[PATCH] libc++: Add option to disable access to the global filesystem namespace

Ed Schouten ed at nuxi.nl
Tue Mar 10 04:03:12 PDT 2015

Hi jroelofs,

Systems like FreeBSD's Capsicum and Nuxi CloudABI apply the concept of capability-based security on the way processes can interact with the filesystem API. It is no longer to interact with the VFS through calls like open(), unlink(), rename(), etc. Instead, processes are only allowed to interact with files and directories to which they have been granted access. The *at() functions can be used for this purpose.

This change adds a new config switch called _LIBCPP_HAS_GLOBAL_FILESYSTEM_NAMESPACE. If not set, all functionality that requires the global filesystem namespace will be disabled. More concretely:

- fstream's open() function will be removed.
- cstdio will no longer pull in fopen(), rename(), etc.
- The test suite's get_temp_file_name() will be removed. This will cause all tests that use the global filesystem namespace to break, but will at least make all the other tests run (as get_temp_file_name will not build anyway).

It is important to mention that this change will make fstream rather useless on those systems for now. Still, I'd rather not have fstream disabled entirely, as it is of course possible to come up with an extension for fstream that would allow access to local filesystem namespaces (e.g., by adding an openat() member function).




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