Dircache: A bit of follow-up code cleanup suggested by Amaury Pouly.

[kugel-rb.git] / firmware / common / dircache.c

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2005 by Miika Pekkarinen
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/

/* TODO:
   - Allow cache live updating while transparent rebuild is running.
*/

#include "config.h"

#include <stdio.h>
#include <errno.h>
#include "string-extra.h"
#include <stdbool.h>
#include <stdlib.h>
#include "debug.h"
#include "system.h"
#include "logf.h"
#include "dircache.h"
#include "thread.h"
#include "kernel.h"
#include "usb.h"
#include "file.h"
#include "buffer.h"
#include "dir.h"
#include "storage.h"
#if CONFIG_RTC
#include "time.h"
#include "timefuncs.h"
#endif
#include "rbpaths.h"


/* Queue commands. */
#define DIRCACHE_BUILD 1
#define DIRCACHE_STOP  2

#if (MEMORYSIZE > 8)
#define MAX_OPEN_DIRS 12
#else
#define MAX_OPEN_DIRS 8
#endif

#define MAX_PENDING_BINDINGS 2
struct fdbind_queue {
    char path[MAX_PATH];
    int fd;
};

/* Exported structures. */
struct dircache_entry {
    struct dirinfo info;
    struct dircache_entry *next;
    struct dircache_entry *up;
    struct dircache_entry *down;
    long startcluster;
    char *d_name;
};

/* Cache Layout:
 *
 * x - array of struct dircache_entry
 * r - reserved buffer
 * d - name buffer for the d_name entry of the struct dircache_entry
 * |xxxxxx|rrrrrrrrr|dddddd|
 *
 * subsequent x are allocated from the front, d are allocated from the back,
 * using the reserve buffer for entries added after initial scan
 *
 * after a while the cache may look like:
 * |xxxxxxxx|rrrrr|dddddddd|
 *
 * after a reboot, the reserve buffer is restored in it's size, so that the
 * total allocation size grows
 * |xxxxxxxx|rrrrrrrrr|dddddddd|
 */
/* this points to the beginnging of the buffer and the first entry */
static struct dircache_entry *dircache_root;
/* these point to the start and end of the name buffer (d above) */
static char                  *d_names_start, *d_names_end;
/* put "." and ".." into the d_names buffer to enable easy pointer logic */
static char                  *dot, *dotdot;
#ifdef HAVE_MULTIVOLUME
static struct dircache_entry *append_position;
#endif

static DIR_CACHED opendirs[MAX_OPEN_DIRS];
static struct dircache_entry *fd_bindings[MAX_OPEN_FILES];

static bool dircache_initialized = false;
static bool dircache_initializing = false;
static bool thread_enabled = false;
static unsigned long allocated_size = DIRCACHE_LIMIT;
static unsigned long dircache_size = 0;
static unsigned long entry_count = 0;
static unsigned long reserve_used = 0;
static unsigned int  cache_build_ticks = 0;
static unsigned long appflags = 0;

static struct event_queue dircache_queue SHAREDBSS_ATTR;
static long dircache_stack[(DEFAULT_STACK_SIZE + 0x400)/sizeof(long)];
static const char dircache_thread_name[] = "dircache";

static struct fdbind_queue fdbind_cache[MAX_PENDING_BINDINGS];
static int fdbind_idx = 0;

/* --- Internal cache structure control functions --- */

static inline struct dircache_entry* get_entry(int id)
{
    return &dircache_root[id];
}

#ifdef HAVE_EEPROM_SETTINGS
/**
 * Open the dircache file to save a snapshot on disk
 */
static int open_dircache_file(unsigned flags, int permissions)
{
    if (permissions != 0)
        return open(DIRCACHE_FILE, flags, permissions);

    return open(DIRCACHE_FILE, flags);
}

/**
 * Remove the snapshot file
 */
static int remove_dircache_file(void)
{
    return remove(DIRCACHE_FILE);
}
#endif
/** 
 * Internal function to allocate a new dircache_entry from memory.
 */
static struct dircache_entry* allocate_entry(void)
{
    struct dircache_entry *next_entry;
    
    if (dircache_size > allocated_size - MAX_PATH*2)
    {
        logf("size limit reached");
        return NULL;
    }
    
    next_entry = &dircache_root[entry_count++];
    next_entry->d_name = NULL;
    next_entry->up = NULL;
    next_entry->down = NULL;
    next_entry->next = NULL;

    dircache_size += sizeof(struct dircache_entry);

    return next_entry;
}

/**
 * Internal function to allocate a dircache_entry and set 
 * ->next entry pointers.
 */
static struct dircache_entry* dircache_gen_next(struct dircache_entry *ce)
{
    struct dircache_entry *next_entry;

    if ( (next_entry = allocate_entry()) == NULL)
        return NULL;
    next_entry->up = ce->up;
    ce->next = next_entry;
    
    return next_entry;
}

/*
 * Internal function to allocate a dircache_entry and set
 * ->down entry pointers.
 */
static struct dircache_entry* dircache_gen_down(struct dircache_entry *ce)
{
    struct dircache_entry *next_entry;

    if ( (next_entry = allocate_entry()) == NULL)
        return NULL;
    next_entry->up = ce;
    ce->down = next_entry;
    
