gstreamer_core/plugins/elements/gstfilesrc.c
changeset 0 0e761a78d257
child 8 4a7fac7dd34a
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gstreamer_core/plugins/elements/gstfilesrc.c	Thu Dec 17 08:53:32 2009 +0200
@@ -0,0 +1,1123 @@
+/* GStreamer
+ * Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
+ *               2000,2005 Wim Taymans <wim@fluendo.com>
+ *
+ * gstfilesrc.c:
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+/**
+ * SECTION:element-filesrc
+ * @short_description: read from arbitrary point in a file
+ * @see_also: #GstFileSrc
+ *
+ * Read data from a file in the local file system.
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+#ifdef __SYMBIAN32__
+#include <gst_global.h>
+#endif
+
+#include <gst/gst.h>
+#include "gstfilesrc.h"
+
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#ifdef __SYMBIAN32__
+#include <glib_global.h>
+#include <gobject_global.h>
+#endif
+
+#ifdef HAVE_UNISTD_H
+#  include <unistd.h>
+#endif
+
+#ifdef HAVE_MMAP
+# include <sys/mman.h>
+#endif
+
+#ifdef HAVE_WIN32
+#  include <io.h>               /* lseek, open, close, read */
+#endif
+
+#include <errno.h>
+#include <string.h>
+
+#include "../../gst/gst-i18n-lib.h"
+#include <gstelement.h>
+
+static GstStaticPadTemplate srctemplate = GST_STATIC_PAD_TEMPLATE ("src",
+    GST_PAD_SRC,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS_ANY);
+
+/* FIXME we should be using glib for this */
+#ifndef S_ISREG
+#define S_ISREG(mode) ((mode)&_S_IFREG)
+#endif
+#ifndef S_ISDIR
+#define S_ISDIR(mode) ((mode)&_S_IFDIR)
+#endif
+#ifndef S_ISSOCK
+#define S_ISSOCK(x) (0)
+#endif
+#ifndef O_BINARY
+#define O_BINARY (0)
+#endif
+
+
+/**********************************************************************
+ * GStreamer Default File Source
+ * Theory of Operation
+ *
+ * Update: see GstFileSrc:use-mmap property documentation below
+ *         for why use of mmap() is disabled by default.
+ *
+ * This source uses mmap(2) to efficiently load data from a file.
+ * To do this without seriously polluting the applications' memory
+ * space, it must do so in smaller chunks, say 1-4MB at a time.
+ * Buffers are then subdivided from these mmap'd chunks, to directly
+ * make use of the mmap.
+ *
+ * To handle refcounting so that the mmap can be freed at the appropriate
+ * time, a buffer will be created for each mmap'd region, and all new
+ * buffers will be sub-buffers of this top-level buffer.  As they are
+ * freed, the refcount goes down on the mmap'd buffer and its free()
+ * function is called, which will call munmap(2) on itself.
+ *
+ * If a buffer happens to cross the boundaries of an mmap'd region, we
+ * have to decide whether it's more efficient to copy the data into a
+ * new buffer, or mmap() just that buffer.  There will have to be a
+ * breakpoint size to determine which will be done.  The mmap() size
+ * has a lot to do with this as well, because you end up in double-
+ * jeopardy: the larger the outgoing buffer, the more data to copy when
+ * it overlaps, *and* the more frequently you'll have buffers that *do*
+ * overlap.
+ *
+ * Seeking is another tricky aspect to do efficiently.  The initial
+ * implementation of this source won't make use of these features, however.
+ * The issue is that if an application seeks backwards in a file, *and*
+ * that region of the file is covered by an mmap that hasn't been fully
+ * deallocated, we really should re-use it.  But keeping track of these
+ * regions is tricky because we have to lock the structure that holds
+ * them.  We need to settle on a locking primitive (GMutex seems to be
+ * a really good option...), then we can do that.
