Misplaced Pages

#211788

64-521: A server for the LPD protocol listens for requests on TCP port 515. A request begins with a byte containing the request code, followed by the arguments to the request, and is terminated by an ASCII LF character. An LPD printer is identified by the IP address of the server machine and the queue name on that machine. Many different queue names may exist in one LPD server, with each queue having unique settings. Note that

128-442: A UNIX shell script written in a Windows text editor like Notepad ). The concepts of carriage return (CR) and line feed (LF) are closely associated and can be considered either separately or together. In the physical media of typewriters and printers , two axes of motion, "down" and "across", are needed to create a new line on the page . Although the design of a machine (typewriter or printer) must consider them separately,

192-410: A computer or automaton . A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about the hardware being used. A driver communicates with the device through the computer bus or communications subsystem to which the hardware connects. When a calling program invokes

256-618: A message-based protocol for communicating with their devices—as user-mode drivers. If such drivers malfunction, they do not cause system instability. The Kernel-Mode Driver Framework (KMDF) model continues to allow development of kernel-mode device drivers, but attempts to provide standard implementations of functions that are known to cause problems, including cancellation of I/O operations, power management, and plug and play device support. Apple has an open-source framework for developing drivers on macOS , called I/O Kit. In Linux environments, programmers can build device drivers as parts of

320-414: A routine in the driver, the driver issues commands to the device (drives it). Once the device sends data back to the driver, the driver may invoke routines in the original calling program. Drivers are hardware dependent and operating-system-specific. They usually provide the interrupt handling required for any necessary asynchronous time-dependent hardware interface. The main purpose of device drivers

384-510: A "TCP/IP printer" ( TCP/IP is used to establish connections between printers and clients on a network), although that term would be equally applicable to a printer that supports the Internet Printing Protocol . This network -related software article is a stub . You can help Misplaced Pages by expanding it . Newline A newline (frequently called line ending , end of line ( EOL ), next line ( NEL ) or line break )

448-451: A device driver implementing these functions would communicate to the particular serial port controller installed on a user's computer. The commands needed to control a 16550 UART are much different from the commands needed to control an FTDI serial port converter, but each hardware-specific device driver abstracts these details into the same (or similar) software interface. Writing a device driver requires an in-depth understanding of how

512-405: A device driver to translate this character to whatever sequence a printer needed (including extra padding characters ), and the single byte was more convenient for programming. What seems like a more obvious choice— CR —was not used, as CR provided the useful function of overprinting one line with another to create boldface , underscore and strikethrough effects. Perhaps more importantly,

576-483: A file, e.g. some configuration file, encoded using the foreign newline convention, as a valid file. The problem can be hard to spot because some programs handle the foreign newlines properly while others do not. For example, a compiler may fail with obscure syntax errors even though the source file looks correct when displayed on the console or in an editor . Modern text editors generally recognize all flavours of CR + LF newlines and allow users to convert between

640-762: A file. Some languages have created special variables , constants , and subroutines to facilitate newlines during program execution. In some languages such as PHP and Perl , double quotes are required to perform escape substitution for all escape sequences, including '\n' and '\r' . In PHP, to avoid portability problems, newline sequences should be issued using the PHP_EOL constant. Example in C# : The different newline conventions cause text files that have been transferred between systems of different types to be displayed incorrectly. Text in files created with programs which are common on Unix-like or classic Mac OS , appear as

704-434: A full line that automatically add the native newline sequence, and functions for reading lines that accept any of CR , LF , or CR + LF as a line terminator (see BufferedReader.readLine() ). The System.lineSeparator() method can be used to retrieve the underlying line separator. Example: Python permits "Universal Newline Support" when opening a file for reading, when importing modules, and when executing

SECTION 10

#1732869325212

768-438: A line break is required independent of whether the next word would fit on the same line, such as between paragraphs and in vertical lists. Therefore, in the logic of word processing and most text editors , newline is used as a paragraph break and is known as a "hard return", in contrast to "soft returns" which are dynamically created to implement word wrapping and are changeable with each display instance. In many applications

832-408: A newline is considered a separator, there will be no newline after the last line of a file. Some programs have problems processing the last line of a file if it is not terminated by a newline. On the other hand, programs that expect newline to be used as a separator will interpret a final newline as starting a new (empty) line. Conversely, if a newline is considered a terminator, all text lines including

