add character driver fops struct + implementation

1 files changed, 27 insertions, 0 deletions

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+# sources
+
+- [Kbuild object variable name rationale][kbuild-obj-var]
+- [Kbuild kernel module setup guide][kbuild-module-makefile]
+- [`struct file_operations`][c-struct-file-operations] documentation, also
+    - write(2)
+    - read(2)
+- (Sadly) [the Linux kernel source][kernel] itself, especially
+    - drivers/char/random.c
+    - drivers/char/mem.c
+
+[kbuild-obj-var]: https://docs.kernel.org/kbuild/makefiles.html#loadable-module-goals-obj-m
+[kbuild-module-makefile]: https://www.kernel.org/doc/html/latest/kbuild/modules.html#creating-a-kbuild-file-for-an-external-module
+[c-struct-file-operations]: https://www.kernel.org/doc/html/latest/filesystems/vfs.html#struct-file-operations
+[kernel]: https://github.com/torvalds/linux
+
+# tips
+
+- When the kernel documentation references manpages, these actually contain
+  useful information. Manpages are not only for commands, but also include
+  detailed documentation for the syscall interface and other C APIs.
+
+  Since most of the manpages referenced by the kernel are from section 2 (on
+  system calls), you should append the number between brackets to the `man`
+  command, i.e. to read 'write(2)' use the command `man 2 write`.
+- Use `dmesg` with the `-w` or `-W` option (see man dmesg(1))
+