Debian Linux Kernel Handbook / Chapter 5. Version numbers and ABIs
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The version that Linus or a stable series maintainer uses for a release.
Currently Linus will use the version format:
4.x[-rcy]. Stable series
maintainers use the version format:
4.x.y.
The version used in a Debian package. Following Debian policy, it should
follow the format
upstreamversion-debianrevision.
However, for an upstream release candidate, the string '-rc' must be replaced
with '~rc' so that it will be recognised as an earlier version than the
following release.
This is the version that appears in kernel messages, filenames, package names
and the output of 'uname -r'. In official kernel packages it follows the
format
upstreamversion[-abiname][-featureset]-flavour.
It is not changed for every new package version. The
abiname is changed as explained below.
Many programs parse the kernel version string reported by the uname system call or command and expect to find at least 3 version components separated by dots. For compatibility, the official kernel packages currently add '.0' to the upstream version.
An ABI (Application Binary Interface) is an interface between two software components, considered at the level of register allocation and memory layout. The ABI between the kernel and user-space is generally maintained carefully, and is not a concern here. However, the ABI between the kernel and its modules is not. In order to support out-of-tree modules, the kernel version should be changed when the ABI between the kernel and modules changes.
In official kernel packages, we change the abiname
part of the kernel version to mark ABI changes that aren't due to a new
upstream version. This part comes from the abiname setting
in debian/config/defines. We use either a number or 'trunk'
(for experimental).
If you are rebuilding the package with local modifications, you should
change the ABI name to some other string, for example
0.local. Then run the command
$debian/rules debian/control-real
to regenerate the package definitions for this ABI name.
In order to avoid the need for users to rebuild out-of-tree modules frequently, we try to avoid changing the kernel ABI during updates to a Debian stable or oldstable release. Most importantly, we avoid making such changes without changing the ABI name, except where it appears that out-of-tree modules do not depend on that part of the ABI.
Bug fixes or configuration changes to the kernel may alter the ABI. If an
exported function is conditional on
CONFIG_FOO, or it uses a type
whose definition depends on
CONFIG_FOO, then turning
CONFIG_FOO on or off changes the
ABI of that function, and thus of the kernel as a whole. Enabling or changing
the configuration of a single driver usually doesn't change the ABI, because
most drivers don't export anything.
The kernel build process generates a 'symbol version' for each exported function or variable. This is a hash of the definitions that it depends on, and should change whenever the function's ABI changes. The kernel module loader detects incompatible modules by comparing symbol versions. The whole set of symbol versions represents the kernel ABI.
We collect the symbol versions for previously uploaded packages under the
directory debian/abi and then compare the new kernel with
those. If the ABI name is unchanged but the ABI itself is changed - except for
additions, or changes that we have marked as acceptable - then the build is
aborted.
If the kernel ABI has changed you must then change the ABI name in
debian/config/defines. Then run the command
$debian/rules debian/control-real
to regenerate the package definitions for this ABI name.