lx_fs: support for unlink

This is based on the work of @ehmry and @sidhussmann.

Issue #4070

repos/base-linux/run/lx_fs.run

@@ -51,9 +51,10 @@ install_config {
 }
 
 #
-# Create test-directory structure
+# Create test-directory structure and ensure it is empty
 #
 
+exec rm -rf bin/libc_vfs
 exec mkdir -p bin/libc_vfs
 
 #

repos/libports/src/test/libc_vfs/main.cc

@@ -119,10 +119,10 @@ static void test(Genode::Xml_node node)
 	for (unsigned int i = 0; i < iterations; i++) {
 
 		/* create directory given with a trailing slash */
-		CALL_AND_CHECK(ret, mkdir(trailing_slash_dir_name, 0777), (ret == 0), "dir_name=%s", dir_name);
+		CALL_AND_CHECK(ret, mkdir(trailing_slash_dir_name, 0777), (ret == 0), "dir_name=%s", trailing_slash_dir_name);
 
 		/* remove directory given with a trailing slash */
-		CALL_AND_CHECK(ret, rmdir(trailing_slash_dir_name), (ret == 0), "dir_name=%s", dir_name);
+		CALL_AND_CHECK(ret, rmdir(trailing_slash_dir_name), (ret == 0), "dir_name=%s", trailing_slash_dir_name);
 
 		/* create directory (short name) */
 		CALL_AND_CHECK(ret, mkdir(dir_name, 0777), ((ret == 0) || (errno == EEXIST)), "dir_name=%s", dir_name);

repos/os/src/server/lx_fs/directory.h

@@ -2,6 +2,8 @@
  * \brief  File-system directory node
  * \author Norman Feske
  * \author Christian Helmuth
+ * \author Emery Hemingway
+ * \author Sid Hussmann
  * \date   2013-11-11
  */
 
@@ -19,13 +21,14 @@
 #include <file_system/util.h>
 #include <os/path.h>
 
-/* local includes */
-#include <node.h>
-#include <file.h>
-
-#include <lx_util.h>
+/* libc includes */
 #include <stdio.h>
 
+/* local includes */
+#include "file.h"
+#include "lx_util.h"
+#include "node.h"
+
 
 namespace Lx_fs {
 	using namespace Genode;
@@ -44,8 +47,6 @@ class Lx_fs::Directory : public Node
 		Directory(Directory const &);
 		Directory &operator = (Directory const &);
 
-		typedef Genode::Path<MAX_PATH_LEN> Path;
-
 		DIR       *_fd;
 		Path       _path;
 		Allocator &_alloc;
@@ -261,6 +262,11 @@ class Lx_fs::Directory : public Node
 				.modification_time = { st.st_mtime }
 			};
 		}
+
+		Path path() const override
+		{
+			return _path;
+		}
 };
 
 #endif /* _DIRECTORY_H_ */

repos/os/src/server/lx_fs/lx_util.h

@@ -1,22 +1,33 @@
 /*
  * \brief  Linux utilities
  * \author Christian Helmuth
+ * \author Pirmin Duss
  * \date   2013-11-11
  */
 
+/*
+ * Copyright (C) 2013-2020 Genode Labs GmbH
+ * Copyright (C) 2020 gapfruit AG
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
 #ifndef _LX_UTIL_H_
 #define _LX_UTIL_H_
 
 /* Genode includes */
 #include <file_system_session/file_system_session.h>
+#include <util/string.h>
 
 /* Linux includes */
 #define _FILE_OFFSET_BITS 64
-#include <errno.h>
-#include <unistd.h>
-#include <fcntl.h>
 #include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
 #include <sys/stat.h>
+#include <unistd.h>
 
 
 namespace File_system {
@@ -24,6 +35,24 @@ namespace File_system {
 }
 
 
+namespace Lx_fs {
+
+	using namespace Genode;
+
+	using Path_string = Genode::String<File_system::MAX_PATH_LEN>;
+
+	/*
+	 * Calculate the absolute path that the root of a File_system session is
+	 * located at.
+	 *
+	 * @param  root_path  root path specified in the policy of a File_system
+	 *                    session.
+	 *
+	 */
+	Path_string absolute_root_directory(char const *root_path);
+}
+
+
 int File_system::access_mode(File_system::Mode const &mode)
 {
 	switch (mode) {
@@ -36,4 +65,18 @@ int File_system::access_mode(File_system::Mode const &mode)
 	return O_RDONLY;
 }
 
-#endif
+
+Lx_fs::Path_string Lx_fs::absolute_root_directory(char const *root_path)
+{
+	char cwd[PATH_MAX];
+	char real_path[PATH_MAX];
+
+	getcwd(cwd, PATH_MAX);
+
+	realpath(Path_string { cwd, "/", root_path }.string(), real_path);
+
+	return Path_string { real_path };
+}
+
+
+#endif  /* _LX_UTIL_H_ */

repos/os/src/server/lx_fs/main.cc

@@ -1,28 +1,34 @@
 /*
- * \brief  RAM file system
+ * \brief  Linux host file system
  * \author Norman Feske
+ * \author Emery Hemingway
+ * \author Sid Hussmann
+ * \author Pirmin Duss
  * \date   2012-04-11
  */
 
 /*
- * Copyright (C) 2012-2017 Genode Labs GmbH
+ * Copyright (C) 2013-2020 Genode Labs GmbH
+ * Copyright (C) 2020 gapfruit AG
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
  */
 
 /* Genode includes */
+#include <base/attached_rom_dataspace.h>
 #include <base/component.h>
 #include <base/heap.h>
-#include <base/attached_rom_dataspace.h>
-#include <root/component.h>
 #include <file_system_session/rpc_object.h>
 #include <os/session_policy.h>
+#include <root/component.h>
 #include <util/xml_node.h>
 
 /* local includes */
-#include <directory.h>
-#include <open_node.h>
+#include "directory.h"
+#include "node.h"
+#include "open_node.h"
+
 
 namespace Lx_fs {
 
@@ -47,6 +53,7 @@ class Lx_fs::Session_component : public Session_rpc_object
 		Directory                   &_root;
 		Id_space<File_system::Node>  _open_node_registry { };
 		bool                         _writable;
+		Absolute_path const          _root_dir;
 
 		Signal_handler<Session_component> _process_packet_dispatcher;
 
@@ -88,8 +95,6 @@ class Lx_fs::Session_component : public Session_rpc_object
 
 					/* File system session can't handle partial writes */
 					if (res_length != length) {
-						Genode::error("partial write detected ",
-						              res_length, " vs ", length);
 						/* don't acknowledge */
 						return;
 					}
@@ -206,6 +211,7 @@ class Lx_fs::Session_component : public Session_rpc_object
 			_md_alloc(md_alloc),
 			_root(*new (&_md_alloc) Directory(_md_alloc, root_dir, false)),
 			_writable(writable),
+			_root_dir(root_dir),
 			_process_packet_dispatcher(env.ep(), *this, &Session_component::_process_packets)
 		{
 			/*
@@ -263,6 +269,9 @@ class Lx_fs::Session_component : public Session_rpc_object
 
 		Symlink_handle symlink(Dir_handle, Name const &, bool /* create */) override
 		{
+			/*
+			 * We do not support symbolic links for security reasons.
+			 */
 			Genode::error(__func__, " not implemented");
 			throw Permission_denied();
 		}
@@ -337,9 +346,59 @@ class Lx_fs::Session_component : public Session_rpc_object
 			Genode::error(__func__, " not implemented");
 		}
 
-		void unlink(Dir_handle, Name const &) override
+		void unlink(Dir_handle dir_handle, Name const &name) override
 		{
-			Genode::error(__func__, " not implemented");
+			if (!valid_name(name.string()))
+				throw Invalid_name();
+
+			if (!_writable)
+				throw Permission_denied();
+
+			auto unlink_fn = [&] (Open_node &open_node) {
+
+				Absolute_path absolute_path("/");
+
+				try {
+					absolute_path.append(open_node.node().path().string());
+					absolute_path.append("/");
+					absolute_path.append(name.string());
+				} catch (Path_base::Path_too_long const &) {
+					Genode::error("Path too long. path=", absolute_path);
+					throw Invalid_name();
+				}
+
+				char const *path_str = absolute_path.string();
+				_assert_valid_path(path_str);
+
+				/* skip leading '/' */
+				path_str++;
+
+				struct stat s;
+				int ret = lstat(path_str, &s);
+				if (ret == -1) {
+					throw Lookup_failed();
+				}
+
+				if (S_ISDIR(s.st_mode)) {
+					ret = rmdir(path_str);
+				} else if (S_ISREG(s.st_mode) || S_ISLNK(s.st_mode)) {
+					ret = ::unlink(path_str);
+				} else {
+					throw Lookup_failed();
+				}
+
+				if (ret == -1) {
+					auto err = errno;
+					if (err == EACCES)
+						throw Permission_denied();
+				}
+			};
+
+			try {
+				_open_node_registry.apply<Open_node>(dir_handle, unlink_fn);
+			} catch (Id_space<File_system::Node>::Unknown_id const &) {
+				throw Invalid_handle();
+			}
 		}
 
