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Unfortunately, generic sanity checks are often not enough. You immediately run into problems where very file-specific concepts (owner, RWX permissions) aren't sufficient to handle certain types of represented-as-files objects (such as procfs files, where privileges with regard to a process aren't accurately described through Unix DAC permissions).

And then you get into some of the really hairy issues -- any user can trick a privileged program into writing or reading from any file by simply spawning a setuid program with stdio set to the file they wish to operate on. Thus, any interface which is administrative is simply unsafe to expose through the standard open/read/write interfaces -- which means that you have to come up with some alternative interface anyway.

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