abstract

问：对同一个文件多次mmap，返回的地址相同吗?

答：不相同

code

#ifdef __linux__#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <errno.h>
#include <string.h>
#include <vector>
#include <stdint.h>
#include <stdio.h>// 问：对同一个文件多次mmap，返回的地址相同吗?
// 答：不相同
void linux_mmap_test1(void)
{const char* file = "/userdata/lxz/test/Makefile";struct stat fileInfo = {0};int fd = -1;std::vector<int> fds;std::vector<uint8_t*> ptrs;uint8_t* ptr = nullptr;if (stat(file, &fileInfo) != 0) {fprintf(stderr, "stat error,%s\n", strerror(errno));return;}for (int i = 0; i < 5; ++i) {fd = open(file, O_RDONLY);if (fd < 0) {fprintf(stderr, "i:%d,open error,%s\n", i, strerror(errno));break;}fds.push_back(fd);ptr = (uint8_t*)mmap(nullptr, (size_t)fileInfo.st_size, PROT_READ, MAP_SHARED, fd, 0);if (!ptr) {fprintf(stderr, "i:%d,mmap error,%s\n", i, strerror(errno));break;}fprintf(stderr, "%d <=> %llu\n", fd, (size_t)ptr);ptrs.push_back(ptr);}for (size_t n = 0; n < ptrs.size(); ++n) {if (munmap(ptrs[n], size_t(fileInfo.st_size)) != 0) {fprintf(stderr, "n:%llu,munmap error,%s\n", n, strerror(errno));}}for (size_t n = 0; n < fds.size(); ++n) {close(fds[n]);}
}#endif

performance