lightningbolt/lib/base/MmapFile.linux.cpp

// Copyright 2023 The LightningBolt Authors
// SPDX-License-Identifier: MIT

#include "MmapFile.hpp"
#include <fcntl.h>
#include <sys/file.h>
#include <sys/mman.h>

namespace lightningbolt {

	struct MmapFile::Impl {

		~Impl() {
			Close();
		}

		void Close() {
			if(mapping) {
				munmap(mapping, mappingSize);
				mapping = nullptr;
				mappingSize = 0;
			}
		}

		ErrorOr<void> Open(const fs::path& path) {
			int fd = open(path.string().c_str(), O_RDONLY);

			// Error opening file.
			if(fd == -1)
				return std::error_code{errno, std::system_category()};

			{
				auto last = lseek64(fd, 0, SEEK_END);
				mappingSize = lseek64(fd, 0, SEEK_CUR);
				lseek64(fd, last, SEEK_SET);
			}

			mapping = static_cast<u8*>(mmap(nullptr, mappingSize, PROT_READ, MAP_PRIVATE, fd, 0));
			if(mapping == static_cast<u8*>(MAP_FAILED)) {
				mappingSize = 0;
				return std::error_code{errno, std::system_category()};
			}

			// Once the mapping has successfully been created
			// we can close the file descriptor instead of needing
			// to remember it (the kernel will do so for us.)
			close(fd);

			// No error.
			return {};
		}

		u8* GetMapping() const {
			return mapping;
		}

		usize GetMappingSize() const {
			return mappingSize;
		}

	private:
		u8* mapping;
		usize mappingSize;
	};

} // namespace lightningbolt