path: root/libbsd.txt

RTEMS BSD USB and TCP/IP Developers Guide
=========================================
Joel Sherrill <joel.sherrill@oarcorp.com>
:Author Initials: JRS
:toc:
:icons:
:numbered:
:website: http://www.rtems.org/

RTEMS uses FreeBSD as the source of its TCP/IP and USB stacks.
This is a developers guide which captures information on the
process of merging code from FreeBSD, building this library,
RTEMS specific support files, and general guidelines on what
modifications to the FreeBSD source are permitted.

Goals of this effort are:

* Update TCP/IP and provide USB in RTEMS
* Ease updating to future FreeBSD versions
* Ease tracking changes in FreeBSD code
* Minimize manual changes in FreeBSD code
* Define stable kernel/device driver API which is implemented
by both RTEMS and FreeBSD. This is the foundation of the port.

We will work to push our changes upstream to the FreeBSD Project
and minimize changes required at each update point.

**************************************************************
This is a work in progress and is very likely to be incomplete.
Please help by adding to it.
**************************************************************

== Source Code Version Information

* FreeBSD 8.2 SVN r222496
* RTEMS 4.11
  - BSP must have support for all new BSD sys sections
  - It is preferable if the BSP uses linkcmds.base.
  - BSP must be from an architecture with Programmable Interrupt Controller
    interrupt model.

The FreeBSD 8.2 SVN checkout will generally be referred to as the
FreeBSD source in this document. An archive of the FreeBSD 8.2 SVN
archive used is located at http://www.rtems.org/ftp/pub/rtems/people/joel/freebsd

== Issues and To Do
* Sebastian Huber: mentioned some simple test code which would verify
  that the BSD code/and or USB stack was initialized.  This has been
  sent to Joel Sherrill and is pending merger.

* Sebastian Huber and Joel Sherrill discussed the need for a a basic USB
  functionality test that is known to work on qemu pc.

* Adapt generic IRQ PIC interface code to Simple Vectored Interrupt Model
  so that those architectures can use new TCP/IP and USB code. 

* in_cksum implementations for architectures not supported by FreeBSD.
  This will require figuring out where to put implementations that do
  not originate from FreeBSD and are populated via the script.

* FreeBSD generic in_cksum implementation is missing in_cksum_split so
  currently cannot be used.

* How does one initialize the TCP/IP stack?

* linker section issues: I have undefined symbols for
  _bsd__start_set_sysinit_set and _bsd__stop_set_sysinit_set.
  Is this the only type of new section magic?  What about the old sysctl_set?
  I added this to my linkcmds.  

[listing]
----
    /* sysinit section? */
    . = ALIGN (16);
    _bsd__start_set_sysinit_set = .;
    *(set_sys_init_*);
    _bsd__stop_set_sysinit_set = .;

----

* Convert all BSP linkcmds to use a linkcmds.base so the sections are 
easier to insert.

* rtems-bsd-init-with-irq.c:
  rtems_bsd_initialize_with_interrupt_server() has reference to 
    rtems_interrupt_server_initialize() and this method is unimplemented
    - XXX BSP implements pieces
    - BSPs using this software stack must support it apparently.
    - What about Simple Vectored architectures?

* maxproc variable referenced by rtems-bsd-resource.c.  What should it
be set to?

* ngroups_max variable referenced by rtems-bsd-prot.c.  - What should
it be set to?

* NIC Device Drivers
- Only common NIC drivers have been included in the initial set. These do not
include any system on chip or ISA drivers.
- The ISA drivers require more BSD infrastructure to be addressed. This was 
outside the scope of the initial porting effort.

== FreeBSD Source

You should be able to rely on FreebSD manual pages and documentation
for details on the code itself.

=== Automatically Generated FreeBSD Files

The FreeBSD source tarball includes a file named Makefile.rtems which
has stanzas to automatically generate some files using awk. For details
on this, see http://www.freebsd.org/cgi/man.cgi?query=kobj&apropos=0&sektion=0&manpath=FreeBSD+9.0-RELEASE&arch=default&format=html

XXX This needs more detail.

=== Rules for Modifying FreeBSD Source

* Only add lines.  Subtract code by added "ifndef __rtems__". This makes
merging easier in the future.

== libbsd Source

=== What is in git

The git source is a self-contained kit with FreeBSD and RTEMS components
pre-merged. The Makefile in this kit is automatically generated.

Any changes to sources in the freebsd or contrib directories will need to
be merged upstream into our master FreeBSD svn checkout.

The FreeBSD sources managed in RTEMS libbsd git repository (e.g. contrib
and freebsd directories) contain the "managed" version of the
FreeBSD source.  The FreeBSD SVN source is the "master" version. The
freebsd-to-rtems.py script is used to transfer files between the two
trees. In general terms, if you have modified FreeBSD in the RTEMS libbsd
tree, you want to run the script in "revert" or "reverse" mode to move
the source back so you can run an "svn diff" against the upstream FreeBSD
source. If you want to transfer source from the FreeBSD SVN checkout to
the RTEMS libbsd tree, then you want to run the script in "forward" or
default mode.

