Replaced the configure option --enable-diretio with --enable-scsi-directio

and --enable-parport-directio.

NOTE: While I know, what the SCSI direct IO means, I have no idea, what
direct IO means in the context of the parport, so somebody needs to add
some useful description about parport direct io to configure.in and to
README (or README.linux)

README.linux

@@ -50,9 +50,11 @@ in devfs".
 
 Adaptec 1542 SCSI adapter:
   Using buffer sizes of more than 32768 bytes with the aha1542 driver can
-  lead to kernel panic with older kernels. To avoid this, set 
-  --enable-scsibuffersize or SANE_SG_BUFFERSIZE to 32768, or download and
-  install the SG driver 2.1.37 or newer from http://www.torque.net/sg.
+  lead to kernel panic with older kernels. To avoid this, run configure with 
+  the option --enable-scsibuffersize or set the environment variable
+  SANE_SG_BUFFERSIZE to 32768 before running scanimage or another frontend, 
+  or download and install the SG driver 2.1.37 or newer from 
+  http://www.torque.net/sg.
 
 idescsi:
   The Linux kernel "Emulation of a SCSI host adapter for IDE ATAPI
@@ -60,14 +62,13 @@ idescsi:
   SANE. If your scanner isn't found or you encounter segmentation faults
   try to disable idescsi.
 
-Direct IO: Recent versions of the Linux SG driver for the 2.4 kernels support 
-  direct IO, i.e., the SCSI adapter's DMA chip copies data directly to/from 
-  user memory. Direct IO reduces memory usage and it may give better 
-  throughput for very fast scanners, but it can lead to access conflicts, 
-  if a backend uses shared memory. SANE does not use direct IO by default,
-  if you want to use it, run
+SCSI Direct IO: Recent versions of the Linux SG driver for the 2.4 kernels 
+  support direct IO, i.e., the SCSI adapter's DMA chip copies data directly 
+  to/from user memory. Direct IO reduces memory usage, but it can lead to 
+  access conflicts, if a backend uses shared memory. SANE does not use 
+  direct IO by default. If you want to use it, run
 
-	configure --enable-directio=yes
+	configure --enable-scsi-directio=yes
 
 
 Other Information

configure.in

@@ -314,12 +314,27 @@ AC_DEFINE_UNQUOTED(SCSIBUFFERSIZE, $set_scsibuffersize,
                    [SCSI command buffer size])
 echo "scsi buffersize: $set_scsibuffersize"
 
-AC_ARG_ENABLE(directio,
-  [  --enable-directio       enable direct IO (Linux only; can lead to crashes
-                          with backends using shared memory) [default=no]],
+AC_ARG_ENABLE(scsi-directio,
+  [  --enable-scsi-directio  enable SCSI direct IO (Linux only; can lead to 
+                          crashes with backends using shared memory) 
+                          [default=no]
+                          This option is in no way related to
+                          --enable-parport-directio. See README.linux for 
+                          more information],
   [
-    if eval "test x$enable_directio = xyes"; then
-      CFLAGS="$CFLAGS -DENABLE_DIRECTIO"
+    if eval "test x$enable_scsi_directio = xyes"; then
+      CFLAGS="$CFLAGS -DENABLE_SCSI_DIRECTIO"
+    fi
+  ])
+
+AC_ARG_ENABLE(parport-directio,
+  [  --enable-parport-directio  enable parallel port direct IO
+                          XXXX short descrption needed [default=no]
+                          This option is inno way related to 
+                          --enable-scsi-directio],
+  [
+    if eval "test x$enable_parport_directio = xyes"; then
+      CFLAGS="$CFLAGS -DENABLE_PARPORT_DIRECTIO"
     fi
   ])
 

sanei/sanei_scsi.c

@@ -1931,7 +1931,7 @@ sanei_scsi_req_enter2 (int fd,
       req->sgdata.sg3.hdr.sbp = &(req->sgdata.sg3.sense_buffer[0]);
       /* 10 minutes should be ok even for slow scanners */
       req->sgdata.sg3.hdr.timeout = 1000 * 60 * 10;
-#ifdef ENABLE_DIRECTIO
+#ifdef ENABLE_SCSI_DIRECTIO
       /* for the adventurous: If direct IO is used,
          the kernel locks the buffer. This can lead to conflicts,
          if a backend uses shared memory.