Add option to disable access to the global filesystem namespace.

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 possible 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_NO_GLOBAL_FILESYSTEM_NAMESPACE. If 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).

Differential revision:	http://reviews.llvm.org/D8194
Reviewed by:		jroelofs (thanks!)


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@232049 91177308-0d34-0410-b5e6-96231b3b80d8

include/fstream

@@ -206,8 +206,10 @@ public:
 
     // 27.9.1.4 Members:
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     basic_filebuf* open(const char* __s, ios_base::openmode __mode);
     basic_filebuf* open(const string& __s, ios_base::openmode __mode);
+#endif
     basic_filebuf* close();
 
 protected:
@@ -463,6 +465,7 @@ basic_filebuf<_CharT, _Traits>::is_open() const
     return __file_ != 0;
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 basic_filebuf<_CharT, _Traits>*
 basic_filebuf<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -550,6 +553,7 @@ basic_filebuf<_CharT, _Traits>::open(const string& __s, ios_base::openmode __mod
 {
     return open(__s.c_str(), __mode);
 }
+#endif
 
 template <class _CharT, class _Traits>
 basic_filebuf<_CharT, _Traits>*
@@ -1005,8 +1009,10 @@ public:
     typedef typename traits_type::off_type off_type;
 
     basic_ifstream();
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     explicit basic_ifstream(const char* __s, ios_base::openmode __mode = ios_base::in);
     explicit basic_ifstream(const string& __s, ios_base::openmode __mode = ios_base::in);
+#endif
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
     basic_ifstream(basic_ifstream&& __rhs);
 #endif
@@ -1018,8 +1024,10 @@ public:
 
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::in);
     void open(const string& __s, ios_base::openmode __mode = ios_base::in);
+#endif
     void close();
 
 private:
@@ -1033,6 +1041,7 @@ basic_ifstream<_CharT, _Traits>::basic_ifstream()
 {
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
 basic_ifstream<_CharT, _Traits>::basic_ifstream(const char* __s, ios_base::openmode __mode)
@@ -1050,6 +1059,7 @@ basic_ifstream<_CharT, _Traits>::basic_ifstream(const string& __s, ios_base::ope
     if (__sb_.open(__s, __mode | ios_base::in) == 0)
         this->setstate(ios_base::failbit);
 }
+#endif
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
@@ -1107,6 +1117,7 @@ basic_ifstream<_CharT, _Traits>::is_open() const
     return __sb_.is_open();
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 void
 basic_ifstream<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -1126,6 +1137,7 @@ basic_ifstream<_CharT, _Traits>::open(const string& __s, ios_base::openmode __mo
     else
         this->setstate(ios_base::failbit);
 }
+#endif
 
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
@@ -1163,8 +1175,10 @@ public:
 
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::out);
     void open(const string& __s, ios_base::openmode __mode = ios_base::out);
+#endif
     void close();
 
 private:
@@ -1178,6 +1192,7 @@ basic_ofstream<_CharT, _Traits>::basic_ofstream()
 {
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
 basic_ofstream<_CharT, _Traits>::basic_ofstream(const char* __s, ios_base::openmode __mode)
@@ -1195,6 +1210,7 @@ basic_ofstream<_CharT, _Traits>::basic_ofstream(const string& __s, ios_base::ope
     if (__sb_.open(__s, __mode | ios_base::out) == 0)
         this->setstate(ios_base::failbit);
 }
+#endif
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
@@ -1252,6 +1268,7 @@ basic_ofstream<_CharT, _Traits>::is_open() const
     return __sb_.is_open();
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 void
 basic_ofstream<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -1271,6 +1288,7 @@ basic_ofstream<_CharT, _Traits>::open(const string& __s, ios_base::openmode __mo
     else
         this->setstate(ios_base::failbit);
 }
+#endif
 
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
@@ -1295,8 +1313,10 @@ public:
     typedef typename traits_type::off_type off_type;
 
     basic_fstream();
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     explicit basic_fstream(const char* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
     explicit basic_fstream(const string& __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
+#endif
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
     basic_fstream(basic_fstream&& __rhs);
 #endif
@@ -1308,8 +1328,10 @@ public:
 
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
     void open(const string& __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
+#endif
     void close();
 
 private:
@@ -1323,6 +1345,7 @@ basic_fstream<_CharT, _Traits>::basic_fstream()
 {
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
 basic_fstream<_CharT, _Traits>::basic_fstream(const char* __s, ios_base::openmode __mode)
@@ -1340,6 +1363,7 @@ basic_fstream<_CharT, _Traits>::basic_fstream(const string& __s, ios_base::openm
     if (__sb_.open(__s, __mode) == 0)
         this->setstate(ios_base::failbit);
 }
+#endif
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
@@ -1397,6 +1421,7 @@ basic_fstream<_CharT, _Traits>::is_open() const
     return __sb_.is_open();
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 void
 basic_fstream<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -1416,6 +1441,7 @@ basic_fstream<_CharT, _Traits>::open(const string& __s, ios_base::openmode __mod
     else
         this->setstate(ios_base::failbit);
 }
+#endif
 
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY