VFS: Support writing to files

kernel/include/fs/FileDescriptor.h

@@ -14,14 +14,20 @@ struct Descriptor
         return m_can_read && m_is_open;
     }
 
+    bool can_write()
+    {
+        return m_can_write && m_is_open;
+    }
+
     void close()
     {
         m_is_open = false;
     }
 
     ssize_t read(size_t size, char* buffer);
+    ssize_t write(size_t size, const char* buffer);
 
-    void open(VFS::Node* node, bool can_read);
+    void open(VFS::Node* node, bool can_read, bool can_write);
 
     Descriptor(const Descriptor& other);
     Descriptor();
@@ -29,6 +35,7 @@ struct Descriptor
   private:
     bool m_is_open;
     bool m_can_read;
+    bool m_can_write;
     VFS::Node* m_node;
     uint64_t m_offset;
 };

kernel/include/fs/VFS.h

@@ -14,6 +14,7 @@ namespace VFS
     struct Node;
 
     typedef ssize_t (*node_read)(Node*, size_t, size_t, char*);
+    typedef ssize_t (*node_write)(Node*, size_t, size_t, const char*);
     typedef Node* (*node_finddir)(Node*, const char*);
     typedef int (*node_mkdir)(Node*, const char*);
 
@@ -27,10 +28,12 @@ namespace VFS
         node_read read_func;
         node_finddir find_func;
         node_mkdir mkdir_func;
+        node_write write_func;
         Node* link;
     };
 
     ssize_t read(Node* node, size_t offset, size_t length, char* buffer);
+    ssize_t write(Node* node, size_t offset, size_t length, const char* buffer);
     int mkdir(const char* path, const char* name); // FIXME: Support deducing this via a single path.
 
     void mount_root(Node* root);

kernel/src/fs/FileDescriptor.cpp

@@ -5,13 +5,15 @@ Descriptor::Descriptor() : m_is_open(false)
 }
 
 Descriptor::Descriptor(const Descriptor& other)
-    : m_is_open(other.m_is_open), m_can_read(other.m_can_read), m_node(other.m_node), m_offset(other.m_offset)
+    : m_is_open(other.m_is_open), m_can_read(other.m_can_read), m_can_write(other.m_can_write), m_node(other.m_node),
+      m_offset(other.m_offset)
 {
 }
 
-void Descriptor::open(VFS::Node* node, bool can_read)
+void Descriptor::open(VFS::Node* node, bool can_read, bool can_write)
 {
     m_can_read = can_read;
+    m_can_write = can_write;
     m_node = node;
     m_offset = 0;
     m_is_open = true;
@@ -23,3 +25,10 @@ ssize_t Descriptor::read(size_t size, char* buffer)
     m_offset += result;
     return result;
 }
+
+ssize_t Descriptor::write(size_t size, const char* buffer)
+{
+    ssize_t result = VFS::write(m_node, m_offset, size, buffer);
+    m_offset += result;
+    return result;
+}

kernel/src/fs/VFS.cpp

@@ -26,12 +26,30 @@ ssize_t VFS::read(Node* node, size_t offset, size_t length, char* buffer)
         return -1;
     }
 
-    kdbgln("read(): node %s (inode %ld), offset %zd, %zd bytes, into %p", node->name, node->inode, offset, length,
-           (void*)buffer);
-
     return node->read_func(node, offset, length, buffer);
 }
 
+ssize_t VFS::write(Node* node, size_t offset, size_t length, const char* buffer)
+{
+    if (!node)
+    {
+        kwarnln("write() failed: trying to write to nullptr");
+        return -1;
+    }
+    if (node->type == VFS_DIRECTORY)
+    {
+        kwarnln("write() failed: is a directory");
+        return -EISDIR;
+    }
+    if (!node->write_func)
+    {
+        kwarnln("write() failed: the chosen node doesn't support writing");
+        return -1;
+    }
+
+    return node->write_func(node, offset, length, buffer);
+}
+
 void VFS::mount_root(Node* root)
 {
     if (!root)
@@ -92,15 +110,12 @@ VFS::Node* VFS::resolve_path(const char* filename, Node* root)
             }
             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);