LddDeviceNumbers < Training2

%SECTION0{name=LddDeviceNumbers}% Device numbers

   * major and minor numbers
   * used by kernel to identify driver that handles request
   * many statically assigned (=Documentation/devices.txt=) (but no new ones will be)
   * need to be allocated (=claimed)
   * static or dynamic allocation
   * mapping number -> device can vary (1:1, n:1)


---++API: Device numbers

*type:*

<verbatim>
dev_t
</verbatim>

_include/linux/types.h_

*creation, accessors:*

<verbatim>
MKDEV(int major, int minor)
MAJOR(dev_t dev)
MINOR(dev_t dev)
</verbatim>

_include/linux/kdev_t.h_

*register a (known) range of numbers:*

<verbatim>
int register_chrdev_region(dev_t first, unsigned int count, char *name);
</verbatim>

   * *first:* first number in range
   * *count:* how many minor numbers?
   * *name:* name of device

*allocate a range of free numbers:*

<verbatim>
int alloc_chrdev_region(dev_t *dev, unsigned int firstminor, unsigned int count, char *name);
</verbatim>

   * *dev:* pointer to existing dev_t, will contain allocated major/minor
   * *firstminor:* usually 0 (but not required)
   * *name:* name of device

*free allocated or registered range of numbers:*

<verbatim>
void unregister_chrdev_region(dev_t first, unsigned int count);
</verbatim>

_include/linux/fs.h_
5.3.1. Introduction to character drivers		1. Denx Training Topics		5.3.3. Registering a character driver
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