offset += delta;
        DEBUGF("shrink_handle(%d): audio, %ld bytes freed\n",
               handle_id, (long)delta);
    }
}

/* Fill the buffer by buffering as much data as possible for handles that still
   have data left to buffer */
static void fill_buffer(struct queue_event *ev)
{
    DEBUGF("fill buffer()\n");
    struct memory_handle *m = first_handle;
    while (m) {
        if (m->filerem > 0) {
            buffer_handle(m->id, ev);
            if (ev->id != SYS_TIMEOUT)
                return;
        }
        m = m->next;
    }
}

/* Check whether it's safe to add a new handle and reserve space to let the
   current one finish buffering its data. Used by bufopen and bufalloc as
   a preliminary check before even trying to physically add the handle.
   Returns true if it's ok to add a new handle, false if not.
*/
static bool can_add_handle(void)
{
    if (cur_handle && cur_handle->filerem > 0) {
        /* the current handle hasn't finished buffering. We can only add
           a new one if there is already enough free space to finish
           the buffering. */
        if (cur_handle->filerem < (buffer_len - BUF_USED)) {
            /* Before adding the new handle we reserve some space for the
               current one to finish buffering its data. */
            buf_widx = RINGBUF_ADD(buf_widx, cur_handle->filerem);
        } else {
            return false;
        }
    }

    return true;
}

/* Return the total amount of data left to be buffered for all the handles */
static size_t data_rem(void)
{
    size_t ret = 0;

    struct memory_handle *m = first_handle;
    while (m) {
        ret += m->filerem;
        m = m->next;
    }

    return ret;
}

/* Return the amount of data we have but don't need anymore. This data can be
   safely erased to reclaim buffer space. */
static size_t wasted_space(void)
{
    size_t ret = 0;

    struct memory_handle *m = first_handle;
    while (m) {
        ret += RINGBUF_SUB(m->ridx, m->data);
        m = m->next;
    }

    return ret;
}

static size_t buffered_data(void)
{
    size_t ret = 0;
    struct memory_handle *m = first_handle;
    while (m) {
        ret += m->available;
        m = m->next;
    }
    return ret;
}


/*
BUFFERING API FUNCTIONS
=======================

bufopen     : Request the opening of a new handle for a file
bufalloc    : Open a new handle for data other than a file.
bufclose    : Close an open handle
bufseek     : Set the read pointer in a handle
bufadvance  : Move the read pointer in a handle
bufread     : Copy data from a handle into a given buffer
bufgetdata  : Give a pointer to the handle's data
bufused     : Return the amount of buffer space used

These functions are exported, to allow interaction with the buffer.
They take care of the content of the structs, and rely on the linked list
management functions for all the actual handle management work.
*/


/* Reserve space in the buffer for a file.
   filename : name of the file to open
   offset   : offset at which to start buffering the file, useful when the first
              (offset-1) bytes of the file aren't needed.
   returns  : <0 if the file cannot be opened, or one file already
   queued to be opened, otherwise the handle for the file in the buffer
*/
int bufopen(char *file, size_t offset, enum data_type type)
{
    if (!can_add_handle())
        return -2;

    int fd = open(file, O_RDONLY);
    if (fd < 0)
        return -1;

    size_t size = filesize(fd) - offset;

    if (type != TYPE_AUDIO &&
        size + sizeof(struct memory_handle) > buffer_len - buf_widx)
    {
        /* for types other than audio, the data can't wrap, so we force it */
        buf_widx = 0;
    }

    DEBUGF("bufopen: %s (offset: %ld) (%ld bytes needed)...\n",
           file, (long)offset, (long)size);

    struct memory_handle *h = add_handle(&size);
    if (!h)
    {
        DEBUGF("bufopen: failed to add handle\n");
        close(fd);
        return -2;
    }

    strncpy(h->path, file, MAX_PATH);
    h->fd = -1;
    h->filesize = filesize(fd);
    h->filerem = h->filesize - offset;
    h->offset = offset;
    h->ridx = buf_widx;
    h->widx = buf_widx;
    h->data = buf_widx;
    h->available = 0;
    h->type = type;

    close(fd);

    DEBUGF("bufopen: allocated %ld bytes. ID: %d\n", (long)size, h->id);

    if (type == TYPE_CODEC || type == TYPE_CUESHEET || type == TYPE_IMAGE) {
        /* Immediately buffer those */
        LOGFQUEUE("? >| buffering Q_BUFFER_HANDLE");
        queue_send(&buffering_queue, Q_BUFFER_HANDLE, h->id);
    }

