This document discusses system devices and how operating systems interact with and configure devices. It provides an overview of device interconnects, configuration from the hardware and software perspectives, and device naming schemes in various operating systems. Specific topics covered include generic system architecture, device terminology, viewing the system device configuration, and adding new devices to Windows and Linux systems.
Writing Character driver (loadable module) in linuxRajKumar Rampelli
It covers the step by step approach on how to write a simple loadable character device driver in linux. What are Device files in linux detail. How user application interact with character driver using a device file.
The document discusses key concepts related to processes and threads in operating systems. It defines a process as an actively running program with its own memory space and resources. Processes contain code, data, and stack segments. Lightweight processes (LWPs) appear as virtual processors to user threads and are attached to kernel threads that the OS schedules. Threads are lightweight processes that share memory and resources within a process and run concurrently to improve performance. The document also discusses process descriptors, interrupts, system calls, and kernel threads.
The Linux kernel acts as an interface between applications and hardware, managing system resources and providing access through system calls; it uses a monolithic design where all components run in the kernel thread for high performance but can be difficult to maintain, though Linux allows dynamic loading of modules. Device drivers interface hardware like keyboards, hard disks, and network devices with the operating system, and are implemented as loadable kernel modules that are compiled using special makefiles and registered with the kernel through system calls.
A character device typically transfers data to and from a user appli.pdfaptind
A character device typically transfers data to and from a user application — they behave like
pipes or serial ports, instantly reading or writing the byte data in a character-by-character stream.
They provide the framework for many typical drivers, such as those that are required for
interfacing to serial communications, video capture, and audio devices. The main alternative to a
character device is a block device. Block devices behave in a similar fashion to regular files,
allowing a buffered array of cached data to be viewed or manipulated with operations such as
reads, writes, and seeks. Both device types can be accessed through device files that are attached
to the file system tree. For example, the program code that is presented in this article builds to
become a device /dev/ebbchar, which appears on your Linux system as follows:
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ lsmod
Module Size Used by
ebbchar 2754 0
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ ls -l /dev/ebb*
crw-rw-rwT 1 root root 240, 0 Apr 11 15:34 /dev/ebbchar
A straightforward character driver that can be used to pass information between a Linux user-
space program and a loadable kernel module (LKM), which is running in Linux kernel space. In
this example, a C user-space application sends a string to the LKM. The LKM then responds
with the message that was sent along with the number of letters that the sent message contains.
Later in the article I describe why we need to solve synchronization problems that arise with this
approach, and I provide a version of the program that uses mutex locks to provide a solution.
Before describing the source code for the driver in this article, there are a few concepts that need
to be discussed, such as device driver major and minor numbers, and the File Operations data
structure.
Major and Minor Numbers
Device drivers have an associated major and minor number. For example, /dev/ram0 and
/dev/null are associated with a driver with major number 1, and /dev/tty0 and /dev/ttyS0 are
associated with a driver with major number 4. The major number is used by the kernel to identify
the correct device driver when the device is accessed. The role of the minor number is device
dependent, and is handled internally within the driver. You can see the major/minor number pair
for each device if you perform a listing in the /dev directory. For example:
molloyd@beaglebone:/dev$ ls -l
crw-rw---T 1 root i2c 89, 0 Jan 1 2000 i2c-0
brw-rw---T 1 root disk 1, 0 Mar 1 20:46 ram0
brw-rw---T 1 root floppy 179, 0 Mar 1 20:46 mmcblk0
crw-rw-rw- 1 root root 1, 3 Mar 1 20:46 null
crw------- 1 root root 4, 0 Mar 1 20:46 tty0
crw-rw---T 1 root dialout 4, 64 Mar 1 20:46 ttyS0
…
Character devices are identified by a ‘c‘ in the first column of a listing, and block devices are
identified by a ‘b‘. The access permissions, owner, and group of the device is provided for each
device. Regular user accounts on the BeagleBone are members of some of these .
A character device typically transfers data to and from a user appli.pdfaptind
A character device typically transfers data to and from a user application — they behave like
pipes or serial ports, instantly reading or writing the byte data in a character-by-character stream.
They provide the framework for many typical drivers, such as those that are required for
interfacing to serial communications, video capture, and audio devices. The main alternative to a
character device is a block device. Block devices behave in a similar fashion to regular files,
allowing a buffered array of cached data to be viewed or manipulated with operations such as
reads, writes, and seeks. Both device types can be accessed through device files that are attached
to the file system tree. For example, the program code that is presented in this article builds to
become a device /dev/ebbchar, which appears on your Linux system as follows:
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ lsmod
Module Size Used by
ebbchar 2754 0
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ ls -l /dev/ebb*
crw-rw-rwT 1 root root 240, 0 Apr 11 15:34 /dev/ebbchar
A straightforward character driver that can be used to pass information between a Linux user-
space program and a loadable kernel module (LKM), which is running in Linux kernel space. In
this example, a C user-space application sends a string to the LKM. The LKM then responds
with the message that was sent along with the number of letters that the sent message contains.
Later in the article I describe why we need to solve synchronization problems that arise with this
approach, and I provide a version of the program that uses mutex locks to provide a solution.
Before describing the source code for the driver in this article, there are a few concepts that need
to be discussed, such as device driver major and minor numbers, and the File Operations data
structure.
Major and Minor Numbers
Device drivers have an associated major and minor number. For example, /dev/ram0 and
/dev/null are associated with a driver with major number 1, and /dev/tty0 and /dev/ttyS0 are
associated with a driver with major number 4. The major number is used by the kernel to identify
the correct device driver when the device is accessed. The role of the minor number is device
dependent, and is handled internally within the driver. You can see the major/minor number pair
for each device if you perform a listing in the /dev directory. For example:
molloyd@beaglebone:/dev$ ls -l
crw-rw---T 1 root i2c 89, 0 Jan 1 2000 i2c-0
brw-rw---T 1 root disk 1, 0 Mar 1 20:46 ram0
brw-rw---T 1 root floppy 179, 0 Mar 1 20:46 mmcblk0
crw-rw-rw- 1 root root 1, 3 Mar 1 20:46 null
crw------- 1 root root 4, 0 Mar 1 20:46 tty0
crw-rw---T 1 root dialout 4, 64 Mar 1 20:46 ttyS0
…
Character devices are identified by a ‘c‘ in the first column of a listing, and block devices are
identified by a ‘b‘. The access permissions, owner, and group of the device is provided for each
device. Regular user accounts on the BeagleBone are members of some of these .
This document provides an overview of input/output (I/O) in Linux, including device drivers, block and character devices, and network devices. It defines device drivers as software that allows programs to interact with hardware devices. Device drivers can be built into the Linux kernel or loaded as modules. Block devices access storage through caches and support random access to fixed size blocks, while character devices do not require this functionality and the kernel simply passes read/write requests to these drivers. Network devices exchange data packets through interfaces using network-specific driver functions rather than read/write calls.
This document discusses principles of computer input/output (I/O) hardware and software. It covers topics like I/O devices, device controllers, buses, I/O techniques (programmed I/O, interrupt-driven I/O, and direct memory access), device drivers, layers of I/O software, file systems, and storage devices like disks. The document provides details on how operating systems manage and interface with various I/O components to facilitate data transfer and storage.
This document discusses system devices and how operating systems interact with and configure devices. It provides an overview of device interconnects, configuration from the hardware and software perspectives, and device naming schemes in various operating systems. Specific topics covered include generic system architecture, device terminology, viewing the system device configuration, and adding new devices to Windows and Linux systems.
