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diff --git a/documentation/ref-manual/closer-look.xml b/documentation/ref-manual/closer-look.xml index d22de8fd99..a690544364 100644 --- a/documentation/ref-manual/closer-look.xml +++ b/documentation/ref-manual/closer-look.xml | |||
@@ -830,6 +830,97 @@ | |||
830 | </note> | 830 | </note> |
831 | </para> | 831 | </para> |
832 | </section> | 832 | </section> |
833 | |||
834 | <section id='image-generation-dev-environment'> | ||
835 | <title>Image Generation</title> | ||
836 | |||
837 | <para> | ||
838 | Once packages are split and stored in the Package Feeds area, | ||
839 | the OpenEmbedded build system uses BitBake to generate the | ||
840 | root filesystem image: | ||
841 | <imagedata fileref="figures/image-generation.png" align="center" width="6in" depth="7in" /> | ||
842 | </para> | ||
843 | |||
844 | <para> | ||
845 | The image generation process consists of several stages and | ||
846 | depends on many variables. | ||
847 | The <filename>do_rootfs</filename> uses these key variables | ||
848 | to help create the list of packages to actually install: | ||
849 | <itemizedlist> | ||
850 | <listitem><para><link linkend='var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></link>: | ||
851 | Lists out the base set of packages to install from | ||
852 | the Package Feeds area.</para></listitem> | ||
853 | <listitem><para><link linkend='var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></link>: | ||
854 | Specifies features to include in the image. | ||
855 | These features map to additional packages for | ||
856 | installation.</para></listitem> | ||
857 | <listitem><para><link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link>: | ||
858 | Specifies the package manager to use and consequently | ||
859 | helps determine where to locate packages within the | ||
860 | Package Feeds area.</para></listitem> | ||
861 | <listitem><para><link linkend='var-PACKAGE_EXCLUDE'><filename>PACKAGE_EXCLUDE</filename></link>: | ||
862 | Specifies packages that should not be installed. | ||
863 | </para></listitem> | ||
864 | </itemizedlist> | ||
865 | </para> | ||
866 | |||
867 | <para> | ||
868 | In addition to the previously mentioned variables, the image | ||
869 | generation process uses | ||
870 | <link linkend='var-IMAGE_LINGUAS'><filename>IMAGE_LINGUAS</filename></link> | ||
871 | to determine what language for which packages are being | ||
872 | installed. | ||
873 | </para> | ||
874 | |||
875 | <para> | ||
876 | Part of the image generation process includes compressing the | ||
877 | root filesystem image. | ||
878 | Compression is accomplished through several optimization | ||
879 | routines designed to reduce the overall size of the image. | ||
880 | </para> | ||
881 | |||
882 | <para> | ||
883 | The process runs as many post installation scripts as possible. | ||
884 | Any scripts that cannot be run are run when the system is | ||
885 | first booted. | ||
886 | If you are using a read-only root filesystem, all the post | ||
887 | installation scripts are run during the package installation | ||
888 | phase since the root filesystem cannot be written into. | ||
889 | </para> | ||
890 | |||
891 | <para> | ||
892 | During the Prelink phase, optimization processes are run across | ||
893 | the image. | ||
894 | These processes include <filename>mklibs</filename> and | ||
895 | <filename>prelink</filename>. | ||
896 | The <filename>mklibs</filename> optimizes the size of the | ||
897 | libraries. | ||
898 | The <filename>prelink</filename> process optimizes the dynamic | ||
899 | linking of shared libraries to reduce start up time of the | ||
900 | executables. | ||
901 | See the | ||
902 | <link linkend='var-IMAGE_POSTPROCESS_COMMAND'><filename>IMAGE_POSTPROCESS_COMMAND</filename></link> | ||
903 | and | ||
904 | <link linkend='var-ROOTFS_POSTPROCESS_COMMAND'><filename>ROOTFS_POSTPROCESS_COMMAND</filename></link> | ||
905 | variables for additional information. | ||
906 | </para> | ||
907 | |||
908 | <para> | ||
909 | After the root filesystem has been constructed, the image | ||
910 | generation process turns everything into an image file or | ||
911 | a set of image files. | ||
912 | we need to turn into an image file or set of image files. | ||
913 | The formats used for the root filesystem depend on the | ||
914 | <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link> | ||
915 | variable. | ||
916 | </para> | ||
917 | |||
918 | <note> | ||
919 | The entire image generation process is run under Pseudo. | ||
920 | Running under Pseudo ensures that the files in the root | ||
921 | filesystem have correct ownership. | ||
922 | </note> | ||
923 | </section> | ||
833 | </section> | 924 | </section> |
834 | 925 | ||
835 | <section id="package-feeds-dev-environment"> | 926 | <section id="package-feeds-dev-environment"> |