* Copyright 2010, Axel Dörfler, axeld@pinc-software.de.
* This file may be used under the terms of the MIT License.
*/
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <algorithm>
void
test_for_content(int fd, off_t start, const char* contents, size_t length)
{
char buffer[4096];
while (length > 0) {
size_t toRead = std::min(length, sizeof(buffer));
if (pread(fd, buffer, toRead, start) != (ssize_t)toRead) {
perror("reading failed");
exit(1);
}
if (memcmp(contents, buffer, toRead)) {
fprintf(stderr, "Contents at %lld differ!\n", start);
exit(1);
}
contents += toRead;
start += toRead;
length -= toRead;
}
}
void
test_for_zero(int fd, off_t start, off_t end)
{
while (start < end) {
char buffer[4096];
size_t length = std::min((size_t)(end - start), sizeof(buffer));
if (pread(fd, buffer, length, start) != (ssize_t)length) {
perror("reading failed");
exit(1);
}
for (size_t i = 0; i < length; i++) {
if (buffer[i] != 0) {
fprintf(stderr, "Buffer at %lld is not empty (%#x)!\n",
start + i, buffer[i]);
exit(1);
}
}
start += length;
}
}
int
main(int argc, char** argv)
{
const char* name = "/tmp/seek_and_write";
bool prefill = true;
for (int i = 1; i < argc; i++) {
if (argv[i][0] == '-') {
if (argv[i][1] == 'n')
prefill = false;
else {
fprintf(stderr, "Unknown option\n");
return 1;
}
continue;
}
name = argv[i];
}
int fd = open(name, O_RDWR | O_TRUNC | O_CREAT, 0644);
if (fd < 0) {
perror("failed to open file");
return 1;
}
char buffer[256];
for (size_t i = 0; i < 256; i++)
buffer[i] = i;
if (prefill) {
for (size_t i = 0; i < 100; i++) {
if (write(fd, buffer, sizeof(buffer)) != (ssize_t)sizeof(buffer)) {
perror("writing failed");
return 1;
}
}
}
ftruncate(fd, 0);
pwrite(fd, "---", 3, 100 * 1024);
pwrite(fd, "+++", 3, 200 * 1024);
test_for_zero(fd, 0, 100 * 1024);
test_for_content(fd, 100 * 1024, "---", 3);
test_for_zero(fd, 100 * 1024 + 256, 200 * 1024);
test_for_content(fd, 200 * 1024, "+++", 3);
return 0;
}