+ */
+
+
+GST_DEBUG_CATEGORY_STATIC (gst_file_src_debug);
+#define GST_CAT_DEFAULT gst_file_src_debug
+
+/* FileSrc signals and args */
+enum
+{
+  /* FILL ME */
+  LAST_SIGNAL
+};
+
+#define DEFAULT_BLOCKSIZE       4*1024
+#define DEFAULT_MMAPSIZE        4*1024*1024
+#define DEFAULT_TOUCH           TRUE
+#define DEFAULT_USEMMAP         FALSE
+#define DEFAULT_SEQUENTIAL      FALSE
+
+enum
+{
+  ARG_0,
+  ARG_LOCATION,
+  ARG_FD,
+  ARG_MMAPSIZE,
+  ARG_SEQUENTIAL,
+  ARG_TOUCH,
+  ARG_USEMMAP
+};
+
+static void gst_file_src_finalize (GObject * object);
+
+static void gst_file_src_set_property (GObject * object, guint prop_id,
+    const GValue * value, GParamSpec * pspec);
+static void gst_file_src_get_property (GObject * object, guint prop_id,
+    GValue * value, GParamSpec * pspec);
+
+static gboolean gst_file_src_start (GstBaseSrc * basesrc);
+static gboolean gst_file_src_stop (GstBaseSrc * basesrc);
+
+static gboolean gst_file_src_is_seekable (GstBaseSrc * src);
+static gboolean gst_file_src_get_size (GstBaseSrc * src, guint64 * size);
+static GstFlowReturn gst_file_src_create (GstBaseSrc * src, guint64 offset,
+    guint length, GstBuffer ** buffer);
+
+static void gst_file_src_uri_handler_init (gpointer g_iface,
+    gpointer iface_data);
+
+static void
+_do_init (GType filesrc_type)
+{
+  static const GInterfaceInfo urihandler_info = {
+    gst_file_src_uri_handler_init,
+    NULL,
+    NULL
+  };
+
+  g_type_add_interface_static (filesrc_type, GST_TYPE_URI_HANDLER,
+      &urihandler_info);
+  GST_DEBUG_CATEGORY_INIT (gst_file_src_debug, "filesrc", 0, "filesrc element");
+}
+
+GST_BOILERPLATE_FULL (GstFileSrc, gst_file_src, GstBaseSrc, GST_TYPE_BASE_SRC,
+    _do_init);
+
+static void
+gst_file_src_base_init (gpointer g_class)
+{
+  GstElementClass *gstelement_class = GST_ELEMENT_CLASS (g_class);
+
+  gst_element_class_set_details_simple (gstelement_class,
+      "File Source",
+      "Source/File",
+      "Read from arbitrary point in a file",
+      "Erik Walthinsen <omega@cse.ogi.edu>");
+  gst_element_class_add_pad_template (gstelement_class,
+      gst_static_pad_template_get (&srctemplate));
+}
+
+static void
+gst_file_src_class_init (GstFileSrcClass * klass)
+{
+  GObjectClass *gobject_class;
+  GstElementClass *gstelement_class;
+  GstBaseSrcClass *gstbasesrc_class;
+
+  gobject_class = G_OBJECT_CLASS (klass);
+  gstelement_class = GST_ELEMENT_CLASS (klass);
+  gstbasesrc_class = GST_BASE_SRC_CLASS (klass);
+
+  gobject_class->set_property = gst_file_src_set_property;
+  gobject_class->get_property = gst_file_src_get_property;
+
+  g_object_class_install_property (gobject_class, ARG_FD,
+      g_param_spec_int ("fd", "File-descriptor",
+          "File-descriptor for the file being mmap()d", 0, G_MAXINT, 0,
+          G_PARAM_READABLE));
+  g_object_class_install_property (gobject_class, ARG_LOCATION,
+      g_param_spec_string ("location", "File Location",
+          "Location of the file to read", NULL, G_PARAM_READWRITE));
+  g_object_class_install_property (gobject_class, ARG_MMAPSIZE,
+      g_param_spec_ulong ("mmapsize", "mmap() Block Size",
+          "Size in bytes of mmap()d regions", 0, G_MAXULONG, DEFAULT_MMAPSIZE,
+          G_PARAM_READWRITE));
+  g_object_class_install_property (gobject_class, ARG_TOUCH,
+      g_param_spec_boolean ("touch", "Touch mapped region read data",
+          "Touch mmapped data regions to force them to be read from disk",
+          DEFAULT_TOUCH, G_PARAM_READWRITE));
+  /**
+   * GstFileSrc:use-mmap
+   *
+   * Whether to use mmap(). Set to TRUE to force use of mmap() instead of
+   * read() for reading data.
+   *
+   * Use of mmap() is disabled by default since with mmap() there are a
+   * number of occasions where the process/application will be notified of
+   * read errors via a SIGBUS signal from the kernel, which will lead to
+   * the application being killed if not handled by the application. This
+   * is something that is difficult to work around for a library like
+   * GStreamer, hence use of mmap() is disabled by default. Said errors
+   * can occur for example when an external device (e.g. an external hard
+   * drive or a portable music player) are unplugged while in use, or when
+   * a CD/DVD medium cannot be be read because the medium is scratched or
+   * otherwise damaged.
