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Kernel: Add a comment block about the Device class.

This commit is contained in:
Andreas Kling 2019-04-24 02:37:57 +02:00
parent f7a23f3668
commit d7cf841d3d

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@ -1,5 +1,38 @@
#pragma once
// Device is the base class of everything that lives in the /dev directory.
//
// All Devices will automatically register with the VFS.
// To expose a Device to the filesystem, simply pass two unique numbers to the constructor,
// and then mknod a file in /dev with those numbers.
//
// There are two main subclasses:
// - BlockDevice (random access)
// - CharacterDevice (sequential)
//
// The most important functions in Device are:
//
// class_name()
// - Used in the /proc filesystem to identify the type of Device.
//
// read() and write()
// - Implement reading and writing.
// - Return the number of bytes read/written, OR a negative error code.
//
// can_read() and can_write()
//
// - Used to implement blocking I/O, and the select() and poll() syscalls.
// - Return true if read() or write() would succeed, respectively.
// - Note that can_read() should return true in EOF conditions,
// and a subsequent call to read() should return 0.
//
// ioctl()
//
// - Optional. If unimplemented, ioctl() on the device will fail with -ENOTTY.
// - Can be overridden in subclasses to implement arbitrary functionality.
// - Subclasses should take care to validate incoming addresses before dereferencing.
//
#include <AK/Retainable.h>
#include <AK/Types.h>
#include <Kernel/FileSystem/FileDescriptor.h>