    return next_entry;
}

/**
 * Returns true if there is an event waiting in the queue
 * that requires the current operation to be aborted.
 */
static bool check_event_queue(void)
{
    struct queue_event ev;
    
    if(!queue_peek(&dircache_queue, &ev))
        return false;
    
    switch (ev.id)
    {
        case DIRCACHE_STOP:
        case SYS_USB_CONNECTED:
#ifdef HAVE_HOTSWAP
        case SYS_FS_CHANGED:
#endif
            return true;
    }
    
    return false;
}

#if (CONFIG_PLATFORM & PLATFORM_NATIVE)
/* scan and build static data (avoid redundancy on stack) */
static struct
{
#ifdef HAVE_MULTIVOLUME
    int volume;
#endif
    struct fat_dir *dir;
    struct fat_direntry *direntry;
}sab;

static int sab_process_dir(unsigned long startcluster, struct dircache_entry *ce)
{
    /* normally, opendir expects a full fat_dir as parent but in our case,
     * it's completely useless because we don't modify anything
     * WARNING: this heavily relies on current FAT implementation ! */
    
    /* those field are necessary to update the FAT entry in case of modification
       here we don't touch anything so we put dummy values */
    sab.dir->entry = 0;
    sab.dir->entrycount = 0;
    sab.dir->file.firstcluster = 0;
    /* open directory */
    int rc = fat_opendir(IF_MV2(sab.volume,) sab.dir, startcluster, sab.dir);
    if(rc < 0)
    {
        logf("fat_opendir failed: %d", rc);
        return rc;
    }
    
    /* first pass : read dir */
    struct dircache_entry *first_ce = ce;
    
    /* read through directory */
    while((rc = fat_getnext(sab.dir, sab.direntry)) >= 0 && sab.direntry->name[0])
    {
        if(!strcmp(".", sab.direntry->name) ||
                !strcmp("..", sab.direntry->name))
            continue;

        size_t size = strlen(sab.direntry->name) + 1;
        ce->d_name = (d_names_start -= size);
        ce->startcluster = sab.direntry->firstcluster;
        ce->info.size = sab.direntry->filesize;
        ce->info.attribute = sab.direntry->attr;
        ce->info.wrtdate = sab.direntry->wrtdate;
        ce->info.wrttime = sab.direntry->wrttime;

        strcpy(ce->d_name, sab.direntry->name); 
        dircache_size += size;
        
        if(ce->info.attribute & FAT_ATTR_DIRECTORY)
            dircache_gen_down(ce);
                
        ce = dircache_gen_next(ce);
        if(ce == NULL)
            return -5;
        
        /* When simulator is used, it's only safe to yield here. */
        if(thread_enabled)
        {
            /* Stop if we got an external signal. */
            if(check_event_queue())
                return -6;
            yield();
        }
    }
    
    /* add "." and ".." */
    ce->d_name = dot;
    ce->info.attribute = FAT_ATTR_DIRECTORY;
    ce->startcluster = startcluster;
    ce->info.size = 0;
    ce->down = first_ce;
    
    ce = dircache_gen_next(ce);
    
    ce->d_name = dotdot;
    ce->info.attribute = FAT_ATTR_DIRECTORY;
    ce->startcluster = (first_ce->up ? first_ce->up->startcluster : 0);
    ce->info.size = 0;
    ce->down = first_ce->up;
    
    /* second pass: recurse ! */
    ce = first_ce;
    
    while(rc >= 0 && ce)
    {
        if(ce->d_name != NULL && ce->down != NULL && strcmp(ce->d_name, ".")
                && strcmp(ce->d_name, ".."))
            rc = sab_process_dir(ce->startcluster, ce->down);
        
        ce = ce->next;
    }
    
    return rc;
}

/* used during the generation */
static struct fat_dir sab_fat_dir;

static int dircache_scan_and_build(IF_MV2(int volume,) struct dircache_entry *ce)
{
    memset(ce, 0, sizeof(struct dircache_entry));

#ifdef HAVE_MULTIVOLUME
    if (volume > 0)
    {
        ce->d_name = (d_names_start -= sizeof(VOL_NAMES));
        size_t len = snprintf(ce->d_name, VOL_ENUM_POS + 3, VOL_NAMES, volume)+1;
        dircache_size += len;
        ce->info.attribute = FAT_ATTR_DIRECTORY | FAT_ATTR_VOLUME;
        ce->info.size = 0;
        append_position = dircache_gen_next(ce);
        ce = dircache_gen_down(ce);
    }
#endif

    struct fat_direntry direntry; /* ditto */
#ifdef HAVE_MULTIVOLUME
    sab.volume = volume;
#endif
    sab.dir = &sab_fat_dir;
    sab.direntry = &direntry;
    
    return sab_process_dir(0, ce);
}
#elif (CONFIG_PLATFORM & PLATFORM_HOSTED) /* PLATFORM_HOSTED */
static char sab_path[MAX_PATH];

static int sab_process_dir(struct dircache_entry *ce)
{
    struct dirent_uncached *entry;
    struct dircache_entry *first_ce = ce;
    DIR_UNCACHED *dir = opendir_uncached(sab_path);
    if(dir == NULL)
    {
        logf("Failed to opendir_uncached(%s)", sab_path);
        return -1;
    }
    