+   *
+   **/
+  g_object_class_install_property (gobject_class, ARG_USEMMAP,
+      g_param_spec_boolean ("use-mmap", "Use mmap to read data",
+          "Whether to use mmap() instead of read()",
+          DEFAULT_USEMMAP, G_PARAM_READWRITE));
+  g_object_class_install_property (gobject_class, ARG_SEQUENTIAL,
+      g_param_spec_boolean ("sequential", "Optimise for sequential mmap access",
+          "Whether to use madvise to hint to the kernel that access to "
+          "mmap pages will be sequential",
+          DEFAULT_SEQUENTIAL, G_PARAM_READWRITE));
+
+  gobject_class->finalize = GST_DEBUG_FUNCPTR (gst_file_src_finalize);
+
+  gstbasesrc_class->start = GST_DEBUG_FUNCPTR (gst_file_src_start);
+  gstbasesrc_class->stop = GST_DEBUG_FUNCPTR (gst_file_src_stop);
+  gstbasesrc_class->is_seekable = GST_DEBUG_FUNCPTR (gst_file_src_is_seekable);
+  gstbasesrc_class->get_size = GST_DEBUG_FUNCPTR (gst_file_src_get_size);
+  gstbasesrc_class->create = GST_DEBUG_FUNCPTR (gst_file_src_create);
+
+  if (sizeof (off_t) < 8) {
+    GST_LOG ("No large file support, sizeof (off_t) = %" G_GSIZE_FORMAT "!",
+        sizeof (off_t));
+  }
+}
+
+static void
+gst_file_src_init (GstFileSrc * src, GstFileSrcClass * g_class)
+{
+#ifdef HAVE_MMAP
+  src->pagesize = getpagesize ();
+#endif
+
+  src->filename = NULL;
+  src->fd = 0;
+  src->uri = NULL;
+
+  src->touch = DEFAULT_TOUCH;
+
+  src->mapbuf = NULL;
+  src->mapsize = DEFAULT_MMAPSIZE;      /* default is 4MB */
+  src->use_mmap = DEFAULT_USEMMAP;
+  src->sequential = DEFAULT_SEQUENTIAL;
+
+  src->is_regular = FALSE;
+}
+
+static void
+gst_file_src_finalize (GObject * object)
+{
+  GstFileSrc *src;
+
+  src = GST_FILE_SRC (object);
+
+  g_free (src->filename);
+  g_free (src->uri);
+
+  G_OBJECT_CLASS (parent_class)->finalize (object);
+}
+
+static gboolean
+gst_file_src_set_location (GstFileSrc * src, const gchar * location)
+{
+  GstState state;
+
+  /* the element must be stopped in order to do this */
+  GST_OBJECT_LOCK (src);
+  state = GST_STATE (src);
+  if (state != GST_STATE_READY && state != GST_STATE_NULL)
+    goto wrong_state;
+  GST_OBJECT_UNLOCK (src);
+
+  g_free (src->filename);
+  g_free (src->uri);
+
+  /* clear the filename if we get a NULL (is that possible?) */
+  if (location == NULL) {
+    src->filename = NULL;
+    src->uri = NULL;
+  } else {
+    src->filename = g_strdup (location);
+    src->uri = gst_uri_construct ("file", src->filename);
+  }
+  g_object_notify (G_OBJECT (src), "location");
+  gst_uri_handler_new_uri (GST_URI_HANDLER (src), src->uri);
+
+  return TRUE;
+
+  /* ERROR */
+wrong_state:
+  {
+    GST_DEBUG_OBJECT (src, "setting location in wrong state");
+    GST_OBJECT_UNLOCK (src);
+    return FALSE;
+  }
+}
+
+static void
+gst_file_src_set_property (GObject * object, guint prop_id,
+    const GValue * value, GParamSpec * pspec)
+{
+  GstFileSrc *src;
+
+  g_return_if_fail (GST_IS_FILE_SRC (object));
+
+  src = GST_FILE_SRC (object);
+
+  switch (prop_id) {
+    case ARG_LOCATION:
+      gst_file_src_set_location (src, g_value_get_string (value));
+      break;
+    case ARG_MMAPSIZE:
+      if ((src->mapsize % src->pagesize) == 0) {
+        src->mapsize = g_value_get_ulong (value);
+      } else {
+        GST_INFO_OBJECT (src,
+            "invalid mapsize, must be a multiple of pagesize, which is %d",
+            src->pagesize);
+      }
+      break;
+    case ARG_TOUCH:
+      src->touch = g_value_get_boolean (value);
+      break;
+    case ARG_SEQUENTIAL:
+      src->sequential = g_value_get_boolean (value);
+      break;
+    case ARG_USEMMAP:
+      src->use_mmap = g_value_get_boolean (value);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
+gst_file_src_get_property (GObject * object, guint prop_id, GValue * value,
+    GParamSpec * pspec)
+{
+  GstFileSrc *src;
+
+  g_return_if_fail (GST_IS_FILE_SRC (object));
+
+  src = GST_FILE_SRC (object);
+
+  switch (prop_id) {
+    case ARG_LOCATION:
+      g_value_set_string (value, src->filename);
+      break;
+    case ARG_FD:
+      g_value_set_int (value, src->fd);
+      break;
+    case ARG_MMAPSIZE:
