4.1. PTXdist’s Directory Hierarchy

Note

Referenced directories are meant relative to the PTXdist main installation location (if not otherwise stated). If not configured differently, this main path is /usr/local/lib/ptxdist-2020.07.0

Rule Files

When building a single package, PTXdist needs the information on how to handle the package, i.e. on how to get it from the source up to what the target needs at run-time. This information is provided by a rule file per package.

PTXdist collects all rule files in its rules/ directory. Whenever PTXdist builds something, all these rule files are scanned at once. These rule files are global rule files, valid for all projects. PTXdist uses a mechanism to be able to add or replace specific rule files on a per project base. If a rules/ directory exists in the current project, its content is scanned too. These project local rule files are used in addition to the global rule files or – if they are using the same name as a global rule file – replacing the global rule file.

The replacing mechanism can be used to extend or adapt packages for specific project requirements. Or it can be used for bug fixing by backporting rule files from more recent PTXdist revisions to projects that are stuck to an older PTXdist revision for maintenance only.

Patch Series

There are many packages in the wild that are not cross build aware. They fail compiling some files, use wrong include paths or try to link against host libraries. To be successful in the embedded world, these types of failures must be fixed. If required, PTXdist provides such fixes per package. They are organized in patch series and can be found in a patches/ directory within a subdirectory using the same name as the package itself.

PTXdist uses the utility patch or quilt (or git on demand) to apply an existing patch series after extracting the archive. So, every patch series contains a set of patches and one series file to define the order in which the patches must be applied.

Note

Patches can be compressed.

Patches are looked for at several locations:

  1. the patches/ folder in your BSP (${PTXDIST_WORKSPACE}/patches)
  2. the folder patches/ folder relative to your selected platformconfig file (${PTXDIST_PLATFORMCONFIGDIR}/patches). If your platformconfig file is at configs/platform-versatilepb/platformconfig, this patch folder will be configs/platform-versatilepb/patches/.
  3. the patches/ folder in PTXdist’s main installation directory (${PTXDIST_TOPDIR}/patches)

The list is tried from first to last. If no patches were found in one of the locations, the next location is tried. When all locations have been tried unsuccessfully, the package is not patched.

This search order can be used to use specific patch series for specific cases.

  • platform specific
  • project specific
  • common case
  • bug fixing

The bug fixing case is used in accordance to a replacement of a rule file. If this was done due to a backport, and the more recent PTXdist revision does not only exchange the rule file but also the patch series, this mechanism ensures that both relevant parts can be updated in the project.

Runtime Configuration

Many packages are using run-time configuration files along with their executables and libraries. PTXdist provides default configuration files for the most common cases. These files can be found in the projectroot/etc directory and they are using the same names as the ones at run-time (and their install directory on the target side will also be /etc).

But some of these default configuration files are empty, due to the absence of a common case. The project must provide replacements of these files with a more useful content in every case where the (empty) default one does not meet the target’s requirements.

PTXdist first searches in the local project directory for a specific configuration file and falls back to use the default one if none exists locally. Refer section install_alternative for further details in which order and locations PTXdist searches for these kind of files.

A popular example is the configuration file /etc/fstab. The default one coming with PTXdist works for the most common cases. But if our project requires a special setup, we can just copy the default one to the local ./projectroot/etc/fstab, modify it and we are done. The next time PTXdist builds the root filesystem it will use the local fstab instead of the global (default) one.