    DEBUGF("bufopen: opened handle %d\n", h->id);
    return h->id;
}

/* Open a new handle from data that needs to be copied from memory.
   src is the source buffer from which to copy data. It can be NULL to simply
   reserve buffer space.
   size is the requested size. The call will only be successful if the
   requested amount of data can entirely fit in the buffer without wrapping.
   Return value is the handle id for success or <0 for failure.
*/
int bufalloc(void *src, size_t size, enum data_type type)
{
    if (!can_add_handle())
        return -2;

    if (size + sizeof(struct memory_handle) > buffer_len - buf_widx) {
        /* The data would need to wrap. */
        DEBUGF("bufalloc: data wrap\n");
        return -2;
    }

    size_t allocsize = size;
    struct memory_handle *h = add_handle(&allocsize);

    if (!h || allocsize != size)
        return -2;

    if (src) {
        if (type == TYPE_ID3 && size == sizeof(struct mp3entry)) {
            DEBUGF("bufalloc: allocating metadata\n");
            /* specially take care of struct mp3entry */
            copy_mp3entry((struct mp3entry *)&buffer[buf_widx],
                          (struct mp3entry *)src);
        } else {
            memcpy(&buffer[buf_widx], src, size);
        }
    }

    h->fd = -1;
    *h->path = 0;
    h->filesize = size;
    h->filerem = 0;
    h->offset = 0;
    h->ridx = buf_widx;
    h->widx = buf_widx;
    h->data = buf_widx;
    h->available = size;
    h->type = type;

    buf_widx = RINGBUF_ADD(buf_widx, size);

    DEBUGF("bufalloc: opened handle %d\n", h->id);
    return h->id;
}

/* Close the handle. Return 0 for success and < 0 for failure */
int bufclose(int handle_id)
{
    DEBUGF("bufclose(%d)\n", handle_id);
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return -1;

    if (h->fd >= 0) {
        close(h->fd);
        h->fd = -1;
    }

    rm_handle(h);
    return 0;
}

/* Set reading index in handle (relatively to the start of the file).
   Access before the available data will trigger a rebuffer.
   Return 0 for success and < 0 for failure:
     -1 if the handle wasn't found
     -2 if the new requested position was beyond the end of the file
*/
int bufseek(int handle_id, size_t newpos)
{
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return -1;

    if (newpos > h->filesize) {
        /* access beyond the end of the file */
        return -3;
    }
    else if (newpos < h->offset || h->offset + h->available < newpos) {
        /* access before or after buffered data. A rebuffer is needed. */
        rebuffer_handle(handle_id, newpos);
    }
    else {
        h->ridx = RINGBUF_ADD(h->data, newpos - h->offset);
    }
    return 0;
}

/* Advance the reading index in a handle (relatively to its current position).
   Return 0 for success and < 0 for failure */
int bufadvance(int handle_id, off_t offset)
{
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return -1;

    size_t newpos = h->offset + RINGBUF_SUB(h->ridx, h->data) + offset;

    return bufseek(handle_id, newpos);
}

/* Copy data from the given handle to the dest buffer.
   Return the number of bytes copied or < 0 for failure. */
ssize_t bufread(int handle_id, size_t size, void *dest)
{
    struct memory_handle *h = find_handle(handle_id);
    size_t buffered_data;
    if (!h)
        return -1;

    if (size == 0 && h->filerem > 0 &&
        h->available - RINGBUF_SUB(h->ridx, h->data) == 0)
        /* Data isn't ready */
        return -2;

    if (h->available - RINGBUF_SUB(h->ridx, h->data) < size && h->filerem > 0)
        /* Data isn't ready */
        return -2;

    if (h->available - RINGBUF_SUB(h->ridx, h->data) == 0 && h->filerem == 0)
        /* File is finished reading */
        return 0;

    buffered_data = MIN(size, h->available - RINGBUF_SUB(h->ridx, h->data));

    if (h->ridx + buffered_data > buffer_len)
    {
        /* the data wraps around the end of the buffer */
        size_t read = buffer_len - h->ridx;
        memcpy(dest, &buffer[h->ridx], read);
        memcpy(dest+read, buffer, buffered_data - read);
    }
    else memcpy(dest, &buffer[h->ridx], buffered_data);

    return buffered_data;
}

/* Update the "data" pointer to make the handle's data available to the caller.
   Return the length of the available linear data or < 0 for failure.
   size is the amount of linear data requested. it can be 0 to get as
   much as possible.
   The guard buffer may be used to provide the requested size */
ssize_t bufgetdata(int handle_id, size_t size, void **data)
{
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return -1;

    if (size == 0 && h->filerem > 0 &&
        h->available - RINGBUF_SUB(h->ridx, h->data) == 0)
        /* Data isn't ready */
        return -2;

    if (h->available - RINGBUF_SUB(h->ridx, h->data) < size && h->filerem > 0)
        /* Data isn't ready */
        return -2;

    if (h->available - RINGBUF_SUB(h->ridx, h->data) == 0 && h->filerem == 0)
        /* File is finished reading */
        return 0;

    ssize_t ret;

    if (h->ridx + size > buffer_len &&
        h->available - RINGBUF_SUB(h->ridx, h->data) >= size)
    {
        /* the data wraps around the end of the buffer :
           use the guard buffer to provide the requested amount of data. */
        size_t copy_n = MIN(h->ridx + size - buffer_len, GUARD_BUFSIZE);
        memcpy(guard_buffer, (unsigned char *)buffer, copy_n);
        ret = buffer_len - h->ridx + copy_n;
        DEBUGF("used the guard buffer to complete\n");
    }
    else
    {
        ret = MIN(h->available - RINGBUF_SUB(h->ridx, h->data),
                  buffer_len - h->ridx);
    }

