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. :^)

Kernel/API/Syscall.h

@@ -198,7 +198,8 @@ namespace Kernel {
     S(prctl)                  \
     S(mremap)                 \
     S(set_coredump_metadata)  \
-    S(abort)
+    S(abort)                  \
+    S(anon_create)
 
 namespace Syscall {
 

Kernel/CMakeLists.txt

@@ -47,6 +47,7 @@ set(KERNEL_SOURCES
     Storage/PATADiskDevice.cpp
     Storage/StorageManagement.cpp
     DoubleBuffer.cpp
+    FileSystem/AnonymousFile.cpp
     FileSystem/BlockBasedFileSystem.cpp
     FileSystem/Custody.cpp
     FileSystem/DevFS.cpp
@@ -103,6 +104,7 @@ set(KERNEL_SOURCES
     SharedBuffer.cpp
     StdLib.cpp
     Syscall.cpp
+    Syscalls/anon_create.cpp
     Syscalls/abort.cpp
     Syscalls/access.cpp
     Syscalls/alarm.cpp

Kernel/FileSystem/AnonymousFile.cpp

@@ -0,0 +1,57 @@
+/*
+ * 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/Process.h>
+#include <Kernel/VM/AnonymousVMObject.h>
+
+namespace Kernel {
+
+AnonymousFile::AnonymousFile(NonnullRefPtr<AnonymousVMObject> vmobject)
+    : m_vmobject(move(vmobject))
+{
+}
+
+AnonymousFile::~AnonymousFile()
+{
+}
+
+KResultOr<Region*> AnonymousFile::mmap(Process& process, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot, bool shared)
+{
+    if (offset != 0)
+        return KResult(-EINVAL);
+
+    if (size != m_vmobject->size())
+        return KResult(-EINVAL);
+
+    auto* region = process.allocate_region_with_vmobject(preferred_vaddr, size, m_vmobject, offset, {}, prot, shared);
+    if (!region)
+        return KResult(-ENOMEM);
+
+    return region;
+}
+
+}

Kernel/FileSystem/AnonymousFile.h

@@ -0,0 +1,57 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <Kernel/FileSystem/File.h>
+
+namespace Kernel {
+
+class AnonymousFile final : public File {
+public:
+    static NonnullRefPtr<AnonymousFile> create(NonnullRefPtr<AnonymousVMObject> vmobject)
+    {
+        return adopt(*new AnonymousFile(move(vmobject)));
+    }
+
+    virtual ~AnonymousFile() override;
+
+    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot, bool shared) override;
+
+private:
+    virtual const char* class_name() const override { return "AnonymousFile"; }
+    virtual String absolute_path(const FileDescription&) const override { return ":anonymous-file:"; }
+    virtual bool can_read(const FileDescription&, size_t) const override { return false; }
+    virtual bool can_write(const FileDescription&, size_t) const override { return false; }
+    virtual KResultOr<size_t> read(FileDescription&, size_t, UserOrKernelBuffer&, size_t) override { return KResult(-ENOTSUP); }
+    virtual KResultOr<size_t> write(FileDescription&, size_t, const UserOrKernelBuffer&, size_t) override { return KResult(-ENOTSUP); }
+
+    explicit AnonymousFile(NonnullRefPtr<AnonymousVMObject>);
+
+    NonnullRefPtr<AnonymousVMObject> m_vmobject;
+};
+
+}

Kernel/Process.h

@@ -368,6 +368,7 @@ public:
     int sys$prctl(int option, FlatPtr arg1, FlatPtr arg2);
     int sys$set_coredump_metadata(Userspace<const Syscall::SC_set_coredump_metadata_params*>);
     void sys$abort();
+    int sys$anon_create(size_t, int options);
 
     template<bool sockname, typename Params>
     int get_sock_or_peer_name(const Params&);

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;
+}
+
+}

Userland/Libraries/LibC/serenity.cpp

@@ -136,4 +136,10 @@ int get_stack_bounds(uintptr_t* user_stack_base, size_t* user_stack_size)
     int rc = syscall(SC_get_stack_bounds, user_stack_base, user_stack_size);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
+
+int anon_create(size_t size, int options)
+{
+    int rc = syscall(SC_anon_create, size, options);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
 }

Userland/Libraries/LibC/serenity.h

@@ -73,6 +73,8 @@ int perf_event(int type, uintptr_t arg1, uintptr_t arg2);
 
 int get_stack_bounds(uintptr_t* user_stack_base, size_t* user_stack_size);
 
+int anon_create(size_t size, int options);
+
 #ifdef __i386__
 ALWAYS_INLINE void send_secret_data_to_userspace_emulator(uintptr_t data1, uintptr_t data2, uintptr_t data3)
 {