Writing Character driver (loadable module) in linuxRajKumar Rampelli
It covers the step by step approach on how to write a simple loadable character device driver in linux. What are Device files in linux detail. How user application interact with character driver using a device file.
The document discusses key concepts related to processes and threads in operating systems. It defines a process as an actively running program with its own memory space and resources. Processes contain code, data, and stack segments. Lightweight processes (LWPs) appear as virtual processors to user threads and are attached to kernel threads that the OS schedules. Threads are lightweight processes that share memory and resources within a process and run concurrently to improve performance. The document also discusses process descriptors, interrupts, system calls, and kernel threads.
The Linux kernel acts as an interface between applications and hardware, managing system resources and providing access through system calls; it uses a monolithic design where all components run in the kernel thread for high performance but can be difficult to maintain, though Linux allows dynamic loading of modules. Device drivers interface hardware like keyboards, hard disks, and network devices with the operating system, and are implemented as loadable kernel modules that are compiled using special makefiles and registered with the kernel through system calls.
A character device typically transfers data to and from a user appli.pdfaptind
A character device typically transfers data to and from a user application — they behave like
pipes or serial ports, instantly reading or writing the byte data in a character-by-character stream.
They provide the framework for many typical drivers, such as those that are required for
interfacing to serial communications, video capture, and audio devices. The main alternative to a
character device is a block device. Block devices behave in a similar fashion to regular files,
allowing a buffered array of cached data to be viewed or manipulated with operations such as
reads, writes, and seeks. Both device types can be accessed through device files that are attached
to the file system tree. For example, the program code that is presented in this article builds to
become a device /dev/ebbchar, which appears on your Linux system as follows:
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ lsmod
Module Size Used by
ebbchar 2754 0
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ ls -l /dev/ebb*
crw-rw-rwT 1 root root 240, 0 Apr 11 15:34 /dev/ebbchar
A straightforward character driver that can be used to pass information between a Linux user-
space program and a loadable kernel module (LKM), which is running in Linux kernel space. In
this example, a C user-space application sends a string to the LKM. The LKM then responds
with the message that was sent along with the number of letters that the sent message contains.
Later in the article I describe why we need to solve synchronization problems that arise with this
approach, and I provide a version of the program that uses mutex locks to provide a solution.
Before describing the source code for the driver in this article, there are a few concepts that need
to be discussed, such as device driver major and minor numbers, and the File Operations data
structure.
Major and Minor Numbers
Device drivers have an associated major and minor number. For example, /dev/ram0 and
/dev/null are associated with a driver with major number 1, and /dev/tty0 and /dev/ttyS0 are
associated with a driver with major number 4. The major number is used by the kernel to identify
the correct device driver when the device is accessed. The role of the minor number is device
dependent, and is handled internally within the driver. You can see the major/minor number pair
for each device if you perform a listing in the /dev directory. For example:
molloyd@beaglebone:/dev$ ls -l
crw-rw---T 1 root i2c 89, 0 Jan 1 2000 i2c-0
brw-rw---T 1 root disk 1, 0 Mar 1 20:46 ram0
brw-rw---T 1 root floppy 179, 0 Mar 1 20:46 mmcblk0
crw-rw-rw- 1 root root 1, 3 Mar 1 20:46 null
crw------- 1 root root 4, 0 Mar 1 20:46 tty0
crw-rw---T 1 root dialout 4, 64 Mar 1 20:46 ttyS0
…
Character devices are identified by a ‘c‘ in the first column of a listing, and block devices are
identified by a ‘b‘. The access permissions, owner, and group of the device is provided for each
device. Regular user accounts on the BeagleBone are members of some of these .
A character device typically transfers data to and from a user appli.pdfaptind
A character device typically transfers data to and from a user application — they behave like
pipes or serial ports, instantly reading or writing the byte data in a character-by-character stream.
They provide the framework for many typical drivers, such as those that are required for
interfacing to serial communications, video capture, and audio devices. The main alternative to a
character device is a block device. Block devices behave in a similar fashion to regular files,
allowing a buffered array of cached data to be viewed or manipulated with operations such as
reads, writes, and seeks. Both device types can be accessed through device files that are attached
to the file system tree. For example, the program code that is presented in this article builds to
become a device /dev/ebbchar, which appears on your Linux system as follows:
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ lsmod
Module Size Used by
ebbchar 2754 0
molloyd@beaglebone:~/exploringBB/extras/kernel/ebbchar$ ls -l /dev/ebb*
crw-rw-rwT 1 root root 240, 0 Apr 11 15:34 /dev/ebbchar
A straightforward character driver that can be used to pass information between a Linux user-
space program and a loadable kernel module (LKM), which is running in Linux kernel space. In
this example, a C user-space application sends a string to the LKM. The LKM then responds
with the message that was sent along with the number of letters that the sent message contains.
Later in the article I describe why we need to solve synchronization problems that arise with this
approach, and I provide a version of the program that uses mutex locks to provide a solution.
Before describing the source code for the driver in this article, there are a few concepts that need
to be discussed, such as device driver major and minor numbers, and the File Operations data
structure.
Major and Minor Numbers
Device drivers have an associated major and minor number. For example, /dev/ram0 and
/dev/null are associated with a driver with major number 1, and /dev/tty0 and /dev/ttyS0 are
associated with a driver with major number 4. The major number is used by the kernel to identify
the correct device driver when the device is accessed. The role of the minor number is device
dependent, and is handled internally within the driver. You can see the major/minor number pair
for each device if you perform a listing in the /dev directory. For example:
molloyd@beaglebone:/dev$ ls -l
crw-rw---T 1 root i2c 89, 0 Jan 1 2000 i2c-0
brw-rw---T 1 root disk 1, 0 Mar 1 20:46 ram0
brw-rw---T 1 root floppy 179, 0 Mar 1 20:46 mmcblk0
crw-rw-rw- 1 root root 1, 3 Mar 1 20:46 null
crw------- 1 root root 4, 0 Mar 1 20:46 tty0
crw-rw---T 1 root dialout 4, 64 Mar 1 20:46 ttyS0
…
Character devices are identified by a ‘c‘ in the first column of a listing, and block devices are
identified by a ‘b‘. The access permissions, owner, and group of the device is provided for each
device. Regular user accounts on the BeagleBone are members of some of these .
This document provides an overview of input/output (I/O) in Linux, including device drivers, block and character devices, and network devices. It defines device drivers as software that allows programs to interact with hardware devices. Device drivers can be built into the Linux kernel or loaded as modules. Block devices access storage through caches and support random access to fixed size blocks, while character devices do not require this functionality and the kernel simply passes read/write requests to these drivers. Network devices exchange data packets through interfaces using network-specific driver functions rather than read/write calls.
This document discusses principles of computer input/output (I/O) hardware and software. It covers topics like I/O devices, device controllers, buses, I/O techniques (programmed I/O, interrupt-driven I/O, and direct memory access), device drivers, layers of I/O software, file systems, and storage devices like disks. The document provides details on how operating systems manage and interface with various I/O components to facilitate data transfer and storage.
The document discusses the Windows registry, which is a central database that contains configuration settings and options for the operating system, installed programs, and hardware settings. It provides information on the structure and organization of the registry, including the root keys that categories registry settings. The summary also mentions that the registry contains information about users, programs, files and browsing activity that can be useful for troubleshooting or forensic analysis. It provides examples of how to modify registry settings to disable USB storage, internet access and restrict applications on a system.
Device Dependent Software:Device Drivers: Definition, Purpose of a device driver, Device Drivers for Interrupt Handling, Memory Device Drivers, On-Board Bus Device Drivers, and Board I/O Driver Examples confined to initialization of Ethernet and RS 232.
