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https://github.com/morgan9e/systemd
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46b0844743
We nowadays expose pidfdid at various places, e.g. envvars and dbus properties. Also the sd_notify() MAINPID= message has been complemented with MAINPIDFDID=. But acquiring pidfdid is actually non-trivial especially considering the 32-bit case, hence let's introduce a public helper in sd-daemon specifically for that purpose.
108 lines
4.0 KiB
XML
108 lines
4.0 KiB
XML
<?xml version='1.0'?>
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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/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_pidfd_get_inode_id"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_pidfd_get_inode_id</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_pidfd_get_inode_id</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_pidfd_get_inode_id</refname>
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<refpurpose>Acquire the 64-bit inode ID of a PID file descriptor (PIDFD)</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_pidfd_get_inode_id</function></funcdef>
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<paramdef>int <parameter>pidfd</parameter></paramdef>
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<paramdef>uint64_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_pidfd_get_inode_id()</function> may be invoked to acquire the 64-bit inode ID of
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a PID file descriptor (PIDFD), which can be used to reliably identify a process for the current boot.</para>
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<para>As a typical example, the service manager sets <varname>$MAINPIDFDID</varname> and <varname>$MANAGERPIDFDID</varname>
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environment variables to the inode IDs of the service main process and the service manager itself, respectively,
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if such functionality is supported by the kernel.</para>
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<para>On 64-bit architectures, the inode ID can be directly obtained via a call to
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<citerefentry project='man-pages'><refentrytitle>fstat</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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on a given pidfd. However, on 32-bit architectures <structname>struct stat</structname>'s .st_ino
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field is also 32-bit, which similar to PIDs is subject to reuse. Therefore, a second mechanism leveraging
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<citerefentry project='man-pages'><refentrytitle>name_to_handle_at</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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has been added to kernel in v6.14. This helper is added to simplify downstream handling of pidfd/pidfs internals.
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</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, the function returns 0 or a positive integer. On failure, a negative errno-style
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error code is returned.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EOPNOTSUPP</constant></term>
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<listitem><para>The stable PIDFD inode ID is not supported by the running kernel, or the system
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is 32-bit and <function>name_to_handle_at()</function> is unavailable.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EBADF</constant></term>
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<listitem><para>The specified file descriptor is invalid, or is not a PIDFD.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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</refsect1>
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<refsect1>
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<title>History</title>
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<para><function>sd_pidfd_get_inode_id()</function> was added in version 258.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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