1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0
2*4882a593Smuzhiyun /*
3*4882a593Smuzhiyun * Copyright (c) 2018 Dmitry Safonov, Arista Networks
4*4882a593Smuzhiyun *
5*4882a593Smuzhiyun * MAP_POPULATE | MAP_PRIVATE should COW VMA pages.
6*4882a593Smuzhiyun */
7*4882a593Smuzhiyun
8*4882a593Smuzhiyun #define _GNU_SOURCE
9*4882a593Smuzhiyun #include <errno.h>
10*4882a593Smuzhiyun #include <fcntl.h>
11*4882a593Smuzhiyun #include <sys/mman.h>
12*4882a593Smuzhiyun #include <sys/socket.h>
13*4882a593Smuzhiyun #include <sys/types.h>
14*4882a593Smuzhiyun #include <sys/wait.h>
15*4882a593Smuzhiyun #include <stdio.h>
16*4882a593Smuzhiyun #include <stdlib.h>
17*4882a593Smuzhiyun #include <string.h>
18*4882a593Smuzhiyun #include <unistd.h>
19*4882a593Smuzhiyun
20*4882a593Smuzhiyun #ifndef MMAP_SZ
21*4882a593Smuzhiyun #define MMAP_SZ 4096
22*4882a593Smuzhiyun #endif
23*4882a593Smuzhiyun
24*4882a593Smuzhiyun #define BUG_ON(condition, description) \
25*4882a593Smuzhiyun do { \
26*4882a593Smuzhiyun if (condition) { \
27*4882a593Smuzhiyun fprintf(stderr, "[FAIL]\t%s:%d\t%s:%s\n", __func__, \
28*4882a593Smuzhiyun __LINE__, (description), strerror(errno)); \
29*4882a593Smuzhiyun exit(1); \
30*4882a593Smuzhiyun } \
31*4882a593Smuzhiyun } while (0)
32*4882a593Smuzhiyun
parent_f(int sock,unsigned long * smap,int child)33*4882a593Smuzhiyun static int parent_f(int sock, unsigned long *smap, int child)
34*4882a593Smuzhiyun {
35*4882a593Smuzhiyun int status, ret;
36*4882a593Smuzhiyun
37*4882a593Smuzhiyun ret = read(sock, &status, sizeof(int));
38*4882a593Smuzhiyun BUG_ON(ret <= 0, "read(sock)");
39*4882a593Smuzhiyun
40*4882a593Smuzhiyun *smap = 0x22222BAD;
41*4882a593Smuzhiyun ret = msync(smap, MMAP_SZ, MS_SYNC);
42*4882a593Smuzhiyun BUG_ON(ret, "msync()");
43*4882a593Smuzhiyun
44*4882a593Smuzhiyun ret = write(sock, &status, sizeof(int));
45*4882a593Smuzhiyun BUG_ON(ret <= 0, "write(sock)");
46*4882a593Smuzhiyun
47*4882a593Smuzhiyun waitpid(child, &status, 0);
48*4882a593Smuzhiyun BUG_ON(!WIFEXITED(status), "child in unexpected state");
49*4882a593Smuzhiyun
50*4882a593Smuzhiyun return WEXITSTATUS(status);
51*4882a593Smuzhiyun }
52*4882a593Smuzhiyun
child_f(int sock,unsigned long * smap,int fd)53*4882a593Smuzhiyun static int child_f(int sock, unsigned long *smap, int fd)
54*4882a593Smuzhiyun {
55*4882a593Smuzhiyun int ret, buf = 0;
56*4882a593Smuzhiyun
57*4882a593Smuzhiyun smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,
58*4882a593Smuzhiyun MAP_PRIVATE | MAP_POPULATE, fd, 0);
59*4882a593Smuzhiyun BUG_ON(smap == MAP_FAILED, "mmap()");
60*4882a593Smuzhiyun
61*4882a593Smuzhiyun BUG_ON(*smap != 0xdeadbabe, "MAP_PRIVATE | MAP_POPULATE changed file");
62*4882a593Smuzhiyun
63*4882a593Smuzhiyun ret = write(sock, &buf, sizeof(int));
64*4882a593Smuzhiyun BUG_ON(ret <= 0, "write(sock)");
65*4882a593Smuzhiyun
66*4882a593Smuzhiyun ret = read(sock, &buf, sizeof(int));
67*4882a593Smuzhiyun BUG_ON(ret <= 0, "read(sock)");
68*4882a593Smuzhiyun
69*4882a593Smuzhiyun BUG_ON(*smap == 0x22222BAD, "MAP_POPULATE didn't COW private page");
70*4882a593Smuzhiyun BUG_ON(*smap != 0xdeadbabe, "mapping was corrupted");
71*4882a593Smuzhiyun
72*4882a593Smuzhiyun return 0;
73*4882a593Smuzhiyun }
74*4882a593Smuzhiyun
main(int argc,char ** argv)75*4882a593Smuzhiyun int main(int argc, char **argv)
76*4882a593Smuzhiyun {
77*4882a593Smuzhiyun int sock[2], child, ret;
78*4882a593Smuzhiyun FILE *ftmp;
79*4882a593Smuzhiyun unsigned long *smap;
80*4882a593Smuzhiyun
81*4882a593Smuzhiyun ftmp = tmpfile();
82*4882a593Smuzhiyun BUG_ON(ftmp == 0, "tmpfile()");
83*4882a593Smuzhiyun
84*4882a593Smuzhiyun ret = ftruncate(fileno(ftmp), MMAP_SZ);
85*4882a593Smuzhiyun BUG_ON(ret, "ftruncate()");
86*4882a593Smuzhiyun
87*4882a593Smuzhiyun smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,
88*4882a593Smuzhiyun MAP_SHARED, fileno(ftmp), 0);
89*4882a593Smuzhiyun BUG_ON(smap == MAP_FAILED, "mmap()");
90*4882a593Smuzhiyun
91*4882a593Smuzhiyun *smap = 0xdeadbabe;
92*4882a593Smuzhiyun /* Probably unnecessary, but let it be. */
93*4882a593Smuzhiyun ret = msync(smap, MMAP_SZ, MS_SYNC);
94*4882a593Smuzhiyun BUG_ON(ret, "msync()");
95*4882a593Smuzhiyun
96*4882a593Smuzhiyun ret = socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sock);
97*4882a593Smuzhiyun BUG_ON(ret, "socketpair()");
98*4882a593Smuzhiyun
99*4882a593Smuzhiyun child = fork();
100*4882a593Smuzhiyun BUG_ON(child == -1, "fork()");
101*4882a593Smuzhiyun
102*4882a593Smuzhiyun if (child) {
103*4882a593Smuzhiyun ret = close(sock[0]);
104*4882a593Smuzhiyun BUG_ON(ret, "close()");
105*4882a593Smuzhiyun
106*4882a593Smuzhiyun return parent_f(sock[1], smap, child);
107*4882a593Smuzhiyun }
108*4882a593Smuzhiyun
109*4882a593Smuzhiyun ret = close(sock[1]);
110*4882a593Smuzhiyun BUG_ON(ret, "close()");
111*4882a593Smuzhiyun
112*4882a593Smuzhiyun return child_f(sock[0], smap, fileno(ftmp));
113*4882a593Smuzhiyun }
114