Buffering: Remove buf_ridx and buf_widx; these data are verbose.

It is trivial to obtain all required information from the allocated
handles without maintaining global indexes. In fact, it is less
complicated and increases general thread safety.

Other miscellaneous changes (some are nice to do at this time due to
required alterations, with some particularly more relevant than others):
* Handle value 0 will no longer be returned as a valid handle but all
failures will still return a negative value. Creates consistency with
buflib and removes the need to explicitly initialize them.

* Linking a new handle is delayed until explicitly
added by the code that called add_handle, keeping it invisible
until every operation succeeds, which is safer thread-wise. If anything
fails, the handle itself may just be abandoned rather than reqiring it
be freed.

* Dump the special handling to slow buffering when the PCM buffer
is low that calls PCM buffer functions. It doesn't seem to help much
of anything these days and it's a bit of a nasty hack to directly
tie those bits together. It can of course be put back (again!) if
there really is a need for it.

* Make data waiters ping the buffering thread more than just once if
the request is taking too long. Somehow I figured out how the requests
could get forgotten about but can't remember why months later after
making the change in my branch. :-)

* Neaten up some code by using (inline) functions and packing down
parameters; remember handle allocation and movement attributes in the
handle itself rather than figuring it out each time they're needed.

Change-Id: Ibf863370da3dd805132fc135e0ad104953365183
Reviewed-on: http://gerrit.rockbox.org/764
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Tested: Michael Sevakis <jethead71@rockbox.org>

2 files changed, 457 insertions, 480 deletions

diff --git a/apps/buffering.c b/apps/buffering.c
index 326228cbfa..abf1e4b821 100644
--- a/apps/buffering.c
+++ b/apps/buffering.c
@@ -18,44 +18,23 @@
  * KIND, either express or implied.
  *
  ****************************************************************************/
-
 #include "config.h"
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
-#include <ctype.h>
-#include <inttypes.h>
-#include "buffering.h"
-
-#include "storage.h"
 #include "system.h"
+#include "storage.h"
 #include "thread.h"
-#include "file.h"
-#include "panic.h"
-#include "lcd.h"
-#include "font.h"
-#include "button.h"
 #include "kernel.h"
-#include "tree.h"
+#include "panic.h"
 #include "debug.h"
-#include "settings.h"
-#include "codecs.h"
-#include "audio.h"
-#include "mp3_playback.h"
-#include "usb.h"
-#include "screens.h"
-#include "playlist.h"
-#include "pcmbuf.h"
+#include "file.h"
 #include "appevents.h"
 #include "metadata.h"
+#include "bmp.h"
 #ifdef HAVE_ALBUMART
 #include "albumart.h"
 #include "jpeg_load.h"
-#include "bmp.h"
 #include "playback.h"
 #endif
-
-#define GUARD_BUFSIZE   (32*1024)
+#include "buffering.h"
 
 /* Define LOGF_ENABLE to enable logf output in this file */
 /* #define LOGF_ENABLE */
@@ -82,31 +61,37 @@
 #define LOGFQUEUE_SYS_TIMEOUT(...)
 #endif
 
+#define GUARD_BUFSIZE   (32*1024)
+
 /* amount of data to read in one read() call */
 #define BUFFERING_DEFAULT_FILECHUNK      (1024*32)
 
 #define BUF_HANDLE_MASK                  0x7FFFFFFF
 
+enum handle_flags
+{
+    H_CANWRAP   = 0x1,   /* Handle data may wrap in buffer */
+    H_ALLOCALL  = 0x2,   /* All data must be allocated up front */
+    H_FIXEDDATA = 0x4,   /* Data is fixed in position */
+};
 
-/* assert(sizeof(struct memory_handle)%4==0) */
 struct memory_handle {
-    int id;                    /* A unique ID for the handle */
-    enum data_type type;       /* Type of data buffered with this handle */
-    int8_t pinned;             /* Count of references */
-    int8_t signaled;           /* Stop any attempt at waiting to get the data */
-    char path[MAX_PATH];       /* Path if data originated in a file */
-    int fd;                    /* File descriptor to path (-1 if closed) */
-    size_t data;               /* Start index of the handle's data buffer */
-    volatile size_t ridx;      /* Read pointer, relative to the main buffer */
-    size_t widx;               /* Write pointer, relative to the main buffer */
-    size_t filesize;           /* File total length */
-    size_t filerem;            /* Remaining bytes of file NOT in buffer */
-    volatile size_t available; /* Available bytes to read from buffer */
-    size_t offset;             /* Offset at which we started reading the file */
+    int     id;             /* A unique ID for the handle */
+    enum data_type type;    /* Type of data buffered with this handle */
+    uint8_t flags;          /* Handle property flags */
+    int8_t  pinned;         /* Count of pinnings */
+    int8_t  signaled;       /* Stop any attempt at waiting to get the data */
+    char    path[MAX_PATH]; /* Path if data originated in a file */
+    int     fd;             /* File descriptor to path (-1 if closed) */
+    size_t  data;           /* Start index of the handle's data buffer */
+    size_t  ridx;           /* Read pointer, relative to the main buffer */
+    size_t  widx;           /* Write pointer, relative to the main buffer */
+    ssize_t filesize;       /* File total length */
+    off_t   start;          /* Offset at which we started reading the file */
+    off_t   pos;            /* Read position in file */
+    off_t volatile end;     /* Offset at which we stopped reading the file */
     struct memory_handle *next;
 };
-/* invariant: filesize == offset + available + filerem */
-
 
 struct buf_message_data
 {
@@ -119,10 +104,6 @@ static char *guard_buffer;
 
 static size_t buffer_len;
 
-static volatile size_t buf_widx;  /* current writing position */
-static volatile size_t buf_ridx;  /* current reading position */
-/* buf_*idx are values relative to the buffer, not real pointers. */
-
 /* Configuration */
 static size_t conf_watermark = 0; /* Level to trigger filebuf fill */
 static size_t high_watermark = 0; /* High watermark for rebuffer */
@@ -146,7 +127,6 @@ static struct memory_handle *cached_handle = NULL;
 static struct data_counters
 {
     size_t remaining;   /* Amount of data needing to be buffered */
-    size_t wasted;      /* Amount of space available for freeing */
     size_t buffered;    /* Amount of data currently in the buffer */
     size_t useful;      /* Amount of data still useful to the user */
 } data_counters;
@@ -176,13 +156,24 @@ static unsigned int buffering_thread_id = 0;
 static struct event_queue buffering_queue SHAREDBSS_ATTR;
 static struct queue_sender_list buffering_queue_sender_list SHAREDBSS_ATTR;
 
-
+static void close_fd(int *fd_p)
+{
+    int fd = *fd_p;
+    if (fd >= 0) {
+        close(fd);
+        *fd_p = -1;
+    }
+}
 
 /* Ring buffer helper functions */
+static inline void * ringbuf_ptr(uintptr_t p)
+{
+    return buffer + p;
+}
 
 static inline uintptr_t ringbuf_offset(const void *ptr)
 {
-    return (uintptr_t)(ptr - (void*)buffer);
+    return (uintptr_t)(ptr - (void *)buffer);
 }
 
 /* Buffer pointer (p) plus value (v), wrapped if necessary */
@@ -194,7 +185,6 @@ static inline uintptr_t ringbuf_add(uintptr_t p, size_t v)
     return res;
 }
 
-
 /* Buffer pointer (p) minus value (v), wrapped if necessary */
 static inline uintptr_t ringbuf_sub(uintptr_t p, size_t v)
 {
@@ -205,7 +195,6 @@ static inline uintptr_t ringbuf_sub(uintptr_t p, size_t v)
     return res - v;
 }
 
-
 /* How far value (v) plus buffer pointer (p1) will cross buffer pointer (p2) */
 static inline ssize_t ringbuf_add_cross(uintptr_t p1, size_t v, uintptr_t p2)
 {
@@ -216,9 +205,6 @@ static inline ssize_t ringbuf_add_cross(uintptr_t p1, size_t v, uintptr_t p2)
     return res;
 }
 
-/* Bytes available in the buffer */
-#define BUF_USED ringbuf_sub(buf_widx, buf_ridx)
-
 /* Real buffer watermark */
 #define BUF_WATERMARK MIN(conf_watermark, high_watermark)
 
@@ -232,112 +218,119 @@ 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.
+contents of the struct memory_handle headers.
 