+      g_value_set_ulong (value, src->mapsize);
+      break;
+    case ARG_TOUCH:
+      g_value_set_boolean (value, src->touch);
+      break;
+    case ARG_SEQUENTIAL:
+      g_value_set_boolean (value, src->sequential);
+      break;
+    case ARG_USEMMAP:
+      g_value_set_boolean (value, src->use_mmap);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+/***
+ * mmap code below
+ */
+
+#ifdef HAVE_MMAP
+
+/* GstMmapBuffer */
+
+typedef struct _GstMmapBuffer GstMmapBuffer;
+typedef struct _GstMmapBufferClass GstMmapBufferClass;
+
+#define GST_TYPE_MMAP_BUFFER                         (gst_mmap_buffer_get_type())
+
+#define GST_IS_MMAP_BUFFER(obj)  (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GST_TYPE_MMAP_BUFFER))
+#define GST_IS_MMAP_BUFFER_CLASS(klass)  (G_TYPE_CHECK_CLASS_TYPE ((klass), GST_TYPE_MMAP_BUFFER))
+#define GST_MMAP_BUFFER_GET_CLASS(obj)   (G_TYPE_INSTANCE_GET_CLASS ((obj), GST_TYPE_MMAP_BUFFER, GstMmapBufferClass))
+#define GST_MMAP_BUFFER(obj)     (G_TYPE_CHECK_INSTANCE_CAST ((obj), GST_TYPE_MMAP_BUFFER, GstMmapBuffer))
+#define GST_MMAP_BUFFER_CLASS(klass)  (G_TYPE_CHECK_CLASS_CAST ((klass), GST_TYPE_MMAP_BUFFER, GstMmapBufferClass))
+
+
+
+struct _GstMmapBuffer
+{
+  GstBuffer buffer;
+
+  GstFileSrc *filesrc;
+};
+
+struct _GstMmapBufferClass
+{
+  GstBufferClass buffer_class;
+};
+
+static void gst_mmap_buffer_init (GTypeInstance * instance, gpointer g_class);
+static void gst_mmap_buffer_class_init (gpointer g_class, gpointer class_data);
+static void gst_mmap_buffer_finalize (GstMmapBuffer * mmap_buffer);
+static GstBufferClass *mmap_buffer_parent_class = NULL;
+
+static GType
+gst_mmap_buffer_get_type (void)
+{
+  static GType _gst_mmap_buffer_type;
+
+  if (G_UNLIKELY (_gst_mmap_buffer_type == 0)) {
+    static const GTypeInfo mmap_buffer_info = {
+      sizeof (GstMmapBufferClass),
+      NULL,
+      NULL,
+      gst_mmap_buffer_class_init,
+      NULL,
+      NULL,
+      sizeof (GstMmapBuffer),
+      0,
+      gst_mmap_buffer_init,
+      NULL
+    };
+
+    _gst_mmap_buffer_type = g_type_register_static (GST_TYPE_BUFFER,
+        "GstMmapBuffer", &mmap_buffer_info, 0);
+  }
+  return _gst_mmap_buffer_type;
+}
+
+static void
+gst_mmap_buffer_class_init (gpointer g_class, gpointer class_data)
+{
+  GstMiniObjectClass *mini_object_class = GST_MINI_OBJECT_CLASS (g_class);
+
+  mmap_buffer_parent_class = g_type_class_peek_parent (g_class);
+
+  mini_object_class->finalize =
+      (GstMiniObjectFinalizeFunction) gst_mmap_buffer_finalize;
+}
+
+static void
+gst_mmap_buffer_init (GTypeInstance * instance, gpointer g_class)
+{
+  GstBuffer *buf = (GstBuffer *) instance;
+
+  GST_BUFFER_FLAG_SET (buf, GST_BUFFER_FLAG_READONLY);
+  /* before we re-enable this flag, we probably need to fix _copy()
+   * _make_writable(), etc. in GstMiniObject/GstBuffer as well */
+  /* GST_BUFFER_FLAG_SET (buf, GST_BUFFER_FLAG_ORIGINAL); */
+}
+
+static void
+gst_mmap_buffer_finalize (GstMmapBuffer * mmap_buffer)
+{
+  guint size;
+  gpointer data;
+  guint64 offset;
+  GstFileSrc *src;
+  GstBuffer *buffer = GST_BUFFER (mmap_buffer);
+
+  /* get info */
+  size = GST_BUFFER_SIZE (buffer);
+  offset = GST_BUFFER_OFFSET (buffer);
+  data = GST_BUFFER_DATA (buffer);
+  src = mmap_buffer->filesrc;
+
+  GST_LOG ("freeing mmap()d buffer at %" G_GUINT64_FORMAT "+%u", offset, size);
+
+#ifdef MADV_DONTNEED
+  /* madvise to tell the kernel what to do with it */
+  if (madvise (data, size, MADV_DONTNEED) < 0) {
+    GST_WARNING_OBJECT (src, "warning: madvise failed: %s", g_strerror (errno));
+  }
+#endif
+
+  /* now unmap the memory */
+  if (munmap (data, size) < 0) {
+    GST_WARNING_OBJECT (src, "warning: munmap failed: %s", g_strerror (errno));
+  }
+
+  /* cast to unsigned long, since there's no gportable way to print
+   * guint64 as hex */
+  GST_LOG ("unmapped region %08lx+%08lx at %p",
+      (gulong) offset, (gulong) size, data);
+
+  GST_MINI_OBJECT_CLASS (mmap_buffer_parent_class)->
+      finalize (GST_MINI_OBJECT (mmap_buffer));
+}
+
+static GstBuffer *
+gst_file_src_map_region (GstFileSrc * src, off_t offset, gsize size,
+    gboolean testonly)
+{
+  GstBuffer *buf;
+  void *mmapregion;
+
+  g_return_val_if_fail (offset >= 0, NULL);
+
+  GST_LOG_OBJECT (src, "mapping region %08llx+%08lx from file into memory",
+      offset, (gulong) size);
+
+  mmapregion = mmap (NULL, size, PROT_READ, MAP_SHARED, src->fd, offset);
+
+  if (mmapregion == NULL || mmapregion == MAP_FAILED)
+    goto mmap_failed;
+
+  GST_LOG_OBJECT (src, "mapped region %08lx+%08lx from file into memory at %p",
+      (gulong) offset, (gulong) size, mmapregion);
+
+  /* time to allocate a new mapbuf */
+  buf = (GstBuffer *) gst_mini_object_new (GST_TYPE_MMAP_BUFFER);
+  /* mmap() the data into this new buffer */
+  GST_BUFFER_DATA (buf) = mmapregion;
+  GST_MMAP_BUFFER (buf)->filesrc = src;
+
+#ifdef MADV_SEQUENTIAL
+  if (src->sequential) {
+    /* madvise to tell the kernel what to do with it */
+  #ifndef __SYMBIAN32__
+    if (madvise (mmapregion, size, MADV_SEQUENTIAL) < 0) {
+      GST_WARNING_OBJECT (src, "warning: madvise failed: %s",
+          g_strerror (errno));
+    }
+  #endif
+#endif
+
+  /* fill in the rest of the fields */
+  GST_BUFFER_SIZE (buf) = size;
+  GST_BUFFER_OFFSET (buf) = offset;
+  GST_BUFFER_OFFSET_END (buf) = offset + size;
+  GST_BUFFER_TIMESTAMP (buf) = GST_CLOCK_TIME_NONE;
+
+  return buf;
+
+  /* ERROR */
+mmap_failed:
+  {
+    if (!testonly) {
+      GST_ELEMENT_ERROR (src, RESOURCE, READ, (NULL),
+          ("mmap (0x%08lx, %d, 0x%" G_GINT64_MODIFIER "x) failed: %s",
+              (gulong) size, src->fd, (guint64) offset, g_strerror (errno)));
+    }
+    return NULL;
+  }
+}
+
+static GstBuffer *
+gst_file_src_map_small_region (GstFileSrc * src, off_t offset, gsize size)
+{
+  GstBuffer *ret;
+  off_t mod;
+  guint pagesize;
+
+  GST_LOG_OBJECT (src,
+      "attempting to map a small buffer at %" G_GUINT64_FORMAT "+%d",
+      (guint64) offset, (gint) size);
+
+  pagesize = src->pagesize;
+
+  mod = offset % pagesize;
+
+  /* if the offset starts at a non-page boundary, we have to special case */
+  if (mod != 0) {
+    gsize mapsize;
+    off_t mapbase;
+    GstBuffer *map;
+
+    mapbase = offset - mod;
+    mapsize = ((size + mod + pagesize - 1) / pagesize) * pagesize;
+
+    GST_LOG_OBJECT (src,
+        "not on page boundaries, resizing to map to %" G_GUINT64_FORMAT "+%d",
+        (guint64) mapbase, (gint) mapsize);
+
+    map = gst_file_src_map_region (src, mapbase, mapsize, FALSE);
+    if (map == NULL)
+      return NULL;
+
+    ret = gst_buffer_create_sub (map, offset - mapbase, size);
+    GST_BUFFER_OFFSET (ret) = GST_BUFFER_OFFSET (map) + offset - mapbase;
+
+    gst_buffer_unref (map);
+  } else {
+    ret = gst_file_src_map_region (src, offset, size, FALSE);
+  }
+
+  return ret;
+}
+
+static GstFlowReturn
+gst_file_src_create_mmap (GstFileSrc * src, guint64 offset, guint length,
+    GstBuffer ** buffer)
+{
+  GstBuffer *buf = NULL;
+  gsize readsize, mapsize;
+  off_t readend, mapstart, mapend;
+  int i;
+
+  /* calculate end pointers so we don't have to do so repeatedly later */
+  readsize = length;
+  readend = offset + readsize;  /* note this is the byte *after* the read */
+
+  mapstart = GST_BUFFER_OFFSET (src->mapbuf);
+  mapsize = GST_BUFFER_SIZE (src->mapbuf);
+  mapend = mapstart + mapsize;  /* note this is the byte *after* the map */
+
+  GST_LOG ("attempting to read %08lx, %08lx, %08lx, %08lx",
+      (unsigned long) readsize, (unsigned long) readend,
+      (unsigned long) mapstart, (unsigned long) mapend);
+
+  /* if the start is past the mapstart */
+  if (offset >= mapstart) {
+    /* if the end is before the mapend, the buffer is in current mmap region... */
+    /* ('cause by definition if readend is in the buffer, so's readstart) */
+    if (readend <= mapend) {
+      GST_LOG_OBJECT (src, "read buf %" G_GUINT64_FORMAT "+%u lives in "
+          "current mapbuf %u+%u, creating subbuffer of mapbuf",
+          offset, (guint) readsize, (guint) mapstart, (guint) mapsize);
+      buf = gst_buffer_create_sub (src->mapbuf, offset - mapstart, readsize);
+      GST_BUFFER_OFFSET (buf) = offset;
+
