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Organization of the file system

In other systems (Multics) entire body of files and directories as a single tree. The very system you search files by name, starting with the roots, demanded the installation of the necessary discs. In the Unix OS to be several archives files, each in their section, which is considered one of the root. After starting the system can "mount" a root file system, and a number of separate file systems in a common file system. Technically, this is done through institutions in the root file system of special empty directories (see also the next chapter). Special systemic challenge to "mount" UNIX OS allows connecting to one of these empty directories root directory specified archive files. After mounting a common file system for naming files produced in the same manner as if it had been from the very beginning centralized. The task OS is a free passage mount point in gaining access to the file through a chain of names. Given that usually mount the file system is subject detail system, the UNIX operating system, users and usually not thinking about the common origin of the source file system. Operation over directories Just as in the case files, the system is obliged to provide a set of user operations required for working with directories, sold through the system calls. Despite the fact that the directory is a file, the logic of working with them is different from the logic of working with a regular file, and determine the nature of these objects, designed to maintain the structure file archive. The combination of system calls for the management of the directory depends on the specific features of the OS. Consider the example of some OS Unix system calls. Create. Creating a directory. The newly created directory includes recordings with the names'. ''..', And it is considered empty. Delete. Removing a directory. Removal can be only an empty directory. Opendir. Opening a directory for later reading. For example, to list the files that are included in the directory should open a directory and take the names of all the files that it includes. Closedir. Closing the directory after its release reading for places in the interior of system tables. Readdir. This challenge to the system returns the contents of the current account in an open directory. Generally speaking, for these purposes can be used Read systemic challenge, but in this case the programmer will need knowledge of the internal structure of the directory. Readdir returns the contents of records in a standard format, regardless of the directory structure used. Rename. Directory names can be changed, as well as the names of files. Link. Tying-technology, which allows information about the file appear in more than one directory. This system connects the call to an existing file with the absolute name directory, using them as parameters. Through Call Link can be traced to a file at once with multiple directories. Unlink. Deleting records on file from the directory. If you want to delete a file is present in only one directory, it is generally removed from the file system, otherwise the system is limited only by removing the spetsifitsiruemoy record.
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