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<h1 class="menu-title">Youki User and Developer Documentation</h1>
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<main>
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<h1 id="libcgroups"><a class="header" href="#libcgroups">libcgroups</a></h1>
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<p>This crate provides an interface for working with cgroups in Linux. cgroups or control groups is a Linux kernel feature which can be used to fine-control resources and permissions given to a particular process or a group of processes. You can read more about them on the <a href="https://man7.org/linux/man-pages/man7/cgroups.7.html">cgroups man page</a>.</p>
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<p>The initial version of cgroups is called the version 1 was implemented in kernel 2.6.24, and later in kernel version 4.5, a new version of cgroups was released, aimed to solve issues with v1, the version v2.</p>
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<p>This crates exposes several functions and modules that can be used to work with cgroups :</p>
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<ul>
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<li>
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<p>Common traits and functions which are used by both v1 and v2 such as</p>
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<ul>
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<li>Trait <code>CgroupManager</code>, this abstracts over the underlying implementation of interacting with specific version of cgroups, and gives functions to add certain process to a certain cgroup, apply resource restrictions, get statistics of a cgroups, freeze a cgroup, remove a cgroup or get list of all processes belonging to a cgroup. v1 and v2 modules both contain a version specific cgroup manager which implements this trait, and thus either can be given to functions or structs which expects a cgroup manager, depending on which cgroups the host system uses.</li>
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<li>Apart from the trait, this also contains functions which help with reading cgroups files, and write data to a cgroup file, which are used throughout this crate.</li>
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<li>Functions to detect which cgroup setup (v1, v2 or hybrid) is on the host system with/without specified mounted cgroup root path, as well as functions to get the corresponding cgroups manager w/o cgroup root path.</li>
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</ul>
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</li>
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<li>
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<p>Functions and structs to get and store the statistics of a cgroups such as</p>
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<ul>
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<li>CPU stats including usage and throttling</li>
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<li>Memory stats including usage of normal and swap memory, usage of kernel memory, page cache in bytes etc</li>
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<li>Pid stat including current active pids and maximum allowed pids</li>
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<li>Block IO stats such as number of bytest transferred to/from a device in the cgroup, io operations performed by a device in the cgroup, amount of time cgroup had access to a device etc</li>
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<li>Huge TLB stats such as usage and maximum usage etc.</li>
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<li>Function to get pid stats</li>
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<li>Function to get supported hugepage size</li>
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<li>Function to parse flat keyed data and nested keyed data that can be in a cgroups file</li>
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<li>Parse a device number</li>
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</ul>
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</li>
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<li>
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<p>Cgroups V1 module which deal with implementing a cgroup manager for systems which have cgroups v1 or hybrid cgroups</p>
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</li>
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<li>
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<p>Cgroups V2 module which deal with implementing a cgroup manager for systems which have cgroups v2</p>
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</li>
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</ul>
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<p>As youki currently depends on systemd as an init system, this crate also exposes module systemd, which provides interface for working with systemd related operations. <a href="https://www.freedesktop.org/software/systemd/man/systemd.resource-control.html">systemd resource control</a> is a good place to read more about systemd and its involvement in resource control.</p>
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<h2 id="dbus-native"><a class="header" href="#dbus-native">Dbus Native</a></h2>
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<p>This module is the native implementation of dbus connection functionality used for connecting with systemd via dbus. Refer to <a href="https://github.com/containers/youki/issues/2208">this issue discussion</a> following for the discussion regarding moving away from existing dbus-interfacing library.</p>
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<p>Note that this implements the minimal required functionality for youki to use dbus, and thus does not have all the dbus features.</p>
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<ul>
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<li>
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<p>Refer to see <a href="https://dbus.freedesktop.org/doc/dbus-specification.html">dbus specification</a> and <a href="https://dbus.freedesktop.org/doc/api/html/structDBusHeader.html">header format</a> for the individual specifications.</p>
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</li>
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<li>
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<p>For systemd interface and types, you can generate the following file and take help from the auto-generated functions
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<code>dbus-codegen-rust -s -g -m None -d org.freedesktop.systemd1 -p /org/freedesktop/systemd1</code>, see https://github.com/diwic/dbus-rs</p>
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