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<H2><A NAME="s6">6.</A> <A HREF="prog.html#toc6">System dependent parts</A></H2>
<H2><A NAME="ss6.1">6.1</A> <A HREF="prog.html#toc6.1">Introduction</A>
</H2>
<P>We've tried to make BIRD as portable as possible, but unfortunately
communication with the network stack differs from one OS to another,
so we need at least some OS specific code. The good news is that this
code is isolated in a small set of modules:
<P>
<DL>
<DT><CODE>config.h</CODE><DD><P>is a header file with configuration information,
definition of the standard set of types and so on.
<DT>Startup module<DD><P>controls BIRD startup. Common for a family of OS's (e.g.,
for all Unices).
<DT>Logging module<DD><P>manages the system logs. [per OS family]
<DT>IO module<DD><P>gives an implementation of sockets, timers and the
global event queue. [per OS family]
<DT>KRT module<DD><P>implements the Kernel and Device protocols. This
is the most arcane part of the system dependent stuff and some
functions differ even between various releases of a single OS.
</DL>
<H2><A NAME="ss6.2">6.2</A> <A HREF="prog.html#toc6.2">Logging</A>
</H2>
<P>
<P>The Logging module offers a simple set of functions for writing
messages to system logs and to the debug output. Message classes
used by this module are described in <CODE>birdlib.h</CODE> and also in the
user's manual.
<P>
<P><HR><H3>Function</H3>
<P><I>void</I>
<B>log_commit</B>
(<I>int</I> <B>class</B>, <I>buffer *</I> <B>buf</B>) -- commit a log message
<P>
<H3>Arguments</H3>
<P>
<DL>
<DT><I>int</I> <B>class</B><DD><P>message class information (<I>L_DEBUG</I> to <I>L_BUG</I>, see <CODE>lib/birdlib.h</CODE>)
<DT><I>buffer *</I> <B>buf</B><DD><P>message to write
</DL>
<H3>Description</H3>
<P>This function writes a message prepared in the log buffer to the
log file (as specified in the configuration). The log buffer is
reset after that. The log message is a full line, <B>log_commit()</B>
terminates it.
<P>The message class is an integer, not a first char of a string like
in <B>log()</B>, so it should be written like *L_INFO.
<HR><H3>Function</H3>
<P><I>void</I>
<B>log_msg</B>
(<I>const char *</I> <B>msg</B>, <I>...</I> <B>...</B>) -- log a message
<P>
<H3>Arguments</H3>
<P>
<DL>
<DT><I>const char *</I> <B>msg</B><DD><P>printf-like formatting string with message class information
prepended (<I>L_DEBUG</I> to <I>L_BUG</I>, see <CODE>lib/birdlib.h</CODE>)
<DT><I>...</I> <B>...</B><DD><P>variable arguments
</DL>
<H3>Description</H3>
<P>This function formats a message according to the format string <B>msg</B>
and writes it to the corresponding log file (as specified in the
configuration). Please note that the message is automatically
formatted as a full line, no need to include <CODE>\n</CODE> inside.
It is essentially a sequence of <B>log_reset()</B>, <B>logn()</B> and <B>log_commit()</B>.
<HR><H3>Function</H3>
<P><I>void</I>
<B>bug</B>
(<I>const char *</I> <B>msg</B>, <I>...</I> <B>...</B>) -- report an internal error
<P>
<H3>Arguments</H3>
<P>
<DL>
<DT><I>const char *</I> <B>msg</B><DD><P>a printf-like error message
<DT><I>...</I> <B>...</B><DD><P>variable arguments
</DL>
<H3>Description</H3>
<P>This function logs an internal error and aborts execution
of the program.
<HR><H3>Function</H3>
<P><I>void</I>
<B>die</B>
(<I>const char *</I> <B>msg</B>, <I>...</I> <B>...</B>) -- report a fatal error
<P>
<H3>Arguments</H3>
<P>
<DL>
<DT><I>const char *</I> <B>msg</B><DD><P>a printf-like error message
<DT><I>...</I> <B>...</B><DD><P>variable arguments
</DL>
<H3>Description</H3>
<P>This function logs a fatal error and aborts execution
of the program.
<HR><H3>Function</H3>
<P><I>void</I>
<B>debug</B>
(<I>const char *</I> <B>msg</B>, <I>...</I> <B>...</B>) -- write to debug output
<P>
<H3>Arguments</H3>
<P>
<DL>
<DT><I>const char *</I> <B>msg</B><DD><P>a printf-like message
<DT><I>...</I> <B>...</B><DD><P>variable arguments
</DL>
<H3>Description</H3>
<P>This function formats the message <B>msg</B> and prints it out
to the debugging output. No newline character is appended.
<H2><A NAME="ss6.3">6.3</A> <A HREF="prog.html#toc6.3">Kernel synchronization</A>
</H2>
<P>
<P>This system dependent module implements the Kernel and Device protocol,
that is synchronization of interface lists and routing tables with the
OS kernel.
<P>The whole kernel synchronization is a bit messy and touches some internals
of the routing table engine, because routing table maintenance is a typical
example of the proverbial compatibility between different Unices and we want
to keep the overhead of our KRT business as low as possible and avoid maintaining
a local routing table copy.
<P>The kernel syncer can work in three different modes (according to system config header):
Either with a single routing table and single KRT protocol [traditional UNIX]
or with many routing tables and separate KRT protocols for all of them
or with many routing tables, but every scan including all tables, so we start
separate KRT protocols which cooperate with each other [Linux].
In this case, we keep only a single scan timer.
<P>We use FIB node flags in the routing table to keep track of route
synchronization status. We also attach temporary <I>rte</I>'s to the routing table,
but it cannot do any harm to the rest of BIRD since table synchronization is
an atomic process.
<P>When starting up, we cheat by looking if there is another
KRT instance to be initialized later and performing table scan
only once for all the instances.
<P>The code uses OS-dependent parts for kernel updates and scans. These parts are
in more specific sysdep directories (e.g. sysdep/linux) in functions krt_sys_*
and kif_sys_* (and some others like <B>krt_replace_rte()</B>) and krt-sys.h header file.
This is also used for platform specific protocol options and route attributes.
<P>There was also an old code that used traditional UNIX ioctls for these tasks.
It was unmaintained and later removed. For reference, see sysdep/krt-* files
in commit 396dfa9042305f62da1f56589c4b98fac57fc2f6
<P>
<P>
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