180 lines
7.0 KiB
Markdown
180 lines
7.0 KiB
Markdown
### Full Code Explanation:
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This code defines a Guix package for a Linux kernel module called `xpad-module`. Let's break it down:
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1. **Package Definition**:
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- The package contains metadata such as name, version, source location (a Git repository), build system (using `linux-module-build-system`), and licensing information.
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- It represents a Linux kernel module for controllers (the 8bitdo ultimate bluetooth, for example).
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```scheme
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(define-public xpad-module
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(package
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(name "xpad-module")
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(version "0.4")
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(source (origin
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(method git-fetch)
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(uri (git-reference
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(url "https://github.com/paroj/xpad")
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(commit "3a215825f981643d164aa4e10fd2ab584fd9987c")))
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(file-name (git-file-name name version))
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(sha256
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(base32
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"1mh4ms5023bcj4ys3qkgchi68q1df4741pr4sv3cp4c3xf6g4ikr"))))
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(build-system linux-module-build-system)
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(arguments
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(list #:tests? #f))
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(home-page "https://github.com/paroj/xpad")
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(synopsis
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"Linux Kernel module for the Xbox/ Xbox 360/ Xbox One Controllers.")
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(description
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"Linux Kernel module for the Xbox/ Xbox 360/ Xbox One Controllers.")
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(license license:gpl2+)))
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```
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2. **Customizing Kernel Version**:
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- A helper function `linux-libre-module->linux-module` is defined. This function takes a Linux module package and optionally a kernel version.
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- It creates a new package that inherits properties from the original module but substitutes the kernel version in its build arguments.
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```scheme
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(define* (linux-libre-module->linux-module module #:optional (linux linux))
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(package
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(inherit module)
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(arguments
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(substitute-keyword-arguments (package-arguments module)
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((#:linux _) linux)))))
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```
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3. **Adapting for Linux Kernel 6.1**
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To make sure our xpad kernel module works with a specific Linux kernel version (6.1 in this case), we need to tweak the module to be built against that version. Here’s how we do it step-by-step:
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3.1. Defining a Variable
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First, we define a new variable to hold our customized module:
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```scheme
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(define xpad-module-for-linux-6.1
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(linux-libre-module->linux-module xpad-module linux-6.1))
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```
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What This Does: We’re creating a new variable called xpad-module-for-linux-6.1.
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3.2. Assigning a Value
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We assign this variable a value by calling a function:
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```scheme
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(linux-libre-module->linux-module xpad-module linux-6.1)
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```
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What's Happening Here:
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We’re calling a function named linux-libre-module->linux-module.
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We pass it two arguments:
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xpad-module: This is the original kernel module we defined earlier.
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linux-6.1: This specifies the Linux kernel version we want to target.
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3.3. Under the Hood
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Let’s break down what happens inside the function:
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```scheme
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(define* (linux-libre-module->linux-module module #:optional (linux linux))
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(package
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(inherit module)
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(arguments
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(substitute-keyword-arguments (package-arguments module)
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((#:linux _) linux)))))
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Function Definition: define* is used to define a function named linux-libre-module->linux-module.
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Parameters:
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module: The original kernel module package.
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#:optional (linux linux): This allows an optional parameter linux, defaulting to a predefined value if not specified.
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Explanation of Parameters and Arguments:
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module: This is the package we want to modify (in this case, xpad-module).
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#
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(linux linux): This parameter allows you to specify a kernel version. If you don’t provide one, it defaults to whatever is set in the environment.
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How Arguments Work:
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Package Arguments:
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```scheme
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(package-arguments module)
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```
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This function retrieves the current build arguments of the module package.
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Arguments typically include details like the source code location, build instructions, dependencies, and other metadata needed to build the package.
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Substituting Arguments:
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scheme
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(substitute-keyword-arguments (package-arguments module)
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((#:linux _) linux))
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substitute-keyword-arguments: This function is used to modify specific arguments within the package’s build instructions.
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Current Arguments: It takes the current arguments from the module package.
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Substitution: It looks for the argument specified by #:linux and replaces its value with the new linux value we provided (linux-6.1).
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Detailed Breakdown:
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Inherit:
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scheme
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(inherit module)
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This keyword means that our new package (xpad-module-for-linux-6.1) will inherit all properties from the original xpad-module.
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Properties include the package name, version, source, build system, description, license, etc.
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Arguments Field:
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scheme
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(arguments
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(substitute-keyword-arguments (package-arguments module)
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((#:linux _) linux)))
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arguments: This defines the build arguments for the new package.
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substitute-keyword-arguments: This function is used to selectively replace certain arguments.
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#
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: This is the keyword argument we are targeting for replacement.
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_: This is a placeholder for the current value of the #:linux argument in the original package.
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linux: This is the new value we are assigning to the #:linux argument (i.e., linux-6.1).
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3.4. Variable Assignment
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Finally, the result of this function call is assigned to xpad-module-for-linux-6.1:
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scheme
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(define xpad-module-for-linux-6.1
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(linux-libre-module->linux-module xpad-module linux-6.1))
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What This Means: xpad-module-for-linux-6.1 now holds a version of the xpad module that is specifically configured to be built against Linux kernel version 6.1.
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Low-Level Details
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When a package is passed to a variable in Scheme, it's not just a simple copy of the code. Here’s a deeper look:
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Copy by Value: The function receives the package object and copies its structure.
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Inheritance: When using the inherit keyword, the properties (like metadata, build instructions, etc.) of the original package are duplicated in the new package.
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Modification: The copied structure is then modified as specified (e.g., changing the kernel version in the arguments).
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This approach means the new package (xpad-module-for-linux-6.1) is a full-fledged package object with its own definition, derived from the original (xpad-module) but tailored for a specific kernel version.
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4. Summary
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Here’s the gist of what we’ve done:
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Define the Original Module: We have a kernel module (xpad-module) ready to go.
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Create a Custom Version: We use a function to modify this module so it’s compatible with a specific kernel version (6.1).
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Assign the Customized Module: The result is stored in a new variable (xpad-module-for-linux-6.1), which we can use to build the module specifically for Linux 6.1.
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This approach allows us to flexibly adapt kernel modules for different kernel versions without manually rewriting the module for each version.
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