Modern Character Devices (Slideshow)¶

Character Devices: Problems ¶

Manually creating device nodes is cumbersome
Number conflicts are much more likely than name conflicts
Want names, not numbers

Linux way: devtmpfs

File system that contains device nodes
Automatically populated by the kernel
… with a little driver support

$ mount
...
devtmpfs on /dev type devtmpfs (rw,relatime,...)
...

Dynamic Device Numbers ¶

jjj

From register_chrdev_region() to alloc_chrdev_region()
- blah

https://www.kernel.org/doc/htmldocs/kernel-api/API-alloc-chrdev-region.html

int alloc_chrdev_region(
    dev_t * dev,
    unsigned baseminor,
    unsigned count,
    const char * name);

Device Classes ¶

Devices ¶

device_create(): register character devices with sysfs

https://www.kernel.org/doc/html/latest/driver-api/infrastructure.html?highlight=device_create#c.device_create
- return value? ⟶ BUG_ON()
- Module loading: ERROR: Unknown symbol in module
  - Only exported to modules with GPL compatible license ⟶ MODULE_LICENSE("GPL");