This document discusses device drivers. It begins by defining a device driver as software that allows operating systems and applications to access hardware functionality. It then describes the main objectives of device drivers and how they handle requests from the operating system. Next, it covers different types of device drivers and provides examples. Applications of device drivers for storage, input/output, virtual machines, and peripherals are also outlined. Finally, the document lists the typical steps taken when developing new device drivers.
The document discusses the driver architecture in Windows CE, including how drivers are loaded, the role of the device manager and registry enumerator, power management, memory management using the CEDDK, and differences from the WDM model in Windows XP. Specifically, it outlines how drivers are loaded from the registry by the registry enumerator and device manager, the types of drivers, and interfaces for power management, memory mapping, and I/O.
The document summarizes how to write a character device driver in Linux. It covers the anatomy of a device driver including the user interface via device files, and kernel interfaces via file operations and major/minor numbers. It describes registering a character driver by defining file operations, reserving major/minor numbers, and associating them. Open and release functions handle initialization and cleanup. Read/write functions transfer data between userspace and hardware. Ioctl allows extending functionality.
These are notes I made while I was studying. The Linux community is so friendly and shares so much, so I am uploading my work to give back to the community. You won't find answers to test questions here, but you will find some solid notes around each of the exam points.
This document summarizes how to write device drivers for MS-DOS. It describes the different types of device drivers, the standard format and components required for all device drivers, and provides details on the device header, strategy and interrupt routines, and command code routines that drivers must implement to interface with the operating system. Specific examples of character and block device drivers are discussed, along with the functions of common drivers like ANSI.SYS.
This document discusses the key components of a file system and disk drive architecture. It covers disk structure, scheduling, management, and swap space. It describes concepts like disk formatting, boot blocks, bad blocks, and swap space location. The document also provides a high-level overview of the Windows 2000 operating system, covering its architecture, kernel, processes and threads, exceptions, and subsystems.
This document discusses the key components of a file system and disk drive operation. It covers disk structure, scheduling, management, and swap space. Disks are made up of logical blocks that are mapped to physical sectors. Scheduling algorithms like FCFS, SSTF, SCAN and C-SCAN are used to optimize disk head movement. Disk formatting partitions disks and writes file system structures. Swap space is used for virtual memory paging.
This document discusses the key components of a file system and disk drive operation. It covers disk structure, scheduling, management, and swap space. Disks are made up of logical blocks that are mapped to physical sectors. Scheduling algorithms like FCFS, SSTF, SCAN and C-SCAN are used to optimize disk head movement. Disk formatting partitions disks and writes file system structures. Swap space is used for virtual memory paging.
This document discusses the key components of a file system and disk drive operation. It covers disk structure, scheduling, management, and swap space. Disks are made up of logical blocks that are mapped to physical sectors. Scheduling algorithms like FCFS, SSTF, SCAN and C-SCAN are used to optimize disk head movement. Disk formatting partitions disks and writes file system structures. Swap space is used for virtual memory paging.
The document discusses managing hardware devices in a Windows Server 2003 environment. It covers topics such as using Device Manager to manage device drivers, resolving hardware resource conflicts, configuring driver signing options, optimizing processor and memory usage, creating hardware profiles, and configuring power options and an uninterruptible power supply. Activities are included to demonstrate exploring Device Manager, installing devices, viewing resource settings, configuring driver signing and rolling back drivers, and modifying settings for virtual memory, hardware profiles, and power schemes.
The document describes basic concepts related to machines, hosts, clients, servers, workstations, processes, daemons, distributed systems, and kernels. It then provides details about the boot PROM including its functions, components, configuration information storage, and commonly used commands. Finally, it outlines the boot PROM booting process and describes emergency sequences and diagnostic modes that can be accessed using stop key sequences.
The document discusses Linux device trees and how they are used to describe hardware configurations. Some key points:
- A device tree is a data structure that describes hardware connections and configurations. It allows the same kernel to support different hardware.
- Device trees contain nodes that represent devices, with properties like compatible strings to identify drivers. They describe things like memory maps, interrupts, and bus attachments.
- The kernel uses the device tree passed by the bootloader to identify and initialize hardware. Drivers match based on compatible properties.
- Device tree files with .dts extension can be compiled to binary blobs (.dtb) and overlays (.dtbo) used at boot time to describe hardware.
A device driver allows operating systems and programs to interact with hardware devices. This document discusses device drivers in Linux, including that drivers are loaded as kernel modules, communicate between user and kernel space, and have character, block, and network classes. It provides examples of initializing and removing a sample "memory" driver that allows reading from and writing to a character device memory buffer.
I/O System and Case Study of Operating System its easy way to find how the I/O's are connected with the Operating System and And the mechanism of the Operating System
This document provides an overview of the key components and boot process of embedded Linux systems. It discusses that embedded Linux systems are typically built using cross-compilation on a host PC. The bootloader then initializes the target hardware and loads the operating system, including the Linux kernel, device tree, and root file system. The kernel mounts the root file system and executes the init process, which determines the runlevel and starts essential processes and services based on that runlevel.
This document discusses system devices and device configuration from both the hardware and software perspectives on various operating systems like Windows, UNIX, Linux, and Solaris. It covers device terminology, device naming schemes, how devices are represented in the operating system, and how to view the system's device configuration from both the PROM and software levels. The goal is to understand how devices are interconnected, configured, and accessed on the system.
The document describes the standard Linux filesystem hierarchy, including the purpose and some examples of the contents of the top-level directories like /bin, /boot, /dev, /etc, /home, /lib, /media, /mnt, /opt, /proc, /root, /sbin, /usr, and /var. Many directories contain essential system files and programs needed for booting, administration, and operation of the system, while others provide variable storage and mounting points for removable devices. The filesystem layout separates core operating system, user, and variable files for security and manageability.
The document discusses the Windows registry, which is a central database that contains configuration settings and options for the operating system, installed programs, and hardware settings. It provides information on the structure and organization of the registry, including the root keys that categories registry settings. The summary also mentions that the registry contains information about users, programs, files and browsing activity that can be useful for troubleshooting or forensic analysis. It provides examples of how to modify registry settings to disable USB storage, internet access and restrict applications on a system.
Device Dependent Software:Device Drivers: Definition, Purpose of a device driver, Device Drivers for Interrupt Handling, Memory Device Drivers, On-Board Bus Device Drivers, and Board I/O Driver Examples confined to initialization of Ethernet and RS 232.
This document discusses device drivers. It begins by defining a device driver as software that allows operating systems and applications to access hardware functionality. It then describes the main objectives of device drivers and how they handle requests from the operating system. Next, it covers different types of device drivers and provides examples. Applications of device drivers for storage, input/output, virtual machines, and peripherals are also outlined. Finally, the document lists the typical steps taken when developing new device drivers.
The document discusses the driver architecture in Windows CE, including how drivers are loaded, the role of the device manager and registry enumerator, power management, memory management using the CEDDK, and differences from the WDM model in Windows XP. Specifically, it outlines how drivers are loaded from the registry by the registry enumerator and device manager, the types of drivers, and interfaces for power management, memory mapping, and I/O.
The document summarizes how to write a character device driver in Linux. It covers the anatomy of a device driver including the user interface via device files, and kernel interfaces via file operations and major/minor numbers. It describes registering a character driver by defining file operations, reserving major/minor numbers, and associating them. Open and release functions handle initialization and cleanup. Read/write functions transfer data between userspace and hardware. Ioctl allows extending functionality.
These are notes I made while I was studying. The Linux community is so friendly and shares so much, so I am uploading my work to give back to the community. You won't find answers to test questions here, but you will find some solid notes around each of the exam points.
