diff options
| -rw-r--r-- | 1/Makefile | 5 | ||||
| -rw-r--r-- | 1/fopdrv.c | 28 | ||||
| -rw-r--r-- | 1/fopdrv.h | 11 | ||||
| -rw-r--r-- | 1/main.c | 13 | ||||
| -rw-r--r-- | readme.md | 27 |
5 files changed, 81 insertions, 3 deletions
@@ -3,8 +3,11 @@ KERNEL := /lib/modules/$(RELEASE)/build # PWD doesn't have to be defined as it's inherited from the current environment # MAKE shouldn't be defined as it's special in GNU make +# the names of these variables are required by the kernel's (imo weird) build +# system, see [kbuild-obj-var] and [kbuild-module-makefile] in ../readme.md obj-m += lork.o -lork-y := main.o +lork-y += main.o +lork-y += fopdrv.o all: $(MAKE) -C $(KERNEL) M=$(PWD) modules diff --git a/1/fopdrv.c b/1/fopdrv.c new file mode 100644 index 0000000..31c76cd --- /dev/null +++ b/1/fopdrv.c @@ -0,0 +1,28 @@ +#include "fopdrv.h" + +// driver/char/mem.c read_null (/dev/null) +ssize_t fop_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) { + return 0; +} + +// driver/char/mem.c write_null +ssize_t fop_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { + return count; +} + +int fop_open(struct inode * inode, struct file * file) { + printk("%s\n", __PRETTY_FUNCTION__); + return 0; + // 0 seems to be a safe return value as it's used in driver/char/mem.c. The + // manual page for open(2) says that the system call returns a nonnegative + // integer representing the file descriptor on success, but it does not + // appears to be required. +} + +int fop_release(struct inode * inode, struct file * file) { + printk("%s\n", __PRETTY_FUNCTION__); + return 0; + // same as above, but found in driver/char/lp.c +} + + diff --git a/1/fopdrv.h b/1/fopdrv.h new file mode 100644 index 0000000..f2ca18c --- /dev/null +++ b/1/fopdrv.h @@ -0,0 +1,11 @@ +#pragma once + +#include <linux/fs.h> +#include <linux/types.h> + +// declarations copied from linux/fs.h +ssize_t fop_read(struct file *, char __user *, size_t, loff_t *); +ssize_t fop_write(struct file *, const char __user *, size_t, loff_t *); +int fop_open(struct inode *, struct file *); +int fop_release(struct inode *, struct file *); + @@ -1,15 +1,24 @@ #include <linux/init.h> #include <linux/module.h> +#include "fopdrv.h" + MODULE_LICENSE("MIT"); +struct file_operations fops = { + .read = fop_read, + .write = fop_write, + .open = fop_open, + .release = fop_release, +}; + static int mod_init(void) { - printk(KERN_ALERT "Hello, world\n"); + printk("%s\n", __PRETTY_FUNCTION__); return 0; } static void mod_exit(void) { - printk(KERN_ALERT "Goodbye, world\n"); + printk("%s\n", __PRETTY_FUNCTION__); } module_init(mod_init); diff --git a/readme.md b/readme.md new file mode 100644 index 0000000..f8f735d --- /dev/null +++ b/readme.md @@ -0,0 +1,27 @@ +# 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)) + |