 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.
+A new handle is added at to the end and becomes the current one.
+
+num_handles = N
+first_handle -> h0 -> h1 -> h2 -> ... hN-1 -> NULL
+                                      ^
+cur_handle   -------------------------+
 */
 
+static int next_handle_id(void)
+{
+    static int cur_handle_id = 0;
+
+    /* Wrap signed int is safe and 0 doesn't happen */
+    int next_hid = (cur_handle_id + 1) & BUF_HANDLE_MASK;
+    if (next_hid == 0)
+        next_hid = 1;
+
+    cur_handle_id = next_hid;
+
+    return next_hid;
+}
+
+/* adds the handle to the linked list */
+static void link_cur_handle(struct memory_handle *h)
+{
+    h->next = NULL;
+
+    if (first_handle)
+        cur_handle->next = h;
+    else
+        first_handle = h; /* the first one */
+
+    cur_handle = h;
+    num_handles++;
+}
 
 /* Add a new handle to the linked list and return it. It will have become the
    new current handle.
+   flags contains information on how this may be allocated
    data_size must contain the size of what will be in the handle.
-   can_wrap tells us whether this type of data may wrap on buffer
-   alloc_all tells us if we must immediately be able to allocate data_size
+   widx_out points to variable to receive first available byte of data area
    returns a valid memory handle if all conditions for allocation are met.
            NULL if there memory_handle itself cannot be allocated or if the
            data_size cannot be allocated and alloc_all is set. */
-static struct memory_handle *add_handle(size_t data_size, bool can_wrap,
-                                        bool alloc_all)
+static struct memory_handle *
+add_handle(unsigned int flags, size_t data_size, size_t *data_out)
 {
-    /* gives each handle a unique id */
-    static int cur_handle_id = 0;
-    size_t shift;
-    size_t widx, new_widx;
-    size_t len;
-    ssize_t overlap;
-
+    /* Gives each handle a unique id */
     if (num_handles >= BUF_MAX_HANDLES)
         return NULL;
 
-    widx = buf_widx;
+    size_t ridx = 0, widx = 0;
+    off_t cur_total = 0;
+
+    if (first_handle) {
+        /* Buffer is not empty */
+        ridx = ringbuf_offset(first_handle);
+        widx = cur_handle->data;
+        cur_total = cur_handle->filesize - cur_handle->start;
+    }
 
-    if (cur_handle && cur_handle->filerem > 0) {
+    if (cur_total > 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. */
-        size_t req = cur_handle->filerem;
-        if (ringbuf_add_cross(cur_handle->widx, req, buf_ridx) >= 0) {
+        if (ringbuf_add_cross(widx, cur_total, ridx) >= 0) {
             /* Not enough space to finish allocation */
             return NULL;
         } else {
-            /* Allocate the remainder of the space for the current handle */
-            widx = ringbuf_add(cur_handle->widx, cur_handle->filerem);
+            /* Apply all the needed reserve */
+            widx = ringbuf_add(widx, cur_total);
         }
     }
 
-    /* align to 4 bytes up always leaving a gap */
-    new_widx = ringbuf_add(widx, 4) & ~3;
-
-    len = data_size + sizeof(struct memory_handle);
+    /* Align to pointer size up */
+    size_t adjust = ALIGN_UP(widx, sizeof(intptr_t)) - widx;
+    size_t index = ringbuf_add(widx, adjust);
+    size_t len = data_size + sizeof(struct memory_handle);
 
     /* First, will the handle wrap? */
     /* If the handle would wrap, move to the beginning of the buffer,
      * or if the data must not but would wrap, move it to the beginning */
-    if (new_widx + sizeof(struct memory_handle) > buffer_len ||
-                   (!can_wrap && new_widx + len > buffer_len)) {
-        new_widx = 0;
+    if (index + sizeof(struct memory_handle) > buffer_len ||
+        (!(flags & H_CANWRAP) && index + len > buffer_len)) {
+        index = 0;
     }
 
-    /* How far we shifted the new_widx to align things, must be < buffer_len */
-    shift = ringbuf_sub(new_widx, widx);
+    /* How far we shifted index to align things, must be < buffer_len */
+    size_t shift = ringbuf_sub(index, widx);
 
     /* How much space are we short in the actual ring buffer? */
-    overlap = ringbuf_add_cross(widx, shift + len, buf_ridx);
-    if (overlap >= 0 && (alloc_all || (size_t)overlap >= data_size)) {
+    ssize_t overlap = ringbuf_add_cross(widx, shift + len, ridx);
+    if (overlap >= 0 &&
+        ((flags & H_ALLOCALL) || (size_t)overlap >= data_size)) {
         /* Not enough space for required allocations */
         return NULL;
     }
 
-    /* There is enough space for the required data, advance the buf_widx and
-     * initialize the struct */
-    buf_widx = new_widx;
-
-    struct memory_handle *new_handle =
-        (struct memory_handle *)(&buffer[buf_widx]);
-
-    /* Prevent buffering thread from looking at it */
-    new_handle->filerem = 0;
-
-    /* Handle can be moved by default */
-    new_handle->pinned = 0;
-
-    /* Handle data can be waited for by default */
-    new_handle->signaled = 0;
+    /* There is enough space for the required data, initialize the struct */
+    struct memory_handle *h = ringbuf_ptr(index);
 
-    /* only advance the buffer write index of the size of the struct */
-    buf_widx = ringbuf_add(buf_widx, sizeof(struct memory_handle));
+    h->id       = next_handle_id();
+    h->flags    = flags;
+    h->pinned   = 0; /* Can be moved */
+    h->signaled = 0; /* Data can be waited for */
 
-    new_handle->id = cur_handle_id;
-    /* Wrap signed int is safe and 0 doesn't happen */
-    cur_handle_id = (cur_handle_id + 1) & BUF_HANDLE_MASK;
-    new_handle->next = NULL;
-    num_handles++;
-
-    if (!first_handle)
-        /* the new handle is the first one */
-        first_handle = new_handle;
+    /* Return the start of the data area */
+    *data_out = ringbuf_add(index, sizeof (struct memory_handle));
 
-    if (cur_handle)
-        cur_handle->next = new_handle;
-
-    cur_handle = new_handle;
-
-    return new_handle;
+    return h;
 }
 
 /* Delete a given memory handle from the linked list
@@ -347,28 +340,25 @@ static bool rm_handle(const struct memory_handle *h)
     if (h == NULL)
         return true;
 
-    if (h == first_handle) {
-        first_handle = h->next;
-        if (h == cur_handle) {
+    struct memory_handle *m = first_handle;
+    struct memory_handle *c = cur_handle;
+
+    if (h == m) {
+        m = m->next;
+        first_handle = m;
+        if (!m) {
             /* h was the first and last handle: the buffer is now empty */
             cur_handle = NULL;
-            buf_ridx = buf_widx = 0;
-        } else {
-            /* update buf_ridx to point to the new first handle */
-            buf_ridx = (size_t)ringbuf_offset(first_handle);
         }
     } else {
-        struct memory_handle *m = first_handle;
         /* Find the previous handle */
         while (m && m->next != h) {
             m = m->next;
         }
         if (m && m->next == h) {
             m->next = h->next;
-            if (h == cur_handle) {
+            if (h == c)
                 cur_handle = m;
-                buf_widx = cur_handle->widx;
-            }
         } else {
             /* If we don't find ourselves, this is a seriously incoherent
                state with a corrupted list and severe action is needed! */
@@ -392,15 +382,18 @@ static struct memory_handle *find_handle(int handle_id)
     if (handle_id < 0 || !first_handle)
         return NULL;
 
