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diff --git a/doc/index.html b/doc/index.html index f78398f..50ff20d 100644 --- a/doc/index.html +++ b/doc/index.html @@ -42,6 +42,46 @@ entirely compatible with advanced mdev usage such as <a href="https://github.com/slashbeast/mdev-like-a-boss">mdev-like-a-boss</a>. </p> +<a name="mdev"> +<h2> Comparison with <tt>mdev -d</tt> </h2> +</a> + +<p> + Recent versions of <a href="https://git.busybox.net/busybox/tree/util-linux/mdev.c">mdev</a> +have a <tt>-d</tt> option that allow it to run as a daemon. However, +mdevd still has advantages over <tt>mdev -d</tt>: +</p> + +<ul> + <li> Better log management: <tt>mdev -d</tt> logs to a fixed text file, with +all the issues it implies (need for the filesystem to be read-write, +uncontrollable log file growth). By contrast, mdevd logs to stderr and its +messages can be handled by any log infrastructure such as the one provided +by a supervision suite. </li> + <li> Better memory efficiency: <tt>mdev -d</tt> uses its own environment +(via <a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/putenv.html">putenv()</a> +and <a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/unsetenv.html">unsetenv()</a>) +to store uevent data for each event. This implies repeated allocations of +heap memory. By contrast, mdevd does not use its own environment, and +even does not use heap memory at all. </li> + <li> Better speed: <tt>mdev -d</tt> parses its config file for every +event it receives, and has to perform expensive operations such as +<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwnam.html">getpwnam()</a> +every time it receives an event (which can add up to hundreds of time at boot!). +By contrast, mdevd parses its config file only once, when it starts - or when +it is told to read it again by a SIGHUP. So it processes events significantly +faster. </li> + <li> Independence from busybox: <tt>mdev</tt> is part of the +<a href="https://busybox.net/">busybox</a> software. It is an advantage +when Busybox is also used to provide other functionality, such as +coreutils or util-linux equivalents. However, some distributions find +that functionality lacking in compatibility, and choose to use alternatives +to busybox. In that case, having to use the whole busybox configuration +and build process just for mdev is a drawback, and the code is bigger than +it needs to be. mdevd, on the other hand, is independent software, and +building it is simple and does not pull in any unnecessary code. </li> +</ul> + <hr /> <h2> Installation </h2> diff --git a/doc/mdevd.html b/doc/mdevd.html index 4e68356..911b770 100644 --- a/doc/mdevd.html +++ b/doc/mdevd.html @@ -41,6 +41,9 @@ a daemon: it's long-lived, and there is only one instance, reading a series of uevents and performing actions without forking; the configuration file is read and parsed only once. </li> + <li> Even when mdev is run as a daemon (via the recent <tt>-d</tt> +option), there are <a href="index.html#mdev">technical advantages</a> +to running mdevd over mdev. </li> </ul> <h2> Interface </h2> |