896-414: A separate control character called "manual line break" exists for forcing line breaks inside a single paragraph. The glyph for the control character for a hard return is usually a pilcrow (¶), and for the manual line break is usually a carriage return arrow (↵). RI ( U +008D REVERSE LINE FEED , ISO/IEC 6429 8D, decimal 141) is used to move the printing position back one line (by reverse feeding

960-410: A single character (e.g. LF ), because Unicode is designed to preserve all information when converting a text file from any existing encoding to Unicode and back ( round-trip integrity ), Unicode needs to make the same distinctions between line breaks made by other encodings. For example: NL is part of EBCDIC , which uses code 0x15 ; it is normally mapped to Unicode NEL , 0x85 , which

1024-450: A single long line on most programs common to MS-DOS and Microsoft Windows because these do not display a single line feed or a single carriage return as a line break. Conversely, when viewing a file originating from a Windows computer on a Unix-like system, the extra CR may be displayed as a second line break, as ^M , or as <cr> at the end of each line. Furthermore, programs other than text editors may not accept

1088-437: A target for exploits . Bring Your Own Vulnerable Driver (BYOVD) uses signed, old drivers that contain flaws that allow hackers to insert malicious code into the kernel. Drivers that may be vulnerable include those for WiFi and Bluetooth, gaming/graphics drivers, and drivers for printers. There is a lack of effective kernel vulnerability detection tools, especially for closed-source OSes such as Microsoft Windows where

1152-444: A user-visible character to the reader of the document, and are thus not recognized themselves as a newline. To facilitate creating portable programs, programming languages provide some abstractions to deal with the different types of newline sequences used in different environments. The C language provides the escape sequences '\n' (newline) and '\r' (carriage return). However, these are not required to be equivalent to

1216-513: Is a control character or sequence of control characters in character encoding specifications such as ASCII , EBCDIC , Unicode , etc. This character, or a sequence of characters, is used to signify the end of a line of text and the start of a new one. In the mid-1800s, long before the advent of teleprinters and teletype machines, Morse code operators or telegraphists invented and used Morse code prosigns to encode white space text formatting in formal written text messages. In particular,

1280-541: Is a control character in the C1 control set . As such, it is defined by ECMA 48, and recognized by encodings compliant with ISO/IEC 2022 (which is equivalent to ECMA 35). C1 control set is also compatible with ISO-8859-1 . The approach taken in the Unicode standard allows round-trip transformation to be information-preserving while still enabling applications to recognize all possible types of line terminators. Recognizing and using

1344-455: Is available on virtually every Unix-like system and can be used to perform arbitrary replacement operations on single characters. A DOS/Windows text file can be converted to Unix format by simply removing all ASCII CR characters with or, if the text has only CR newlines, by converting all CR newlines to LF with The same tasks are sometimes performed with awk , sed , or in Perl if

SECTION 20

#1732869325212

1408-563: Is important that the hardware manufacturer provide information on how the device communicates. Although this information can instead be learned by reverse engineering , this is much more difficult with hardware than it is with software. Microsoft has attempted to reduce system instability due to poorly written device drivers by creating a new framework for driver development, called Windows Driver Frameworks (WDF). This includes User-Mode Driver Framework (UMDF) that encourages development of certain types of drivers—primarily those that implement

1472-407: Is improved stability, since a poorly written user-mode device driver cannot crash the system by overwriting kernel memory. Because of the diversity of modern hardware and operating systems, drivers operate in many different environments. Drivers may interface with: Common levels of abstraction for device drivers include: So choosing and installing the correct device drivers for given hardware

1536-472: Is often a key component of computer system configuration. Virtual device drivers represent a particular variant of device drivers. They are used to emulate a hardware device, particularly in virtualization environments, for example when a DOS program is run on a Microsoft Windows computer or when a guest operating system is run on, for example, a Xen host. Instead of enabling the guest operating system to dialog with hardware, virtual device drivers take

1600-504: Is that they can be loaded only when necessary and then unloaded, thus saving kernel memory. Depending on the operating system, device drivers may be permitted to run at various different privilege levels . The choice of which level of privilege the drivers are in is largely decided by the type of kernel an operating system uses. An operating system which uses a monolithic kernel , such as the Linux kernel , will typically run device drivers with

1664-415: Is the use of '\n' when communicating using an Internet protocol that mandates the use of ASCII CR + LF for ending lines. Writing '\n' to a text mode stream works correctly on Windows systems, but produces only LF on Unix, and something completely different on more exotic systems. Using "\r\n" in binary mode is slightly better. Many languages, such as C++ , Perl , and Haskell provide

1728-413: Is to provide abstraction by acting as a translator between a hardware device and the applications or operating systems that use it. Programmers can write higher-level application code independently of whatever specific hardware the end-user is using. For example, a high-level application for interacting with a serial port may simply have two functions for "send data" and "receive data". At a lower level,

1792-400: Is via protection rings . On many systems, such as those with x86 and ARM processors, switching between rings imposes a performance penalty, a factor that operating system developers and embedded software engineers consider when creating drivers for devices which are preferred to be run with low latency, such as network interface cards . The primary benefit of running a driver in user mode

1856-591: The ASCII CR and LF control codes , also provides a "next line" ( NEL ) control code, as well as control codes for "line separator" and "paragraph separator" markers. Unicode also contains printable characters for visually representing line feed ␊, carriage return ␍, and other C0 control codes (as well as a generic newline, ␤) in the Control Pictures block. Many communications protocols have some sort of new line convention. In particular, protocols published by

1920-530: The Internet Engineering Task Force (IETF) typically use the ASCII CRLF sequence. In some older protocols, the new line may be followed by a checksum or parity character. The Unicode standard defines a number of characters that conforming applications should recognize as line terminators: While it may seem overly complicated compared to an approach such as converting all line terminators to

1984-529: The Morse prosign BT (mnemonic break text), represented by the concatenation of literal textual Morse codes "B" and "T" characters, sent without the normal inter-character spacing, is used in Morse code to encode and indicate a new line or new section in a formal text message. Later, in the age of modern teleprinters , standardized character set control codes were developed to aid in white space text formatting. ASCII

Line Printer Daemon protocol - Misplaced Pages Continue

2048-609: The PCI bus or USB is identified by two IDs which consist of two bytes each. The vendor ID identifies the vendor of the device. The device ID identifies a specific device from that manufacturer/vendor. A PCI device has often an ID pair for the main chip of the device, and also a subsystem ID pair that identifies the vendor, which may be different from the chip manufacturer. Computers often have many diverse and customized device drivers running in their operating system (OS) kernel which often contain various bugs and vulnerabilities , making them

2112-525: The kernel , separately as loadable modules , or as user-mode drivers (for certain types of devices where kernel interfaces exist, such as for USB devices). Makedev includes a list of the devices in Linux, including ttyS (terminal), lp ( parallel port ), hd (disk), loop, and sound (these include mixer , sequencer , dsp , and audio). Microsoft Windows .sys files and Linux .ko files can contain loadable device drivers. The advantage of loadable device drivers

2176-571: The ASCII LF and CR control characters. The C standard only guarantees two traits: On Unix operating system platforms, where C originated, the native newline sequence is ASCII LF ( 0x0A ), so '\n' was simply defined to be that value. With the internal and external representation being identical, the translation performed in text mode is a no-op , and Unix has no notion of text mode or binary mode. This has caused many programmers who developed their software on Unix systems simply to ignore

2240-408: The LPD queue name is case sensitive. Some modern implementations of LPD on network printers might ignore the case or queue name altogether and send all jobs to the same printer. Others have the option to automatically create a new queue when a print job with a new queue name is received. This helps to simplify the setup of the LPD server. A printer that supports LPD/LPR is sometimes referred to as

2304-457: The abstract logic of software can combine them together as one event. This is why a newline in character encoding can be defined as CR and LF combined into one (commonly called CR+LF or CRLF ). Some character sets provide a separate newline character code. EBCDIC , for example, provides an NL character code in addition to the CR and LF codes. Unicode , in addition to providing

2368-462: The body". Differences between SMTP implementations in how they treat bare LF and/or bare CR characters have led to SMTP spoofing attacks referred to as "SMTP smuggling". The File Transfer Protocol can automatically convert newlines in files being transferred between systems with different newline representations when the transfer is done in "ASCII mode". However, transferring binary files in this mode usually has disastrous results: any occurrence of

2432-399: The dictated standard, many applications erroneously use the C newline escape sequence '\n' ( LF ) instead of the correct combination of carriage return escape and newline escape sequences '\r\n' ( CR + LF ) (see section Newline in programming languages above). This accidental use of the wrong escape sequences leads to problems when trying to communicate with systems adhering to

2496-402: The different standards. Web browsers are usually also capable of displaying text files and websites which use different types of newlines. Even if a program supports different newline conventions, these features are often not sufficiently labeled, described, or documented. Typically a menu or combo-box enumerating different newline conventions will be displayed to users without an indication if