+      /* if the start actually is within the current mmap region, map an overlap buffer */
+    } else if (offset < mapend) {
+      GST_LOG_OBJECT (src, "read buf %" G_GUINT64_FORMAT "+%u starts in "
+          "mapbuf %u+%u but ends outside, creating new mmap",
+          offset, (guint) readsize, (guint) mapstart, (guint) mapsize);
+      buf = gst_file_src_map_small_region (src, offset, readsize);
+      if (buf == NULL)
+        goto could_not_mmap;
+    }
+
+    /* the only other option is that buffer is totally outside, which means we search for it */
+
+    /* now we can assume that the start is *before* the current mmap region */
+    /* if the readend is past mapstart, we have two options */
+  } else if (readend >= mapstart) {
+    /* either the read buffer overlaps the start of the mmap region */
+    /* or the read buffer fully contains the current mmap region    */
+    /* either way, it's really not relevant, we just create a new region anyway */
+    GST_LOG_OBJECT (src, "read buf %" G_GUINT64_FORMAT "+%d starts before "
+        "mapbuf %d+%d, but overlaps it", (guint64) offset, (gint) readsize,
+        (gint) mapstart, (gint) mapsize);
+    buf = gst_file_src_map_small_region (src, offset, readsize);
+    if (buf == NULL)
+      goto could_not_mmap;
+  }
+
+  /* then deal with the case where the read buffer is totally outside */
+  if (buf == NULL) {
+    /* first check to see if there's a map that covers the right region already */
+    GST_LOG_OBJECT (src, "searching for mapbuf to cover %" G_GUINT64_FORMAT
+        "+%d", offset, (int) readsize);
+
+    /* if the read buffer crosses a mmap region boundary, create a one-off region */
+    if ((offset / src->mapsize) != (readend / src->mapsize)) {
+      GST_LOG_OBJECT (src, "read buf %" G_GUINT64_FORMAT "+%d crosses a "
+          "%d-byte boundary, creating a one-off", offset, (int) readsize,
+          (int) src->mapsize);
+      buf = gst_file_src_map_small_region (src, offset, readsize);
+      if (buf == NULL)
+        goto could_not_mmap;
+
+      /* otherwise we will create a new mmap region and set it to the default */
+    } else {
+      gsize mapsize;
+
+      off_t nextmap = offset - (offset % src->mapsize);
+
+      GST_LOG_OBJECT (src, "read buf %" G_GUINT64_FORMAT "+%d in new mapbuf "
+          "at %" G_GUINT64_FORMAT "+%d, mapping and subbuffering",
+          offset, (gint) readsize, (guint64) nextmap, (gint) src->mapsize);
+      /* first, we're done with the old mapbuf */
+      gst_buffer_unref (src->mapbuf);
+      mapsize = src->mapsize;
+
+      /* double the mapsize as long as the readsize is smaller */
+      while (readsize + offset > nextmap + mapsize) {
+        GST_LOG_OBJECT (src, "readsize smaller then mapsize %08x %d",
+            (guint) readsize, (gint) mapsize);
+        mapsize <<= 1;
+      }
+      /* create a new one */
+      src->mapbuf = gst_file_src_map_region (src, nextmap, mapsize, FALSE);
+      if (src->mapbuf == NULL)
+        goto could_not_mmap;
+
+      /* subbuffer it */
+      buf = gst_buffer_create_sub (src->mapbuf, offset - nextmap, readsize);
+      GST_BUFFER_OFFSET (buf) =
+          GST_BUFFER_OFFSET (src->mapbuf) + offset - nextmap;
+    }
+  }
+
+  /* if we need to touch the buffer (to bring it into memory), do so */
+  if (src->touch) {
+    volatile guchar *p = GST_BUFFER_DATA (buf), c;
+
+    /* read first byte of each page */
+    for (i = 0; i < GST_BUFFER_SIZE (buf); i += src->pagesize)
+      c = p[i];
+  }
+
+  /* we're done, return the buffer */
+  *buffer = buf;
+
+  return GST_FLOW_OK;
+
+  /* ERROR */
+could_not_mmap:
+  {
+    return GST_FLOW_ERROR;
+  }
+}
+#endif
+
+/***
+ * read code below
+ * that is to say, you shouldn't read the code below, but the code that reads
+ * stuff is below.  Well, you shouldn't not read the code below, feel free
+ * to read it of course.  It's just that "read code below" is a pretty crappy
+ * documentation string because it sounds like we're expecting you to read
+ * the code to understand what it does, which, while true, is really not
+ * the sort of attitude we want to be advertising.  No sir.