This document summarizes how to write device drivers for MS-DOS. It describes the different types of device drivers, the standard format and components required for all device drivers, and provides details on the device header, strategy and interrupt routines, and command code routines that drivers must implement to interface with the operating system. Specific examples of character and block device drivers are discussed, along with the functions of common drivers like ANSI.SYS.
This document discusses the key components of a file system and disk drive architecture. It covers disk structure, scheduling, management, and swap space. It describes concepts like disk formatting, boot blocks, bad blocks, and swap space location. The document also provides a high-level overview of the Windows 2000 operating system, covering its architecture, kernel, processes and threads, exceptions, and subsystems.
This document discusses the key components of a file system and disk drive operation. It covers disk structure, scheduling, management, and swap space. Disks are made up of logical blocks that are mapped to physical sectors. Scheduling algorithms like FCFS, SSTF, SCAN and C-SCAN are used to optimize disk head movement. Disk formatting partitions disks and writes file system structures. Swap space is used for virtual memory paging.
This document discusses the key components of a file system and disk drive operation. It covers disk structure, scheduling, management, and swap space. Disks are made up of logical blocks that are mapped to physical sectors. Scheduling algorithms like FCFS, SSTF, SCAN and C-SCAN are used to optimize disk head movement. Disk formatting partitions disks and writes file system structures. Swap space is used for virtual memory paging.
This document discusses the key components of a file system and disk drive operation. It covers disk structure, scheduling, management, and swap space. Disks are made up of logical blocks that are mapped to physical sectors. Scheduling algorithms like FCFS, SSTF, SCAN and C-SCAN are used to optimize disk head movement. Disk formatting partitions disks and writes file system structures. Swap space is used for virtual memory paging.
The document discusses managing hardware devices in a Windows Server 2003 environment. It covers topics such as using Device Manager to manage device drivers, resolving hardware resource conflicts, configuring driver signing options, optimizing processor and memory usage, creating hardware profiles, and configuring power options and an uninterruptible power supply. Activities are included to demonstrate exploring Device Manager, installing devices, viewing resource settings, configuring driver signing and rolling back drivers, and modifying settings for virtual memory, hardware profiles, and power schemes.
The document describes basic concepts related to machines, hosts, clients, servers, workstations, processes, daemons, distributed systems, and kernels. It then provides details about the boot PROM including its functions, components, configuration information storage, and commonly used commands. Finally, it outlines the boot PROM booting process and describes emergency sequences and diagnostic modes that can be accessed using stop key sequences.
The document discusses Linux device trees and how they are used to describe hardware configurations. Some key points:
- A device tree is a data structure that describes hardware connections and configurations. It allows the same kernel to support different hardware.
- Device trees contain nodes that represent devices, with properties like compatible strings to identify drivers. They describe things like memory maps, interrupts, and bus attachments.
- The kernel uses the device tree passed by the bootloader to identify and initialize hardware. Drivers match based on compatible properties.
- Device tree files with .dts extension can be compiled to binary blobs (.dtb) and overlays (.dtbo) used at boot time to describe hardware.
A device driver allows operating systems and programs to interact with hardware devices. This document discusses device drivers in Linux, including that drivers are loaded as kernel modules, communicate between user and kernel space, and have character, block, and network classes. It provides examples of initializing and removing a sample "memory" driver that allows reading from and writing to a character device memory buffer.
I/O System and Case Study of Operating System its easy way to find how the I/O's are connected with the Operating System and And the mechanism of the Operating System
This document provides an overview of the key components and boot process of embedded Linux systems. It discusses that embedded Linux systems are typically built using cross-compilation on a host PC. The bootloader then initializes the target hardware and loads the operating system, including the Linux kernel, device tree, and root file system. The kernel mounts the root file system and executes the init process, which determines the runlevel and starts essential processes and services based on that runlevel.
This document discusses system devices and device configuration from both the hardware and software perspectives on various operating systems like Windows, UNIX, Linux, and Solaris. It covers device terminology, device naming schemes, how devices are represented in the operating system, and how to view the system's device configuration from both the PROM and software levels. The goal is to understand how devices are interconnected, configured, and accessed on the system.
The document describes the standard Linux filesystem hierarchy, including the purpose and some examples of the contents of the top-level directories like /bin, /boot, /dev, /etc, /home, /lib, /media, /mnt, /opt, /proc, /root, /sbin, /usr, and /var. Many directories contain essential system files and programs needed for booting, administration, and operation of the system, while others provide variable storage and mounting points for removable devices. The filesystem layout separates core operating system, user, and variable files for security and manageability.
Similar to Unit 5.2 Device Driver.pdf (Device Driver) (20)
- The Unix operating system originated from the MULTICS project in the 1960s. Bell Labs researchers Ken Thompson and Dennis Ritchie developed the first version of Unix in 1969.
- Unix became popular due to its portability, simplicity, and ability to support complex programs built from simpler ones. It introduced a hierarchical file system, consistent file format, and multi-user capabilities.
- Over time, Unix evolved into two main versions - System V (SVR) and Berkeley Software Distribution (BSD). Linux was later developed as a Unix-like system and shares many similarities with SVR.
How to Build a Module in Odoo 17 Using the Scaffold MethodCeline George
Odoo provides an option for creating a module by using a single line command. By using this command the user can make a whole structure of a module. It is very easy for a beginner to make a module. There is no need to make each file manually. This slide will show how to create a module using the scaffold method.
A review of the growth of the Israel Genealogy Research Association Database Collection for the last 12 months. Our collection is now passed the 3 million mark and still growing. See which archives have contributed the most. See the different types of records we have, and which years have had records added. You can also see what we have for the future.
Executive Directors Chat Leveraging AI for Diversity, Equity, and InclusionTechSoup
Let’s explore the intersection of technology and equity in the final session of our DEI series. Discover how AI tools, like ChatGPT, can be used to support and enhance your nonprofit's DEI initiatives. Participants will gain insights into practical AI applications and get tips for leveraging technology to advance their DEI goals.
LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
Exploiting Artificial Intelligence for Empowering Researchers and Faculty, In...Dr. Vinod Kumar Kanvaria
Exploiting Artificial Intelligence for Empowering Researchers and Faculty,
International FDP on Fundamentals of Research in Social Sciences
at Integral University, Lucknow, 06.06.2024
By Dr. Vinod Kumar Kanvaria
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This presentation was provided by Steph Pollock of The American Psychological Association’s Journals Program, and Damita Snow, of The American Society of Civil Engineers (ASCE), for the initial session of NISO's 2024 Training Series "DEIA in the Scholarly Landscape." Session One: 'Setting Expectations: a DEIA Primer,' was held June 6, 2024.
How to Fix the Import Error in the Odoo 17Celine George
An import error occurs when a program fails to import a module or library, disrupting its execution. In languages like Python, this issue arises when the specified module cannot be found or accessed, hindering the program's functionality. Resolving import errors is crucial for maintaining smooth software operation and uninterrupted development processes.
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
1. The I/O Subsystem
The I/O subsystem allows a process to communicate with peripheral devices such as
disks, tape drives, terminals, printers, and networks, and the kernel modules that control
devices are known as device drivers. Usually, there is a one-to-one correspondence
between device drivers and device types: Systems may contain one disk driver to control
all disk drives, one terminal driver to control all terminals, and so on. Same type of
devices from different manufacturers may have different device drivers. The system
supports "software devices", which have no associated physical device. For example, it
treats physical memory as a device to allow a process access to physical memory
outside its address space, even though memory is not a peripheral device. The kernel
profiler described previously is implemented as a driver.
Driver Interfaces
There are two types of devices, block and raw or character devices. The block devices
such as disks, appear as random access storage devices to the rest of the system.
