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// SPDX-License-Identifier: GPL-2.0+
/*
* Takes page fault while writev is iterating over the vectors in the IOV
* Copyright (C) 2017 Red Hat, Inc. All Rights reserved.
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sys/uio.h>
#include <limits.h>
#ifndef IOV_MAX
#define IOV_MAX 1024
#endif
#define DEF_IOV_CNT 3
void usage(char *progname)
{
fprintf(stderr, "usage: %s [-i iovcnt] filename\n", progname);
fprintf(stderr, "\t-i iovcnt: the count of io vectors (max is 1024), 3 by default\n");
exit(1);
}
int main(int argc, char *argv[])
{
int fd, i, c;
ssize_t ret;
struct iovec *iov;
int pagesz = 4096;
char *data = NULL;
char *filename = NULL;
int iov_cnt = DEF_IOV_CNT;
while ((c = getopt(argc, argv, "i:")) != -1) {
char *endp;
switch (c) {
case 'i':
iov_cnt = strtol(optarg, &endp, 0);
if (*endp) {
fprintf(stderr, "Invalid iov count %s\n", optarg);
usage(argv[0]);
}
break;
default:
usage(argv[0]);
}
}
if (iov_cnt > IOV_MAX || iov_cnt <= 0)
usage(argv[0]);
if (optind == argc - 1)
filename = argv[optind];
else
usage(argv[0]);
pagesz = getpagesize();
data = malloc(pagesz * iov_cnt);
if (!data) {
perror("malloc failed");
return 1;
}
/*
* NOTE: no pre-writing/reading on the buffer before writev, to prevent
* page prefault from happening, we need it happen at writev time.
*/
iov = calloc(iov_cnt, sizeof(struct iovec));
if (!iov) {
perror("calloc failed");
return 1;
}
for (i = 0; i < iov_cnt; i++) {
(iov + i)->iov_base = (data + pagesz * i);
(iov + i)->iov_len = 1;
}
if ((fd = open(filename, O_TRUNC|O_CREAT|O_RDWR, 0644)) < 0) {
perror("open failed");
return 1;
}
ret = writev(fd, iov, iov_cnt);
if (ret < 0)
perror("writev failed");
else
printf("wrote %zd bytes\n", ret);
close(fd);
return 0;
}
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