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This documentation is by no means complete, but it's a place to start for pretty user-facing documentation for the kernel in Fedora. In addition to the basic export from the wiki, this includes various other related articles in the wiki which I thought might be good user-facing documentation. Signed-off-by: Jeremy Cline <jeremy@jcline.org>
192 lines
8.3 KiB
Text
192 lines
8.3 KiB
Text
= Fedora Linux Kernel Overview
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:toc:
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[[section-update-schedule]]
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== Update Schedule
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The https://src.fedoraproject.org/rpms/kernel[Fedora Linux kernel] closely
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follows the upstream https://www.kernel.org/[kernel releases]. To see the
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current versions in Fedora, https://apps.fedoraproject.org/packages/kernel[check
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out the packages application].
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=== Stable Releases
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Stable releases of Fedora receive two types of kernel updates.
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==== Stable kernel updates
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The upstream kernel community support the latest major version with stable
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updates (4.y.z releases). These updates are released approximately once a week,
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although they can occur more or less frequently. Once the upstream kernel
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community makes a stable release, Fedora builds it and submits it as an update
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to https://bodhi.fedoraproject.org/updates/?packages=kernel[Bodhi]. These
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updates are typically left in Bodhi for testing for several days before being
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submitted to the stable updates repository.
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==== Major kernel updates
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The Linux kernel releases new major versions (4.y releases)
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http://phb-crystal-ball.org/[every few months]. When this occurs, Fedora updates
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to the new major version after a couple upstream stable releases. When the
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updates are submitted to Bodhi, more time is allowed for testing than stable
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updates to ensure there are no serious regressions.
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=== Development Releases
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The development versions of Fedora include Rawhide and the Branched release.
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==== Rawhide
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The Rawhide kernel is the latest git snapshot of Linus'
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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/[upstream
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kernel.org tree]. On a frequent (often daily) basis, a new snapshot is built.
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==== Branched
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https://fedoraproject.org/wiki/Releases/Branched[Branched releases] receive
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updates at less frequent intervals than Rawhide. Early on in the Branched
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release, it is typically using a pre-release version of the kernel, so each
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Release Candidate (RC) is built for Branched releases. Once the kernel is
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released, it receives stable updates just like the stable Fedora releases.
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[[debug-kernels]]
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== Debug Kernels
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The Linux kernel offers a number of configuration options to make debugging
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problems easier. However, some of these options have a performance cost so
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Fedora does not always turn these options on. When the debugging options have
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been turned off in the ``kernel`` package, a separate ``kernel-debug`` package
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is produced with those options on.
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=== Stable and Branched Kernels
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Stable and Branched kernels always disable the debugging options.
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=== Rawhide
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Rawhide kernels enable the debugging options. However, each release candidate
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kernel is built with debugging options disabled. Release candidate kernels
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can be recognized by their release field, which always has the git revision set
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to 0. For example, ``kernel-4.16.0-0.rc7.git0.1.fc28`` is the 7th release
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candidate kernel for Fedora 28.
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== Policies
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=== Out-of-tree Drivers
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The simplest method by far is for the driver to get merged upstream in Linus'
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kernel. Fedora constantly rebases to newer upstream releases, so inherits these
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changes "for free" with little overhead for the Fedora kernel maintainers.
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Adding external drivers to the Fedora kernel that aren't accepted upstream
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requires an ongoing effort for the Fedora kernel team, so where possible, we
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try to avoid doing so. In the few situations where it makes sense to do so,
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there are several criteria that must be met.
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* There must be reasonable demand for the feature for us taking on the burden
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of carrying the code until it gets upstream.
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* Passes basic sanity checks (has been reviewed by at least one Fedora kernel
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maintainer).
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* Has an upstream developer actively trying to get their code merged into Linus'
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tree.
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* Has a Fedora developer responsible for keeping it up to date in Fedora.
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* Causes no discernible overhead for Fedora kernel maintainers. Code that must
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be continually fixed up tends to end up getting dropped.
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* Doesn't add new system calls or similar ABI defining characteristics. This is
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to avoid a situation where we could end up with incompatibilities between
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distros/upstream.