-    /* 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) {
-            return cached_handle;
-        } else if (cached_handle->next &&
-                   (cached_handle->next->id == handle_id)) {
-            cached_handle = cached_handle->next;
-            return cached_handle;
+    /* Simple caching because most of the time the requested handle
+       will either be the same as the last, or the one after the last */
+    struct memory_handle *cached = cached_handle;
+    if (cached) {
+        if (cached->id == handle_id) {
+            return cached;
+        } else {
+            cached = cached->next;
+            if (cached && cached->id == handle_id) {
+                cached_handle = cached;
+                return cached;
+            }
         }
     }
 
@@ -408,6 +401,7 @@ static struct memory_handle *find_handle(int handle_id)
     while (m && m->id != handle_id) {
         m = m->next;
     }
+
     /* This condition can only be reached with !m or m->id == handle_id */
     if (m)
         cached_handle = m;
@@ -425,36 +419,33 @@ static struct memory_handle *find_handle(int handle_id)
            list for adjustment.  This function has no side effects if false
            is returned. */
 static bool move_handle(struct memory_handle **h, size_t *delta,
-                        size_t data_size, bool can_wrap)
+                        size_t data_size)
 {
-    struct memory_handle *dest;
     const struct memory_handle *src;
-    size_t final_delta = *delta, size_to_move;
-    uintptr_t oldpos, newpos;
-    intptr_t overlap, overlap_old;
 
     if (h == NULL || (src = *h) == NULL)
         return false;
 
-    size_to_move = sizeof(struct memory_handle) + data_size;
+    size_t size_to_move = sizeof(struct memory_handle) + data_size;
 
-    /* Align to four bytes, down */
-    final_delta &= ~3;
+    /* Align to pointer size down */
+    size_t final_delta = *delta;
+    final_delta = ALIGN_DOWN(final_delta, sizeof(intptr_t));
     if (final_delta < sizeof(struct memory_handle)) {
         /* It's not legal to move less than the size of the struct */
         return false;
     }
 
-    oldpos = ringbuf_offset(src);
-    newpos = ringbuf_add(oldpos, final_delta);
-    overlap = ringbuf_add_cross(newpos, size_to_move, buffer_len);
-    overlap_old = ringbuf_add_cross(oldpos, size_to_move, buffer_len);
+    uintptr_t oldpos = ringbuf_offset(src);
+    uintptr_t newpos = ringbuf_add(oldpos, final_delta);
+    intptr_t overlap = ringbuf_add_cross(newpos, size_to_move, buffer_len);
+    intptr_t overlap_old = ringbuf_add_cross(oldpos, size_to_move, buffer_len);
 
     if (overlap > 0) {
         /* Some part of the struct + data would wrap, maybe ok */
         ssize_t correction = 0;
         /* If the overlap lands inside the memory_handle */
-        if (!can_wrap) {
+        if (!(src->flags & H_CANWRAP)) {
             /* Otherwise the overlap falls in the data area and must all be
              * backed out.  This may become conditional if ever we move
              * data that is allowed to wrap (ie audio) */
@@ -466,8 +457,8 @@ static bool move_handle(struct memory_handle **h, size_t *delta,
             correction = overlap - data_size;
         }
         if (correction) {
-            /* Align correction to four bytes up */
-            correction = (correction + 3) & ~3;
+            /* Align correction to pointer size up */
+            correction = ALIGN_UP(correction, sizeof(intptr_t));
             if (final_delta < correction + sizeof(struct memory_handle)) {
                 /* Delta cannot end up less than the size of the struct */
                 return false;
@@ -478,11 +469,10 @@ static bool move_handle(struct memory_handle **h, size_t *delta,
         }
     }
 
-    dest = (struct memory_handle *)(&buffer[newpos]);
+    struct memory_handle *dest = ringbuf_ptr(newpos);
 
     if (src == first_handle) {
         first_handle = dest;
-        buf_ridx = newpos;
     } else {
         struct memory_handle *m = first_handle;
         while (m && m->next != src) {
@@ -533,7 +523,7 @@ static bool move_handle(struct memory_handle **h, size_t *delta,
      */
     if (overlap_old > 0) {
         /* Move over already wrapped data by the final delta */
-        memmove(&buffer[final_delta], buffer, overlap_old);
+        memmove(ringbuf_ptr(final_delta), ringbuf_ptr(0), overlap_old);
         if (overlap <= 0)
             size_to_move -= overlap_old;
     }
@@ -541,7 +531,7 @@ static bool move_handle(struct memory_handle **h, size_t *delta,
     if (overlap > 0) {
         /* Move data that now wraps to the beginning */
         size_to_move -= overlap;
-        memmove(buffer, SKIPBYTES(src, size_to_move),
+        memmove(ringbuf_ptr(0), SKIPBYTES(src, size_to_move),
                 overlap_old > 0 ? final_delta : (size_t)overlap);
     }
 
@@ -568,59 +558,44 @@ fill_buffer     : Call buffer_handle for all handles that have data to buffer
 
 These functions are used by the buffering thread to manage buffer space.
 */
-static size_t handle_size_available(const struct memory_handle *h)
-{
-    /* Obtain proper distances from data start */
-    size_t rd = ringbuf_sub(h->ridx, h->data);
-    size_t wr = ringbuf_sub(h->widx, h->data);
-
-    if (LIKELY(wr > rd))
-        return wr - rd;
-
-    return 0; /* ridx is ahead of or equal to widx at this time */
-}
 
-static void update_data_counters(struct data_counters *dc)
+static int update_data_counters(struct data_counters *dc)
 {
-    size_t buffered = 0;
-    size_t wasted = 0;
+    size_t buffered  = 0;
     size_t remaining = 0;
-    size_t useful = 0;
-
-    struct memory_handle *m;
-    bool is_useful;
+    size_t useful    = 0;
 
     if (dc == NULL)
         dc = &data_counters;
 
     mutex_lock(&llist_mutex);
 
-    m = find_handle(base_handle_id);
-    is_useful = m == NULL;
+    int num = num_handles;
+    struct memory_handle *m = find_handle(base_handle_id);
+    bool is_useful = m == NULL;
+
+    for (m = first_handle; m; m = m->next)
+    {
+        off_t pos = m->pos;
+        off_t end = m->end;
 
-    m = first_handle;
-    while (m) {
-        buffered += m->available;
-        /* wasted could come out larger than the buffer size if ridx's are
-           overlapping data ahead of their handles' buffered data */
-        wasted += ringbuf_sub(m->ridx, m->data);
-        remaining += m->filerem;
+        buffered  += end - m->start;
+        remaining += m->filesize - end;
 
         if (m->id == base_handle_id)
             is_useful = true;
 
         if (is_useful)
-            useful += handle_size_available(m);
-
-        m = m->next;
+            useful += end - pos;
     }
 
     mutex_unlock(&llist_mutex);
 
-    dc->buffered = buffered;
-    dc->wasted = wasted;
+    dc->buffered  = buffered;
     dc->remaining = remaining;
-    dc->useful = useful;
+    dc->useful    = useful;
+
+    return num;
 }
 
 static inline bool buffer_is_low(void)
@@ -635,62 +610,64 @@ static bool buffer_handle(int handle_id, size_t to_buffer)
 {
     logf("buffer_handle(%d, %lu)", handle_id, (unsigned long)to_buffer);
     struct memory_handle *h = find_handle(handle_id);
-    bool stop = false;
-
     if (!h)
         return true;
 
     logf("  type: %d", (int)h->type);
 
-    if (h->filerem == 0) {
+    if (h->end >= h->filesize) {
         /* nothing left to buffer */
         return true;
     }
 
     if (h->fd < 0) { /* file closed, reopen */
-        if (*h->path)
+        if (h->path[0] != '\0')
             h->fd = open(h->path, O_RDONLY);
 
-        if (h->fd < 0)
-        {
+        if (h->fd < 0) {
             /* could not open the file, truncate it where it is */
-            h->filesize -= h->filerem;
-            h->filerem = 0;
+            h->filesize = h->end;
             return true;
         }
 