    *data = &buffer[h->ridx];

    /* DEBUGF("bufgetdata(%d): h->ridx=%ld, ret=%ld\n", handle_id,
           (long)h->ridx, ret); */
    return ret;
}

/* Return the amount of buffer space used */
size_t bufused(void)
{
    return BUF_USED;
}

/* Initialise the buffering subsystem */
bool buffering_init(char *filebuf, size_t filebuflen)
{
    if (!filebuf || !filebuflen)
        return false;

    buffer = filebuf;
    buffer_len = filebuflen;
    guard_buffer = buffer + buffer_len;

    buf_widx = 0;
    buf_ridx = 0;

    first_handle = NULL;
    num_handles = 0;

    conf_filechunk = AUDIO_DEFAULT_FILECHUNK;
    conf_watermark = AUDIO_DEFAULT_WATERMARK;

    /* Set the high watermark as 75% full...or 25% empty :) */
#if MEM > 8
    high_watermark = 3*filebuflen / 4;
#endif

    queue_init(&buffering_queue, true);
    queue_enable_queue_send(&buffering_queue, &buffering_queue_sender_list);

    return true;
}

#if MEM > 8
/* we dont want this rebuffering on targets with little ram
   because the disk may never spin down */
static bool ata_fillbuffer_callback(void)
{
    queue_post(&buffering_queue, Q_BUFFERING_FILL_BUFFER_IF_ACTIVE_ATA, 0);
    return true;
}
#endif

void buffering_thread(void)
{
    struct queue_event ev;

    while (true)
    {
        queue_wait_w_tmo(&buffering_queue, &ev, HZ/2);

#if MEM > 8
        if ((ev.id == SYS_TIMEOUT) && (buffered_data() < high_watermark))
            register_ata_idle_func(ata_fillbuffer_callback);
#endif

next_event:
        switch (ev.id)
        {
            case Q_BUFFER_HANDLE:
                LOGFQUEUE("buffering < Q_BUFFER_HANDLE");
                queue_reply(&buffering_queue, 1);
                buffer_handle((int)ev.data, &ev);
                /* ev is now an event received by buffer_handle() */
                goto next_event;
                break;

            case Q_RESET_HANDLE:
                LOGFQUEUE("buffering < Q_RESET_HANDLE");
                queue_reply(&buffering_queue, 1);
                reset_handle((int)ev.data);
                break;


#if MEM > 8
            case Q_BUFFERING_FILL_BUFFER_IF_ACTIVE_ATA:
                 /* only fill if the disk is still spining */
#ifndef SIMULATOR
                if (!ata_disk_is_active())
                    break;
#endif
                if (num_handles > 0 && data_rem() > 0) {
                    fill_buffer(&ev);
                    goto next_event;
                }
                break;
#endif /* MEM > 8 */

#ifndef SIMULATOR
            case SYS_USB_CONNECTED:
                LOGFQUEUE("buffering < SYS_USB_CONNECTED");
                usb_acknowledge(SYS_USB_CONNECTED_ACK);
                usb_wait_for_disconnect(&buffering_queue);
                break;
#endif

            case SYS_TIMEOUT:
                LOGFQUEUE_SYS_TIMEOUT("buffering < SYS_TIMEOUT");
                break;
        }

        if (queue_empty(&buffering_queue) &&
            data_rem() > 0 && wasted_space() > buffered_data()/2) {
            DEBUGF("there is %ld bytes of wasted space\n", (long)wasted_space());

            /* free buffer from outdated audio data */
            struct memory_handle *m = first_handle;
            while (m) {
                if (m->type == TYPE_AUDIO)
                    shrink_handle(m->id);
                m = m->next;
            }

            /* free buffer by moving metadata */
            m = first_handle;
            while (m) {
                if (m->type != TYPE_AUDIO)
                    shrink_handle(m->id);
                m = m->next;
            }

        }

        if (queue_empty(&buffering_queue) &&
            data_rem() > 0 && buffered_data() < conf_watermark)
        {
            DEBUGF("%ld bytes left to buffer and the buffer is low\n",
                   (long)data_rem());
            fill_buffer(&ev);
            goto next_event;
        }
    }
}

/* Get a buffer offset from a pointer */
ssize_t get_offset(int handle_id, void *ptr)
{
    struct memory_handle *h = find_handle(handle_id);
    if (!h)
        return -1;

    return (size_t)ptr - (size_t)&buffer[h->ridx];
}

void buffering_get_debugdata(struct buffering_debug *dbgdata)
{
    dbgdata->num_handles = num_handles;
    dbgdata->data_rem = data_rem();
    dbgdata->wasted_space = wasted_space();
    dbgdata->buffered_data = buffered_data();
}