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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-05 22:26:11 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-05 22:26:11 +0000 |
| commit | 90b12bd71bb9fc79a4640b9112c13ef529d0196a (patch) | |
| tree | 523b3f4ee2969e7a729bab2ba749c4b924ae62af /doc/fifodir.html | |
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diff --git a/doc/fifodir.html b/doc/fifodir.html new file mode 100644 index 0000000..99805ed --- /dev/null +++ b/doc/fifodir.html @@ -0,0 +1,123 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6: fifodirs</title> + <meta name="Description" content="s6: fifodirs" /> + <meta name="Keywords" content="s6 instant notification polling fifodir named pipe filesystem" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> Fifodirs </h1> + +<p> + A <em>fifodir</em> is a rendez-vous point between the <em>notifier</em> +of certain events and its <em>listeners</em>. It is implemented via a +directory in the filesystem. No data is stored; it is appropriate to +create fifodirs in a RAM filesystem. +</p> + +<h2> Manipulating fifodirs </h2> + +<h3> C API </h3> + +<ul> + <li> You can create fifodirs via the +<tt>ftrigw_fifodir_create()</tt> function in +<a href="libftrigw.html">libftrig</a>. </li> + <li> You can send an event to a fifodir via the +<tt>ftrigw_notify()</tt> function in +<a href="libftrigw.html">libftrig</a>. </li> + <li> You can clean up a fifodir via the +<tt>ftrigw_clean()</tt> function in +<a href="libftrigw.html">libftrig</a>. </li> + <li> You can destroy fifodirs via the +<tt>rm_rf()</tt> function in +<a href="http://skarnet.org/software/skalibs/doc/libstddjb/djbunix.html">libstddjb</a>. </li> +</ul> + +<h3> Unix API </h3> + +<ul> + <li> You can create fifodirs with the +<a href="s6-mkfifodir.html">s6-mkfifodir</a> command. </li> + <li> You can send an event to a fifodir with the +<a href="s6-ftrig-notify.html">s6-ftrig-notify</a> command. </li> + <li> You can clean up a fifodir with the +<a href="s6-cleanfifodir.html">s6-cleanfifodir</a> command. </li> + <li> You can destroy fifodirs with the <tt>rm -rf</tt> command. </li> +</ul> + +<h2> Internals and Unix permissions </h2> + +<ul> + <li> Notifiers and listeners agree on a fifodir. </li> + <li> The fifodir directory is created by the notifier. It must be writable +by listeners. </li> + <li> To subscribe, a listener atomically creates a named pipe (FIFO) in this +directory and listens to the reading end. This named pipe must be writable +by the notifier. </li> + <li> To send an event to listeners, the notifier writes the event byte to +all the named pipes in the directory. Credit for this idea goes to Stefan +Karrmann. </li> + <li> To unsubscribe, a listener unlinks his named pipe from the directory. </li> +</ul> + +<p> +Fifodirs are created by, so they always originally have the same uid and gid as, +their notifier. A notifier must be able to make his fifodir either publically +accessible (anyone can subscribe) or restricted (only a given group can +subscribe). +</p> + +<p> + A publically accessible fifodir must have rights 1733: +</p> + +<ul> + <li> Anyone can create a fifo in that fifodir </li> + <li> Only the notifier can see all the subscribers' fifos </li> + <li> A listener can only delete its own fifo </li> + <li> A notifier can delete any fifo for cleaning purposes </li> +</ul> + +<p> + A restricted fifodir must have the gid <em>g</em> of the group of allowed +listeners and have rights 3730. Unless the notifier is root, it +must be in the group of allowed listeners to be able to create +such a fifodir. +</p> + +<ul> + <li> Only members of <em>g</em> can create a fifo in that fifodir </li> + <li> Only the notifier can see all the subscribers' fifos </li> + <li> Fifos are always created with gid <em>g</em> </li> + <li> A listener can only delete its own fifo </li> + <li> A notifier can delete any fifo for cleaning purposes </li> +</ul> + +<p> + A named pipe in a fifodir must always belong to its listener and have +rights 0622: +</p> + +<ul> + <li> Only this listener can read on the fifo </li> + <li> Anyone who has reading rights on the fifodir (i.e. only the notifier) +can write to the fifo </li> +</ul> + +<p> + The <a href="libftrig.html">libftrig<a/> interface takes care of all +the subtleties. +</p> + +</body> +</html> |