    while((entry = readdir_uncached(dir)))
    {
        if(!strcmp(".", entry->d_name) ||
                !strcmp("..", entry->d_name))
            continue;

        size_t size = strlen(entry->d_name) + 1;
        ce->d_name = (d_names_start -= size);
        ce->info = entry->info;

        strcpy(ce->d_name, entry->d_name);
        dircache_size += size;
        
        if(entry->info.attribute & ATTR_DIRECTORY)
        {
            dircache_gen_down(ce);
            if(ce->down == NULL)
            {
                closedir_uncached(dir);
                return -1;
            }
            /* save current paths size */
            int pathpos = strlen(sab_path);
            /* append entry */
            strlcpy(&sab_path[pathpos], "/", sizeof(sab_path) - pathpos);
            strlcpy(&sab_path[pathpos+1], entry->d_name, sizeof(sab_path) - pathpos - 1);
            
            int rc = sab_process_dir(ce->down);
            /* restore path */
            sab_path[pathpos] = '\0';
            
            if(rc < 0)
            {
                closedir_uncached(dir);
                return rc;
            }
        }
        
        ce = dircache_gen_next(ce);
        if(ce == NULL)
            return -5;
        
        /* When simulator is used, it's only safe to yield here. */
        if(thread_enabled)
        {
            /* Stop if we got an external signal. */
            if(check_event_queue())
                return -1;
            yield();
        }
    }
    
    /* add "." and ".." */
    ce->d_name = dot;
    ce->info.attribute = ATTR_DIRECTORY;
    ce->info.size = 0;
    ce->down = first_ce;
    
    ce = dircache_gen_next(ce);
    
    ce->d_name = dotdot;
    ce->info.attribute = ATTR_DIRECTORY;
    ce->info.size = 0;
    ce->down = first_ce->up;
    
    closedir_uncached(dir);
    return 0;
}

static int dircache_scan_and_build(IF_MV2(int volume,) struct dircache_entry *ce)
{
    #ifdef HAVE_MULTIVOLUME
    (void) volume;
    #endif
    memset(ce, 0, sizeof(struct dircache_entry));
    
    strlcpy(sab_path, "/", sizeof sab_path);
    return sab_process_dir(ce);
}
#endif /* PLATFORM_NATIVE */

/**
 * Internal function to get a pointer to dircache_entry for a given filename.
 *   path: Absolute path to a file or directory (see comment)
 *   go_down: Returns the first entry of the directory given by the path (see comment)
 *
 * As a a special case, accept path="" as an alias for "/".
 * Also if the path omits the first '/', it will be accepted.
 *
 * * If get_down=true:
 *   If path="/", the returned entry is the first of root directory (ie dircache_root)
 *   Otherwise, if 'entry' is the returned value when get_down=false, 
 *   the functions returns entry->down (which can be NULL)
 *
 * * If get_down=false:
 *   If path="/chunk_1/chunk_2/.../chunk_n" then this functions returns the entry
 *   root_entry()->chunk_1->chunk_2->...->chunk_(n-1)
 *   Which means that
 *   dircache_get_entry(path)->d_name == chunk_n
 *
 *   If path="/", the returned entry is NULL.
 *   If the entry doesn't exist, return NULL
 *
 *  NOTE: this functions silently handles double '/'
 */
static struct dircache_entry* dircache_get_entry(const char *path, bool go_down)
{
    char namecopy[MAX_PATH];
    char* part;
    char* end;
    
    bool at_root = true;
    struct dircache_entry *cache_entry = dircache_root;
    
    strlcpy(namecopy, path, sizeof(namecopy));
    
    for(part = strtok_r(namecopy, "/", &end); part; part = strtok_r(NULL, "/", &end))
    {
        /* If request another chunk, the current entry has to be directory
         * and so cache_entry->down has to be non-NULL/
         * Special case of root because it's already the first entry of the root directory
         *
         * NOTE: this is safe even if cache_entry->down is NULL */
        if(!at_root)
            cache_entry = cache_entry->down;
        else
            at_root = false;
        
        /* scan dir for name */
        while(cache_entry != NULL)
        {
            /* skip unused entries */
            if(cache_entry->d_name == NULL)
            {
                cache_entry = cache_entry->next;
                continue;
            }
            /* compare names */
            if(!strcasecmp(part, cache_entry->d_name))
                break;
            /* go to next entry */
            cache_entry = cache_entry->next;
        }
        
        /* handle not found case */
        if(cache_entry == NULL)
            return NULL;
    }

    /* NOTE: here cache_entry!=NULL so taking ->down is safe */
    if(go_down)
        return at_root ? cache_entry : cache_entry->down;
    else
        return at_root ? NULL : cache_entry;
}

#ifdef HAVE_EEPROM_SETTINGS

#define DIRCACHE_MAGIC  0x00d0c0a1
struct dircache_maindata {
    long magic;
    long size;
    long entry_count;
    long appflags;
    struct dircache_entry *root_entry;
    char *d_names_start;
};