Character devices include devices such as terminals and network media. Block devices
may have a character device interface too.
The devices are represented by device special files that reside in the file system. A device
special file has its type (block or character) specified in its inode. If a device has both
interfaces, there are two separate files for each interface. System calls such
as open, close, read, and write have appropriate meanings for these device files.
The ioctl system call provides an interface that allows processes to control character
devices, but it is not applicable to regular files. However, each device driver need not
support every system call interface.
System Configuration
System configurations are the parameters provided by administrators that alter the
behavior of the system. Some parameters specify the sizes of kernel tables. Other
parameters specify device configuration, telling the kernel which devices are included in
the installation and their "address".
There are three stages at which device configuration can be specified:
2. It can be hardcoded into files that are compiled and linked when building the
kernel code.
Administrators can supply configuration information when
running; the kernel updates the internal configuration tables dynamically.
Self-identifying devices permit the kernel to recognize which devices are
installed.
The kernel to driver interface is describes by the
the character device switch table
It can be hardcoded into files that are compiled and linked when building the
Administrators can supply configuration information when the system is already
running; the kernel updates the internal configuration tables dynamically.
identifying devices permit the kernel to recognize which devices are
The kernel to driver interface is describes by the block device switch tab
character device switch table, as shown in the figure:
It can be hardcoded into files that are compiled and linked when building the
the system is already
running; the kernel updates the internal configuration tables dynamically.
identifying devices permit the kernel to recognize which devices are
block device switch table and
3. Each device has its entry in one or both the switch tables. The system calls refer to the
switch tables and then invoke the required driver routine, as shown in the diagram
above.
The hardware to driver interface consist
instructions for manipulating devices and interrupt vectors: When a device interrupt
occurs, the system identifies the interrupting device and calls the appropriate interrupt
handler. Obviously, software devi
hardware interface, but other interrupt handlers may call a "software interrupt handler"
directly. For example, the clock interrupt handler calls the kernel profiler interrupt
handler.
Administrators set up device special files with the
(block or character) and major and minor numbers. The
the mknod system call to create the device file. For example:
mknod /dev/tty13 c 2 13
/dev/tty13 is the file name of the device,
(b specifies a block special file), 2 is the major number, and 13 is the minor number. The
major number indicates a device type that corresponds to the appropriate entry in the
block or character device switch tables, and minor number indicates a unit of the device.
Example of the tables is given below:
The entries in the tables describe the routines to be called for respective
The routine nulldev is an "empty" routine, used when there is no need for a particular
Each device has its entry in one or both the switch tables. The system calls refer to the
switch tables and then invoke the required driver routine, as shown in the diagram
The hardware to driver interface consists of machine-dependent control registers or I/O
instructions for manipulating devices and interrupt vectors: When a device interrupt
occurs, the system identifies the interrupting device and calls the appropriate interrupt
handler. Obviously, software devices such as the kernel profile driver do not have a
hardware interface, but other interrupt handlers may call a "software interrupt handler"
directly. For example, the clock interrupt handler calls the kernel profiler interrupt
up device special files with the mknod command, supplying file type
(block or character) and major and minor numbers. The mknod command invokes
system call to create the device file. For example:
is the file name of the device, c specifies that its a character special file
specifies a block special file), 2 is the major number, and 13 is the minor number. The
major number indicates a device type that corresponds to the appropriate entry in the
lock or character device switch tables, and minor number indicates a unit of the device.
Example of the tables is given below:
The entries in the tables describe the routines to be called for respective
is an "empty" routine, used when there is no need for a particular
Each device has its entry in one or both the switch tables. The system calls refer to the
switch tables and then invoke the required driver routine, as shown in the diagram
dependent control registers or I/O
instructions for manipulating devices and interrupt vectors: When a device interrupt
occurs, the system identifies the interrupting device and calls the appropriate interrupt
ces such as the kernel profile driver do not have a
hardware interface, but other interrupt handlers may call a "software interrupt handler"
directly. For example, the clock interrupt handler calls the kernel profiler interrupt
command, supplying file type
command invokes
specifies that its a character special file
specifies a block special file), 2 is the major number, and 13 is the minor number. The
major number indicates a device type that corresponds to the appropriate entry in the
lock or character device switch tables, and minor number indicates a unit of the device.
The entries in the tables describe the routines to be called for respective system calls.
is an "empty" routine, used when there is no need for a particular
4. driver function. Many peripheral devices can be associated with a major number; the
minor number distinguishes them from each other. Device special files do not have to
be created on every boot.
System Calls and the Driver Interface
For system calls that use file descriptors, the kernel follows pointers from user file
descriptor to file table entry and the inode, where it examines the file type and accesses
the block or character device switch table, as appropriate. It extracts the major and
minor number from the inode, uses the major number as an index into the appropriate
table, and calls the driver function according to the system call being made, passing the
minor number as a parameter. An important difference between system calls for devices
and regular files is that the inode of a special file is not locked while the kernel executes
the driver. Drivers frequently sleep, waiting for hardware connections or for the arrival of
data.
The device driver interprets the parameters of the system call as appropriate for the
device. A driver maintains data structures that describe the state of each unit that it
controls; driver functions and interrupt handlers execute according to the state of the
driver and the action being done.
Open
Opening a device file is similar to opening a regular file, in the sense that in-core inode
table, file table entries are made and a user file descriptor is returned. However, device-
specific open procedure is invoked. The algorithm is given below:
/* Algorithm: open
* Input: pathname
* openmode
* Output: file descriptor
*/
{
convert pathname to inode, increment inode reference count,
allocate entry in file table, user file descriptor, as in
open of regular file;
get major, minor number from inode;
save context (algorithm: setjmp) in case of long jump from driver;
if (block device)
{
use major number as index to block device switch table;
call driver open procedure for index:
5. pass minor number, open modes;
}
else
{
use major number as index to character device switch table;
call driver open procedure for index:
pass minor number, open modes;
}
if (open fails in driver)
decrement file table, inode counts;
}
For software devices such as system memory, the open procedure may have to
initialization to do. For the cases where the open call might fail, (for example, if it sleeps
on an event which never occurs) the kernel does a setjmp before invoking the driver
specific routine. And when the call fails, it will restore the previous state by doing
a longjmp and clearing all the structures (user file descriptor, file table entry, inode) it
had allocated.
Close
The driver specific closed is not called for every close operation. It is only called for the
last close call after which no processes are accessing that device. If the driver is not
coded carefully, it can easily loose the count of processes using it. If it sleeps in
a close call and another process opens it, it could easily go out of state. The algorithm is
given below:
/* Algorithm: close
* Input: file descriptor
* Output: none
*/
{
do regular close algorithm;
if (file table reference count not 0)
goto finish;
if (there is another open file and its major, minor numbers are same as
device being closed)
goto finish; // not last close after all
if (character device)
{
use major number to index into character device switch table;
call driver close routine: parameter number;
}
if (block device)
{
if (device mounted)
goto finish;
write device blocks in buffer cache to device;
user major number to index into block device switch table;
6. call driver close routine: parameters minor number;
invalidate device blocks still in buffer cache;
}
finish:
release inode;
}
Considering only inode reference count is not enough to check if any other process is
accessing the device. It is possible to have two different device files for the same file.
Read and Write
If a process is reading or writing a character device, the kernel invokes the device driver
read or write procedure. Although there are important cases where the kernel transmits
data directly between the user address space and the device, device drivers may buffer
data internally. For example, terminal drivers use clists to buffer data (seen later). In such
cases, the device driver copies dat from user space to a buffer during the write, and
outputs the data from the buffer to the device. The driver write procedure throttles the
amount of data being output. If processes generate data faster than the device can
output it, the write procedure puts processes to sleep until the device can accept more
data.
