The package
class supports generating
packages from a build's output.
The core generic functionality is in
package.bbclass
.
The code specific to particular package types resides in these
package-specific classes:
package_deb
,
package_rpm
,
package_ipk
,
and
package_tar
.
You can control the list of resulting package formats by using the
PACKAGE_CLASSES
variable defined in your conf/local.conf
configuration file, which is located in the
Build Directory.
When defining the variable, you can specify one or more package types.
Since images are generated from packages, a packaging class is
needed to enable image generation.
The first class listed in this variable is used for image generation.
If you take the optional step to set up a repository (package feed) on the development host that can be used by Smart, you can install packages from the feed while you are running the image on the target (i.e. runtime installation of packages). For more information, see the "Using Runtime Package Management" section in the Yocto Project Development Manual.
The package-specific class you choose can affect build-time performance
and has space ramifications.
In general, building a package with IPK takes about thirty percent less
time as compared to using RPM to build the same or similar package.
This comparison takes into account a complete build of the package with
all dependencies previously built.
The reason for this discrepancy is because the RPM package manager
creates and processes more
Metadata than the
IPK package manager.
Consequently, you might consider setting
PACKAGE_CLASSES
to "package_ipk" if you are
building smaller systems.
Before making your package manager decision, however, you should consider some further things about using RPM:
RPM starts to provide more abilities than IPK due to the fact that it processes more Metadata. For example, this information includes individual file types, file checksum generation and evaluation on install, sparse file support, conflict detection and resolution for Multilib systems, ACID style upgrade, and repackaging abilities for rollbacks.
For smaller systems, the extra space used for the Berkeley Database and the amount of metadata when using RPM can affect your ability to perform on-device upgrades.
You can find additional information on the effects of the package class at these two Yocto Project mailing list links: