= Dynamic character-device number allocation
\b[Dynamic character-device number allocation] asks the Linux kernel to reserve a range of character-device numbers while choosing its <major device number> at runtime. The API is `alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name)`. It returns zero on success or a negative error code; the first assigned combined <device number> is written through `dev`. The return status is not the allocated major number.<Character-device number registration in the Linux kernel documentation>[Char devices, alloc_chrdev_region, parameters and return convention]{ref}
For an original request, suppose `alloc_chrdev_region(&first, 5, 3, "sample")` succeeds and the returned `first` has major $M$. Its reserved identifiers are $(M,5)$, $(M,6)$ and $(M,7)$, not $(M,8)$. If one illustrative successful run returned major 243, the caller would use 243; another allocation can return a different major. This is a hypothetical range example, not a kernel operation executed here.
Keep `first` and the successful reservation count for cleanup. If a later initialization step fails, `unregister_chrdev_region(first, 3)` releases this reservation; it must not be treated as ownership of every minor under the returned major. <Unwinding a failed character-device registration> releases only resources actually acquired.
Number reservation is separate from associating file operations with a live character-device object and from creating a <device node>. The related `cdev_add` operation makes a registered object live; its name or bookkeeping label does not itself establish a pathname under `/dev`.<Character-device number registration in the Linux kernel documentation>[Char devices, cdev_add, __register_chrdev name description and unregister_chrdev_region]{ref}
Removal must also respect existing users. `cdev_del` prevents new opens, but already open <file descriptors> can still call device operations, so deleting the registration alone does not prove that backing state can be freed immediately.<Character-device number registration in the Linux kernel documentation>[Char devices, cdev_del lifetime note]{ref} A dynamic number is a reserved interface identifier, not a persistent hardware identity or an inode number.
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