The method in which the driver communicates with a device depends on the hardware.
Some machines provide memory mapped I/O, meaning that certain addresses in the
kernel address space are not locations in physical memory but are special registers that
control particular devices.
Other machines have programmed I/O, meaning that the machine contains instructions
to control devices.
The interface between the device drivers and the underlying hardware is machine
dependent, no standard interfaces exist at this level. For both memory mapped I/O and
programmed I/O, a driver can issue control sequences to a device to set up direct
memory access (DMA) between the device and memory. The system allows bulk DMA
transfer of data between the device and memory in parallel to CPU operations, and the
device interrupts the system when such a transfer has completed. The driver sets up the
virtual memory mapping so that the correct locations in memory are used for DMA.
High-speed devices can sometimes transfer data directly between the device and the
user's address space, without intervention of a kernel buffer. This results in higher
transfer speed because there is one less copy operation in the kernel, and the amount of
data transmitted per transfer operation is not bounded by the size of kernel buffers.
7. Strategy Interface
The kernel uses the strategy interface to transmit data between the buffer cache and a
device. The read and write procedures of the character devices sometimes use their
(block counterpart) strategy procedures to transfer data directly between the device and
the user address space. The kernel passes a buffer header address to the driver strategy
procedure; the header contains a list of (page) addresses and sizes for transmission of
data to or from the device. For the buffer cache, the kernel transmits data from one data
address; when swapping, the kernel transmits data from many data addresses (pages). If
data is being copied to or from the user's address space, the driver must lock the
process (or at least, the relevant pages) in memory until the I/O transfer is complete.
Ioctl
In earlier versions of UNIX system, setty (set terminal settings) and getty (get terminal
settings) were the terminal-specific system calls. ioctl is the generalization of both. It has
a general, catch-all entry point for device specific commands, with which hardware
options for the device and software options for the process can be set. The specific
actions specified by the ioctl call vary per device and are defined by the device driver.
This is an exception to the general rule that the system does not differentiate between
different file types.
ioctl (fd, command, arg);
where fd is the file descriptor returned by a prior open system call, command is a request
of the driver to do a particular action, and arg is a parameter (possibly pointer to a
structure) for the command.
Other File System Related Calls
Calls such as stat and chmod work for devices as they do for regular files; they
manipulate the inode without accessing the driver. lseek also works for devices, for
example, on a tape, the kernel updates the file table offset but does on driver-specific
operation.
Interrupt Handlers
The kernel invokes the device specific interrupt handler, passing it the device number or
other parameters to identify the specific unit that caused the interrupt. Figure shows the
structure of device interrupts:
8. Disk Drivers
The disk driver translates a file system address, consisting of a logical device number
and block number, to a particular se
of two ways: Either the strategy procedure uses a buffer from the buffer pool and the
buffer header contains the device and block number, or the
are passed the logical (minor) d
offset saved in the u-area to the appropriate block address. Finally, it adds the block
number of the file system to the start sector number to identify the sector used for the
I/O transmission.
Because of high disk traffic, the disk driver must maximize the data throughput to get
the best system performance. Most modern disk controllers take care of disk job
scheduling, positioning the disk arm, and transferring data between the disk and the
CPU; otherwise, the disk driver must do these tasks.
Two important programs that deal directly with the disk (bypassing the file system)
are mkfs and fsck.
The disk driver translates a file system address, consisting of a logical device number
and block number, to a particular sector on the disk. The driver gets the address in one
of two ways: Either the strategy procedure uses a buffer from the buffer pool and the
buffer header contains the device and block number, or the read and write
are passed the logical (minor) device number as a parameter; they convert the byte
area to the appropriate block address. Finally, it adds the block
number of the file system to the start sector number to identify the sector used for the
high disk traffic, the disk driver must maximize the data throughput to get
the best system performance. Most modern disk controllers take care of disk job
scheduling, positioning the disk arm, and transferring data between the disk and the
, the disk driver must do these tasks.
Two important programs that deal directly with the disk (bypassing the file system)
The disk driver translates a file system address, consisting of a logical device number
ctor on the disk. The driver gets the address in one
of two ways: Either the strategy procedure uses a buffer from the buffer pool and the
write procedures
evice number as a parameter; they convert the byte
area to the appropriate block address. Finally, it adds the block
number of the file system to the start sector number to identify the sector used for the
high disk traffic, the disk driver must maximize the data throughput to get
the best system performance. Most modern disk controllers take care of disk job
scheduling, positioning the disk arm, and transferring data between the disk and the
Two important programs that deal directly with the disk (bypassing the file system)
9. Terminal Drivers
Terminals are special, because they are the user's interface to the system. Terminal
drivers contain an internal interface to line discipline modules, which interpret input and
output. In canonical mode, the line discipline converts the raw data sequences typed at
the keyboard to a canonical form (what the user really meant) before sending the data
to the receiving process; the line discipline also converts the raw output sequences
written by a process to a format that the user expects. In raw mode, the line discipline
passes data between processes and the terminal without such conversions.
For example, if something is typed at the terminal and then a few characters are erased
and then a few more are typed, the terminal sends the entire sequence to the machine,
including the erase characters. In canonical mode, the line discipline buffers the data
into lines (the sequence of characters until a carriage-return character) and processes
erase characters internally before sending the revised sequence to the reading process.
The functions of a line discipline are:
to parse input strings into lines
to process erase characters
to process a "kill" character that invalidates all characters typed so far on the
current line
to echo (write) received characters to the terminal
to expand output such as tab characters to a sequence of blank spaces
to generate signals to processes for terminal hangups, line breaks, or in response
to a user hitting the delete key
to allow a raw mode that does not interpret special characters such as erase, kill
or carriage return
Although, only terminal uses the line discipline, it could be required by other processes
as well, therefore, the correct place to put it, is in the kernel. The following figure shows
the logical flow of data through the terminal driver and line discipline and the
corresponding flow of control through the terminal driver.
10. Clists
Clist is a short form for character list
variable length linked list of
A cblock contains a pointer to the next
indicating the position of the valid data in the
The start offset indicates the first location of valid data in the array and
indicates the first location of invalid data.
aracter list. Line disciplines manipulate data on
cblocks with a count of number of characters on the list.
contains a pointer to the next cblock, a small character array and a set of offsets
ng the position of the valid data in the cblock. It is shown in the figure:
offset indicates the first location of valid data in the array and
indicates the first location of invalid data.
. Line disciplines manipulate data on clists. It is a
with a count of number of characters on the list.
, a small character array and a set of offsets
. It is shown in the figure:
offset indicates the first location of valid data in the array and end offset
11. The kernel maintains a linked list of free cblocks and has six operations on clists and
cblocks:
1. Assign a cblock from free list to a driver.
2. Return a cblock to the free list.
3. Retrieve the first character from a clist. After retrieval, the character count is
decremented, and if the character is the last character in a cblock, it is returned to
the free list.
4. Place a character onto the end of a clist by finding last free cblock on the clist. If
the last cblock is full, kernel allocates a new cblock.
5. Remove a group of characters from the beginning of a clist one cblock at a time.
6. Place a cblock of characters onto the end of a clist.
Example of removing a character from clist:
15. The Terminal Driver in Canonical Mode
The data structures for terminal drivers have three clists associated with them: a clist to
store data for output to the terminal, a clist to store "raw" input data provided by the
terminal interrupt handler as the user typed it in, and a clist to store "cooked" input
data, after the line discipline converts special characters in the raw clist, such as the
erase and kill characters.
