--- IO-AIO/AIO.xs	2005/07/31 18:20:07	1.16
+++ IO-AIO/AIO.xs	2005/07/31 18:45:48	1.17
@@ -232,6 +232,77 @@
   send_req (req);
 }
 
+/* work around various missing functions */
+
+#if !HAVE_PREADWRITE
+# define pread  aio_pread
+# define pwrite aio_pwrite
+
+/*
+ * make our pread/pwrite safe against themselves, but not against
+ * normal read/write by using a mutex. slows down execution a lot,
+ * but that's your problem, not mine.
+ */
+static pthread_mutex_t iolock = PTHREAD_MUTEX_INITIALIZER;
+
+static ssize_t
+pread (int fd, void *buf, size_t count, off_t offset)
+{
+  ssize_t res;
+  off_t ooffset;
+
+  pthread_mutex_lock (&iolock);
+  ooffset = lseek (fd, 0, SEEK_CUR);
+  lseek (fd, offset, SEEK_SET);
+  res = read (fd, buf, count);
+  lseek (fd, ooffset, SEEK_SET);
+  pthread_mutex_unlock (&iolock);
+
+  return res;
+}
+
+static ssize_t
+pwrite (int fd, void *buf, size_t count, off_t offset)
+{
+  ssize_t res;
+  off_t ooffset;
+
+  pthread_mutex_lock (&iolock);
+  ooffset = lseek (fd, 0, SEEK_CUR);
+  lseek (fd, offset, SEEK_SET);
+  res = write (fd, buf, count);
+  lseek (fd, offset, SEEK_SET);
+  pthread_mutex_unlock (&iolock);
+
+  return res;
+}
+#endif
+
+#if !HAVE_FDATASYNC
+# define fdatasync fsync
+#endif
+
+#if !HAVE_READAHEAD
+# define readahead aio_readahead
+
+static char readahead_buf[4096];
+
+static ssize_t
+readahead (int fd, off_t offset, size_t count)
+{
+  while (count > 0)
+    {
+      size_t len = count < sizeof (readahead_buf) ? count : sizeof (readahead_buf);
+
+      pread (fd, readahead_buf, len, offset);
+      offset += len;
+      count  -= len;
+    }
+
+  errno = 0;
+}
+#endif
+
 static void *
 aio_proc (void *thr_arg)
 {
@@ -266,19 +337,10 @@
 
       switch (type)
         {
-#if HAVE_PREADWRITE
           case REQ_READ:      req->result = pread     (req->fd, req->dataptr, req->length, req->offset); break;
           case REQ_WRITE:     req->result = pwrite    (req->fd, req->dataptr, req->length, req->offset); break;
-#else
-# error "pread/pwrite cannot be emulated, fix your os"
-#endif
 
-#if HAVE_READAHEAD
           case REQ_READAHEAD: req->result = readahead (req->fd, req->offset, req->length); break;
-#else
-          // TODO: emulate
-          case REQ_READAHEAD: req->result = -1; errno = ENOSYS; break;
-#endif
 
           case REQ_STAT:      req->result = stat      (req->dataptr, req->statdata); break;
           case REQ_LSTAT:     req->result = lstat     (req->dataptr, req->statdata); break;
@@ -288,10 +350,7 @@
           case REQ_CLOSE:     req->result = close     (req->fd); break;
           case REQ_UNLINK:    req->result = unlink    (req->dataptr); break;
 
-          case REQ_FDATASYNC:
-#if HAVE_FDATASYNC
-                              req->result = fdatasync (req->fd); break;
-#endif
+          case REQ_FDATASYNC: req->result = fdatasync (req->fd); break;
           case REQ_FSYNC:     req->result = fsync     (req->fd); break;
 
           case REQ_QUIT: