LibCore+LibIPC: Add Core::AnonymousBuffer, an IPC-friendly buffer class

This will be used to migrate remaining clients off of shbufs.

Userland/Libraries/LibCore/AnonymousBuffer.cpp

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+/*
+ * 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 <LibCore/AnonymousBuffer.h>
+#include <LibIPC/Decoder.h>
+#include <LibIPC/Encoder.h>
+#include <LibIPC/File.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/mman.h>
+
+#if defined(__serenity__)
+#    include <Kernel/API/Syscall.h>
+#    include <serenity.h>
+#endif
+
+namespace Core {
+
+AnonymousBuffer AnonymousBuffer::create_with_size(size_t size)
+{
+    int fd = -1;
+#if defined(__serenity__)
+    fd = anon_create(round_up_to_power_of_two(size, PAGE_SIZE), O_CLOEXEC);
+    if (fd < 0) {
+        perror("anon_create");
+        return {};
+    }
+#elif defined(__linux__)
+    fd = memfd_create("", MFD_CLOEXEC);
+    if (fd < 0) {
+        perror("memfd_create");
+        return {};
+    }
+    if (ftruncate(fd, size) < 0) {
+        perror("ftruncate");
+        return {};
+    }
+#endif
+    if (fd < 0)
+        return {};
+    return create_from_anon_fd(fd, size);
+}
+
+RefPtr<AnonymousBufferImpl> AnonymousBufferImpl::create(int fd, size_t size)
+{
+    auto* data = mmap(nullptr, round_up_to_power_of_two(size, PAGE_SIZE), PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 0);
+    if (data == MAP_FAILED) {
+        perror("mmap");
+        return {};
+    }
+    return adopt(*new AnonymousBufferImpl(fd, size, data));
+}
+
+AnonymousBufferImpl::~AnonymousBufferImpl()
+{
+    if (m_fd != -1) {
+        auto rc = close(m_fd);
+        ASSERT(rc == 0);
+    }
+    auto rc = munmap(m_data, round_up_to_power_of_two(m_size, PAGE_SIZE));
+    ASSERT(rc == 0);
+}
+
+AnonymousBuffer AnonymousBuffer::create_from_anon_fd(int fd, size_t size)
+{
+    auto impl = AnonymousBufferImpl::create(fd, size);
+    if (!impl)
+        return {};
+    return AnonymousBuffer(impl.release_nonnull());
+}
+
+AnonymousBuffer::AnonymousBuffer(NonnullRefPtr<AnonymousBufferImpl> impl)
+    : m_impl(move(impl))
+{
+}
+
+AnonymousBufferImpl::AnonymousBufferImpl(int fd, size_t size, void* data)
+    : m_fd(fd)
+    , m_size(size)
+    , m_data(data)
+{
+}
+
+AnonymousBuffer::~AnonymousBuffer()
+{
+}
+
+}