Function mmapEntryByDataOffset

KittyMemoryEx/KittyUtils.cpp:664–715

        }

        bool mmapEntryByDataOffset(const std::string &zipPath, uint64_t dataOffset, ZipEntryMMap *out)
        {
            if (out)
                *out = {};

            ZipEntryInfo ent{};
            if (!findEntryInfoByDataOffset(zipPath, dataOffset, &ent))
                return false;

            uint64_t compressedSize = ent.compressedSize;

            int fd = KT_EINTR_RETRY(open(zipPath.c_str(), O_RDONLY));
            if (fd < 0)
                return false;

            struct stat st{};
            if (fstat(fd, &st) < 0)
            {
                KT_EINTR_RETRY(close(fd));
                return false;
            }

            uint64_t fileSize = st.st_size;

            if (dataOffset >= fileSize || dataOffset + compressedSize > fileSize)
            {
                KT_EINTR_RETRY(close(fd));
                return false;
            }

            const size_t pageSize = sysconf(_SC_PAGE_SIZE);
            uint64_t alignedOffset = dataOffset & ~(uint64_t(pageSize - 1));
            uint64_t offsetDiff = dataOffset - alignedOffset;
            uint64_t mapSize = offsetDiff + compressedSize;

            void *map = mmap(nullptr, mapSize, PROT_READ, MAP_PRIVATE, fd, alignedOffset);

            KT_EINTR_RETRY(close(fd));

            if (!map || map == MAP_FAILED)
                return false;

            if (out)
            {
                out->mappingBase = map;
                out->mappingSize = mapSize;
                out->data = static_cast<uint8_t *>(map) + offsetDiff;
                out->size = compressedSize;
            }

            return true;
        }
    } // namespace Zip

} // namespace KittyUtils