2560-496: The distinction completely, resulting in code that is not portable to different platforms. The C library function fgets () is best avoided in binary mode because any file not written with the Unix newline convention will be misread. Also, in text mode, any file not written with the system's native newline sequence (such as a file created on a Unix system, then copied to a Windows system) will be misread as well. Another common problem

2624-529: The editor Vim can make a file compatible with the Windows Notepad text editor. Within vim Editors can be unsuitable for converting larger files or bulk conversion of many files. For larger files (on Windows NT) the following command is often used: Special purpose programs to convert files between different newline conventions include unix2dos and dos2unix , mac2unix and unix2mac , mac2dos and dos2mac , and flip . The tr command

Line Printer Daemon protocol - Misplaced Pages Continue

2688-456: The end it is up to users to make sure their files are transferred in the correct mode. If there is any doubt as to the correct mode, binary mode should be used, as then no files will be altered by FTP, though they may display incorrectly. Text editors are often used for converting a text file between different newline formats; most modern editors can read and write files using at least the different ASCII CR / LF conventions. For example,

2752-401: The hardware and the software works for a given platform function. Because drivers require low-level access to hardware functions in order to operate, drivers typically operate in a highly privileged environment and can cause system operational issues if something goes wrong. In contrast, most user-level software on modern operating systems can be stopped without greatly affecting the rest of

2816-427: The last are expected to be terminated by a newline. If the final character sequence in a text file is not a newline, the final line of the file may be considered to be an improper or incomplete text line, or the file may be considered to be improperly truncated. In text intended primarily to be read by humans using software which implements the word wrap feature, a newline character typically only needs to be stored if

2880-453: The needs of Teletype machines. Most minicomputer systems from DEC used this convention. CP/M also used it in order to print on the same terminals that minicomputers used. From there MS-DOS (1981) adopted CP/M 's CR + LF in order to be compatible, and this convention was inherited by Microsoft's later Windows operating system. The Multics operating system began development in 1964 and used LF alone as its newline. Multics used

2944-401: The newline byte sequence—which does not have line terminator semantics in this context, but is just part of a normal sequence of bytes—will be translated to whatever newline representation the other system uses, effectively corrupting the file. FTP clients often employ some heuristics (for example, inspection of filename extensions ) to automatically select either binary or ASCII mode, but in

3008-584: The newline codes greater than 0x7F ( NEL , LS and PS ) is not often done. They are multiple bytes in UTF-8 , and the code for NEL has been used as the ellipsis ( … ) character in Windows-1252 . For instance: The Unicode special characters U+2424 ( SYMBOL FOR NEWLINE , ␤ ), U+23CE ( RETURN SYMBOL , ⏎ ), U+240D ( SYMBOL FOR CARRIAGE RETURN , ␍ ) and U+240A ( SYMBOL FOR LINE FEED , ␊ ) are glyphs intended for presenting

3072-440: The next character. Any character printed after a CR would often print as a smudge in the middle of the page while the print head was still moving the carriage back to the first position. "The solution was to make the newline two characters: CR to move the carriage to column one, and LF to move the paper up." In fact, it was often necessary to send extra padding characters —extraneous CRs or NULs—which are ignored but give

3136-446: The opposite role and emulates a piece of hardware, so that the guest operating system and its drivers running inside a virtual machine can have the illusion of accessing real hardware. Attempts by the guest operating system to access the hardware are routed to the virtual device driver in the host operating system as e.g.,  function calls . The virtual device driver can also send simulated processor-level events like interrupts into

3200-436: The paper, or by moving a display cursor up one line) so that other characters may be printed over existing text. This may be done to make them bolder, or to add underlines, strike-throughs or other characters such as diacritics . Similarly, PLD ( U +008B PARTIAL LINE FORWARD, decimal 139) and PLU ( U +008C PARTIAL LINE BACKWARD, decimal 140) can be used to advance or reverse the text printing position by some fraction of

3264-520: The platform has a Perl interpreter: The file command can identify the type of line endings: The Unix egrep (extended grep) command can be used to print filenames of Unix or DOS files (assuming Unix and DOS-style files only, no classic Mac OS-style files): Other tools permit the user to visualise the EOL characters: Two ways to view newlines, both of which are self-consistent , are that newlines either separate lines or that they terminate lines. If