The algorithm terminal_write is given below:
terminal_write
{
while (more data to be copied from user space)
{
if (tty flooded with output data)
{
start write operation to hardware with data on output clist;
sleep (event: tty can accept more data);
continue; // back to while loop
}
copy cblock size of data from user space to output clist:
line discipline converts tab characters, etc;
}
start write operation to hardware with data on output clist;
}
If multiple processes are writing to the terminal, the data could be interleaved on the
terminal.
The algorithm terminal_read is given below:
terminal_read
{
if (no data on canonical clist)
{
while (no data on raw clist)
{
if (tty opened with no delay option)
return;
if (tty in raw mode based on timer and timer not active)
arrange for timer wakeup (callout table);
sleep (event: data arrives from terminal);
}
// there is data on raw clist
if (tty in raw mode)
copy all data from raw clist to canonical clist;
else // tty is in canonical mode
{
while (characters on raw clist)
{
16. copy one character at a time from raw clist to
canonical clist:
do erase, kill processing;
if (char is carriage return or end-of-file)
break;
}
}
}
while (characters on canonical list and read count not satisfied)
copy from cblocks on canonical list to user address space;
}
The case for tty in raw mode based on timer and timer not active is studied below. Rest
of the algorithm is self explanatory.
The Terminal Driver in Raw Mode
When a process sets terminal parameters, it does so for all processes using the terminal.
The terminal settings are not automatically reset when the process that changed the
setting exits.
When processes put the terminal into raw mode, where the line discipline transmits
characters exactly as the user typed them. Still the kernel must know when to satisfy
user read calls, since the carriage return is treated as an ordinary input character. It
satisfies read system calls after a minimum number of characters are input at the
terminal. In the latter case, the kernel times the entry of characters from the terminal by
placing entries into callout table. When the particular criterion is met, the line discipline
interrupt handler awakens all sleeping processes. The driver moves all characters from
the raw clist to the canonical clist and satisfies the process read request, following the
same algorithm as for the canonical case.
Terminal Polling
It is sometimes convenient to poll a device, that is, to read it if there is data present but
to continue regular processing otherwise. It is achieved by opening the terminal with the
"no delay" option, subsequent reads will not sleep if there is no data present but will
return immediately.
The BSD system has a select system call that allows device polling:
select (nfds, rfds, wfds, efds, timeout);
where nfds gives the number of file descriptors being selected,
and rfds, wfds and efds point to bit masks that "select" open file descriptors. That is, the
bit 1 << fd is set if a user wants to select file descriptor. timeout indicates how
long select should sleep, waiting for data to arrive.
17. Establishment of a Control Terminal
The control terminal is the terminal on which a user logs into the system, and it controls
processes that the user initiates from the terminal. When a process opens a terminal, the
terminal driver opens the line discipline. If the process is a process group leader as the
result of a prior setpgrp system call and if the process does not have an associated
control terminal, the line discipline makes the opened terminal the control terminal. it
stores the major and minor device number of the terminal device file in the u-area, and
it stores the process group number of the opening process in the terminal driver data
structure. The opening process is the control process, typically the login shell.
Indirect Terminal Driver
Processes frequently need to read or write data directly to the control terminal, even
though the standard input and output may have been redirected to other files. UNIX
systems provide "indirect" terminal access via the device file "/dev/tty", which designates
the control terminal for every process that has one. Users logged onto separate
terminals can access "/dev/tty", but they access different terminals.
There are two common implementations for the kernel to find the control terminal from
the file name "/dev/tty". First, the kernel can define a special device number for the
indirect terminal file with a special entry in the character device switch table. When
invoking the indirect terminal, the driver for the indirect terminal gets the major and
minor number of the control terminal from the u-area and invokes the real terminal
driver through the character device switch table. The second implementation commonly
used to find the control terminal from the name "/dev/tty" tests if the major number is
that of the indirect terminal before calling the driver open routine. If so, it releases the
inode for "/dev/tty", allocates the inode for the control terminal, resets the file table
entry to point to the control terminal inode, and calls the open routine of the terminal
driver. The file descriptor returned when opening "/dev/tty" refers directly to the control
terminal and its regular driver.
18. Logging In
In multi-user state, a primary responsibility of init is to allow users to log into terminals.
The algorithm login is given below:
login
{
getty process executes;
set process group (setpgrp system call);
open tty line; // sleeps until opened
if (open successful)
{
exec login program;
prompt for user name;
turn off echo, prompt for password;
if (successful)
{
put tty in canonical mode (ioctl);
exec shell;
}
else
count login attempts, try again up to a point;
}
}
It spawns processes called getty and keeps track of which getty process opens which
terminal; each getty process resets its process group using the setpgrp system call. The
invocation of shell (exec shell) in the above algorithm, is called the login shell.
Streams
The scheme for implementation of device drivers, though adequate, suffers from some
drawbacks. Different drivers tend to duplicate functionality, particular drivers that
implement network protocols, which typically include a device-control portion and a
protocol portion. Although the protocol portion should be common for all network
devices, this has not been the case, because the kernel did not provide adequate
mechanisms for common use.
To overcome this, Ritchie developed a scheme called streams to provide greater
modularity and flexibility for the I/O subsystem.
A stream is a full-duplex connection between a process and a device driver. It consists of
a set of linearly linked queue pairs, one member of each pair for input and the other for
output. When a process writes data to a stream, the kernel sends the data down the
output queues; when a device driver receives input data, it sends the data up the input
queues to a reading process. The queues pass messages to neighboring queues
according to a well-defined interface. Each queue pair is associated with an instance of a
19. kernel module, such as a driver, line discipline, or protocol, and the modules manipulate
data passed through its queues.
Each queue is a data structure that contains the following elements:
An open procedure, called during an open system call.
A close procedure, called during a close system call.
A "put" procedure, called to pass a message into the queue.
A "service" procedure, called when a queue is scheduled to execute.
A pointer to the next queue in the stream.
A pointer to a list of messages awaiting service.
A pointer to a private data structure that maintains the state of the queue.
Flags and high- and low-water marks, used for flow control, scheduling, and
maintaining the queue state.
The kernel allocates queue pairs, which are adjacent in memory.
A device with a streams driver is a character device; it has a special field in the character
device switch table that points to a streams initialization structure. When the kernel
executes the open system call and discovers that the device file is character special, it
examines the new field in the character device switch table. If there is no entry there, the
driver is not a streams driver. For the first open of a streams driver, the kernel allocates
two pairs of queues, one for the strem-head and other for the device. The stream-head
module is identical for all instances of open streams: It has generic put and service
procedures and is the interface to higher-level kernel modules that implement
the read, write, and ioctl system calls. The kernel initializes the driver queue structure,
assigning queue pointers and copying addresses of driver routines from a per-driver
initialization structure, and invokes the driver open procedure. The driver open
procedure does the usual initialization but also saves information to recall the queue
with which it is associated. Finally, the kernel assigns a special pointer in the in-core
inode to indicate the stream-head. When another process opens the device, the kernel
finds the previously allocated stream via the inode pointer and invokes the open
procedure of all modules on the stream. A diagram of the structure is given below:
20. Modules communicate by passing messages to neighboring models on a stream. A
message consists of a linked list of message block headers; each block header points to
the start and end location of the block's data. There are two types of messages
and data - identified by a type indicator in the message header. Control message may
result from ioctl system calls or from special conditions, such as a terminal hang
data messages may result from
When a process writes a stream, the kernel copies the data from user space into
message blocks allocated by the stream
procedure of the next queue module, which may process the message, pass it
immediately to the next queue, or enqueue it for later processing. In the latter case, the
module links the message block headers on a linked list, forming a two
The structure is shown in the figure:
Modules communicate by passing messages to neighboring models on a stream. A
message consists of a linked list of message block headers; each block header points to
ion of the block's data. There are two types of messages
identified by a type indicator in the message header. Control message may
system calls or from special conditions, such as a terminal hang
data messages may result from write system calls or the arrival of data from a device.