/**
 * Function to load the internal cache structure from disk to initialize
 * the dircache really fast and little disk access.
 */
int dircache_load(void)
{
    struct dircache_maindata maindata;
    ssize_t bytes_read;
    int fd;
        
    if (dircache_initialized)
        return -1;
        
    logf("Loading directory cache");
    dircache_size = 0;
    
    fd = open_dircache_file(O_RDONLY, 0);
    if (fd < 0)
        return -2;
        
    bytes_read = read(fd, &maindata, sizeof(struct dircache_maindata));
    if (bytes_read != sizeof(struct dircache_maindata)
        || maindata.magic != DIRCACHE_MAGIC || maindata.size <= 0)
    {
        logf("Dircache file header error");
        close(fd);
        remove_dircache_file();
        return -3;
    }
    
    dircache_root = buffer_alloc(maindata.size + DIRCACHE_RESERVE);
    entry_count = maindata.entry_count;
    appflags = maindata.appflags;

    /* read the dircache file into memory,
     * start with the struct dircache_entries */
    ssize_t bytes_to_read = entry_count*sizeof(struct dircache_entry);
    bytes_read = read(fd, dircache_root, bytes_to_read);
    
    if (bytes_read != bytes_to_read)
    {
        logf("Dircache read failed #1");
        return -6;
    }

    /* continue with the d_names. Fix up pointers to them if needed */
    d_names_start = ((char*)&dircache_root[entry_count] + DIRCACHE_RESERVE);
    bytes_to_read = maindata.size - bytes_to_read;
    bytes_read = read(fd, d_names_start, bytes_to_read);
    close(fd);
    remove_dircache_file();
    if (bytes_read != bytes_to_read)
    {
        logf("Dircache read failed #2");
        return -7;
    }

    d_names_end = &d_names_start[bytes_read];
    dot = d_names_end - sizeof(".");
    dotdot = dot - sizeof("..");

    /* d_names are in reverse order, so the last entry points to the first string */
    ptrdiff_t offset_d_names = maindata.d_names_start - d_names_start,
              offset_entries = maindata.root_entry - dircache_root;

    /* offset_entries is less likely to differ, so check if it's 0 in the loop
     * offset_d_names however is almost always non-zero, since dircache_save()
     * creates a file which causes the reserve buffer to be used. since
     * we allocate a new, empty DIRCACHE_RESERVE here, the strings are
     * farther behind */
    if (offset_entries != 0 || offset_d_names != 0)
    {
        for(unsigned i = 0; i < entry_count; i++)
        {
            if (dircache_root[i].d_name)
                dircache_root[i].d_name -= offset_d_names;

            if (offset_entries == 0)
                continue;
            if (dircache_root[i].next)
                dircache_root[i].next -= offset_entries;
            if (dircache_root[i].up)
                dircache_root[i].up -= offset_entries;
            if (dircache_root[i].down)
                dircache_root[i].down -= offset_entries;
        }
    }

    /* Cache successfully loaded. */
    dircache_size = maindata.size;
    allocated_size = dircache_size + DIRCACHE_RESERVE;
    reserve_used = 0;
    logf("Done, %ld KiB used", dircache_size / 1024);
    dircache_initialized = true;
    memset(fd_bindings, 0, sizeof(fd_bindings));

    return 0;
}

/**
 * Function to save the internal cache stucture to disk for fast loading
 * on boot.
 */
int dircache_save(void)
{
    struct dircache_maindata maindata;
    int fd;
    unsigned long bytes_written;

    remove_dircache_file();
    
    if (!dircache_initialized)
        return -1;

    logf("Saving directory cache");
    fd = open_dircache_file(O_WRONLY | O_CREAT | O_TRUNC, 0666);

    maindata.magic = DIRCACHE_MAGIC;
    maindata.size = dircache_size;
    maindata.root_entry = dircache_root;
    maindata.d_names_start = d_names_start;
    maindata.entry_count = entry_count;
    maindata.appflags = appflags;

    /* Save the info structure */
    bytes_written = write(fd, &maindata, sizeof(struct dircache_maindata));
    if (bytes_written != sizeof(struct dircache_maindata))
    {
        close(fd);
        logf("dircache: write failed #1");
        return -2;
    }

    /* Dump whole directory cache to disk
     * start by writing the dircache_entries */
    size_t bytes_to_write = entry_count*sizeof(struct dircache_entry);
    bytes_written = write(fd, dircache_root, bytes_to_write);
    if (bytes_written != bytes_to_write)
    {
        logf("dircache: write failed #2");
        return -3;
    }

    /* continue with the d_names */
    bytes_to_write = d_names_end - d_names_start;
    bytes_written = write(fd, d_names_start, bytes_to_write);
    close(fd);
    if (bytes_written != bytes_to_write)
    {
        logf("dircache: write failed #3");
        return -4;
    }

    
    return 0;
}
#endif /* HAVE_EEPROM_SETTINGS */

/**
 * Internal function which scans the disk and creates the dircache structure.
 */
static int dircache_do_rebuild(void)
{
    struct dircache_entry* root_entry;
    unsigned int start_tick;
    int i;
    
    /* Measure how long it takes build the cache. */
    start_tick = current_tick;
    dircache_initializing = true;
    appflags = 0;

    /* reset dircache and alloc root entry */
    entry_count = 0;
    root_entry = allocate_entry();