-        if (h->offset)
-            lseek(h->fd, h->offset, SEEK_SET);
+        if (h->start)
+            lseek(h->fd, h->start, SEEK_SET);
     }
 
     trigger_cpu_boost();
 
     if (h->type == TYPE_ID3) {
-        if (!get_metadata((struct mp3entry *)(buffer + h->data),
-                          h->fd, h->path)) {
+        if (!get_metadata(ringbuf_ptr(h->data), h->fd, h->path)) {
             /* metadata parsing failed: clear the buffer. */
-            wipe_mp3entry((struct mp3entry *)(buffer + h->data));
+            wipe_mp3entry(ringbuf_ptr(h->data));
         }
-        close(h->fd);
-        h->fd = -1;
-        h->filerem = 0;
-        h->available = sizeof(struct mp3entry);
-        h->widx = ringbuf_add(h->widx, sizeof(struct mp3entry));
+        close_fd(&h->fd);
+        h->widx = ringbuf_add(h->data, h->filesize);
+        h->end  = h->filesize;
         send_event(BUFFER_EVENT_FINISHED, &handle_id);
         return true;
     }
 
-    while (h->filerem > 0 && !stop)
+    bool stop = false;
+    while (h->end < h->filesize && !stop)
     {
         /* max amount to copy */
-        ssize_t copy_n = MIN( MIN(h->filerem, BUFFERING_DEFAULT_FILECHUNK),
-                             buffer_len - h->widx);
-        uintptr_t offset = h->next ? ringbuf_offset(h->next) : buf_ridx;
-        ssize_t overlap = ringbuf_add_cross(h->widx, copy_n, offset) + 1;
+        size_t widx = h->widx;
+
+        ssize_t copy_n = h->filesize - h->end;
+        copy_n = MIN(copy_n, BUFFERING_DEFAULT_FILECHUNK);
+        copy_n = MIN(copy_n, (off_t)(buffer_len - widx));
+
+        uintptr_t offset = ringbuf_offset(h->next ?: first_handle);
+        ssize_t overlap = ringbuf_add_cross(widx, copy_n, offset);
+
+        /* read only up to available space and stop if it would overwrite
+           the next handle; stop one byte early for last handle to avoid
+           empty/full alias */
+        if (!h->next)
+            overlap++;
 
         if (overlap > 0) {
-            /* read only up to available space and stop if it would overwrite
-               or be on top of the reading position or the next handle */
             stop = true;
             copy_n -= overlap;
         }
@@ -699,7 +676,7 @@ static bool buffer_handle(int handle_id, size_t to_buffer)
             return false; /* no space for read */
 
         /* rc is the actual amount read */
-        int rc = read(h->fd, &buffer[h->widx], copy_n);
+        ssize_t rc = read(h->fd, ringbuf_ptr(widx), copy_n);
 
         if (rc <= 0) {
             /* Some kind of filesystem error, maybe recoverable if not codec */
@@ -708,31 +685,21 @@ static bool buffer_handle(int handle_id, size_t to_buffer)
                 break;
             }
 
-            logf("File ended %ld bytes early\n", (long)h->filerem);
-            h->filesize -= h->filerem;
-            h->filerem = 0;
+            logf("File ended %lu bytes early\n",
+                 (unsigned long)(h->filesize - h->end));
+            h->filesize = h->end;
             break;
         }
 
-        /* Advance buffer */
-        h->widx = ringbuf_add(h->widx, rc);
-        if (h == cur_handle)
-            buf_widx = h->widx;
-        h->available += rc;
-        h->filerem -= rc;
-
-        /* If this is a large file, see if we need to break or give the codec
-         * more time */
-        if (h->type == TYPE_PACKET_AUDIO &&
-            pcmbuf_is_lowdata() && !buffer_is_low()) {
-            sleep(1);
-        } else {
-            yield();
-        }
+        /* Advance buffer and make data available to users */
+        h->widx = ringbuf_add(widx, rc);
+        h->end += rc;
+
+        yield();
 
         if (to_buffer == 0) {
             /* Normal buffering - check queue */
-            if(!queue_empty(&buffering_queue))
+            if (!queue_empty(&buffering_queue))
                 break;
         } else {
             if (to_buffer <= (size_t)rc)
@@ -741,10 +708,9 @@ static bool buffer_handle(int handle_id, size_t to_buffer)
         }
     }
 
-    if (h->filerem == 0) {
+    if (h->end >= h->filesize) {
         /* finished buffering the file */
-        close(h->fd);
-        h->fd = -1;
+        close_fd(&h->fd);
         send_event(BUFFER_EVENT_FINISHED, &handle_id);
     }
 
@@ -752,21 +718,17 @@ static bool buffer_handle(int handle_id, size_t to_buffer)
 }
 
 /* Close the specified handle id and free its allocation. */
+/* Q_CLOSE_HANDLE */
 static bool close_handle(int handle_id)
 {
     bool retval = true;
-    struct memory_handle *h;
 
     mutex_lock(&llist_mutex);
-    h = find_handle(handle_id);
+    struct memory_handle *h = find_handle(handle_id);
 
     /* If the handle is not found, it is closed */
     if (h) {
-        if (h->fd >= 0) {
-            close(h->fd);
-            h->fd = -1;
-        }
-
+        close_fd(&h->fd);
         /* rm_handle returns true unless the handle somehow persists after
            exit */
         retval = rm_handle(h);
@@ -791,23 +753,23 @@ static void shrink_handle(struct memory_handle *h)
         size_t delta = ringbuf_sub(h->ridx, h->data);
 
         /* The value of delta might change for alignment reasons */
-        if (!move_handle(&h, &delta, 0, true))
+        if (!move_handle(&h, &delta, 0))
             return;
 
         h->data = ringbuf_add(h->data, delta);
-        h->available -= delta;
-        h->offset += delta;
+        h->start += delta;
     } else {
         /* metadata handle: we can move all of it */
-        if (h->pinned || !h->next || h->filerem != 0)
-            return; /* Pinned, last handle or not finished loading */
+        if (h->pinned || !h->next)
+            return; /* Pinned, last handle */
 
+        size_t data_size = h->filesize - h->start;
         uintptr_t handle_distance =
             ringbuf_sub(ringbuf_offset(h->next), h->data);
-        size_t delta = handle_distance - h->available;
+        size_t delta = handle_distance - data_size;
 
         /* The value of delta might change for alignment reasons */
-        if (!move_handle(&h, &delta, h->available, h->type==TYPE_CODEC))
+        if (!move_handle(&h, &delta, data_size))
             return;
 
         size_t olddata = h->data;
@@ -815,15 +777,24 @@ static void shrink_handle(struct memory_handle *h)
         h->ridx = ringbuf_add(h->ridx, delta);
         h->widx = ringbuf_add(h->widx, delta);
 
-        if (h->type == TYPE_ID3 && h->filesize == sizeof(struct mp3entry)) {
-            /* when moving an mp3entry we need to readjust its pointers. */
-            adjust_mp3entry((struct mp3entry *)&buffer[h->data],
-                            (void *)&buffer[h->data],
-                            (const void *)&buffer[olddata]);
-        } else if (h->type == TYPE_BITMAP) {
-            /* adjust the bitmap's pointer */
-            struct bitmap *bmp = (struct bitmap *)&buffer[h->data];
-            bmp->data = &buffer[h->data + sizeof(struct bitmap)];
+        switch (h->type)
+        {
+            case TYPE_ID3:
+                if (h->filesize != sizeof(struct mp3entry))
+                    break;
+                /* when moving an mp3entry we need to readjust its pointers */
+                adjust_mp3entry(ringbuf_ptr(h->data), ringbuf_ptr(h->data),
+                                ringbuf_ptr(olddata));
+                break;
+
+            case TYPE_BITMAP:
+                /* adjust the bitmap's pointer */
+                ((struct bitmap *)ringbuf_ptr(h->data))->data =
+                    ringbuf_ptr(h->data + sizeof(struct bitmap));
+                break;
+
+            default:
+                break;
         }
     }
 }
@@ -839,11 +810,9 @@ static bool fill_buffer(void)
     shrink_handle(m);
 
     while (queue_empty(&buffering_queue) && m) {
-        if (m->filerem > 0) {
-            if (!buffer_handle(m->id, 0)) {
-                m = NULL;
-                break;
-            }
+        if (m->end < m->filesize && !buffer_handle(m->id, 0)) {
+            m = NULL;
+            break;
         }
         m = m->next;
     }
@@ -863,26 +832,24 @@ static bool fill_buffer(void)
    buffer, with a struct bitmap and the actual data immediately following.
    Return value is the total size (struct + data). */
 static int load_image(int fd, const char *path,
-                      struct bufopen_bitmap_data *data)
+                      struct bufopen_bitmap_data *data,
+                      size_t bufidx)
 {
     int rc;
-    struct bitmap *bmp = (struct bitmap *)&buffer[buf_widx];
+    struct bitmap *bmp = ringbuf_ptr(bufidx);
     struct dim *dim = data->dim;
     struct mp3_albumart *aa = data->embedded_albumart;
 
