+ for (i = 0; i < 32; ++i) {
+ offset = i * sizeof zero_buf;
+
+ /* Check if the block is already zero before overwriting it. */
+ if (pread (fd, buf, sizeof buf, offset) != sizeof buf) {
+ reply_with_perror ("pread: %s", device);
+ close (fd);
+ return -1;
+ }
+
+ if (!is_zero (buf, sizeof buf)) {
+ if (pwrite (fd, zero_buf, sizeof zero_buf, offset) != sizeof zero_buf) {
+ reply_with_perror ("pwrite: %s", device);
+ close (fd);
+ return -1;
+ }
+ }
+
+ notify_progress ((uint64_t) i, 32);
+ }
+
+ if (close (fd) == -1) {
+ reply_with_perror ("close: %s", device);
+ return -1;
+ }
+
+ return 0;
+}
+
+int
+do_zero_device (const char *device)
+{
+ int64_t ssize = do_blockdev_getsize64 (device);
+ if (ssize == -1)
+ return -1;
+ uint64_t size = (uint64_t) ssize;
+
+ int fd = open (device, O_RDWR);
+ if (fd == -1) {
+ reply_with_perror ("%s", device);
+ return -1;
+ }
+
+ char buf[sizeof zero_buf];
+
+ uint64_t pos = 0;
+
+ while (pos < size) {
+ uint64_t n64 = size - pos;
+ size_t n;
+ if (n64 > sizeof buf)
+ n = sizeof buf;
+ else
+ n = (size_t) n64; /* safe because of if condition */
+
+ /* Check if the block is already zero before overwriting it. */
+ ssize_t r;
+ r = pread (fd, buf, n, pos);
+ if (r == -1) {
+ reply_with_perror ("pread: %s at offset %" PRIu64, device, pos);
+ close (fd);
+ return -1;
+ }
+
+ if (!is_zero (buf, sizeof buf)) {
+ r = pwrite (fd, zero_buf, n, pos);
+ if (r == -1) {
+ reply_with_perror ("pwrite: %s (with %" PRId64 " bytes left to write)",
+ device, size);
+ close (fd);
+ return -1;
+ }
+ pos += r;
+ }
+ else
+ pos += n;
+
+ notify_progress (pos, size);
+ }
+
+ if (close (fd) == -1) {
+ reply_with_perror ("close: %s", device);
+ return -1;
+ }
+
+ return 0;
+}
+
+int
+do_is_zero (const char *path)
+{
+ int fd;
+ char buf[1024*1024];
+ ssize_t r;