SECTION 50

#1732869325212

3328-458: The print head time to move to the left margin. Many early video displays also required multiple character times to scroll the display. On such systems, applications had to talk directly to the Teletype machine and follow its conventions since the concept of device drivers hiding such hardware details from the application was not yet well developed. Therefore, text was routinely composed to satisfy

3392-572: The same interpretation of '\n' as C. C++ has an alternative input/output (I/O) model where the manipulator std::endl can be used to output a newline (and flushes the stream buffer). Java , PHP , and Python provide the '\r\n' sequence (for ASCII CR + LF ). In contrast to C, these are guaranteed to represent the values U+000D and U+000A , respectively. The Java input/output (I/O) libraries do not transparently translate these into platform-dependent newline sequences on input or output. Instead, they provide functions for writing

3456-509: The same privilege as all other kernel objects. By contrast, a system designed around microkernel , such as Minix , will place drivers as processes independent from the kernel but that use it for essential input-output functionalities and to pass messages between user programs and each other. On Windows NT , a system with a hybrid kernel , it is common for device drivers to run in either kernel-mode or user-mode . The most common mechanism for segregating memory into various privilege levels

3520-467: The selection will re-interpret, temporarily convert, or permanently convert the newlines. Some programs will implicitly convert on open, copy, paste, or save—often inconsistently. Most textual Internet protocols (including HTTP , SMTP , FTP , IRC , and many others) mandate the use of ASCII CR + LF ( '\r\n' , 0x0D 0x0A ) on the protocol level, but recommend that tolerant applications recognize lone LF ( '\n' , 0x0A ) as well. Despite

3584-452: The source code of the device drivers is mostly not public (open source) and drivers often have many privileges. A group of security researchers considers the lack of isolation as one of the main factors undermining kernel security , and published an isolation framework to protect operating system kernels, primarily the monolithic Linux kernel whose drivers they say get ~80,000 commits per year. An important consideration in

3648-415: The stricter interpretation of the standards instead of the suggested tolerant interpretation. One such intolerant system is the qmail mail transfer agent that actively refuses to accept messages from systems that send bare LF instead of the required CR + LF . The standard Internet Message Format for email states: "CR and LF MUST only occur together as CRLF; they MUST NOT appear independently in

3712-441: The system. Even drivers executing in user mode can crash a system if the device is erroneously programmed . These factors make it more difficult and dangerous to diagnose problems. The task of writing drivers thus usually falls to software engineers or computer engineers who work for hardware-development companies. This is because they have better information than most outsiders about the design of their hardware. Moreover, it

3776-468: The use of LF alone as a line terminator had already been incorporated into drafts of the eventual ISO/IEC 646 standard. Unix followed the Multics practice, and later Unix-like systems followed Unix. This created conflicts between Windows and Unix-like operating systems , whereby files composed on one operating system could not be properly formatted or interpreted by another operating system (for example

3840-410: The vertical line spacing (typically, half). These can be used in combination for subscripts (by advancing and then reversing) and superscripts (by reversing and then advancing), and may also be useful for printing diacritics. Device driver In the context of an operating system , a device driver is a computer program that operates or controls a particular type of device that is attached to

3904-451: The virtual machine. Virtual devices may also operate in a non-virtualized environment. For example, a virtual network adapter is used with a virtual private network , while a virtual disk device is used with iSCSI . A good example for virtual device drivers can be Daemon Tools . There are several variants of virtual device drivers, such as VxDs , VLMs , and VDDs. Solaris descriptions of commonly used device drivers: A device on

SECTION 60

#1732869325212

3968-403: Was commonly used on many early computer systems that had adopted Teletype machines—typically a Teletype Model 33 ASR—as a console device, because this sequence was required to position those printers at the start of a new line. The separation of newline into two functions concealed the fact that the print head could not return from the far right to the beginning of the next line in time to print

4032-679: Was developed simultaneously by the International Organization for Standardization (ISO) and the American Standards Association (ASA), the latter being the predecessor organization to American National Standards Institute (ANSI). During the period of 1963 to 1968, the ISO draft standards supported the use of either CR + LF or LF alone as a newline, while the ASA drafts supported only CR + LF . The sequence CR + LF

4096-619: Was traditionally considered in the hardware manufacturer 's interest to guarantee that their clients can use their hardware in an optimal way. Typically, the Logical Device Driver (LDD) is written by the operating system vendor, while the Physical Device Driver (PDD) is implemented by the device vendor. However, in recent years, non-vendors have written numerous device drivers for proprietary devices, mainly for use with free and open source operating systems . In such cases, it

#211788