LibCore+AK: Move MappedFile from AK to LibCore

MappedFile is strictly a userspace thing, so it doesn't belong in AK
(which is supposed to be user/kernel agnostic.)

Userland/Libraries/LibCore/MappedFile.cpp

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/ScopeGuard.h>
+#include <AK/String.h>
+#include <LibCore/MappedFile.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+namespace Core {
+
+ErrorOr<NonnullRefPtr<MappedFile>> MappedFile::map(String const& path)
+{
+    int fd = open(path.characters(), O_RDONLY | O_CLOEXEC, 0);
+    if (fd < 0)
+        return Error::from_errno(errno);
+
+    return map_from_fd_and_close(fd, path);
+}
+
+ErrorOr<NonnullRefPtr<MappedFile>> MappedFile::map_from_fd_and_close(int fd, [[maybe_unused]] String const& path)
+{
+    if (fcntl(fd, F_SETFD, FD_CLOEXEC) < 0)
+        return Error::from_errno(errno);
+
+    ScopeGuard fd_close_guard = [fd] {
+        close(fd);
+    };
+
+    struct stat st;
+    if (fstat(fd, &st) < 0)
+        return Error::from_errno(errno);
+
+    auto size = st.st_size;
+    auto* ptr = mmap(nullptr, size, PROT_READ, MAP_SHARED, fd, 0);
+
+    if (ptr == MAP_FAILED)
+        return Error::from_errno(errno);
+
+#ifdef __serenity__
+    if (set_mmap_name(ptr, size, path.characters()) < 0) {
+        perror("set_mmap_name");
+    }
+#endif
+
+    return adopt_ref(*new MappedFile(ptr, size));
+}
+
+MappedFile::MappedFile(void* ptr, size_t size)
+    : m_data(ptr)
+    , m_size(size)
+{
+}
+
+MappedFile::~MappedFile()
+{
+    auto rc = munmap(m_data, m_size);
+    VERIFY(rc == 0);
+}
+
+}