3. Opening a file

• One of the most important operations when accessing data is opening a file with the system call open.
• The system not only has to make the appropriate preparations to ensure access to data without problems, but also has to check the authorizations for the process.
• After finding the file, the open_namei() function then performs a number of tests, such as
• if the file is a directory and if the process is seeking write permission, the function returns error,
• if access to devices has been prohibited and if the file is a device fie, return error,
• if the file is not a device file and if if the process is attempting to gain write access to a read-only file system, error.
• ...
• If the file survives all of those tests, the operation do_open() and open() takes care of the actions specific to the file type
• If no error is returned by any of those open functions, the file has been successfully opened.

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