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8c51e1520b
See #26688: getenv() is not thread-safe, and could a possible source of problems when a multi-threaded program calls setenv()/putenv()/unsetenv() in parallel. It is not possible to avoid getenv() calls in general, since $PATH, $LANG, $SHELL, $USER, $HOME, $TZ may need to be accessed at any time. Add a warning to our docs so that people are aware of the issue. Closes #26688. (Real fixes will need to be in glibc and gnome-shell or other programs.) The text is added to threads-aware.xml to be included in various places. By including it in libsystemd-pkgconfig.xml, it is automatically added to all sd-* pages. The text is also included explicitly in pages for a few other functions which are call getenv().
100 lines
4.4 KiB
XML
100 lines
4.4 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
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<!ENTITY % entities SYSTEM "custom-entities.ent" >
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%entities;
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]>
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="libudev"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>libudev</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>libudev</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>libudev</refname>
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<refpurpose>API for enumerating and introspecting local devices</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <libudev.h></funcsynopsisinfo>
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</funcsynopsis>
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<cmdsynopsis>
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<command>pkg-config --cflags --libs libudev</command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>libudev.h</filename> provides an API to introspect and enumerate devices on the local
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system. This library is supported, but should not be used in new projects. Please see
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<citerefentry><refentrytitle>sd-device</refentrytitle><manvolnum>3</manvolnum></citerefentry> for an
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equivalent replacement with a more modern API.</para>
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<para>All functions require a libudev context to operate. This
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context can be created via
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<citerefentry><refentrytitle>udev_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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It is used to track library state and link objects together. No
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global state is used by libudev, everything is always linked to
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a udev context.</para>
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<xi:include href="threads-aware.xml" xpointer="strict"/>
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<xi:include href="threads-aware.xml" xpointer="getenv"/>
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<para>To introspect a local device on a system, a udev device
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object can be created via
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<citerefentry><refentrytitle>udev_device_new_from_syspath</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and friends. The device object allows one to query current state,
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read and write attributes and lookup properties of the device in
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question.</para>
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<para>To enumerate local devices on the system, an enumeration
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object can be created via
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<citerefentry><refentrytitle>udev_enumerate_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>To monitor the local system for hotplugged or unplugged
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devices, a monitor can be created via
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<citerefentry><refentrytitle>udev_monitor_new_from_netlink</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>Whenever libudev returns a list of objects, the
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<citerefentry><refentrytitle>udev_list_entry</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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API should be used to iterate, access and modify those lists.</para>
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<para>Furthermore, libudev also exports legacy APIs that should
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not be used by new software (and as such are not documented as
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part of this manual). This includes the hardware database known
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as <constant>udev_hwdb</constant> (please use the new
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<citerefentry><refentrytitle>sd-hwdb</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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API instead) and the <constant>udev_queue</constant> object to
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query the udev daemon (which should not be used by new software
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at all).</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>udev_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>udev_device_new_from_syspath</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>udev_enumerate_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>udev_monitor_new_from_netlink</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>udev_list_entry</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-device</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-hwdb</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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