libc: close all open FDs on exit

This is important to issue sync requests for written-to files.

As the closing must be performed by an atexit handler, it happens at a
time _after_ libc plugins are destructed. Consequently an FD allocated
by such a plugin results in a close error, which in turn, does not
destruct the FD. We ultimatedly end up in an infinte loop of
re-attempting the close. For this reason, the patch changes 'close' to
be robust against this special case.

This is generally not a problem because libc plugins are phased out.
However, at present, the libc_noux plugin is still important. With the
changed 'close' in place, there occurred an error message "Error: close:
close not implemented" at the exit of each noux program. This patch
removes the error printing from the libc plugin mechansim to avoid this
noise. The error messages are not important anyway because the
deprecation of the libc plugin interface.

Issue #3578

repos/libports/include/libc-plugin/fd_alloc.h

@@ -112,6 +112,12 @@ namespace Libc {
 			 */
 			File_descriptor *any_cloexec_libc_fd();
 
+			/**
+			 * Return file-descriptor ID of any open file, or -1 if no file is
+			 * open
+			 */
+			int any_open_fd();
+
 			void generate_info(Genode::Xml_generator &);
 	};
 

repos/libports/src/lib/libc/exit.cc

@@ -14,6 +14,9 @@
 #include <base/env.h>
 #include <base/sleep.h>
 
+/* libc-internal includes */
+#include <internal/types.h>
+
 extern void genode_exit(int status) __attribute__((noreturn));
 
 extern "C" void _exit(int status)
@@ -31,6 +34,8 @@ extern "C" {
 
 	void exit(int status)
 	{
+		using namespace Libc;
+
 		if (__cleanup)
 			(*__cleanup)();
 

repos/libports/src/lib/libc/fd_alloc.cc

@@ -125,6 +125,18 @@ File_descriptor *File_descriptor_allocator::any_cloexec_libc_fd()
 }
 
 
+int File_descriptor_allocator::any_open_fd()
+{
+	Lock::Guard guard(_lock);
+
+	int result = -1;
+	_id_space.apply_any<File_descriptor>([&] (File_descriptor &fd) {
+	 	result = fd.libc_fd; });
+
+	return result;
+}
+
+
 void File_descriptor_allocator::generate_info(Xml_generator &xml)
 {
 	Lock::Guard guard(_lock);

repos/libports/src/lib/libc/file_operations.cc

@@ -234,9 +234,14 @@ extern "C" int chdir(const char *path)
 __SYS_(int, close, (int libc_fd),
 {
 	File_descriptor *fd = file_descriptor_allocator()->find_by_libc_fd(libc_fd);
-	return (!fd || !fd->plugin)
-		? Errno(EBADF)
-		: fd->plugin->close(fd);
+
+	if (!fd)
+		return Errno(EBADF);
+
+	if (!fd->plugin || fd->plugin->close(fd) != 0)
+		file_descriptor_allocator()->free(fd);
+
+	return 0;
 })
 
 

repos/libports/src/lib/libc/kernel.cc

@@ -359,10 +359,23 @@ void Libc::execute_in_application_context(Application_code &app_code)
 }
 
 
+static void close_file_descriptors_on_exit()
+{
+	for (;;) {
+		int const fd = Libc::file_descriptor_allocator()->any_open_fd();
+		if (fd == -1)
+			break;
+		close(fd);
+	}
+}
+
+
 Libc::Kernel::Kernel(Genode::Env &env, Genode::Allocator &heap)
 :
 	_env(env), _heap(heap)
 {
+	atexit(close_file_descriptors_on_exit);
+
 	init_pthread_support(env, *this, *this);
 
 	_env.ep().register_io_progress_handler(*this);

repos/libports/src/lib/libc/plugin.cc

@@ -155,7 +155,6 @@ bool Plugin::supports_mmap()
 #define DUMMY(ret_type, ret_val, name, args) \
 ret_type Plugin::name args \
 { \
-	error(__func__, ": " #name " not implemented"); \
 	return ret_val; \
 }