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