kernel/VFS: Add a way to unmount file systems

kernel/src/fs/VFS.cpp

@@ -150,7 +150,7 @@ namespace VFS
         auto parent_path = TRY(parser.dirname());
         auto child = TRY(parser.basename());
 
-        kdbgln("vfs: mounting filesystem on target %s, parent dir %s", child.chars(), parent_path.chars());
+        kdbgln("vfs: Mounting filesystem on target %s", path);
 
         auto parent_inode = TRY(resolve_path(parent_path.chars(), auth, working_directory));
 
@@ -164,4 +164,26 @@ namespace VFS
 
         return {};
     }
+
+    Result<void> umount(const char* path, Credentials auth, SharedPtr<VFS::Inode> working_directory)
+    {
+        auto parser = TRY(PathParser::create(path));
+        auto parent_path = TRY(parser.dirname());
+        auto child = TRY(parser.basename());
+
+        kdbgln("vfs: Unmounting filesystem on target %s", path);
+
+        auto parent_inode = TRY(resolve_path(parent_path.chars(), auth, working_directory));
+
+        auto inode = TRY(parent_inode->find(child.chars()));
+        if (!inode->is_mountpoint()) return err(EINVAL);
+
+        // There are still open file descriptors referencing files within this file system.
+        if (inode->fs()->handles() != 0) return err(EBUSY);
+
+        auto mount = (MountInode*)inode.ptr();
+        TRY(parent_inode->replace_entry(mount->source(), child.chars()));
+
+        return {};
+    }
 }

kernel/src/fs/VFS.h

@@ -260,4 +260,6 @@ namespace VFS
     Result<void> mount_root(SharedPtr<VFS::FileSystem> fs);
     Result<void> mount(const char* path, SharedPtr<VFS::FileSystem> fs, Credentials auth,
                        SharedPtr<Inode> working_directory = {});
+
+    Result<void> umount(const char* path, Credentials auth, SharedPtr<Inode> working_directory = {});
 }

kernel/src/fs/devices/DeviceRegistry.cpp

@@ -34,6 +34,15 @@ namespace DeviceRegistry
         return err(ENODEV);
     }
 
+    Result<void> create_special_device_inode(DeviceDescriptor& descriptor)
+    {
+        auto inode = TRY(g_device_fs->create_device_inode(descriptor.major, descriptor.minor));
+        inode->chmod(descriptor.mode);
+        TRY(g_device_fs->root_inode()->add_entry(inode, descriptor.name));
+
+        return {};
+    }
+
     Result<void> register_special_device(u32 major, u32 minor, SharedPtr<Device> device, const char* name, mode_t mode)
     {
         for (const auto& descriptor : g_available_devices)
@@ -52,15 +61,6 @@ namespace DeviceRegistry
         return {};
     }
 
-    Result<void> create_special_device_inode(DeviceDescriptor& descriptor)
-    {
-        auto inode = TRY(g_device_fs->create_device_inode(descriptor.major, descriptor.minor));
-        inode->chmod(descriptor.mode);
-        TRY(g_device_fs->root_inode()->add_entry(inode, descriptor.name));
-
-        return {};
-    }
-
     Result<void> init()
     {
         auto device_fs = TRY(TmpFS::FileSystem::create());

kernel/src/thread/Thread.cpp

@@ -66,6 +66,22 @@ Result<SharedPtr<VFS::Inode>> Thread::resolve_atfile(int dirfd, const String& pa
     return VFS::resolve_path(path.chars(), this->auth, descriptor->inode);
 }
 
+FileDescriptor::FileDescriptor(SharedPtr<VFS::Inode> _inode, usize _offset, int _flags)
+    : inode(_inode), offset(_offset), flags(_flags)
+{
+    inode->fs()->add_handle();
+}
+
+FileDescriptor::FileDescriptor(const FileDescriptor& f) : inode(f.inode), offset(f.offset), flags(f.flags)
+{
+    inode->fs()->add_handle();
+}
+
+FileDescriptor::~FileDescriptor()
+{
+    inode->fs()->remove_handle();
+}
+
 bool FileDescriptor::should_append()
 {
     return flags & O_APPEND;

kernel/src/thread/Thread.h

@@ -33,6 +33,10 @@ struct FileDescriptor
     usize offset { 0 };
     int flags { 0 };
 
+    FileDescriptor(SharedPtr<VFS::Inode> inode, usize offset, int flags);
+    FileDescriptor(const FileDescriptor& f);
+    ~FileDescriptor();
+
     bool should_append();
     bool should_block();
     bool is_writable();