linux file sysytem& input and output

linux file sysytem& input and output

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  FILESYSTEM& INPUTANDOUTPUT Presented By Mythili A LINUX
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  FILE SYSTEM INTRODUCTION Linux filesystem is generally a built-in layer of a Linux operating system used to handle the data management of the storage. Ithelps to arrangethe file on the disk storage. It manages the file name, file size, creation date, and much more information about a file. The Linux file systemcontains the following sections: 1. The root directory (/) 2. A specific data storageformat(EXT3, EXT4, BTRFS, XFS and so on) 3. A partition or logical volume having a particular file system. LINUXFILESYSTEMFEATURES Specifying paths: Linux does not use the backslash () to separate the components; it uses forward slash (/) as an alternative. For example, as in Windows, the data may be stored in C: My DocumentsWork, whereas, in Linux, it would be stored in /home/ My Document/ Work. Partition, Directories, and Drives: Linux does not usedrive letters to organize the drive as Windows does. In Linux, we cannot tell whether we are addressing a partition, a network device, or an "ordinary" directory and a Drive. Case Sensitivity: Linux file system is case sensitive. It distinguishes between lowercaseand uppercasefile names. Such as,there is a differencebetween test.txt and Test.txt in Linux. This rule is also applied for directories and Linux commands.
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  File Extensions: InLinux, a file may have the extension '.txt,' but it is not necessary that a file should have a file extension. While working with Shell, it creates some problems for the beginners to differentiate between files and directories. If weuse the graphical file manager, it symbolizes thefiles and folders. Hidden files: Linux distinguishes between standard files and hidden files, mostly the configuration files are hidden in Linux OS. Usually, we don't need to access or read the hidden files. The hidden files in Linux are represented by a dot (.) before the file name (e.g., .ignore). To access the files, we need to change the view in the file manager or need to usea specific command in the shell. ROOT(/) DIRECTORY
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  The / inthe instruction aboverefers to the rootdirectory. The rootdirectory is the one fromwhich all other directories branch off from. When you run tree and tell it to start with /, you will see the whole directory tree, all directories and all the subdirectories in the whole system. stay in your terminal window and run tree like this tree -L 1 /
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  TYPESOFFILESYSTEM Ext, Ext2, Ext3and Ext4 file system The file systemExt stands for Extended File System. Itwas primarily developed for MINIXOS.TheExt file systemis an older version,and is no longer used dueto some limitations. Ext: an old one and no longer used due to limitations. Ext2: the firstLinux file systemthat allows managing two terabytes of data. Ext3: developed through Ext2; it is an upgraded version of Ext2 and contains backward compatibility. The major drawback of Ext3 is that it does not support servers becausethis file systemdoes not supportfile recovery and disk snapshot.
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  Ext4: file systemisthe faster file systemamong all the Ext file systems. Itis a very compatible option for the SSD (solid-state drive) disks, and it is the default file systemin Linux distribution. JFS File System JFS stands for Journaled File System, and it is developed by IBM for AIX Unix. It is an alternative to the Ext file system. It can also be used in place of Ext4, where stability is needed with few resources. Itis a handy file systemwhen CPU power is limited. ReiserFS File System ReiserFS is an alternative to the Ext3 file system. Ithas improved performanceand advanced features. In the earlier time, the ReiserFS was used as the default file system in SUSE Linux, but later it has changed some policies, so SUSE returned to Ext3. This file system dynamically supports the file extension, but it has some drawbacks in performance. XFS File System XFS file system was considered as high-speed JFS, which is developed for parallel I/O processing. NASA still using this file system with its high storage server (300+ Terabyte server). Btrfs File System Btrfs stands for the B tree file system. Itis used for fault tolerance, repair system, fun administration, extensive storageconfiguration, and more. Itis not a good suit for the production system.
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  Swap File System Theswap file system is used for memory paging in Linux operating systemduring the systemhibernation. A systemthat never goes in hibernate state is required to have swap spaceequal to its RAM size.
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  INPUT AND OUTPUT INTRODUCTION Tothe user, the I/O systemin Linux looks much like that in any UNIX system. That is, to the extent possible, all device drivers appear as normal files. A user can open an access channelto a device in the sameway sheopens any other file-devices can appear as objects within the file system. The system administrator can create special files within a file systemthat contain references to a specific device driver, and a user opening such a file will be able to read from and write to the device referenced. By using the normal file-protection system, which determines who can access which file, the administrator can set access permissions for each device. STRUCTURE Linux splits all devices into three classes: block devices, character devices, and network devices. Fig 1. Device-Driver Block Structure
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  BLOCK DEVICE Block devicesprovide the main interface to all disk devices in a system or bloc devices allow random access, read only blocks of data and fixed sized blocks of data. Examples: Hard Disk, Floppy Disk, C D ROM and Flash Memory. The work of request manager in block devices and separate list of requests kept for each block device. The request is maintaining in sorted order of increasing starting sector number when a request is accept for processing by a block device driver, it’s not removed from the list. It is removed after only the input output is complete. In the block device there are two problems that may occurs 1. STARVATION: - may be caused by error in a scheduling of work. 2. DEADLINES: - for read request is 0.5 sec and for writing request is 5 sec. Block device also maintains three queues a) Sorted queue b) Read queue c) Write queue
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  CHARACTER DEVICES All characterdevices deal with data one character at a time and process them sequentially or serially only. Examples: The Keyboard, Mouse or Touchpad and Printers, Etc., Any character- device drivers registered to the Linux kernel must also register a set of functional that implement the file I/O operations that the driver can handle. The kernel performs almost no pre-processing of a file read or write request to the device in question and lets the device deal with request. (printers are character devices and after the kernel sends data to the printer, the responsibility for that data passes to the printer the kernel cannot backup and re-examine the data). The exception to this rule is the special subset of character device drivers that implement terminal devices. The kernel maintains a standard interface to these drivers by means of a set of tty_struct structures. Each of these structures provide buffering and flow control on the data stream from the terminal device and feeds those data to a line discipline. A line discipline is an interpreter for the information from the terminal device. the most common line discipline is the tty discipline.
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  tty discipline decideswhich process’s data should be attached or detached from the terminal device. NETWORKSTRUCTUREDEVICES These are deal differently from block and character devices Users cannot directly transfer data to network devices; instead, they must communicate indirectly by opening a connection to the kernel’s networking sub-system. Networking in Linux kernel is implemented by three layers of drivers 1. The socket interfaces 2. Protocol drivers 3. Network device drivers The Socket Interfaces User applications perform all networking requests through the socket interface. It looks like BSD socket layer, so that the program designed for BSD socket can easily run-on Linux without any source code changes. BSD socket is sufficient to represent network addresses for networking protocols. Protocol Devices
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  It is thesecond layer of software. When data arrives to this layer, it is expected to have been tagged with an identifier specifying which network protocol they contain. Functions of protocol layer a) Rewrite packets b) Create new packets c) Split or reassembling packets into fragments d) Discard data Network-device drivers Communication between the layers of networking stack is performed by passing single skbuff structures. An skbuff is a set of pointers into a single continuous area of memory, representing a buffer inside which network packets can be constructed. The networking code either add or trim data from the end of packet.