VFS: Add basic mount(), unmount() and mkdir() functions (not accessible to userspace yet)

kernel/include/fs/VFS.h

@@ -7,12 +7,15 @@ typedef long ssize_t;
 #define VFS_FILE 0x0
 #define VFS_DIRECTORY 0x1
 
+#define VFS_MOUNTPOINT 0x1
+
 namespace VFS
 {
     struct Node;
 
     typedef ssize_t (*node_read)(Node*, size_t, size_t, char*);
     typedef Node* (*node_finddir)(Node*, const char*);
+    typedef int (*node_mkdir)(Node*, const char*);
 
     struct Node
     {
@@ -20,15 +23,23 @@ namespace VFS
         uint64_t inode;
         uint64_t length;
         int type;
+        int flags;
         node_read read_func;
         node_finddir find_func;
+        node_mkdir mkdir_func;
+        Node* link;
     };
 
     ssize_t read(Node* node, size_t offset, size_t length, char* buffer);
+    int mkdir(const char* path, const char* name);
 
     void mount_root(Node* root);
 
     Node* resolve_path(const char* filename, Node* root = nullptr);
 
+    void mount(Node* mountpoint, Node* mounted);
+
+    void unmount(Node* mountpoint);
+
     Node* root();
 }

kernel/src/fs/VFS.cpp

@@ -90,10 +90,53 @@ VFS::Node* VFS::resolve_path(const char* filename, Node* root)
                 kwarnln("Current node did not find our target node");
                 return 0;
             }
+            if (child->flags & VFS_MOUNTPOINT)
+            {
+                kdbgln("Current node (%s, inode=%ld) is a mountpoint, resolving actual node", child->name,
+                       child->inode);
+                if (!child->link)
+                {
+                    kwarnln("Current node's link is null");
+                    return 0;
+                }
+                child = child->link;
+                kdbgln("Resolved to %s (inode %ld)", child->name, child->inode);
+            }
             current_node = child;
             kfree(buffer);
         }
 
         filename += path_section_size;
     }
+}
+
+int VFS::mkdir(const char* path, const char* name)
+{
+    Node* node = resolve_path(path, vfs_root);
+    if (!node)
+    {
+        kwarnln("Attempting to mkdir in %s, which does not exist", path);
+        return -1;
+    }
+    if (!node->mkdir_func)
+    {
+        kwarnln("Chosen node does not support mkdir()");
+        return -1;
+    }
+    return node->mkdir_func(node, name);
+}
+
+void VFS::mount(Node* mountpoint, Node* mounted)
+{
+    if (!mountpoint || !mounted) return;
+    if (mountpoint->flags & VFS_MOUNTPOINT || mounted->flags & VFS_MOUNTPOINT) return;
+    mountpoint->link = mounted;
+    mountpoint->flags |= VFS_MOUNTPOINT;
+}
+
+void VFS::unmount(Node* mountpoint)
+{
+    if (!mountpoint) return;
+    if (!(mountpoint->flags & VFS_MOUNTPOINT)) return;
+    mountpoint->flags &= ~VFS_MOUNTPOINT;
 }

kernel/src/init/InitRD.cpp

@@ -185,6 +185,46 @@ VFS::Node* initrd_scan_dir(VFS::Node* node, const char* filename)
     return 0;
 }
 
+int initrd_mkdir(VFS::Node* node, const char* name) // FIXME: Return proper error numbers.
+{
+    if (total_dirs >= 32)
+    {
+        kwarnln("mkdir() failed: too many directories");
+        return -1;
+    }
+    if (node->inode > total_dirs)
+    {
+        kwarnln("mkdir() failed: invalid node");
+        return -1;
+    }
+    if (!(node->type & VFS_DIRECTORY))
+    {
+        kwarnln("mkdir() failed: not a directory");
+        return -1;
+    }
+    InitRD::Directory& parent = dirs[node->inode];
+    if (parent.entries == INITRD_MAX_FILES_IN_DIR)
+    {
+        kwarnln("mkdir() failed: parent is null");
+        return -1;
+    }
+    uint64_t inode = total_dirs;
+    VFS::Node& new_node = nodes[total_nodes++];
+    new_node.inode = inode;
+    new_node.find_func = initrd_scan_dir;
+    new_node.mkdir_func = initrd_mkdir;
+    new_node.length = 0;
+    new_node.type = VFS_DIRECTORY;
+    strncpy(new_node.name, name, sizeof(new_node.name));
+    InitRD::Directory dir;
+    strncpy(dir.name, name, sizeof(dir.name));
+    dir.entries = 0;
+    dirs[total_dirs++] = dir; // FIXME: Right now this isn't of worry, but there is a possibility for a TOCTOU bug here.
+                              // Should use a spinlock or something.
+    parent.files[parent.entries++] = &new_node;
+    return 0;
+}
+
 static bool initrd_register_dir(InitRD::Directory& dir, uint64_t inode)
 {
     const char* filename = dir.name;
@@ -318,11 +358,13 @@ static void initrd_initialize_root()
 {
     initrd_root.length = 0;
     initrd_root.inode = 0;
+    initrd_root.type |= VFS_DIRECTORY;
     InitRD::Directory& root = dirs[0];
     total_dirs++;
     strncpy(initrd_root.name, "initrd", sizeof(initrd_root.name));
     strncpy(root.name, "initrd", sizeof(root.name));
     initrd_root.find_func = initrd_scan_dir;
+    initrd_root.mkdir_func = initrd_mkdir;
 }
 
 void InitRD::init()

kernel/src/main.cpp

@@ -164,12 +164,11 @@ extern "C" void _start()
 
     kinfoln("Trying VFS");
 
-    VFS::Node* node = VFS::resolve_path("/sys/");
+    if (VFS::mkdir("/", "rootfs") < 0) { kerrorln("Unable to create directory rootfs"); }
-    if (!node) { kerrorln("Unable to find /sys in VFS"); }
     else
     {
-        kinfoln("Found '%s'", node->name);
+        VFS::mount(VFS::resolve_path("/rootfs"), VFS::root());
-        node = VFS::resolve_path("config", node);
+        VFS::Node* node = VFS::resolve_path("/rootfs/sys/config");
         if (!node) kerrorln("unable to find /sys/config in VFS");
         else
         {