kernel: Allow performing extra actions when opening an inode

kernel/src/fs/VFS.h

@@ -118,6 +118,11 @@ namespace VFS
             return err(EACCES);
         }
 
+        virtual Result<SharedPtr<Inode>> open()
+        {
+            return SharedPtr<Inode> { this };
+        }
+
         // Directory-specific methods
         virtual Result<SharedPtr<Inode>> find(const char* name) const = 0;
 

kernel/src/sys/open.cpp

@@ -62,6 +62,8 @@ Result<u64> sys_openat(Registers*, SyscallArgs args)
         if ((flags & O_WRONLY) && !VFS::can_write(inode, current->auth)) return err(EACCES);
     }
 
+    inode = TRY(inode->open());
+
     // This should only be possible if O_NOFOLLOW was in flags.
     if (inode->type() == VFS::InodeType::Symlink) return err(ELOOP);