     /* get the desired image size */
     bmp->width = dim->width, bmp->height = dim->height;
     /* FIXME: alignment may be needed for the data buffer. */
-    bmp->data = &buffer[buf_widx + sizeof(struct bitmap)];
-#ifndef HAVE_JPEG
-    (void) path;
-#endif
+    bmp->data = ringbuf_ptr(bufidx + sizeof(struct bitmap));
+
 #if (LCD_DEPTH > 1) || defined(HAVE_REMOTE_LCD) && (LCD_REMOTE_DEPTH > 1)
     bmp->maskdata = NULL;
 #endif
-
-    int free = (int)MIN(buffer_len - BUF_USED, buffer_len - buf_widx)
-                               - sizeof(struct bitmap);
+    int free = (int)MIN(buffer_len - buf_used(), buffer_len - bufidx)
+                        - sizeof(struct bitmap);
 
 #ifdef HAVE_JPEG
     if (aa != NULL) {
@@ -892,14 +859,16 @@ static int load_image(int fd, const char *path,
     }
     else if (strcmp(path + strlen(path) - 4, ".bmp"))
         rc = read_jpeg_fd(fd, bmp, free, FORMAT_NATIVE|FORMAT_DITHER|
-                         FORMAT_RESIZE|FORMAT_KEEP_ASPECT, NULL);
+                          FORMAT_RESIZE|FORMAT_KEEP_ASPECT, NULL);
     else
 #endif
         rc = read_bmp_fd(fd, bmp, free, FORMAT_NATIVE|FORMAT_DITHER|
                          FORMAT_RESIZE|FORMAT_KEEP_ASPECT, NULL);
+
     return rc + (rc > 0 ? sizeof(struct bitmap) : 0);
+    (void)path;
 }
-#endif
+#endif /* HAVE_ALBUMART */
 
 
 /*
@@ -933,11 +902,9 @@ management functions for all the actual handle management work.
 int bufopen(const char *file, size_t offset, enum data_type type,
             void *user_data)
 {
-#ifndef HAVE_ALBUMART
-    /* currently only used for aa loading */
-    (void)user_data;
-#endif
     int handle_id = ERR_BUFFER_FULL;
+    size_t data;
+    struct memory_handle *h;
 
     /* No buffer refs until after the mutex_lock call! */
 
@@ -945,24 +912,23 @@ int bufopen(const char *file, size_t offset, enum data_type type,
         /* ID3 case: allocate space, init the handle and return. */
         mutex_lock(&llist_mutex);
 
-        struct memory_handle *h =
-            add_handle(sizeof(struct mp3entry), false, true);
+        h = add_handle(H_ALLOCALL, sizeof(struct mp3entry), &data);
 
         if (h) {
             handle_id = h->id;
-            h->fd = -1;
-            h->filesize = sizeof(struct mp3entry);
-            h->offset = 0;
-            h->data = buf_widx;
-            h->ridx = buf_widx;
-            h->widx = buf_widx;
-            h->available = 0;
-            h->type = type;
-            strlcpy(h->path, file, MAX_PATH);
 
-            buf_widx = ringbuf_add(buf_widx, sizeof(struct mp3entry));
+            h->type     = type;
+            strlcpy(h->path, file, MAX_PATH);
+            h->fd       = -1;
+            h->data     = data;
+            h->ridx     = data;
+            h->widx     = data;
+            h->filesize = sizeof(struct mp3entry);
+            h->start    = 0;
+            h->pos      = 0;
+            h->end      = 0;
 
-            h->filerem = sizeof(struct mp3entry);
+            link_cur_handle(h);
 
             /* Inform the buffering thread that we added a handle */
             LOGFQUEUE("buffering > Q_HANDLE_ADDED %d", handle_id);
@@ -975,7 +941,7 @@ int bufopen(const char *file, size_t offset, enum data_type type,
     else if (type == TYPE_UNKNOWN)
         return ERR_UNSUPPORTED_TYPE;
 #ifdef APPLICATION
-    /* loading code from memory is not supported in application builds */
+    /* Loading code from memory is not supported in application builds */
     else if (type == TYPE_CODEC)
         return ERR_UNSUPPORTED_TYPE;
 #endif
@@ -987,27 +953,31 @@ int bufopen(const char *file, size_t offset, enum data_type type,
     size_t size = 0;
 #ifdef HAVE_ALBUMART
     if (type == TYPE_BITMAP) {
-        /* if albumart is embedded, the complete file is not buffered,
+        /* If albumart is embedded, the complete file is not buffered,
          * but only the jpeg part; filesize() would be wrong */
-        struct bufopen_bitmap_data *aa = (struct bufopen_bitmap_data*)user_data;
+        struct bufopen_bitmap_data *aa = user_data;
         if (aa->embedded_albumart)
             size = aa->embedded_albumart->size;
     }
 #endif
+
     if (size == 0)
         size = filesize(fd);
-    bool can_wrap = type==TYPE_PACKET_AUDIO || type==TYPE_CODEC;
+
+    unsigned int hflags = 0;
+    if (type == TYPE_PACKET_AUDIO || type == TYPE_CODEC)
+        hflags = H_CANWRAP;
 
     size_t adjusted_offset = offset;
     if (adjusted_offset > size)
         adjusted_offset = 0;
 
     /* Reserve extra space because alignment can move data forward */
-    size_t padded_size = STORAGE_PAD(size-adjusted_offset);
+    size_t padded_size = STORAGE_PAD(size - adjusted_offset);
 
     mutex_lock(&llist_mutex);
 
-    struct memory_handle *h = add_handle(padded_size, can_wrap, false);
+    h = add_handle(hflags, padded_size, &data);
     if (!h) {
         DEBUGF("%s(): failed to add handle\n", __func__);
         mutex_unlock(&llist_mutex);
@@ -1016,8 +986,10 @@ int bufopen(const char *file, size_t offset, enum data_type type,
     }
 
     handle_id = h->id;
+
+    h->type = type;
     strlcpy(h->path, file, MAX_PATH);
-    h->offset = adjusted_offset;
+    h->fd   = -1;
 
 #ifdef STORAGE_WANTS_ALIGN
     /* Don't bother to storage align bitmaps because they are not
@@ -1025,44 +997,40 @@ int bufopen(const char *file, size_t offset, enum data_type type,
      */
     if (type != TYPE_BITMAP) {
         /* Align to desired storage alignment */
-        size_t alignment_pad = STORAGE_OVERLAP(adjusted_offset -
-                                               (size_t)(&buffer[buf_widx]));
-        buf_widx = ringbuf_add(buf_widx, alignment_pad);
+        size_t alignment_pad = STORAGE_OVERLAP((uintptr_t)adjusted_offset -
+                                               (uintptr_t)ringbuf_ptr(data));
+        data = ringbuf_add(data, alignment_pad);
     }
 #endif /* STORAGE_WANTS_ALIGN */
 
-    h->fd   = -1;
-    h->data = buf_widx;
-    h->ridx = buf_widx;
-    h->widx = buf_widx;
-    h->available = 0;
-    h->type = type;
+    h->data  = data;
+    h->ridx  = data;
+    h->start = adjusted_offset;
+    h->pos   = adjusted_offset;
 
 #ifdef HAVE_ALBUMART
     if (type == TYPE_BITMAP) {
         /* Bitmap file: we load the data instead of the file */
-        int rc;
-        rc = load_image(fd, file, (struct bufopen_bitmap_data*)user_data);
+        int rc = load_image(fd, file, user_data, data);
         if (rc <= 0) {
-            rm_handle(h);
             handle_id = ERR_FILE_ERROR;
         } else {
-            h->filesize = rc;
-            h->available = rc;
-            buf_widx = ringbuf_add(buf_widx, rc);
-            h->widx = buf_widx;
+            data = ringbuf_add(data, rc);
+            size = rc;
+            adjusted_offset = rc;
         }
     }
     else
 #endif
-    {
-        if (type == TYPE_CUESHEET)
-            h->fd = fd;
+    if (type == TYPE_CUESHEET) {
+        h->fd = fd;
+    }
 
+    if (handle_id >= 0) {
+        h->widx     = data;
         h->filesize = size;
-        h->available = 0;
-        h->widx = buf_widx;
-        h->filerem = size - adjusted_offset;
+        h->end      = adjusted_offset;
+        link_cur_handle(h);
     }
 
     mutex_unlock(&llist_mutex);
@@ -1084,6 +1052,9 @@ int bufopen(const char *file, size_t offset, enum data_type type,
 
     logf("bufopen: new hdl %d", handle_id);
     return handle_id;
+
+    /* Currently only used for aa loading */
+    (void)user_data;
 }
 
 /* Open a new handle from data that needs to be copied from memory.
@@ -1095,16 +1066,15 @@ int bufopen(const char *file, size_t offset, enum data_type type,
 */
 int bufalloc(const void *src, size_t size, enum data_type type)
 {
-    int handle_id;
-
     if (type == TYPE_UNKNOWN)
         return ERR_UNSUPPORTED_TYPE;
 
-    handle_id = ERR_BUFFER_FULL;
+    int handle_id = ERR_BUFFER_FULL;
 
     mutex_lock(&llist_mutex);
 
-    struct memory_handle *h = add_handle(size, false, true);
+    size_t data;
+    struct memory_handle *h = add_handle(H_ALLOCALL, size, &data);
 
     if (h) {
         handle_id = h->id;
@@ -1112,23 +1082,24 @@ int bufalloc(const void *src, size_t size, enum data_type type)
         if (src) {
             if (type == TYPE_ID3 && size == sizeof(struct mp3entry)) {
                 /* specially take care of struct mp3entry */
-                copy_mp3entry((struct mp3entry *)&buffer[buf_widx],
-                              (const struct mp3entry *)src);
+                copy_mp3entry(ringbuf_ptr(data), src);
             } else {
-                memcpy(&buffer[buf_widx], src, size);
+                memcpy(ringbuf_ptr(data), src, size);
             }
         }
 
-        h->fd = -1;
-        *h->path = 0;
-        h->filesize = size;
-        h->offset = 0;
-        h->ridx = buf_widx;
-        h->data = buf_widx;
-        buf_widx = ringbuf_add(buf_widx, size);
-        h->widx = buf_widx;
-        h->available = size;
-        h->type = type;
+        h->type      = type;
+        h->path[0]   = '\0';
+        h->fd        = -1;
+        h->data      = data;
+        h->ridx      = data;
+        h->widx      = ringbuf_add(data, size);
+        h->filesize  = size;
+        h->start     = 0;
+        h->pos       = 0;
+        h->end       = size;
+
+        link_cur_handle(h);
     }
 
     mutex_unlock(&llist_mutex);
@@ -1155,32 +1126,36 @@ bool bufclose(int handle_id)
 
 /* Backend to bufseek and bufadvance. Call only in response to
    Q_REBUFFER_HANDLE! */
-static void rebuffer_handle(int handle_id, size_t newpos)
+static void rebuffer_handle(int handle_id, off_t newpos)
 {
     struct memory_handle *h = find_handle(handle_id);
-
     if (!h) {
         queue_reply(&buffering_queue, ERR_HANDLE_NOT_FOUND);
         return;
     }
 
+    /* Check that we still need to do this since the request could have
+       possibly been met by this time */
+    if (newpos >= h->start && newpos <= h->end) {
+        h->ridx = ringbuf_add(h->data, newpos - h->start);
+        h->pos  = newpos;
+        queue_reply(&buffering_queue, 0);
+        return;
+    }
+
     /* When seeking foward off of the buffer, if it is a short seek attempt to
        avoid rebuffering the whole track, just read enough to satisfy */
-    if (newpos > h->offset &&
-        newpos - h->offset < BUFFERING_DEFAULT_FILECHUNK) {
-
-        size_t amount = newpos - h->offset;
-        h->ridx = ringbuf_add(h->data, amount);
-
-        if (buffer_handle(handle_id, amount + 1)) {
-            size_t rd = ringbuf_sub(h->ridx, h->data);
-            size_t wr = ringbuf_sub(h->widx, h->data);
-            if (wr >= rd) {
-                /* It really did succeed */
-                queue_reply(&buffering_queue, 0);
-                buffer_handle(handle_id, 0); /* Ok, try the rest */
-                return;
-            }
+    off_t amount = newpos - h->pos;
+
+    if (amount > 0 && amount <= BUFFERING_DEFAULT_FILECHUNK) {
+        h->ridx = ringbuf_add(h->data, newpos - h->start);
+        h->pos  = newpos;
+
+        if (buffer_handle(handle_id, amount + 1) && h->end >= h->pos) {
+            /* It really did succeed */
+            queue_reply(&buffering_queue, 0);
+            buffer_handle(handle_id, 0); /* Ok, try the rest */
+            return;
         }
         /* Data collision or other file error - must reset */
 
@@ -1188,10 +1163,7 @@ static void rebuffer_handle(int handle_id, size_t newpos)
             newpos = h->filesize; /* file truncation happened above */
     }
 
-    /* Reset the handle to its new position */
-    h->offset = newpos;
-
-    size_t next = h->next ? ringbuf_offset(h->next) : buf_ridx;
+    size_t next = ringbuf_offset(h->next ?: first_handle);
 
 #ifdef STORAGE_WANTS_ALIGN
     /* Strip alignment padding then redo */
@@ -1200,8 +1172,8 @@ static void rebuffer_handle(int handle_id, size_t newpos)
     /* Align to desired storage alignment if space permits - handle could
        have been shrunken too close to the following one after a previous
        rebuffer. */
-    size_t alignment_pad =
-        STORAGE_OVERLAP(h->offset - (size_t)(&buffer[new_index]));
+    size_t alignment_pad = STORAGE_OVERLAP((uintptr_t)newpos -
+                                           (uintptr_t)ringbuf_ptr(new_index));
 
     if (ringbuf_add_cross(new_index, alignment_pad, next) >= 0)
         alignment_pad = 0; /* Forego storage alignment this time */
@@ -1212,23 +1184,19 @@ static void rebuffer_handle(int handle_id, size_t newpos)
     size_t new_index = h->data;
 #endif /* STORAGE_WANTS_ALIGN */
 
+    /* Reset the handle to its new position */
     h->ridx = h->widx = h->data = new_index;
-
-    if (h == cur_handle)
-        buf_widx = new_index;
-
-    h->available = 0;
-    h->filerem = h->filesize - h->offset;
+    h->start = h->pos = h->end = newpos;
 
     if (h->fd >= 0)
-        lseek(h->fd, h->offset, SEEK_SET);
+        lseek(h->fd, newpos, SEEK_SET);
 
-    if (h->next && ringbuf_sub(next, h->data) <= h->filesize - newpos) {
+    off_t filerem = h->filesize - newpos;
+    if (h->next && ringbuf_add_cross(new_index, filerem, next) > 0) {
         /* There isn't enough space to rebuffer all of the track from its new
            offset, so we ask the user to free some */
         DEBUGF("%s(): space is needed\n", __func__);
-        int hid = handle_id;
-        send_event(BUFFER_EVENT_REBUFFER, &hid);
+        send_event(BUFFER_EVENT_REBUFFER, &(int){ handle_id });
     }
 