s a stream, the kernel copies the data from user space into
llocated by the stream-head. The stream-head module invokes the put
procedure of the next queue module, which may process the message, pass it
immediately to the next queue, or enqueue it for later processing. In the latter case, the
ge block headers on a linked list, forming a two-
The structure is shown in the figure:
Modules communicate by passing messages to neighboring models on a stream. A
message consists of a linked list of message block headers; each block header points to
ion of the block's data. There are two types of messages - control
identified by a type indicator in the message header. Control message may
system calls or from special conditions, such as a terminal hang-up, and
system calls or the arrival of data from a device.
s a stream, the kernel copies the data from user space into
head module invokes the put
procedure of the next queue module, which may process the message, pass it
immediately to the next queue, or enqueue it for later processing. In the latter case, the
-way linked list.
21. Then it sets a flag in its queue data structure to indicate that it has data to process, and
schedules itself for servicing. The module places the queue on a linked list of queues
requesting service and invokes a scheduling mechanism; that scheduler calls
procedures of each queue on the list.
The process can "push" modules onto an opened stream by issuing
The kernel inserts the pushed module immediately below the stream head and connects
the queue pointers to keep the structu
stream do not care whether they are communicating with the stream head or with a
pushed module. Example of such structure:
Then it sets a flag in its queue data structure to indicate that it has data to process, and
schedules itself for servicing. The module places the queue on a linked list of queues
requesting service and invokes a scheduling mechanism; that scheduler calls
procedures of each queue on the list.
The process can "push" modules onto an opened stream by issuing ioctl
The kernel inserts the pushed module immediately below the stream head and connects
the queue pointers to keep the structure of the doubly linked list. Lower modules on the
stream do not care whether they are communicating with the stream head or with a
pushed module. Example of such structure:
Then it sets a flag in its queue data structure to indicate that it has data to process, and
schedules itself for servicing. The module places the queue on a linked list of queues
requesting service and invokes a scheduling mechanism; that scheduler calls the service
ioctl system calls.
The kernel inserts the pushed module immediately below the stream head and connects
re of the doubly linked list. Lower modules on the
stream do not care whether they are communicating with the stream head or with a
22. An example of opening a terminal and pushing a line discipline:
fd = open("/dev/ttyxy", O_RDWR);
ioctl(fd, PUSH, TTYLD);
where PUSH is the command name and
discipline module. A process can "pop" the modules off a stream in last
order using another ioctl system call.
ioctl(fd, POP, 0);
An example of opening a terminal and pushing a line discipline:
fd = open("/dev/ttyxy", O_RDWR);
is the command name and TTYLD is a number that identifies the line
discipline module. A process can "pop" the modules off a stream in last
system call.
is a number that identifies the line
discipline module. A process can "pop" the modules off a stream in last-in-first-out
23. A More Detailed Example of Streams
Streams are used in the implementation of
occupies the entire screen, and the user would type a control sequence to
between virtual windows. The figure shows the structure of kernel modules:
The user invokes a process, mpx
terminal line and waits for notification of control events, such as creation of a new
window, switching control to another window, deletion of a window, and so on. When it
receives notification that a user wants to create a new window,
control the new window and communicates with it over a
a software device that operates in pairs: Output directed to one member of the pair is
sent to the input of the other member; input is sent to the up
a window mpx allocates a pty
(the driver open insures that the
new process opens the other member of the
onto its pty stream to convert control messages to data messages, and the child process
pushes a line discipline module its
running on a virtual terminal; to the user, it is indist
The px process is a multiplexer, forwarding output from the virtual terminals to the
physical terminal and demultiplexing input from the physical terminal to the correct
virtual terminal. mpx waits for the arrival of d
When data arrives from the physical terminal,
message, informing it to create a new window or delete an old one, or whether it is a
A More Detailed Example of Streams
Streams are used in the implementation of virtual terminals. Each virtual terminal
occupies the entire screen, and the user would type a control sequence to
between virtual windows. The figure shows the structure of kernel modules:
mpx, to control the physical terminal. mpx read
terminal line and waits for notification of control events, such as creation of a new
window, switching control to another window, deletion of a window, and so on. When it
receives notification that a user wants to create a new window, mpx creates a process to
control the new window and communicates with it over a pseudo-terminal
a software device that operates in pairs: Output directed to one member of the pair is
sent to the input of the other member; input is sent to the upstream module. To set up
pty pair and opens one member, establishing a stream to it
insures that the pty was not previously allocated). mpx
s the other member of the pty pair. mpx pushes a message module
stream to convert control messages to data messages, and the child process
pushes a line discipline module its pty stream before execing the shell. That shell is now
running on a virtual terminal; to the user, it is indistinguishable from a physical terminal.
process is a multiplexer, forwarding output from the virtual terminals to the
physical terminal and demultiplexing input from the physical terminal to the correct
waits for the arrival of data on any line, using the select
When data arrives from the physical terminal, mpx devices whether is is a control
message, informing it to create a new window or delete an old one, or whether it is a
. Each virtual terminal
occupies the entire screen, and the user would type a control sequence to switch
between virtual windows. The figure shows the structure of kernel modules:
reads the physical
terminal line and waits for notification of control events, such as creation of a new
window, switching control to another window, deletion of a window, and so on. When it
reates a process to
terminal (pty). A pty is
a software device that operates in pairs: Output directed to one member of the pair is
stream module. To set up
s one member, establishing a stream to it
mpx forks, and the
hes a message module
stream to convert control messages to data messages, and the child process
ing the shell. That shell is now
inguishable from a physical terminal.
process is a multiplexer, forwarding output from the virtual terminals to the
physical terminal and demultiplexing input from the physical terminal to the correct
select system call.
devices whether is is a control
message, informing it to create a new window or delete an old one, or whether it is a
24. data message to be sent to processes reading a virtual terminal; mpx strips the header
from the message and writes the data to the appropriate pty stream. The pty driver
routes the data through the terminal line discipline to reading processes. The reverse
procedure happens when a process writes the virtual terminal: mpx prepends a header
onto the data, informing the physical terminal which window the data should be printed
to.
If a process issues an ioctl on a virtual terminal, the terminal line discipline sets the
necessary terminal settings for its virtual line; settings may differ for each virtual
terminal. However, some information may have to be sent to the physical terminal,
depending on the device. The message module converts the control messages that are
generated by the ioctl into data messages suitable for reading and writing the mpx, and
these messages are transmitted to the physical device.
The pseudo code is given below:
// assume file descriptors 0 and 1 already refer to physical tty
for (;;)
{
select(input); // wait for some
line with input
read input line;
switch(line with input data)
{
case physical tty: // input on
physical tty line
if (control command) // for eg: create new
window
{
open a free pseudo-tty;
fork a new process;
if (parent)
{
push a msg discipline on mpx side;
continue;
}
// child here
close unnecessary file descriptors;
open other member of pseduo-tty pair, get stdin, stdout,
stderr;
push tty line discipline;
exec shell; // looks
like virtual tty
}
// "regular" data from tty coming up for virtual tty
demultiplex data read from physical tty, strip off headers and write
to appropriate pty;
continue;
25. case logical tty: // a virtual tty
is writing a window
encode header indicating what window data is for;
write header and data to physical tty;
continue;
}
}