Polish char device chapter a little.

[cascardo/kernel/slides/.git] / 04char / chrdev

diff --git a/04char/chrdev b/04char/chrdev
index 5b6f7e9..a48e677 100644 (file)
--- a/04char/chrdev
+++ b/04char/chrdev
@@ -1,3 +1,6 @@
+%Character Devices
+%Thadeu Cascardo
+
 # Introduction
 
 Devices in POSIX Systems are files in /dev directory. As with any files
@@ -28,14 +31,100 @@ Linux devices may be of different types, including character devices,
 block devices or network devices. Both character and block devices have
 identifying numbers, a major and a minor number.
 
+# VFS
+
+# Introduction
+
+The virtual file system is the hub for almost all operations in a Linux-based
+system. It allows IPC with pipes, access to devices, including storage through
+regular files and organization with directories.
+
+# Everything is a file
+
+In Unix, there's a say: "everything is a file, if it's not a file, it's a
+process". Well, most things are really files, and that's why the VFS is at the
+center of the system, including for device drivers.
+
+# Special files, procfs and others
+
+When handling with special files (character and block device nodes), procfs
+files and others, we'll use some common structures. These include the
+*struct file\\_operations*, *struct file* and *struct inode*.
+
+Do not forget to include linux/fs.h.
+
+# File Operations
+
+* owner
+* open
+* release
+* flush
+* read
+* write
+* ioctl
+* unlocked_ioctl
+* llseek
+* poll
+* mmap
+* many others
+
+# Opened File
+
+* f\\_mode
+* f\\_flags
+* f\\_pos
+* f\\_op
+* private\\_data
+
+# Filesystem File: inode
+
+The inode is a representation of the file as in its filesystem, including its
+major/minor numbers and pointers to the corresponding device representation.
+
+# Character Devices
+
+# Device Number Macros
+
+Nowadays, major number is 12 bits and minor number is 20 bits. This may change
+in the future, so macros should be used.
+
+* include linux/kdev_t.h
+* MAJOR
+* MINOR
+* MKDEV
+
 # Character devices allocation
 
 In Linux, major and minor numbers have to be requested or allocated. The
 calls to do that for character devices are:
 
-
 * int register\\_chrdev\\_region (dev\\_t first, unsigned int count, char
 *name);
 * int alloc\\_chrdev\\_region (dev\\_t *dev, unsigned int firstminor,
 unsigned int count, char *name);
 * void unregister\\_chrdev\\_region (dev\\_t dev, unsigned int count);
+
+# cdev structure
+
+Use *cdev\\_alloc* or *cdev\\_init* to allocate or initalize a cdev structure.
+
+Use *cdev\\_add* and *cdev\\_del* to register and unregister it.
+
+# Open/Release
+
+Implementing open and release should be very simple for many devices. They
+usually allocate data, and multiplex devices by minor number.
+
+# Inode structure
+
+Use *imajor* and *iminor* to get the major and minor number from an inode
+structure.
+
+# Read
+
+Read may write to user space less bytes than requested.
+
+# Write
+
+Write is very similar to read. Only problem is that many applications misbehave
+when driver writes less bytes than requested.