我需要打开一个文件并通过mmap将其加载到共享内存中,但是如果该文件尚不存在,我想打开它,写一些(假的)数据,然后mmap它.我在C中编写了以下函数,但是我在写入时遇到错误(见下文). (我知道mmap部分可能是错误的(数据被分配了两次!),但错误发生在此之前,所以它不应该对这个问题产生任何影响).
// These 2 are global so they can be referenced in other functions.
int dfd = -1;
long* data = NULL;
void load_data(char* filename)
{
dfd = open(filename, O_RDONLY);
if (dfd == -1) {
printf("Creating file %s\n", filename);
dfd = open(filename, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
if (dfd == -1) {
fprintf(stderr, "Couldn't create file %s\n", filename);
perror("create");
exit(1);
}
data = (long *) valloc(M * GB);
if (data == nullptr) {
fprintf(stderr, "Couldn't allocate %ld bytes", (M * GB));
perror("malloc");
exit(1);
}
for (size_t i = 0; i < M * GB / sizeof(long); ++i)
data[i] = (long) i;
printf("%d %p %ld\n", dfd, data, M * GB);
ssize_t w = write(dfd, (void*) data, M * GB);
if (w != M * GB) {
fprintf(stderr, "Couldn't write %ld bytes to file %s\n", (M * GB), filename);
fprintf(stderr, "Wrote %ld bytes\n", w);
perror("write");
exit(1);
}
}
data = (long *) mmap(0, M * GB, PROT_READ, MAP_SHARED, dfd, 0);
if (data == MAP_FAILED) {
perror("mmap");
exit(1);
}
}
MacOS 64位输出和错误,Apple g:
Creating file bench2_datafile.bin
3 0x101441000 2147483648
Couldn't write 2147483648 bytes to file bench2_datafile.bin
Wrote -1 bytes
write: Invalid argument
任何指针?我一直在阅读开放和编写文档,并在互联网上寻找示例,但我似乎无法克服这个错误.
受益于评论后:
RHEL 6上的输出,g 4.8:
Creating file bench2_datafile.bin
3 0x7f79048af000 2147483648
write: Success
Couldn't write 2147483648 bytes to file bench2_datafile.bin
Wrote 2147479552 bytes
和2147479552确实是ls中的文件大小.
此外,它适用于1 GB的Mac – 但它耗尽2 GB的蒸汽.哦 – 好吧 – 我的真正目标是Linux无论如何,在Mac上工作直到我收到错误更方便:-)
最佳答案 许多平台使用32位值作为文件位置.此外,接口需要对值进行签名.这意味着,只要您想处理大于2 GB的文件,就会遇到麻烦.
某些平台提供非标准功能来操作较大的文件.
您需要检查平台文档以了解要定位的平台的内容.