--- IO-AIO/AIO.xs	2012/07/27 18:43:25	1.219
+++ IO-AIO/AIO.xs	2012/07/30 16:44:12	1.220
@@ -167,56 +167,86 @@
   req->result = -1;
 
 #if HAVE_FIEMAP
+  /* assume some c99 */
+  struct fiemap *fiemap = 0;
+  size_t end_offset;
   int count = req->int3;
 
-  /* heuristic: first try with 72 extents if we don't know how many, */
-  /* as most files have (hopefully) fewer than this many extents */
-  /* in fact, most should have <= 2, so the 72 below is probably overkill */
+  req->flags |= EIO_FLAG_PTR1_FREE;
+
+  /* heuristic: start with 512 bytes (8 extents), and if that isn't enough, */
+  /* increase in 3.5kb steps */
   if (count < 0)
-    count = 72; /* for what it's worth, 72 extents fit nicely into 4kb */
+    count = 8;
+
+  fiemap = malloc (sizeof (*fiemap) + sizeof (struct fiemap_extent) * count);
+  errno = ENOMEM;
+  if (!fiemap)
+    return;
+
+  req->ptr1 = fiemap;
+
+  fiemap->fm_start        = req->offs;
+  fiemap->fm_length       = req->size;
+  fiemap->fm_flags        = req->int2;
+  fiemap->fm_extent_count = count;
+
+  if (ioctl (req->int1, FS_IOC_FIEMAP, fiemap))
+    return;
+
+  if (req->int3 >= 0 /* not autosizing */
+      || !fiemap->fm_mapped_extents /* no more extents */
+      || fiemap->fm_extents [fiemap->fm_mapped_extents - 1].fe_flags & FIEMAP_EXTENT_LAST /* hit eof */)
+    goto done;
+
+  /* else we have to loop -
+   * it would be tempting (atcually I tried that first) to just query the
+   * number of extents needed, but linux often feels like not returning all
+   * extents, without telling us it left any out. this complicates
+   * this quite a bit.
+   */
+
+  end_offset = fiemap->fm_length + (fiemap->fm_length == FIEMAP_MAX_OFFSET ? 0 : fiemap->fm_start);
 
   for (;;)
     {
-      struct fiemap *fiemap = malloc (sizeof (*fiemap) + sizeof (struct fiemap_extent) * count);
+      /* we go in 54 extent steps - 3kb, in the hope that this fits nicely on the eio stack (normally 16+ kb) */
+      char scratch[3072];
+      struct fiemap *incmap = (struct fiemap *)scratch;
+
+      incmap->fm_start        = fiemap->fm_extents [fiemap->fm_mapped_extents - 1].fe_logical
+                                + fiemap->fm_extents [fiemap->fm_mapped_extents - 1].fe_length;
+      incmap->fm_length       = fiemap->fm_length - (incmap->fm_start - fiemap->fm_start);
+      incmap->fm_flags        = fiemap->fm_flags;
+      incmap->fm_extent_count = (sizeof (scratch) - sizeof (struct fiemap)) / sizeof (struct fiemap_extent);
+
+      if (ioctl (req->int1, FS_IOC_FIEMAP, incmap))
+        return;
+
+      count = fiemap->fm_mapped_extents + incmap->fm_mapped_extents;
+      fiemap = realloc (fiemap, sizeof (*fiemap) + sizeof (struct fiemap_extent) * count);
       errno = ENOMEM;
       if (!fiemap)
         return;
 
       req->ptr1 = fiemap;
-      req->flags |= EIO_FLAG_PTR1_FREE;
-
-      fiemap->fm_start        = req->offs;
-      fiemap->fm_length       = req->size;
-      fiemap->fm_flags        = req->int2;
-      fiemap->fm_extent_count = count;
 
-      if (ioctl (req->int1, FS_IOC_FIEMAP, fiemap))
-        return;
+      for (count = 0; count < incmap->fm_mapped_extents; ++count)
+        {
+          struct fiemap_extent *e = incmap->fm_extents + count;
 
-      if (req->int3 >= 0)
-        break; /* when not autosizing we are done */
+          if (e->fe_logical + e->fe_length >= end_offset)
+            goto done;
 
-      if (fiemap->fm_mapped_extents < count)
-        /* either autosizing succeeded,
-         * or the file had no extents
-         * or we luckily had enough space */
-        break;
-
-      /* some kernels overwrite fm_length, so just reset everything */
-      fiemap->fm_start        = req->offs;
-      fiemap->fm_length       = req->size;
-      fiemap->fm_flags        = req->int2;
-      fiemap->fm_extent_count = 0;
-
-      if (ioctl (req->int1, FS_IOC_FIEMAP, fiemap))
-        return;
+          fiemap->fm_extents [fiemap->fm_mapped_extents++] = *e;
 
-      /* to work around a kernel bug, we allocate one more */
-      count = fiemap->fm_mapped_extents + 1;
+          if (e->fe_flags & FIEMAP_EXTENT_LAST)
+            goto done;
 
-      free (fiemap);
+        }
     }
 
+done:
   req->result = 0;
 
 #else