In Debian packaging, a patch refers to a file containing changes to a source file or directory. They help you fix bugs, add features, or make other changes without affecting the original code directly. Quilt is a tool used to manage these patches efficiently.Patches are like small updates to your code.

Common Terms :

  • Export QUILT_PATCHES: This command sets the environment variable QUILT_PATCHES to specify the directory containing patches. For example: export QUILT_PATCHES=debian/patches.

  • Quilt Push: Applies patches to the source files. The -a flag applies all patches. Usage: quilt push -a.

  • Quilt New: Creates a new patch. Use this command when manual patching is required. Usage: quilt new <patch_name>.

  • Adding a File: To add a file to a patch, use the quilt add command. For example: quilt add README (where ‘README’ is the name of the file you want to modify).

  • Quilt Refresh: Updates a patch with changes made to its files. This command can be executed as often as needed. Usage: quilt refresh.

  • Quilt Header: Edits the header of a patch. You can use this command to add descriptions or update the metadata of the patch. For example: quilt header -e --dep3.

  • Quilt Pop: Removes all patches from the stack and returns the source to its original state. Usage: quilt pop -a.

  • .pc/ Directory: This directory, hidden from plain sight, stores vital information about each patch, including its name, description, and application status. It acts like a behind-the-scenes organizer for Quilt’s patching operations.

  • Series File: This file acts as the roadmap for applying patches. It contains a simple list of patch names, indicating the exact order in which Quilt should apply them. Imagine it as a recipe for Quilt, guiding it through the patching process step-by-step.

Tutorial :

Exporting Quilt

To begin, export the QUILT_PATCHES environment variable to specify the directory containing patches:

export QUILT_PATCHES=debian/patches

Applying Patches

Apply patches using the quilt push -a command:

quilt push -a

If any patch fails with an offset, follow the manual patching process.

Manual Patching Process :

If a patch fails with an offset, you’ll need to apply it manually. For example:

    Applying patch 008-setup-xstatic
    patching file
    Hunk #1 FAILED at 90.
    1 out of 1 hunk FAILED -- rejects in file
    Patch 008-setup-xstatic does not apply (enforce with -f)

If you encounter an error like the one above, manual patching is required. Follow these steps:

  1. Delete the failed patch from the patches directory and the series file
  2. Create a new patch with quilt new and manually apply changes to the file
  3. Add the file to the patch with quilt add
  4. Edit the file using quilt edit
  5. Refresh the patch with quilt refresh

Handling Patches with Offsets :

If a patch fails with an offset, For example:

    Applying patch 010-setup-contrib-intermap
    patching file
    Hunk #1 succeeded at 63 (offset 1 line).

    Applying patch 011-setup-package-data
    patching file
    Hunk #3 succeeded at 67 (offset 1 line).

Follow these steps:

  1. If a patch fails with an offset, use quilt pop -a to revert changes
  2. Push the failed patch individually using quilt push <patch_name>
  3. Refresh the patch with quilt refresh
  4. Do quilt push -a to apply all the patches again
  5. Repeat the process until all patches are successfully applied

Before Committing :

Before committing changes, ensure all patches are popped. (Also Remember not to commit this directory to version control as it contains temporary and metadata files specific to the patch management process.)

quilt pop -a
git add debian/patches/
git commit -m "Applied patches using Quilt"