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* How a symbol is exported needs to be accepted upstream first. This includes:
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** Adding an EXPORT_SYMBOL to export something that previously wasn't exported
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** Changing an EXPORT_SYMBOL_GPL to EXPORT_SYMBOL
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** Changing an EXPORT_SYMBOL to EXPORT_SYMBOL_GPL
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* In the rare case where we add exports that aren't upstream, we err on the side
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of caution and use EXPORT_SYMBOL_GPL to export them. This is done partly as a
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deterrent for 3rd-party modules not to use them. (As they may go away in the
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future). The only exception to all of the above is in new not-yet-merged
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upstream code that's being added. New symbols get to be exported however the
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author intended.
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=== Staging
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The drivers in the staging directory of the Linux kernel are known to be in a
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rough and incomplete state. For the vast majority of these drivers, the kernel
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team considers it unsafe to build and ship them. We do not have the confidence
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in the existing code, nor do we have the time to debug issues in known
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problematic drivers.
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As with every policy, there are exceptions. Fedora ships a few staging drivers
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at the moment for various pieces of hardware. For the Fedora kernel team to
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enable a staging driver, the following conditions must be satisfied:
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* There must be substantive code review and improvement upstream. This means
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actual fixes, and not just stylistic changes.
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* There must be a contributor willing to be assigned bug reports and deal with
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upstream.
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* The contributor must be actively involved improving the driver upstream.
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* The driver must not result in an undue burden on the kernel team. This means
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that if a large number of bug reports result from the driver, then fixes are
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not occurring upstream quickly enough.
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* It must be understood that if any of these conditions are not met, or
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eventually fail to be met, the driver will be disabled.
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=== Builtin Features
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From time to time, the Fedora kernel maintainers get asked to build something
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into the kernel. That is, the functionality is included in the vmlinux binary
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that every Fedora machine runs as opposed to being built as a module that is
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only loaded if needed. Given that it is loaded on every machine, we tend to
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build functionality as modules as much as possible. While one person might need
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the driver for an ATI card, another will not and having that built into the
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kernel is wasteful for really no reason.
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There are no set criteria that map exactly to whether something is built-in or
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not, but they generally follow these guidelines:
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* The option cannot be built as a module and is widely used
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* The option is not a driver/filesystem and used by something that is a Fedora
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default
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* The option is a driver and used by a wide variety of machines (keyboard/mouse
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drivers, VT support)
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* The option is a filesystem and is used by all machines or is the default
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Fedora filesystem (tmpfs, ext4).
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Again, the above are general guidelines but for the most part we try and limit
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the overall size of the vmlinux that is loaded to a core set of functionality.
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If you find that the Fedora configuration options are not sufficient for your
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needs, you can rebuild the kernel and change options as you see fit. See the
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documentation on <<build-custom-kernel.adoc#,building a custom kernel>>.
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[[community]]
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== Getting Involved
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If you're interested in contributing to the development and maintenance of the
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Fedora kernel, check out the https://fedoraproject.org/wiki/Kernel[kernel wiki]
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for more information.
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[[mailing-lists]]
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=== Mailing Lists
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The mailto:kernel@lists.fedoraproject.org[Fedora kernel mailing list] is for
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Fedora-related kernel topics only. This includes Fedora-specific packaging and
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kernel configuration settings. For discussions about Linux itself see the
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https://kernelnewbies.org/ML[Kernelnewbies mailing lists] or the
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http://vger.kernel.org/vger-lists.html[Linux Kernel mailing lists].
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You can subscribe to the Fedora kernel mailing list and view the archive on
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https://lists.fedoraproject.org/archives/list/kernel@lists.fedoraproject.org/[
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Hyperkitty].
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[[irc]]
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=== IRC
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Users interested in the Fedora kernel hang out in the ``#fedora-kernel`` channel
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on https://freenode.net[freenode].
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'''
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See a typo, something missing or out of date, or anything else which can be
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improved? Edit this document at https://pagure.io/fedora-docs/quick-docs.
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