+ *
+ */
+
+static GstFlowReturn
+gst_file_src_create_read (GstFileSrc * src, guint64 offset, guint length,
+    GstBuffer ** buffer)
+{
+  int ret;
+  GstBuffer *buf;
+
+  if (G_UNLIKELY (src->read_position != offset)) {
+    off_t res;
+
+    res = lseek (src->fd, offset, SEEK_SET);
+    if (G_UNLIKELY (res < 0 || res != offset))
+      goto seek_failed;
+
+    src->read_position = offset;
+  }
+
+  buf = gst_buffer_new_and_alloc (length);
+
+  GST_LOG_OBJECT (src, "Reading %d bytes", length);
+  ret = read (src->fd, GST_BUFFER_DATA (buf), length);
+  if (G_UNLIKELY (ret < 0))
+    goto could_not_read;
+
+  /* seekable regular files should have given us what we expected */
+  if (G_UNLIKELY ((guint) ret < length && src->seekable))
+    goto unexpected_eos;
+
+  /* other files should eos if they read 0 and more was requested */
+  if (G_UNLIKELY (ret == 0 && length > 0))
+    goto eos;
+
+  length = ret;
+
+  GST_BUFFER_SIZE (buf) = length;
+  GST_BUFFER_OFFSET (buf) = offset;
+  GST_BUFFER_OFFSET_END (buf) = offset + length;
+
+  *buffer = buf;
+
+  src->read_position += length;
+
+  return GST_FLOW_OK;
+
+  /* ERROR */
+seek_failed:
+  {
+    GST_ELEMENT_ERROR (src, RESOURCE, READ, (NULL), GST_ERROR_SYSTEM);
+    return GST_FLOW_ERROR;
+  }
+could_not_read:
+  {
+    GST_ELEMENT_ERROR (src, RESOURCE, READ, (NULL), GST_ERROR_SYSTEM);
+    gst_buffer_unref (buf);
+    return GST_FLOW_ERROR;
+  }
+unexpected_eos:
+  {
+    GST_ELEMENT_ERROR (src, RESOURCE, READ, (NULL),
+        ("unexpected end of file."));
+    gst_buffer_unref (buf);
+    return GST_FLOW_ERROR;
+  }
+eos:
+  {
+    GST_DEBUG ("non-regular file hits EOS");
+    gst_buffer_unref (buf);
+    return GST_FLOW_UNEXPECTED;
+  }
+}
+
+static GstFlowReturn
+gst_file_src_create (GstBaseSrc * basesrc, guint64 offset, guint length,
+    GstBuffer ** buffer)
+{
+  GstFileSrc *src;
+  GstFlowReturn ret;
+
+  src = GST_FILE_SRC (basesrc);
+
+#ifdef HAVE_MMAP
+  if (src->using_mmap) {
+    ret = gst_file_src_create_mmap (src, offset, length, buffer);
+  } else {
+    ret = gst_file_src_create_read (src, offset, length, buffer);
+  }
+#else
+  ret = gst_file_src_create_read (src, offset, length, buffer);
+#endif
+
+  return ret;
+}
+
+static gboolean
+gst_file_src_is_seekable (GstBaseSrc * basesrc)
+{
+  GstFileSrc *src = GST_FILE_SRC (basesrc);
+
+  return src->seekable;
+}
+
+static gboolean
+gst_file_src_get_size (GstBaseSrc * basesrc, guint64 * size)
+{
+  struct stat stat_results;
+  GstFileSrc *src;
+
+  src = GST_FILE_SRC (basesrc);
+
+  if (!src->seekable) {
+    /* If it isn't seekable, we won't know the length (but fstat will still
+     * succeed, and wrongly say our length is zero. */
+    return FALSE;
+  }
+
+  if (fstat (src->fd, &stat_results) < 0)
+    goto could_not_stat;
+
+  *size = stat_results.st_size;
+
+  return TRUE;
+
+  /* ERROR */
+could_not_stat:
+  {
+    return FALSE;
+  }
+}
+
+/* open the file and mmap it, necessary to go to READY state */
+static gboolean
+gst_file_src_start (GstBaseSrc * basesrc)
+{
+  GstFileSrc *src = GST_FILE_SRC (basesrc);
+  struct stat stat_results;
+
+  if (src->filename == NULL || src->filename[0] == '\0')
+    goto no_filename;
+
+  GST_INFO_OBJECT (src, "opening file %s", src->filename);
+
+  /* open the file */
+  src->fd = open (src->filename, O_RDONLY | O_BINARY);
+  if (src->fd < 0)
+    goto open_failed;
+
+  /* check if it is a regular file, otherwise bail out */
+  if (fstat (src->fd, &stat_results) < 0)
+    goto no_stat;
+
+  if (S_ISDIR (stat_results.st_mode))
+    goto was_directory;
+
+  if (S_ISSOCK (stat_results.st_mode))
+    goto was_socket;
+
+  src->using_mmap = FALSE;
+  src->read_position = 0;
+
+  /* record if it's a regular (hence seekable and lengthable) file */
+  if (S_ISREG (stat_results.st_mode))
+    src->is_regular = TRUE;
+
+#ifdef HAVE_MMAP
+  if (src->use_mmap) {
+    /* FIXME: maybe we should only try to mmap if it's a regular file */
+    /* allocate the first mmap'd region if it's a regular file ? */
+    src->mapbuf = gst_file_src_map_region (src, 0, src->mapsize, TRUE);
+    if (src->mapbuf != NULL) {
+      GST_DEBUG_OBJECT (src, "using mmap for file");
+      src->using_mmap = TRUE;
+      src->seekable = TRUE;
+    }
+  }
+  if (src->mapbuf == NULL)
+#endif
+  {
+    /* If not in mmap mode, we need to check if the underlying file is