#ifdef HAVE_MULTIVOLUME
    append_position = root_entry;

    for (i = NUM_VOLUMES; i >= 0; i--)
    {
        if (fat_ismounted(i))
        {
#endif
            cpu_boost(true);
#ifdef HAVE_MULTIVOLUME
            if (dircache_scan_and_build(IF_MV2(i,) append_position) < 0)
#else
            if (dircache_scan_and_build(IF_MV2(0,) root_entry) < 0)
#endif /* HAVE_MULTIVOLUME */
            {
                logf("dircache_scan_and_build failed");
                cpu_boost(false);
                dircache_size = 0;
                dircache_initializing = false;
                return -2;
            }
            cpu_boost(false);
#ifdef HAVE_MULTIVOLUME
        }
    }
#endif

    logf("Done, %ld KiB used", dircache_size / 1024);
    
    dircache_initialized = true;
    dircache_initializing = false;
    cache_build_ticks = current_tick - start_tick;
    
    /* Initialized fd bindings. */
    memset(fd_bindings, 0, sizeof(fd_bindings));
    for (i = 0; i < fdbind_idx; i++)
        dircache_bind(fdbind_cache[i].fd, fdbind_cache[i].path);
    fdbind_idx = 0;
    
    if (thread_enabled)
    {
        if (allocated_size - dircache_size < DIRCACHE_RESERVE)
            reserve_used = DIRCACHE_RESERVE - (allocated_size - dircache_size);
    }
    
    return 1;
}

/**
 * Internal thread that controls transparent cache building.
 */
static void dircache_thread(void)
{
    struct queue_event ev;

    while (1)
    {
        queue_wait(&dircache_queue, &ev);

        switch (ev.id)
        {
#ifdef HAVE_HOTSWAP
            case SYS_FS_CHANGED:
                if (!dircache_initialized)
                    break;
                dircache_initialized = false;
#endif
            case DIRCACHE_BUILD:
                thread_enabled = true;
                dircache_do_rebuild();
                thread_enabled = false;
                break ;
                
            case DIRCACHE_STOP:
                logf("Stopped the rebuilding.");
                dircache_initialized = false;
                break ;
            
#if (CONFIG_PLATFORM & PLATFORM_NATIVE)
            case SYS_USB_CONNECTED:
                usb_acknowledge(SYS_USB_CONNECTED_ACK);
                usb_wait_for_disconnect(&dircache_queue);
                break ;
#endif
        }
    }
}

static void generate_dot_d_names(void)
{
    dot = (d_names_start -= sizeof("."));
    dotdot = (d_names_start -= sizeof(".."));
    dircache_size += sizeof(".") + sizeof("..");
    strcpy(dot, ".");
    strcpy(dotdot, "..");
}
/**
 * Start scanning the disk to build the dircache.
 * Either transparent or non-transparent build method is used.
 */
int dircache_build(int last_size)
{
    if (dircache_initialized || thread_enabled)
        return -3;

    logf("Building directory cache");
#ifdef HAVE_EEPROM_SETTINGS
    remove_dircache_file();
#endif

    /* Background build, dircache has been previously allocated */
    if (dircache_size > 0)
    {
        thread_enabled = true;
        dircache_initializing = true;
        queue_post(&dircache_queue, DIRCACHE_BUILD, 0);
        return 2;
    }
    if (last_size > DIRCACHE_RESERVE && last_size < DIRCACHE_LIMIT )
    {
        allocated_size = last_size + DIRCACHE_RESERVE;
        dircache_root = buffer_alloc(allocated_size);
        d_names_start =
        d_names_end = ((char*)dircache_root)+allocated_size-1;
        dircache_size = 0;
        thread_enabled = true;
        generate_dot_d_names();

        /* Start a transparent rebuild. */
        queue_post(&dircache_queue, DIRCACHE_BUILD, 0);
        return 3;
    }

    /* We'll use the entire audiobuf to allocate the dircache
     * struct dircache_entrys are allocated from the beginning
     * and their corresponding d_name from the end
     * after generation the buffer will be compacted with DIRCACHE_RESERVE
     * free bytes inbetween */
    audiobuf = (char*)(((intptr_t)audiobuf & ~0x03) + 0x04);
    dircache_root = (struct dircache_entry*)audiobuf;
    d_names_start = d_names_end = audiobufend - 1;
    dircache_size = 0;
    generate_dot_d_names();

    /* Start a non-transparent rebuild. */
    int res = dircache_do_rebuild();
    if (res < 0)
        return res;

    /* now compact the dircache buffer */
    char* dst = ((char*)&dircache_root[entry_count] + DIRCACHE_RESERVE);
    ptrdiff_t offset = d_names_start - dst, size_to_move;
    if (offset <= 0) /* something went wrong */
        return -1;

    /* memmove d_names down, there's a possibility of overlap */
    size_to_move = dircache_size - entry_count*sizeof(struct dircache_entry);
    memmove(dst, d_names_start, size_to_move);
    
    /* fix up pointers to the d_names */
    for(unsigned i = 0; i < entry_count; i++)
        dircache_root[i].d_name -= offset;

    d_names_end -= offset;
    /* equivalent to dircache_size + DIRCACHE_RESERVE */
    allocated_size = (d_names_end - (char*)dircache_root);
    reserve_used = 0;
    audiobuf += allocated_size;

    return res;
}

/**
 * Steal the allocated dircache buffer and disable dircache.
 */
void* dircache_steal_buffer(long *size)
{
    dircache_disable();
    if (dircache_size == 0)
    {
        *size = 0;
        return NULL;
    }
    
    *size = dircache_size + (DIRCACHE_RESERVE-reserve_used);
    
    return dircache_root;
}

/**
 * Main initialization function that must be called before any other
 * operations within the dircache.
 */
void dircache_init(void)
{
    int i;
    int thread_id __attribute__((unused));
    
    dircache_initialized = false;
    dircache_initializing = false;
    
    memset(opendirs, 0, sizeof(opendirs));
    for (i = 0; i < MAX_OPEN_DIRS; i++)
    {
        opendirs[i].theent.d_name = buffer_alloc(MAX_PATH);
    }
    
    queue_init(&dircache_queue, true);
    thread_id = create_thread(dircache_thread, dircache_stack,
                sizeof(dircache_stack), 0, dircache_thread_name
                IF_PRIO(, PRIORITY_BACKGROUND)
                IF_COP(, CPU));
#ifdef HAVE_IO_PRIORITY
    thread_set_io_priority(thread_id,IO_PRIORITY_BACKGROUND);
#endif

}

/**
 * Returns true if dircache has been initialized and is ready to be used.
 */
bool dircache_is_enabled(void)
{
    return dircache_initialized;
}

/**
 * Returns true if dircache is being initialized.
 */
bool dircache_is_initializing(void)
{
    return dircache_initializing || thread_enabled;
}

/**
 * Set application flags used to determine if dircache is still intact.
 */
void dircache_set_appflag(long mask)
{
    appflags |= mask;
}

/**
 * Get application flags used to determine if dircache is still intact.
 */
bool dircache_get_appflag(long mask)
{
    return dircache_is_enabled() && (appflags & mask);
}

/**
 * Returns the current number of entries (directories and files) in the cache.
 */
int dircache_get_entry_count(void)
{
    return entry_count;
}

/**
 * Returns the allocated space for dircache (without reserve space).
 */
int dircache_get_cache_size(void)
{
    return dircache_is_enabled() ? dircache_size : 0;
}

/**
 * Returns how many bytes of the reserve allocation for live cache
 * updates have been used.
 */
int dircache_get_reserve_used(void)
{
    return dircache_is_enabled() ? reserve_used : 0;
}

/**
 * Returns the time in kernel ticks that took to build the cache.
 */
int dircache_get_build_ticks(void)
{
    return dircache_is_enabled() ? cache_build_ticks : 0;
}

/**
 * Disables the dircache. Usually called on shutdown or when
 * accepting a usb connection.
 */
void dircache_disable(void)
{
    int i;
    bool cache_in_use;
    
    if (thread_enabled)
        queue_post(&dircache_queue, DIRCACHE_STOP, 0);
    
    while (thread_enabled)
        sleep(1);
    dircache_initialized = false;

    logf("Waiting for cached dirs to release");
    do {
        cache_in_use = false;
        for (i = 0; i < MAX_OPEN_DIRS; i++) {
            if (!opendirs[i].regulardir && opendirs[i].busy)
            {
                cache_in_use = true;
                sleep(1);
                break ;
            }
        }
    } while (cache_in_use) ;
    
    logf("Cache released");
    entry_count = 0;
}

/**
 * Usermode function to return dircache_entry index to the given path.
 */
static int dircache_get_entry_id_ex(const char *filename, bool go_down)
{
    if (!dircache_initialized || filename == NULL)
        return -1;
    
    struct dircache_entry* res = dircache_get_entry(filename, go_down);
    return res ? res - dircache_root : -1;
}

int dircache_get_entry_id(const char* filename)
{
    return dircache_get_entry_id_ex(filename, false);
}

/**
 * Internal: Get the startcluster for the index
 */
long _dircache_get_entry_startcluster(int id)
{
    return get_entry(id)->startcluster;
}

/**
 * Internal: Get the struct dirinfo for the index
 */
struct dirinfo* _dircache_get_entry_dirinfo(int id)
{
    return &get_entry(id)->info;
}

/*
 * build a path from an entry upto the root using recursion
 *
 * it appends '/' after strlcat, therefore buf[0] needs to be prepared with '/'
 * and it will leave a trailing '/'
 *
 * returns the position of that trailing '/' so it can be deleted afterwards
 * (or, in case of truncation, the position of the nul byte */
static size_t copy_path_helper(const struct dircache_entry *entry, char *buf, size_t size)
{
    int offset = 1;
    /* has parent? */
    if (entry->up)
        offset += copy_path_helper(entry->up, buf, size);

    size_t len = strlcpy(buf+offset, entry->d_name, size - offset) + offset;
    if (len < size)
    {
        buf[len++] = '/';
        buf[len]   = '\0';
    }
    return len-1;
}
/**
 * Function to copy the full absolute path from dircache to the given buffer
 * using the given dircache_entry pointer.
 *
 * Returns the size of the resulting string, or 0 if an error occured
 */
size_t dircache_copy_path(int index, char *buf, size_t size)
{
    if (!size || !buf || index < 0)
        return 0;

    buf[0] = '/';
    size_t res = copy_path_helper(&dircache_root[index], buf, size - 1);
    /* fixup trailing '/' */
    buf[res] = '\0';
    return res;
}