=== Building RTEMS libbsd source

You need to configure RTEMS for the desired BSP and install it. The
following is the script used to build the powerpc/psim BSP for our
internal testing purposes:

[listing]
----
#! /bin/sh

cd ${HOME}/newbsd
rm -rf b-psim
mkdir b-psim
cd b-psim
../git/rtems/configure --target=powerpc-rtems4.11 \
  --enable-rtemsbsp=psim --disable-networking \
  --enable-tests=samples \
  --prefix=${HOME}/newbsd/bsp-install >c.log 2>&1 && \
  make >b.log 2>&1 && \
  make install >i.log 2>&1
echo $?
----

Then edit the file config.inc to set RTEMS_MAKEFILE_PATH appropriately
to indicate the ${prefix}/${target}/${BSP}.  Continuing on the above,
the config.inc used to match the above is:

[listing]
----
RTEMS_MAKEFILE_PATH = ${HOME}/newbsd/bsp-install/powerpc-rtems4.11/psim/
INSTALL_BASE = ${HOME}/newbsd/install
----

The above installs the RTEMS libbsd kit into a separate place from 
RTEMS and the BSP. The RTEMS libbsd tests are built against an installed
image of the RTEMS libbsd. By keeping it in a separate installation point
from RTEMS itself, this makes it easier to remove a libbsd installation
and have a clean test point.

[listing]
----
make
make install
make -C testsuite
----

At this point, we expect multiple linker errors. That is what we are
currently working on.

=== Organization

The top level directory contains a few directories and files. The following
are important to understand:

* freebsd-to-rtems.py - script to convert to and free FreeBSD and RTEMS trees
* Makefile - automatically generated
* contrib/ - from FreeBSD by script.
* freebsd/ - from FreeBSD by script.
* rtemsbsd/ - RTEMS specific implementations of FreeBSD kernel support routines.
* testsuite/ - RTEMS specific tests
* libbsd.txt - Documentation in Asciidoc

== Moving Code Between FreeBSD SVN and RTEMS libbsd

The script freebsd-to-rtems.py is used to copy code from FreeBSD to the
RTEMS libbsd tree and to reverse this process. This script attempts to
automate this process as much as possible and performs some transformations
on the FreeBSD code. Its command line arguments are shown below:

[listing]
----
freebsd-to-rtems.py [args]
  -?|-h|--help     print this and exit
  -d|--dry-run     run program but no modifications
  -D|--diff        provide diff of files between trees
  -e|--early-exit  evaluate arguments, print results, and exit
  -m|--makefile    just generate Makefile
  -R|--reverse     default FreeBSD -> RTEMS, reverse that
  -r|--rtems       RTEMS directory
  -f|--freebsd     FreeBSD directory
  -v|--verbose     enable verbose output mode
----

In its default mode of operation, freebsd-to-rtems.py is used to copy code
from FreeBSD to the RTEMS libbsd tree and perform transformations.  In forward
mode, the script may be requested to just generate the Makefile.

In "reverse mode", this script undoes those transformations and copies 
the source code back to the FreeBSD SVN tree. This allows us to do 
'svn diff', evaluate changes made by the RTEMS Project, and report changes
back to FreeBSD upstream.

In either mode, the script may be asked to perform a dry-run or be verbose.
Also, in either mode, the script is also smart enough to avoid copying over
files which have not changed. This means that the timestamps of files are
not changed unless the contents change. The script will also report the
number of files which changed. In verbose mode, the script will print
the name of the files which are changed.

The following is an example forward run with no changes.

[listing]
----
$ ~/newbsd/git/libbsd-8.2/freebsd-to-rtems.py \
    -r /home/joel/newbsd/git/libbsd-8.2 \
    -f /home/joel/newbsd/libbsd/freebsd-8.2 -v
Verbose:                yes
Dry Run:                no
Only Generate Makefile: no
RTEMS Directory:        /home/joel/newbsd/git/libbsd-8.2
FreeBSD Directory:      /home/joel/newbsd/libbsd/freebsd-8.2
Direction:              forward
Generating into /home/joel/newbsd/git/libbsd-8.2
0 files were changed.
----

The script may also be used to generate a diff in either forward or reverse
direction.

== Initialization of RTEMS Libbsd

The initialization of the RTEMS Libbsd is based on the FreeBSD SYSINIT 
infrastructure. This is simply because we are initializing a subset of
FreeBSD. For details refer to http://www.freebsd.org/cgi/man.cgi?query=SYSINIT&sektion=9&apropos=0&manpath=FreeBSD+9-current

The key to initializing a system is to ensure that the desired device
drivers are explicitly pulled into the linked application. This plus
linking against the Libsd library will pull in the necessary FreeBSD
infrastructure. The SYSINIT structures are automatically built at link
time and the various initialization routines will thus be executed in'
the correct order.

XXX This needs more details.

=== SYSCTL_NODE Example

During development, we had an undefined reference to
_bsd_sysctl__net_children that we had trouble tracking down. Thanks to
Chris Johns, we located it. He explained how to read SYSCTL_NODE
definitions. This line from freebsd/netinet/in_proto.c is attempting
to add the "inet" node to the parent node "_net".

[listing]
----
SYSCTL_NODE(_net,      PF_INET,         inet,   CTLFLAG_RW, 0,
        "Internet Family");
----

Our problem was that we could not find where _bsd_sysctl__net_children
was defined. Chris suggested that when in doubt compile with -save-temps
and look at the preprocessed .i files. But he did not need that. He
explained that this the symbol name _bsd_sysctl__net_children was
automatically generated by a SYSCTL_NODE as follows:

* _bsd_ - added by RTEMS modifications to SYSCTL_NODE macro
* sysctl_ - boilerplace added by SYSCTL_NODE macro
* "" - empty string for parent node
* net - name of SYSCTL_NODE
* children - added by SYSCTL macros
  
This was all generated by a support macro declaring the node as this:

[listing]
----
struct sysctl_oid_list SYSCTL_NODE_CHILDREN(parent, name);
----

Given this information, we located this SYSCTL_NODE declaration in 
kern/kern_mib.c

[listing]
----
SYSCTL_NODE(, CTL_KERN,   kern,   CTLFLAG_RW, 0,
        "High kernel, proc, limits &c");
----