/[gxemul]/trunk/doc/misc.html

This is repository of my old source code which isn't updated any more. Go to git.rot13.org for current projects!

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-revision 24 by dpavlin,
Mon Oct  8 16:19:56 2007 UTC
+revision 40 by dpavlin,
Mon Oct  8 16:22:11 2007 UTC
 Line 10
  <!--
- $Id: misc.html,v 1.63 2006/05/22 04:53:52 debug Exp $
+ $Id: misc.html,v 1.68 2007/04/28 09:18:34 debug Exp $
- Copyright (C) 2003-2006  Anders Gavare.  All rights reserved.
+ Copyright (C) 2003-2007  Anders Gavare.  All rights reserved.
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are met:
 Line 47 
 SUCH DAMAGE.
  <p>
  <ul>
-   <li><a href="#networking">Networking</a>
    <li><a href="#devel">Writing operating system code, or
          developing firmware, using GXemul</a>
    <li><a href="#compilercontruct">Using GXemul in compiler contruction courses</a>
    <li><a href="#disk">How to start the emulator with a disk image</a>
+   <li><a href="#tape_images">How to start the emulator with tape images</a>
+   <li><a href="#disk_overlays">How to use disk image overlays</a>
    <li><a href="#filexfer">Transfering files to/from the guest OS</a>
    <li><a href="#largeimages">How to extract large gzipped disk images</a>
    <li><a href="#userland">Running userland binaries</a>
-Line 64 
 SUCH DAMAGE.
+Line 65 
 SUCH DAMAGE.
- <p><br>
- <a name="networking"></a>
- <h3>Networking:</h3>
- It is possible to let the guest OS running inside the emulator get access to
- the Internet. If you are interested in the technical details, and the
- reasons why networking is implemented in the emulator the way it currently
- is implemented, you might want to read the <a href="technical.html#net">
- networking section in the technical documentation</a>.
- <p><font color="#ff0000">This is still experimental, hackish, and
- rather buggy. With NetBSD running as guest operating system, it mostly
- works.</font>
- <p>When only one machine is being emulated, the following default values
- apply:<pre>
-         IPv4 address:                   10.0.0.1
-         Netmask:                        255.0.0.0
-         Gateway / default route:        10.0.0.254
-         Nameserver:                     10.0.0.254
- </pre>
- <p>The emulated machine must of course have a NIC which is emulated
- correctly. At the moment, the following NICs should work:
- <ul>
-   <li><tt><b>ether</b></tt>, the "fake" experimental ethernet device
-         (documented <a href="experiments.html#expdevices_ether">here</a>)
-   <li><tt><b>le</b></tt>, Turbochannel Lance Ethernet, as used in
-         DECstation 5000/200 ("3max")
-   <li><tt><b>mec</b></tt>, the SGI O2's ethernet controller
-   <li><tt><b>dec21143</b></tt>, Digital's 21143 NIC (known as <tt>dc</tt>
-         in OpenBSD, or <tt>tlp</tt> in NetBSD)
- </ul>
- <p>The emulator acts as a NAT-like gateway/firewall; to the outside world
- it will seem like it is the host's OS that connects to other machines on
- the internet, not the guest OS.
  <p><br>
-Line 145 
 complement to testing on real hardware.
+Line 105 
 complement to testing on real hardware.
          <li>CPU details in GXemul are usually wrong. If your code depends
          on, say, R10000 or MIPS64 specifics, chances are that GXemul will
          not be sufficient. One example is different revisions of ISAs;
--bit MIPS instructions which should trigger an exception on a
+         some instructions which should trigger an exception on a
-         real 32-bit MIPS processor usually execute anyway in GXemul. Another
+         real MIPS processor usually execute anyway in GXemul. Another
          example is if userland code tries to access kernel memory; in some
          cases there is protection against this, but not in all cases (to get
          higher performance).
-Line 239 