/* --- Directory cache live updating functions --- */
static int block_until_ready(void)
{
    /* Block until dircache has been built. */
    while (!dircache_initialized && dircache_is_initializing())
        sleep(1);
    
    if (!dircache_initialized)
        return -1;
    
    return 0;
}

static struct dircache_entry* dircache_new_entry(const char *path, int attribute)
{
    struct dircache_entry *entry;
    char basedir[MAX_PATH*2];
    char *new;
    long last_cache_size = dircache_size;

    strlcpy(basedir, path, sizeof(basedir));
    new = strrchr(basedir, '/');
    if (new == NULL)
    {
        logf("error occurred");
        dircache_initialized = false;
        return NULL;
    }

    *new = '\0';
    new++;

    entry = dircache_get_entry(basedir, true);
    if (entry == NULL)
    {
        logf("basedir not found!");
        logf("%s", basedir);
        dircache_initialized = false;
        return NULL;
    }

    if (reserve_used + 2*sizeof(struct dircache_entry) + strlen(new)+1
        >= DIRCACHE_RESERVE)
    {
        logf("not enough space");
        dircache_initialized = false;
        return NULL;
    }
    
    while (entry->next != NULL)
        entry = entry->next;

    if (entry->d_name != NULL)
    {
        entry = dircache_gen_next(entry);
        if (entry == NULL)
        {
            dircache_initialized = false;
            return NULL;
        }
    }

    size_t size = strlen(new) + 1;
    entry->d_name = (d_names_start -= size);
    entry->startcluster = 0;
    memset(&entry->info, 0, sizeof(entry->info));
    entry->info.attribute = attribute;

    strcpy(entry->d_name, new);
    dircache_size += size;

    if (attribute & ATTR_DIRECTORY)
    {
        logf("gen_down");
        dircache_gen_down(entry);
    }
        
    reserve_used += dircache_size - last_cache_size;

    return entry;
}

void dircache_bind(int fd, const char *path)
{
    struct dircache_entry *entry;
    
    /* Queue requests until dircache has been built. */
    if (!dircache_initialized && dircache_is_initializing())
    {
        if (fdbind_idx >= MAX_PENDING_BINDINGS)
            return ;
        strlcpy(fdbind_cache[fdbind_idx].path, path, 
                sizeof(fdbind_cache[fdbind_idx].path));
        fdbind_cache[fdbind_idx].fd = fd;
        fdbind_idx++;
        return ;
    }
    
    if (!dircache_initialized)
        return ;

    logf("bind: %d/%s", fd, path);
    entry = dircache_get_entry(path, false);
    if (entry == NULL)
    {
        logf("not found!");
        dircache_initialized = false;
        return ;
    }

    fd_bindings[fd] = entry;
}

void dircache_update_filesize(int fd, long newsize, long startcluster)
{
    if (!dircache_initialized || fd < 0)
        return ;

    if (fd_bindings[fd] == NULL)
    {
        logf("dircache fd(%d) access error", fd);
        dircache_initialized = false;
        return ;
    }
    
    fd_bindings[fd]->info.size = newsize;
    fd_bindings[fd]->startcluster = startcluster;
}
void dircache_update_filetime(int fd)
{
#if CONFIG_RTC == 0
    (void)fd;
#else
    short year;
    struct tm *now = get_time();
    if (!dircache_initialized || fd < 0)
        return ;

    if (fd_bindings[fd] == NULL)
    {
        logf("dircache fd access error");
        dircache_initialized = false;
        return ;
    }
    year = now->tm_year+1900-1980;
    fd_bindings[fd]->info.wrtdate = (((year)&0x7f)<<9)           |
                                    (((now->tm_mon+1)&0xf)<<5)   |
                                    (((now->tm_mday)&0x1f));
    fd_bindings[fd]->info.wrttime = (((now->tm_hour)&0x1f)<<11)  |
                                    (((now->tm_min)&0x3f)<<5)    |
                                    (((now->tm_sec/2)&0x1f));
#endif
}

void dircache_mkdir(const char *path)
{ /* Test ok. */
    if (block_until_ready())
        return ;
        
        
    logf("mkdir: %s", path);
    dircache_new_entry(path, ATTR_DIRECTORY);
}

void dircache_rmdir(const char *path)
{ /* Test ok. */
    struct dircache_entry *entry;
    
    if (block_until_ready())
        return ;
        
    logf("rmdir: %s", path);
    entry = dircache_get_entry(path, false);
    if (entry == NULL || entry->down == NULL)
    {
        logf("not found or not a directory!");
        dircache_initialized = false;
        return ;
    }

    entry->down = NULL;
    entry->d_name = NULL;
}

/* Remove a file from cache */
void dircache_remove(const char *name)
{ /* Test ok. */
    struct dircache_entry *entry;
    
    if (block_until_ready())
        return ;
        
    logf("remove: %s", name);
    
    entry = dircache_get_entry(name, false);

    if (entry == NULL)
    {
        logf("not found!");
        dircache_initialized = false;
        return ;
    }
    
    entry->d_name = NULL;
}

void dircache_rename(const char *oldpath, const char *newpath)
{ /* Test ok. */
    struct dircache_entry *entry, *newentry;
    struct dircache_entry oldentry;
    char absolute_path[MAX_PATH*2];
    char *p;
    
    if (block_until_ready())
        return ;
        
    logf("rename: %s->%s", oldpath, newpath);
    
    entry = dircache_get_entry(oldpath, false);
    if (entry == NULL)
    {
        logf("not found!");
        dircache_initialized = false;
        return ;
    }