 		void truncate(File_handle file_handle, file_size_t size) override

repos/os/src/server/lx_fs/node.h

@@ -2,11 +2,15 @@
  * \brief  File-system node
  * \author Norman Feske
  * \author Christian Helmuth
+ * \author Emery Hemingway
+ * \author Sid Hussmann
+ * \author Pirmin Duss
  * \date   2013-11-11
  */
 
 /*
- * Copyright (C) 2013-2017 Genode Labs GmbH
+ * Copyright (C) 2013-2020 Genode Labs GmbH
+ * Copyright (C) 2020 gapfruit AG
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -20,7 +24,13 @@
 
 
 namespace Lx_fs {
+
 	using namespace File_system;
+
+	enum { MAX_ABSOLUTE_PATH_LEN = 2048 };
+
+	using Absolute_path = Genode::Path<MAX_ABSOLUTE_PATH_LEN>;
+
 	class Node;
 	class File;
 }
@@ -29,6 +39,7 @@ class Lx_fs::Node : public File_system::Node_base
 {
 	public:
 
+		using Path = Genode::Path<MAX_PATH_LEN>;
 		typedef char Name[128];
 
 	private:
@@ -38,10 +49,14 @@ class Lx_fs::Node : public File_system::Node_base
 
 	public:
 
-		Node(unsigned long inode) : _inode(inode) { _name[0] = 0; }
+		Node(unsigned long inode)
+		: _inode { inode }
+		{
+			_name[0] = 0;
+		}
 
-		unsigned long inode() const { return _inode; }
-		char   const *name()  const { return _name; }
+		unsigned long  inode()     const { return _inode; }
+		char   const  *name()      const { return _name; }
 
 		/**
 		 * Assign name
@@ -73,6 +88,8 @@ class Lx_fs::Node : public File_system::Node_base
 			Genode::error(__PRETTY_FUNCTION__, " called on a non-directory node");
 			return nullptr;
 		}
+
+		virtual Path path() const  { return Path { }; }
 };
 
 #endif /* _NODE_H_ */

repos/os/src/server/lx_fs/symlink.h

@@ -2,13 +2,17 @@
  * \brief  Symlink file-system node
  * \author Norman Feske
  * \author Christian Helmuth
+ * \author Emery Hemingway
+ * \author Sid Hussmann
+ * \author Pirmin Duss
  * \date   2013-11-11
  *
  * FIXME unfinished
  */
 
 /*
- * Copyright (C) 2013-2017 Genode Labs GmbH
+ * Copyright (C) 2013-2020 Genode Labs GmbH
+ * Copyright (C) 2020 gapfruit AG
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -18,16 +22,16 @@
 #define _SYMLINK_H_
 
 /* local includes */
-#include <node.h>
-#include <lx_util.h>
+#include "node.h"
+#include "lx_util.h"
 
 
-namespace File_system {
+namespace Lx_fs {
 	class Symlink;
 }
 
 
-class File_system::Symlink : public Node
+class Lx_fs::Symlink : public Node
 {
 	private:
 
@@ -37,11 +41,16 @@ class File_system::Symlink : public Node
 
 	public:
 
-		Symlink(char const *name) { Node::name(name); }
-
-		size_t read(char *dst, size_t len, seek_off_t seek_offset) override
+		Symlink(char const *name)
+		:
+			Node { 0 }
 		{
-			size_t count = min(len, sizeof(_link_to) + 1);
+			Node::name(basename(name));
+		}
+
+		size_t read(char *dst, size_t len, seek_off_t /*seek_offset*/) override
+		{
+			size_t count = min(len, _length());
 			Genode::copy_cstring(dst, _link_to, count);
 			return count;
 		}
@@ -51,7 +60,7 @@ class File_system::Symlink : public Node
 			/* Ideal symlink operations are atomic. */
 			if (seek_offset) return 0;
 
-			size_t count = min(len, sizeof(_link_to) + 1);
+			size_t count = min(len, _length());
 			Genode::copy_cstring(_link_to, src, count);
 			return count;
 		}