Linux Kernel

Bootconfig

https://www.kernel.org/doc/html/latest/admin-guide/bootconfig.html#proc-bootconfig

The “kernel command line” can also be inspected: cat /proc/cmdline | sed "s/ /\n/g"

This introduces the distinction between Kernel Parameters and Kernel Module Parameters.

It also seems that within Kernel Modules, they can either be built-in or loadable

to intospect I need to figure out what i’m actually dealing with

good SE post on kernel parameters vs module parameters vs sysctl parameters https://unix.stackexchange.com/a/123050

Kernel Parameters

https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.rst:

list of the kernel parameters as implemented by the __setup(), early_param(), core_param() and module_param() macros

modprobe looks through the kernel command line (/proc/cmdline) and collects module parameters when it loads a module, so the kernel command line can be used for loadable modules too.

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/include/linux/moduleparam.h

• The macro module_param is a “typesafe helper for a module/cmdline parameter”
• core_param is a special case of module_param
• macro __module_param_call refers to “registering boot/module parameters”

https://sysprog21.github.io/lkmpg/

__init and __exit are defined in <linux/init.h> module_init and module_exit are defined in <linux/module.h>

__init and __exit are used to annotate functions for the kernel’s use

For built-in modules __init is used to free the module_init function. For built-in modules __exit is used to omit the module_exit function. For loadable modules both __init and __exit are ignored.

It seems to me that “external” is the same as “out-of-tree” is the same as “loadable”, and vice versa with “in-tree” and “built-in” (https://www.kernel.org/doc/html/latest/kbuild/modules.html).

Device drivers are a specific type of module. Character Devices are associated with an abstract file <linux/fs.h>, which are accessed through /dev

<linux/sysfs.h> can be inside a module source file to define a module attribute

DAMON

https://www.kernel.org/doc/html/latest/mm/damon/design.html#modules

Kernel Modules fall under the DAMON subsystem, which itself falls under the Memory Management subsystem. There are two types of DAMON modules: General Purpose User Interface Modules and Special-Purpose Access-aware Kernel Modules.

Maybe DAMON modules are different from Kernel Modules?

sysfs

https://docs.kernel.org/filesystems/sysfs.html sysfs is used to “export kernel data structures, their attributes, and the linkages between them to userspace”

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/include/linux/sysfs.h sysfs defines struct attribute {const char *name; umode_t mode;}