    /* Delete the old entry. */
    entry->d_name = NULL;

    /** If we rename the same filename twice in a row, we need to
     * save the data, because the entry will be re-used. */
    oldentry = *entry;

    /* Generate the absolute path for destination if necessary. */
    if (newpath[0] != '/')
    {
        strlcpy(absolute_path, oldpath, sizeof(absolute_path));
        p = strrchr(absolute_path, '/');
        if (!p)
        {
            logf("Invalid path");
            dircache_initialized = false;
            return ;
        }
        
        *p = '\0';
        strlcpy(p, absolute_path, sizeof(absolute_path)-strlen(p));
        newpath = absolute_path;
    }
    
    newentry = dircache_new_entry(newpath, entry->info.attribute);
    if (newentry == NULL)
    {
        dircache_initialized = false;
        return ;
    }

    newentry->down = oldentry.down;
    newentry->startcluster = oldentry.startcluster;
    newentry->info.size    = oldentry.info.size;
    newentry->info.wrtdate = oldentry.info.wrtdate;
    newentry->info.wrttime = oldentry.info.wrttime;
}

void dircache_add_file(const char *path, long startcluster)
{
    struct dircache_entry *entry;
    
    if (block_until_ready())
        return ;
    
    logf("add file: %s", path);
    entry = dircache_new_entry(path, 0);
    if (entry == NULL)
        return ;
    
    entry->startcluster = startcluster;
}

static bool is_disable_msg_pending(void)
{
    return check_event_queue();
}

DIR_CACHED* opendir_cached(const char* name)
{
    int dd;
    DIR_CACHED* pdir = opendirs;

    if ( name[0] != '/' )
    {
        DEBUGF("Only absolute paths supported right now\n");
        return NULL;
    }

    /* find a free dir descriptor */
    for ( dd=0; dd<MAX_OPEN_DIRS; dd++, pdir++)
        if ( !pdir->busy )
            break;

    if ( dd == MAX_OPEN_DIRS )
    {
        DEBUGF("Too many dirs open\n");
        errno = EMFILE;
        return NULL;
    }
    
    pdir->busy = true;

    if (!dircache_initialized || is_disable_msg_pending())
    {
        pdir->internal_entry = -1;
        pdir->regulardir = opendir_uncached(name);   
    }
    else
    {
        pdir->regulardir = NULL;
        pdir->internal_entry = dircache_get_entry_id_ex(name, true);
        pdir->theent.info.attribute = -1; /* used to make readdir_cached aware of the first call */
    }

    if (pdir->internal_entry == -1 && pdir->regulardir == NULL)
    {
        pdir->busy = false;
        return NULL;
    }

    return pdir;
}

struct dirent_cached* readdir_cached(DIR_CACHED* dir)
{
    struct dircache_entry *ce = get_entry(dir->internal_entry);
    struct dirent_uncached *regentry;
    
    if (!dir->busy)
        return NULL;

    if (dir->regulardir != NULL)
    {
        regentry = readdir_uncached(dir->regulardir);
        if (regentry == NULL)
            return NULL;

        strlcpy(dir->theent.d_name, regentry->d_name, MAX_PATH);
        dir->theent.startcluster = regentry->startcluster;
        dir->theent.info = regentry->info;
        
        return &dir->theent;
    }
    
    /* if theent.attribute=-1 then this is the first call */
    /* otherwise, this is is not so we first take the entry's ->next */
    /* NOTE: normal file can't have attribute=-1 */
    if(dir->theent.info.attribute != -1)
        ce = ce->next;
    /* skip unused entries */
    while(ce != NULL && ce->d_name == NULL)
        ce = ce->next;
    
    if (ce == NULL)
            return NULL;

    strlcpy(dir->theent.d_name, ce->d_name, MAX_PATH);
    /* Can't do `dir->theent = *ce`
       because that modifies the d_name pointer. */
    dir->theent.startcluster = ce->startcluster;
    dir->theent.info = ce->info;
    dir->internal_entry = ce - dircache_root;

    //logf("-> %s", ce->d_name);
    return &dir->theent;
}

int closedir_cached(DIR_CACHED* dir)
{
    if (!dir->busy)
        return -1;
        
    dir->busy=false;
    if (dir->regulardir != NULL)
        return closedir_uncached(dir->regulardir);
    
    return 0;
}

int mkdir_cached(const char *name)
{
    int rc=mkdir_uncached(name);
    if (rc >= 0)
        dircache_mkdir(name);
    return(rc);
}

int rmdir_cached(const char* name)
{
    int rc=rmdir_uncached(name);
    if(rc >= 0)
        dircache_rmdir(name);
    return(rc);
}