 use it as a CD-ROM directly accessible f
+Line 199 
 use it as a CD-ROM directly accessible f
  </pre>
  It is probably possible to use harddisks as well this way, but I would not
  recommend it.
- <p>
+ <p><br>
+ <a name="tape_images"></a>
+ <h3>How to start the emulator with tape images:</h3>
  Using emulated tape drives is a bit more complicated than disks, because a
  tape can be made up of several "files" with space in between. The solution
  I have choosen is to have one file in the host's file system space for each
-Line 289 
 every time a tape is rewound, it is reop
+Line 258 
 every time a tape is rewound, it is reop
  on the command line. By changing what the symbolic name points to,
  you can "switch tapes" without quiting and restarting the emulator.
+ <p>
+ <font color="#ff0000">Note: Tape support is most likely very buggy,
+ because it has not been tested much, and has probably also suffered
+ from bit-rot by now.</font>
+ <p><br>
+ <a name="disk_overlays"></a>
+ <h3>How to use disk image overlays:</h3>
+ This is most likely best understood by an example:
+ <p><ul>
+   <li>Install e.g. <a href="guestoses.html#netbsdcatsinstall">NetBSD/cats</a>.
+         You will end up with a disk image called
+         <tt>nbsd_cats.img</tt>.
+   <p>
+   <li>Running the following command will boot straight from the disk
+         image, with no overlay images:<pre>
+         <b>gxemul -XEcats -d nbsd_cats.img netbsd.aout-GENERIC.gz</b>
+ </pre>
+   <li>You may now create an overlay file, a corresponding map file,
+         and start the emulator with the overlay image connected to
+         the same (explicit) ID as the base disk image:<pre>
+         <b>touch overlay.img overlay.img.map
+         gxemul -XEcats -d 0:nbsd_cats.img -d V0:overlay.img netbsd.aout-GENERIC.gz</b>
+ </pre>
+   <li>Any changes to the filesystem you perform when using the overlay
+         will only be written to that overlay. For example, to perform
+         a "roll back", you can do the following:<pre>
+         <b>rm -f overlay.img overlay.img.map
+         touch overlay.img overlay.img.map</b>
+ </pre>
+         and then simply start the emulator again, with the newly created
+         overlay image.
+ </ul>
+ <p>It is also possible to add multiple overlays. In that case, writes
+ always go the the <i>last</i> added overlay.
+ <p>GXemul uses Unix' way of supporting files with "holes",
+ so even if <tt>ls -l overlay.img</tt> says that the overlay is several
+ gigabytes large, <tt>du overlay.img</tt> should reveal that only the
+ blocks that have actually been written to have been stored in the
+ overlay, e.g.:<pre>
+         <b>$ ls -l
+         ..
+         -rw-r--r--  1 debug  wheel  3072319488 Mar 24 11:59 nbsd_cats.img
+         -rw-r--r--  1 debug  wheel     2465354 Mar 24 11:44 netbsd.aout-GENERIC.gz
+         -rw-r--r--  1 debug  wheel  2930841600 Mar 24 14:02 overlay.img
+         -rw-r--r--  1 debug  wheel      715538 Mar 24 14:02 overlay.img.map
+         $ du overlay.img
+    overlay.img
+ </b>
+ </pre>
+ <p>The .map file is simply a raw bitmap telling which blocks of the
+ overlay file that are in use.
-Line 298 
 you can "switch tapes" without quiting a
+Line 332 
 you can "switch tapes" without quiting a
  <a name="filexfer"></a>
  <h3>Transfering files to/from the guest OS:</h3>
- If the emulated machine supports networking (see
+ If the emulated machine supports networking (see <a
- <a href="#networking">above</a>), then transfering files via FTP is
+ href="networking.html#intro">this section</a> for more info), then the easiest
- probably easiest.
+ way to transfer files is probably to use FTP or similar methods.
  <p>There is another way of transfering files which works for any kind of
  emulated machine which supports disks (either SCSI or IDE). Any file can

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