     /* Now we do the rebuffer */
@@ -1237,25 +1205,20 @@ static void rebuffer_handle(int handle_id, size_t newpos)
 }
 
 /* Backend to bufseek and bufadvance */
-static int seek_handle(struct memory_handle *h, size_t newpos)
+static int seek_handle(struct memory_handle *h, off_t newpos)
 {
-    if (newpos > h->filesize) {
-        /* access beyond the end of the file */
-        return ERR_INVALID_VALUE;
-    }
-    else if ((newpos < h->offset || h->offset + h->available <= newpos) &&
-             (newpos < h->filesize || h->filerem > 0)) {
+    if ((newpos < h->start || newpos >= h->end) &&
+        (newpos < h->filesize || h->end < h->filesize)) {
         /* access before or after buffered data and not to end of file or file
            is not buffered to the end-- a rebuffer is needed. */
-        struct buf_message_data parm = { h->id, newpos };
         return queue_send(&buffering_queue, Q_REBUFFER_HANDLE,
-                          (intptr_t)&parm);
+                    (intptr_t)&(struct buf_message_data){ h->id, newpos });
     }
     else {
-        h->ridx = ringbuf_add(h->data, newpos - h->offset);
+        h->ridx = ringbuf_add(h->data, newpos - h->start);
+        h->pos  = newpos;
+        return 0;
     }
-
-    return 0;
 }
 
 /* Set reading index in handle (relatively to the start of the file).
@@ -1271,14 +1234,17 @@ int bufseek(int handle_id, size_t newpos)
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
 
+    if (newpos > (size_t)h->filesize)
+        return ERR_INVALID_VALUE;
+
     return seek_handle(h, newpos);
 }
 
 /* Advance the reading index in a handle (relatively to its current position).
    Return 0 for success and for failure:
      ERR_HANDLE_NOT_FOUND if the handle wasn't found
-     ERR_INVALID_VALUE if the new requested position was beyond the end of
-     the file
+     ERR_INVALID_VALUE if the new requested position was before the beginning
+     or beyond the end of the file
  */
 int bufadvance(int handle_id, off_t offset)
 {
@@ -1286,8 +1252,13 @@ int bufadvance(int handle_id, off_t offset)
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
 
-    size_t newpos = h->offset + ringbuf_sub(h->ridx, h->data) + offset;
-    return seek_handle(h, newpos);
+    off_t pos = h->pos;
+
+    if ((offset < 0 && offset < -pos) ||
+        (offset >= 0 && offset > h->filesize - pos))
+        return ERR_INVALID_VALUE;
+
+    return seek_handle(h, pos + offset);
 }
 
 /* Get the read position from the start of the file
@@ -1299,63 +1270,76 @@ off_t bufftell(int handle_id)
     const struct memory_handle *h = find_handle(handle_id);
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
-    return h->offset + ringbuf_sub(h->ridx, h->data);
+
+    return h->pos;
 }
 
 /* Used by bufread and bufgetdata to prepare the buffer and retrieve the
- * actual amount of data available for reading.  This function explicitly
- * does not check the validity of the input handle.  It does do range checks
- * on size and returns a valid (and explicit) amount of data for reading */
+ * actual amount of data available for reading. It does range checks on
+ * size and returns a valid (and explicit) amount of data for reading */
 static struct memory_handle *prep_bufdata(int handle_id, size_t *size,
                                           bool guardbuf_limit)
 {
     struct memory_handle *h = find_handle(handle_id);
-    size_t realsize;
-
     if (!h)
         return NULL;
 
-    size_t avail = handle_size_available(h);
-
-    if (avail == 0 && h->filerem == 0) {
+    if (h->pos >= h->filesize) {
         /* File is finished reading */
         *size = 0;
         return h;
     }
 
-    realsize = *size;
+    off_t realsize = *size;
+    off_t filerem = h->filesize - h->pos;
 
-    if (realsize == 0 || realsize > avail + h->filerem)
-        realsize = avail + h->filerem;
+    if (realsize <= 0 || realsize > filerem)
+        realsize = filerem; /* clip to eof */
 
-    if (guardbuf_limit && h->type == TYPE_PACKET_AUDIO
-            && realsize > GUARD_BUFSIZE) {
+    if (guardbuf_limit && realsize > GUARD_BUFSIZE) {
         logf("data request > guardbuf");
         /* If more than the size of the guardbuf is requested and this is a
          * bufgetdata, limit to guard_bufsize over the end of the buffer */
-        realsize = MIN(realsize, buffer_len - h->ridx + GUARD_BUFSIZE);
+        realsize = MIN((size_t)realsize, buffer_len - h->ridx + GUARD_BUFSIZE);
         /* this ensures *size <= buffer_len - h->ridx + GUARD_BUFSIZE */
     }
 
-    if (h->filerem > 0 && avail < realsize) {
-        /* Data isn't ready. Request buffering */
-        LOGFQUEUE("buffering >| Q_START_FILL %d",handle_id);
-        queue_send(&buffering_queue, Q_START_FILL, handle_id);
+    off_t end = h->end;
+    off_t wait_end = h->pos + realsize;
+
+    if (end < wait_end && end < h->filesize) {
         /* Wait for the data to be ready */
+        unsigned int request = 1;
+
         do
         {
+            if (--request == 0) {
+                request = 100;
+                /* Data (still) isn't ready; ping buffering thread */
+                LOGFQUEUE("buffering >| Q_START_FILL %d",handle_id);
+                queue_send(&buffering_queue, Q_START_FILL, handle_id);
+            }
+
             sleep(0);
             /* it is not safe for a non-buffering thread to sleep while
              * holding a handle */
             h = find_handle(handle_id);
-            if (!h || h->signaled != 0)
+            if (!h)
                 return NULL;
-            avail = handle_size_available(h);
+
+            if (h->signaled != 0)
+                return NULL; /* Wait must be abandoned */
+
+            end = h->end;
         }
-        while (h->filerem > 0 && avail < realsize);
+        while (end < wait_end && end < h->filesize);
+
+        filerem = h->filesize - h->pos;
+        if (realsize > filerem)
+            realsize = filerem;
     }
 
-    *size = MIN(realsize, avail);
+    *size = realsize;
     return h;
 }
 
@@ -1374,23 +1358,21 @@ static struct memory_handle *prep_bufdata(int handle_id, size_t *size,
 */
 ssize_t bufread(int handle_id, size_t size, void *dest)
 {
-    const struct memory_handle *h;
-    size_t adjusted_size = size;
-
-    h = prep_bufdata(handle_id, &adjusted_size, false);
+    const struct memory_handle *h =
+        prep_bufdata(handle_id, &size, false);
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
 
-    if (h->ridx + adjusted_size > buffer_len) {
+    if (h->ridx + size > 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, adjusted_size - read);
+        memcpy(dest, ringbuf_ptr(h->ridx), read);
+        memcpy(dest + read, ringbuf_ptr(0), size - read);
     } else {
-        memcpy(dest, &buffer[h->ridx], adjusted_size);
+        memcpy(dest, ringbuf_ptr(h->ridx), size);
     }
 
-    return adjusted_size;
+    return size;
 }
 
 /* Update the "data" pointer to make the handle's data available to the caller.
@@ -1404,81 +1386,80 @@ ssize_t bufread(int handle_id, size_t size, void *dest)
 */
 ssize_t bufgetdata(int handle_id, size_t size, void **data)
 {
-    const struct memory_handle *h;
-    size_t adjusted_size = size;
-
-    h = prep_bufdata(handle_id, &adjusted_size, true);
+    struct memory_handle *h =
+        prep_bufdata(handle_id, &size, true);
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
 