+     * seekable. */
+    off_t res = lseek (src->fd, 0, SEEK_END);
+
+    if (res < 0) {
+      GST_LOG_OBJECT (src, "disabling seeking, not in mmap mode and lseek "
+          "failed: %s", g_strerror (errno));
+      src->seekable = FALSE;
+    } else {
+      src->seekable = TRUE;
+    }
+    lseek (src->fd, 0, SEEK_SET);
+  }
+
+  /* We can only really do seeking on regular files - for other file types, we
+   * don't know their length, so seeking isn't useful/meaningful */
+  src->seekable = src->seekable && src->is_regular;
+
+  return TRUE;
+
+  /* ERROR */
+no_filename:
+  {
+    GST_ELEMENT_ERROR (src, RESOURCE, NOT_FOUND,
+        (_("No file name specified for reading.")), (NULL));
+    return FALSE;
+  }
+open_failed:
+  {
+    switch (errno) {
+      case ENOENT:
+        GST_ELEMENT_ERROR (src, RESOURCE, NOT_FOUND, (NULL),
+            ("No such file \"%s\"", src->filename));
+        break;
+      default:
+        GST_ELEMENT_ERROR (src, RESOURCE, OPEN_READ,
+            (_("Could not open file \"%s\" for reading."), src->filename),
+            GST_ERROR_SYSTEM);
+        break;
+    }
+    return FALSE;
+  }
+no_stat:
+  {
+    GST_ELEMENT_ERROR (src, RESOURCE, OPEN_READ,
+        (_("Could not get info on \"%s\"."), src->filename), (NULL));
+    close (src->fd);
+    return FALSE;
+  }
+was_directory:
+  {
+    GST_ELEMENT_ERROR (src, RESOURCE, OPEN_READ,
+        (_("\"%s\" is a directory."), src->filename), (NULL));
+    close (src->fd);
+    return FALSE;
+  }
+was_socket:
+  {
+    GST_ELEMENT_ERROR (src, RESOURCE, OPEN_READ,
+        (_("File \"%s\" is a socket."), src->filename), (NULL));
+    close (src->fd);
+    return FALSE;
+  }
+}
+
+/* unmap and close the file */
+static gboolean
+gst_file_src_stop (GstBaseSrc * basesrc)
+{
+  GstFileSrc *src = GST_FILE_SRC (basesrc);
+
+  /* close the file */
+  close (src->fd);
+
+  /* zero out a lot of our state */
+  src->fd = 0;
+  src->is_regular = FALSE;
+
+  if (src->mapbuf) {
+    gst_buffer_unref (src->mapbuf);
+    src->mapbuf = NULL;
+  }
+
+  return TRUE;
+}
+
+/*** GSTURIHANDLER INTERFACE *************************************************/
+#ifdef __SYMBIAN32__
+GstURIType
+#else
+static guint
+#endif 
+gst_file_src_uri_get_type (void)
+{
+  return GST_URI_SRC;
+}
+static gchar **
+gst_file_src_uri_get_protocols (void)
+{
+  static gchar *protocols[] = { "file", NULL };
+
+  return protocols;
+}
+static const gchar *
+gst_file_src_uri_get_uri (GstURIHandler * handler)
+{
+  GstFileSrc *src = GST_FILE_SRC (handler);
+
+  return src->uri;
+}
+
+static gboolean
+gst_file_src_uri_set_uri (GstURIHandler * handler, const gchar * uri)
+{
+  gchar *protocol, *location;
+  gboolean ret;
+  GstFileSrc *src = GST_FILE_SRC (handler);
+
+  protocol = gst_uri_get_protocol (uri);
+  if (strcmp (protocol, "file") != 0) {
+    g_free (protocol);
+    return FALSE;
+  }
+  g_free (protocol);
+
+  /* allow file://localhost/foo/bar by stripping localhost but fail
+   * for every other hostname */
+  if (g_str_has_prefix (uri, "file://localhost/")) {
+    char *tmp;
+
+    /* 16 == strlen ("file://localhost") */
+    tmp = g_strconcat ("file://", uri + 16, NULL);
+    /* we use gst_uri_get_location() although we already have the
+     * "location" with uri + 16 because it provides unescaping */
+    location = gst_uri_get_location (tmp);
+    g_free (tmp);
+  } else if (strcmp (uri, "file://") == 0) {
+    /* Special case for "file://" as this is used by some applications
+     *  to test with gst_element_make_from_uri if there's an element
+     *  that supports the URI protocol. */
+    gst_file_src_set_location (src, NULL);
+    return TRUE;
+  } else {
+    location = gst_uri_get_location (uri);
+  }
+
+  if (!location)
+    return FALSE;
+  if (!g_path_is_absolute (location)) {
+    g_free (location);
+    return FALSE;
+  }
+
+  ret = gst_file_src_set_location (src, location);
+  g_free (location);
+
+  return ret;
+}
+
+static void
+gst_file_src_uri_handler_init (gpointer g_iface, gpointer iface_data)
+{
+  GstURIHandlerInterface *iface = (GstURIHandlerInterface *) g_iface;
+
+  iface->get_type = gst_file_src_uri_get_type;
+  iface->get_protocols = gst_file_src_uri_get_protocols;
+  iface->get_uri = gst_file_src_uri_get_uri;
+  iface->set_uri = gst_file_src_uri_set_uri;
+}