Kernel: Add anonymous files, created with sys$anon_create()

This patch adds a new AnonymousFile class which is a File backed by
an AnonymousVMObject that can only be mmap'ed and nothing else, really.

I'm hoping that this can become a replacement for shbufs. :^)

1 files changed, 64 insertions, 0 deletions

diff --git a/Kernel/Syscalls/anon_create.cpp b/Kernel/Syscalls/anon_create.cpp
new file mode 100644
index 0000000000..fcfb268e32
--- /dev/null
+++ b/Kernel/Syscalls/anon_create.cpp
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/FileSystem/AnonymousFile.h>
+#include <Kernel/FileSystem/FileDescription.h>
+#include <Kernel/Process.h>
+#include <Kernel/VM/AnonymousVMObject.h>
+
+namespace Kernel {
+
+int Process::sys$anon_create(size_t size, int options)
+{
+    if (size % PAGE_SIZE)
+        return -EINVAL;
+
+    int new_fd = alloc_fd();
+    if (new_fd < 0)
+        return -new_fd;
+
+    auto vmobject = AnonymousVMObject::create_with_size(size, AllocationStrategy::Reserve);
+    if (!vmobject)
+        return -ENOMEM;
+
+    auto anon_file = AnonymousFile::create(vmobject.release_nonnull());
+    auto description_or_error = FileDescription::create(*anon_file);
+    if (description_or_error.is_error())
+        return description_or_error.error();
+
+    auto description = description_or_error.release_value();
+    description->set_writable(true);
+    description->set_readable(true);
+
+    u32 fd_flags = 0;
+    if (options & O_CLOEXEC)
+        fd_flags |= FD_CLOEXEC;
+
+    m_fds[new_fd].set(move(description), fd_flags);
+    return new_fd;
+}
+
+}