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<title>bcnm: the bcnm-waitif program</title>
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<h1> The <tt>bcnm-waitif</tt> program </h1>
<p>
<tt>bcnm-waitif</tt> waits until a set of network interfaces are in the desired state,
or a timeout occurs. Then it exits. It is typically used to avoid race conditions
in a service startup sequence.
</p>
<h2> Interface </h2>
<pre>
bcnm-waitif [ -u | -d ] [ -t <em>timeout</em> ] [ -k <em>kbufsize</em> ] <em>mask</em> <em>interface...</em>
</pre>
<ul>
<li> <tt>bcnm-waitif</tt> reads the state of all the interfaces specified by
name as the <em>interface...</em> arguments. </li>
<li> If all the listed interfaces match the state defined in <em>mask</em>,
it exits 0. </li>
<li> Else, it waits for network interface state changes, and performs the
check again. </li>
<li> It loops until all the listed interfaces are in the desired state,
or a timeout (if defined) occurs. </li>
</ul>
<h2> <em>mask</em> meaning </h2>
<p>
<em>mask</em> is an unsigned integer representing a bitmask for the
flags to be tested. If several bits are given, the wanted state is the
conjunction of these flags: the condition will be true if <em>all</em>
those checks pass.
</p>
<ul>
<li> 1: the interface exists (the kernel knows about it) </li>
<li> 2: the interface is UP (the administrator has activated it) </li>
<li> 4: the interface is RUNNING (functional, not unplugged) </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-u</tt> : up. <tt>bcnm-waitif</tt> will wait until all
the states defined in <em>mask</em> are reached by all the interfaces
in <em>interface...</em>. This is the default. </li>
<li> <tt>-d</tt> : down. <tt>bcnm-waitif</tt> will wait until
<em>none</em> of the states defined in <em>mask</em> is true. </li>
<li> <tt>-t <em>timeout</em></tt> : if the desired state
still has not been reached after <em>timeout</em> milliseconds,
<tt>bcnm-waitif</tt> will exit 99 with an error message. The default
is 0, meaning there is no timeout and the program can wait forever. </li>
<li> <tt>-k <em>kbufsize</em></tt> : use <em>kbufsize</em>
bytes for the netlink socket buffer. Too small a buffer risks losing
state change events and reporting incorrect results. Too large a buffer
wastes memory. Default is 131072, which is probably on the large side. </li>
</ul>
<h2> Exit codes </h2>
<ul>
<li> 0: success </li>
<li> 99: timed out </li>
<li> 100: wrong usage </li>
<li> 111: system call failed </li>
</ul>
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