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Organization of the file system

Examples resolve conflicts and deadlocks The logic of the system is running in difficult situations it may illustrate multidostupa particular organization. Consider the example of education, with a potential deadlock Education Communications (link) with joint access to the file Two process while performing the following functions: A process: link (a / b / c / d, e / f / g); process B: link ( "e / f", "a / b / c / d / ee"); can you go to a standstill. Suppose that the A index file found "a / b / c / d" at the very moment when the index file found B "e / f". The phrase "at the same time" means that the system reached a state in which each received the desired code. When A process now try to obtain an index file "e / f", it would suspend its implementation until the index file "f" is not free. At the same time, the process of trying to obtain B index directory "a / b / c / d" and suspended pending the release of the index file "d ". A process will retain blocked index, the desired process B, and process B, in turn, will retain blocked index, the desired process of A. To prevent this classic example of mutual locking in the file system taken to the kernel source file index released after increasing importance meter connections. Then, as the first of resources (index), with free treatment to the next resource, mutual blocking is not the case. Reasons for unwanted competition between the processes of a lot, especially when deleting names of directories. Suppose that a process of trying to find a data file for a symbolic its full name, consistently passing component for component, and another process removes the directory whose name is the path search. For example, A makes the process of reviewing the "a / b / c / d" and suspended at the time of receipt of the index file to the node "c". He may pause while trying to block a site index, or when trying to appeal to the disk block, where the index node is stored. If you want to remove the link B for a directory named "c", it can stop for the same reason that the process of A. Let kernel later decide to renew the process before the process of B A. Before A process will continue to execute the process B will end by removing the link directory "c" and the contents of this communication. Later, the A try to appeal to the non-existent index node, which has already been removed. Search Algorithm file verifier primarily inequality meter ties zero value to report the error. There are other examples that demonstrate the need for careful design of the file system to follow its reliable operation. The reliability of the file system. Life is full of unpleasant surprises, and the destruction of the file system often more dangerous than the destruction of the computer. It is therefore necessary to take special measures to preserve the structure of the file system on the disk. In addition to the obvious solutions, such as the duplication of timely information (backup)
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