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#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>
int main(int argc, char** argv) {
const char kTestFilePath[] = "testfile.txt";
const char kOldFileData[] = "old data\n";
const char kNewFileData[] = "new data\n";
const size_t kPageSize = sysconf(_SC_PAGE_SIZE);
// Open a file that already exists in a host overlayfs lower layer.
const int fd_rdonly = open(kTestFilePath, O_RDONLY);
if (fd_rdonly < 0) {
err(1, "open(%s, O_RDONLY)", kTestFilePath);
}
// Check that the file's initial contents are what we expect when read via
// syscall.
char oldbuf[sizeof(kOldFileData)] = {};
ssize_t n = pread(fd_rdonly, oldbuf, sizeof(oldbuf), 0);
if (n < 0) {
err(1, "initial pread");
}
if (n != strlen(kOldFileData)) {
errx(1, "short initial pread (%ld/%lu bytes)", n, strlen(kOldFileData));
}
if (strcmp(oldbuf, kOldFileData) != 0) {
errx(1, "initial pread returned wrong data: %s", oldbuf);
}
// Check that the file's initial contents are what we expect when read via
// memory mapping.
void* page = mmap(NULL, kPageSize, PROT_READ, MAP_SHARED, fd_rdonly, 0);
if (page == MAP_FAILED) {
err(1, "mmap");
}
if (strcmp(page, kOldFileData) != 0) {
errx(1, "mapping contains wrong initial data: %s", (const char*)page);
}
// Open the same file writably, causing host overlayfs to copy it up, and
// replace its contents.
const int fd_rdwr = open(kTestFilePath, O_RDWR);
if (fd_rdwr < 0) {
err(1, "open(%s, O_RDWR)", kTestFilePath);
}
n = write(fd_rdwr, kNewFileData, strlen(kNewFileData));
if (n < 0) {
err(1, "write");
}
if (n != strlen(kNewFileData)) {
errx(1, "short write (%ld/%lu bytes)", n, strlen(kNewFileData));
}
if (ftruncate(fd_rdwr, strlen(kNewFileData)) < 0) {
err(1, "truncate");
}
int failed = 0;
// Check that syscalls on the old FD return updated contents. (Before Linux
// 4.18, this requires that runsc use a post-copy-up FD to service the read.)
char newbuf[sizeof(kNewFileData)] = {};
n = pread(fd_rdonly, newbuf, sizeof(newbuf), 0);
if (n < 0) {
err(1, "final pread");
}
if (n != strlen(kNewFileData)) {
warnx("short final pread (%ld/%lu bytes)", n, strlen(kNewFileData));
failed = 1;
} else if (strcmp(newbuf, kNewFileData) != 0) {
warnx("final pread returned wrong data: %s", newbuf);
failed = 1;
}
// Check that the memory mapping of the old FD has been updated. (Linux
// overlayfs does not do this, so regardless of kernel version this requires
// that runsc replace existing memory mappings with mappings of a
// post-copy-up FD.)
if (strcmp(page, kNewFileData) != 0) {
warnx("mapping contains wrong final data: %s", (const char*)page);
failed = 1;
}
return failed;
}
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