library/src/SharedMemoryAccess.cpp

#include <cstdio>
#include <cstring>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/types.h>

#include "SharedMemoryAccess.hpp"
#include "internal.hpp"
#include "log.hpp"

namespace vkvm {
    constexpr int PERMISSION = 0666;
    constexpr int LOCK = -1;
    constexpr int UNLOCK = 1;
    constexpr int SEM_KEY = 123458L;

    int semId;
    struct sembuf semaphore;

    std::vector<char> localSharedMemory;

    auto initSemaphore() -> int {
        /* Testen, ob das Semaphor bereits existiert */
        semId = semget(SEM_KEY, 0, IPC_PRIVATE);
        if (semId < 0) {
            /* ... existiert noch nicht, also anlegen        */
            /* Alle Zugriffsrechte der Dateikreierungsmaske */
            /* erlauben                                     */
            umask(0);
            semId = semget(SEM_KEY, 1, IPC_CREAT | IPC_EXCL | PERMISSION);
            if (semId < 0) {
                return -1;
            }
            /* Semaphor mit 1 initialisieren */
            if (semctl(semId, 0, SETVAL, 1) == -1) {
                return -1;
            }
        }
        return 1;
    }

    auto semaphoreOperation(int op) -> int {
        semaphore.sem_op = static_cast<int16_t>(op);
        semaphore.sem_flg = SEM_UNDO;
        if (semop(semId, &semaphore, 1) == -1) {
            perror(" semop ");
            log(LogLevel::CRITICAL, "could not operate on semaphore, exiting");
            return -1;
        }
        return 1;
    }

    auto writeSharedMemory(char *data, int size, int offset) -> void {
        lockSharedMemory();
        memcpy(getSharedMemory() + offset, data, size);
        unlockSharedMemory();
    }

    char *getLocalMemory(){
        static bool givenWarning {false};
        if(!givenWarning && impl.localMemoryWarn){
            givenWarning = true;
            log(LogLevel::WARNING, "no shared memory found, using local memory instead!");
        }
        if (localSharedMemory.empty()) {
            constexpr int kilo = 1024;
            localSharedMemory.resize(impl.sharedMemorySize * kilo);
        }
        return &localSharedMemory[0];
    }

    auto getSharedMemory() -> char * {
        if(impl.sharedMemory != nullptr){
            return impl.sharedMemory;
        }
        int shmId = shmget(impl.sharedMemoryKey, 0, 0);
        if (shmId < 0) {
            //using a local buffer for shared memory testing
            return getLocalMemory();
        }
        char *ptr =  static_cast<char *>(shmat(shmId, nullptr, 0));
        if(reinterpret_cast<size_t>(ptr) == static_cast<size_t>(-1)){
            log(LogLevel::WARNING, strerror(errno));
        }else{
            impl.sharedMemory = ptr;
            return ptr;
        }
        return getLocalMemory();
    }

    auto getSharedMemory(char *address, int size, int offset) -> void {
        lockSharedMemory();
        memcpy(address, getSharedMemory() + offset, size);
        unlockSharedMemory();
    }

    auto getSharedMemorySize() -> int {
        return impl.sharedMemorySize;
    }

    auto lockSharedMemory() -> void {
        semaphoreOperation(LOCK);
    }

    auto unlockSharedMemory() -> void {
        semaphoreOperation(UNLOCK);
    }

}