-    if (h->ridx + adjusted_size > buffer_len) {
+    if (h->ridx + size > buffer_len) {
         /* the data wraps around the end of the buffer :
            use the guard buffer to provide the requested amount of data. */
-        size_t copy_n = h->ridx + adjusted_size - buffer_len;
+        size_t copy_n = h->ridx + size - buffer_len;
         /* prep_bufdata ensures
            adjusted_size <= buffer_len - h->ridx + GUARD_BUFSIZE,
            so copy_n <= GUARD_BUFSIZE */
-        memcpy(guard_buffer, (const unsigned char *)buffer, copy_n);
+        memcpy(guard_buffer, ringbuf_ptr(0), copy_n);
     }
 
     if (data)
-        *data = &buffer[h->ridx];
+        *data = ringbuf_ptr(h->ridx);
 
-    return adjusted_size;
+    return size;
 }
 
 ssize_t bufgettail(int handle_id, size_t size, void **data)
 {
-    size_t tidx;
-
-    const struct memory_handle *h;
+    if (thread_self() != buffering_thread_id)
+        return ERR_WRONG_THREAD; /* only from buffering thread */
 
-    h = find_handle(handle_id);
+    /* We don't support tail requests of > guardbuf_size, for simplicity */
+    if (size > GUARD_BUFSIZE)
+        return ERR_INVALID_VALUE;
 
+    const struct memory_handle *h = find_handle(handle_id);
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
 
-    if (h->filerem)
-        return ERR_HANDLE_NOT_DONE;
+    if (h->end >= h->filesize) {
+        size_t tidx = ringbuf_sub(h->widx, size);
 
-    /* We don't support tail requests of > guardbuf_size, for simplicity */
-    if (size > GUARD_BUFSIZE)
-        return ERR_INVALID_VALUE;
-
-    tidx = ringbuf_sub(h->widx, size);
+        if (tidx + size > buffer_len) {
+            size_t copy_n = tidx + size - buffer_len;
+            memcpy(guard_buffer, ringbuf_ptr(0), copy_n);
+        }
 
-    if (tidx + size > buffer_len) {
-        size_t copy_n = tidx + size - buffer_len;
-        memcpy(guard_buffer, (const unsigned char *)buffer, copy_n);
+        *data = ringbuf_ptr(tidx);
+    }
+    else {
+        size = ERR_HANDLE_NOT_DONE;
     }
 
-    *data = &buffer[tidx];
     return size;
 }
 
 ssize_t bufcuttail(int handle_id, size_t size)
 {
-    struct memory_handle *h;
-    size_t adjusted_size = size;
-
-    h = find_handle(handle_id);
+    if (thread_self() != buffering_thread_id)
+        return ERR_WRONG_THREAD; /* only from buffering thread */
 
+    struct memory_handle *h = find_handle(handle_id);
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
 
-    if (h->filerem)
-        return ERR_HANDLE_NOT_DONE;
-
-    if (h->available < adjusted_size)
-        adjusted_size = h->available;
+    if (h->end >= h->filesize) {
+        /* Cannot trim to before read position */
+        size_t available = h->end - MAX(h->start, h->pos);
+        if (available < size)
+            size = available;
 
-    h->available -= adjusted_size;
-    h->filesize -= adjusted_size;
-    h->widx = ringbuf_sub(h->widx, adjusted_size);
-    if (h == cur_handle)
-        buf_widx = h->widx;
+        h->widx = ringbuf_sub(h->widx, size);
+        h->filesize -= size;
+        h->end -= size;
+    } else {
+        size = ERR_HANDLE_NOT_DONE;
+    }
 
-    return adjusted_size;
+    return size;
 }
 
 
@@ -1507,7 +1488,7 @@ ssize_t buf_handle_offset(int handle_id)
     const struct memory_handle *h = find_handle(handle_id);
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
-    return h->offset;
+    return h->start;
 }
 
 void buf_set_base_handle(int handle_id)
@@ -1530,7 +1511,7 @@ ssize_t buf_handle_remaining(int handle_id)
     const struct memory_handle *h = find_handle(handle_id);
     if (!h)
         return ERR_HANDLE_NOT_FOUND;
-    return h->filerem;
+    return h->filesize - h->end;
 }
 
 bool buf_is_handle(int handle_id)
@@ -1572,7 +1553,11 @@ size_t buf_length(void)
 /* Return the amount of buffer space used */
 size_t buf_used(void)
 {
-    return BUF_USED;
+    struct memory_handle *first = first_handle;
+    if (!first)
+        return 0;
+
+    return ringbuf_sub(cur_handle->widx, ringbuf_offset(first));
 }
 
 void buf_set_watermark(size_t bytes)
@@ -1615,7 +1600,6 @@ static void NORETURN_ATTR buffering_thread(void)
 {
     bool filling = false;
     struct queue_event ev;
-    struct buf_message_data *parm;
 
     while (true)
     {
@@ -1654,11 +1638,14 @@ static void NORETURN_ATTR buffering_thread(void)
                 break;
 
             case Q_REBUFFER_HANDLE:
-                parm = (struct buf_message_data *)ev.data;
+            {
+                struct buf_message_data *parm =
+                    (struct buf_message_data *)ev.data;
                 LOGFQUEUE("buffering < Q_REBUFFER_HANDLE %d %ld",
                           parm->handle_id, parm->data);
                 rebuffer_handle(parm->handle_id, parm->data);
                 break;
+                }
 
             case Q_CLOSE_HANDLE:
                 LOGFQUEUE("buffering < Q_CLOSE_HANDLE %d", (int)ev.data);
@@ -1689,7 +1676,7 @@ static void NORETURN_ATTR buffering_thread(void)
             if (num_handles > 0 && data_counters.useful <= high_watermark)
                 send_event(BUFFER_EVENT_BUFFER_LOW, 0);
 
-            if (data_counters.remaining > 0 && BUF_USED <= high_watermark) {
+            if (data_counters.remaining > 0 && buf_used() <= high_watermark) {
                 /* This is a new fill, shrink the buffer up first */
                 if (!filling)
                     shrink_buffer();
@@ -1769,9 +1756,6 @@ bool buffering_reset(char *buf, size_t buflen)
     buffer_len = buflen;
     guard_buffer = buf + buflen;
 
-    buf_widx = 0;
-    buf_ridx = 0;
-
     first_handle = NULL;
     cur_handle = NULL;
     cached_handle = NULL;
@@ -1794,10 +1778,8 @@ bool buffering_reset(char *buf, size_t buflen)
 void buffering_get_debugdata(struct buffering_debug *dbgdata)
 {
     struct data_counters dc;
-    update_data_counters(&dc);
-    dbgdata->num_handles = num_handles;
+    dbgdata->num_handles = update_data_counters(&dc);
     dbgdata->data_rem = dc.remaining;
-    dbgdata->wasted_space = dc.wasted;
     dbgdata->buffered_data = dc.buffered;
     dbgdata->useful_data = dc.useful;
     dbgdata->watermark = BUF_WATERMARK;
diff --git a/apps/buffering.h b/apps/buffering.h
index 6d52794233..218f77ed85 100644
--- a/apps/buffering.h
+++ b/apps/buffering.h
@@ -45,7 +45,7 @@ enum data_type {
 #define ERR_FILE_ERROR          -4
 #define ERR_HANDLE_NOT_DONE     -5
 #define ERR_UNSUPPORTED_TYPE    -6
-
+#define ERR_WRONG_THREAD        -7
 
 /* Initialise the buffering subsystem */
 void buffering_init(void) INIT_ATTR;
@@ -116,10 +116,6 @@ void buf_back_off_storage(bool back_off);
 #endif
 
 /* Settings */
-enum {
-    BUFFERING_SET_WATERMARK = 1,
-    BUFFERING_SET_CHUNKSIZE,
-};
 void buf_set_watermark(size_t bytes);
 size_t buf_get_watermark(void);
 
@@ -127,7 +123,6 @@ size_t buf_get_watermark(void);
 struct buffering_debug {
     int num_handles;
     size_t buffered_data;
-    size_t wasted_space;
     size_t data_rem;
     size_t useful_data;
     size_t watermark;