92 lines
2.3 KiB
Markdown
92 lines
2.3 KiB
Markdown
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# Kernel Modules
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The Toaru kernel supports loadable modules which provide most of the device driver support.
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A simple module requires a load and unload method, which are exposed along with a module
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name through the `MODULE_DEF` macro available from `<kernel/module.h>`.
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```c
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#include <kernel/module.h>
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static int load(void) {
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/* Run on module installation */
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return 0;
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}
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static int unload(void) {
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/* Clean up for removal */
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return 0;
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}
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MODULE_DEF(example_mod, load, unload);
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```
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## Module Dependencies
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If your module depends on another module being loaded, list each dependency using the `MODULE_DEPENDS` macro:
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```c
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MODULE_DEF(extension_mod, load, unload);
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MODULE_DEPENDS(example_mod);
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```
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Currently, dependencies are tested at load time, but the kernel will not load dependencies for you.
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Dependency lists can be parsed by external tools to ensure modules are properly linked.
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## Kernel Functions
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All non-static kernel functions are available for use in modules.
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For example, the logging functions may be used:
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```c
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#include <kernel/logging.h>
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#include <kernel/module.h>
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static int load(void) {
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debug_print(WARNING, "Hello, world.");
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return 0;
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}
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static int unload(void) {
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return 0;
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}
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MODULE_DEF(printing_mod, load, unload);
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```
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## Background Tasks
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Device drivers, such as those for network devices, may want to create a background process to manage tasks.
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This can be done through the `create_kernel_tasklet` interface at device startup.
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```c
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#include <kernel/process.h>
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#include <kernel/module.h>
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static void tasklet_run(void * data, char * name) {
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/* Perform tasklet activities */
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while (1) {
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do_thing();
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}
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}
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static int load(void) {
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create_kernel_tasklet(tasklet_run, "[demo-tasklet]", NULL);
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return 0;
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}
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static int unload(void) {
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/* Maybe clean up your tasklet here. */
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return 0;
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}
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MODULE_DEF(tasklet_mod, load, unload);
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```
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## Caveats
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- Currently, unloading modules is not supported.
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- Modules which are expected to be loaded at runtime should be very careful of memory allocations they make, as they happen in a context which may not be shared with other processes. If you wish to make use of memory mappings, ensure that you are creating a new kernel tasklet to perform work. Attempting to access mapped memory from an interrupt handler or a device driver may not be possible if it was mapped at module installation.
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