kernel: Remove FileDescriptorTable and add a helper to resolve fds to FileDescriptors

kernel/src/sys/file.cpp

@@ -15,17 +15,13 @@ Result<u64> sys_read(Registers*, SyscallArgs args)
 
     if (!MemoryManager::validate_user_write(buf, size)) return err(EFAULT);
 
-    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
-
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+    auto& descriptor = *TRY(current->resolve_fd(fd));
 
-    if (!descriptor.has_value()) return err(EBADF);
+    usize nread = TRY(descriptor.inode->read(buf, descriptor.offset, size));
 
-    usize nread = TRY(descriptor->inode->read(buf, descriptor->offset, size));
+    descriptor.offset += nread;
-
-    descriptor->offset += nread;
 
     return nread;
 }
@@ -38,17 +34,13 @@ Result<u64> sys_write(Registers*, SyscallArgs args)
 
     if (!MemoryManager::validate_user_read(buf, size)) return err(EFAULT);
 
-    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
-
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+    auto& descriptor = *TRY(current->resolve_fd(fd));
 
-    if (!descriptor.has_value()) return err(EBADF);
+    usize nwritten = TRY(descriptor.inode->write(buf, descriptor.offset, size));
 
-    usize nwritten = TRY(descriptor->inode->write(buf, descriptor->offset, size));
+    descriptor.offset += nwritten;
-
-    descriptor->offset += nwritten;
 
     return nwritten;
 }
@@ -59,27 +51,23 @@ Result<u64> sys_lseek(Registers*, SyscallArgs args)
     off_t offset = (long)args[1];
     int whence = (int)args[2];
 
-    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
-
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+    auto& descriptor = *TRY(current->resolve_fd(fd));
-
-    if (!descriptor.has_value()) return err(EBADF);
 
     off_t new_offset;
 
     switch (whence)
     {
     case SEEK_SET: new_offset = offset; break;
-    case SEEK_CUR: new_offset = TRY(safe_add((long)descriptor->offset, offset)); break;
+    case SEEK_CUR: new_offset = TRY(safe_add((long)descriptor.offset, offset)); break;
     case SEEK_END: todo();
     default: return err(EINVAL);
     }
 
     if (new_offset < 0) return err(EINVAL);
 
-    descriptor->offset = (usize)new_offset;
+    descriptor.offset = (usize)new_offset;
 
     return (u64)new_offset;
 }

kernel/src/sys/open.cpp

@@ -20,7 +20,7 @@ Result<u64> sys_open(Registers*, SyscallArgs args)
 
     int fd = TRY(current->allocate_fd(0));
 
-    current->fd_table->fds[fd] = FileDescriptor { inode, 0, flags };
+    current->fd_table[fd] = FileDescriptor { inode, 0, flags };
 
     kinfoln("open: allocated file descriptor %d for inode %zu", fd, inode->inode_number());
 
@@ -34,7 +34,7 @@ Result<u64> sys_close(Registers*, SyscallArgs args)
 
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+    Option<FileDescriptor>& descriptor = current->fd_table[fd];
 
     if (!descriptor.has_value()) return err(EBADF);
 

kernel/src/thread/Scheduler.cpp

@@ -151,8 +151,6 @@ namespace Scheduler
         guard.deactivate();
         directory_guard.deactivate();
 
-        thread->fd_table = FileDescriptorTable {};
-
         kinfoln("Created userspace thread: id %lu with ip %#.16lx and sp %#.16lx (ksp %#lx)", thread->id, thread->ip(),
                 thread->sp(), thread->kernel_stack.top());
 

kernel/src/thread/Thread.cpp

@@ -27,8 +27,19 @@ Result<int> Thread::allocate_fd(int min)
     {
         // FIXME: Possible race condition if multiple threads share a FileDescriptorTable? Let's not worry about it for
         // now, we're still a long way away from reaching that point.
-        if (!fd_table->fds[i].has_value()) { return i; }
+        if (!fd_table[i].has_value()) { return i; }
     }
 
     return err(EMFILE);
 }
+
+Result<FileDescriptor*> Thread::resolve_fd(int fd)
+{
+    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
+
+    Option<FileDescriptor>& maybe_descriptor = fd_table[fd];
+
+    if (!maybe_descriptor.has_value()) return err(EBADF);
+
+    return maybe_descriptor.value_ptr();
+}

kernel/src/thread/Thread.h

@@ -31,11 +31,6 @@ struct FileDescriptor
 
 static constexpr int FD_MAX = 64;
 
-struct FileDescriptorTable
-{
-    Option<FileDescriptor> fds[FD_MAX] = {};
-};
-
 struct Thread : public LinkedListNode<Thread>
 {
     Registers regs;
@@ -53,9 +48,10 @@ struct Thread : public LinkedListNode<Thread>
     Stack kernel_stack;
 
     OwnedPtr<UserVM> vm_allocator;
-    Option<FileDescriptorTable> fd_table;
+    Option<FileDescriptor> fd_table[FD_MAX] = {};
 
     Result<int> allocate_fd(int min);
+    Result<FileDescriptor*> resolve_fd(int fd);
 
     FPData fp_data;
 

libluna/include/luna/Option.h

@@ -116,6 +116,18 @@ template <typename T> class Option
         return &m_storage.fetch_reference();
     }
 
+    T& operator*()
+    {
+        expect(has_value(), "Option::operator* called on an empty Option");
+        return m_storage.fetch_reference();
+    }
+
+    T* value_ptr(SourceLocation caller = SourceLocation::current())
+    {
+        expect_at(has_value(), caller, "Option::value_ptr called on an empty Option");
+        return &m_storage.fetch_reference();
+    }
+
     ~Option()
     {
         if (has_value()) m_storage.destroy();