From c28bcc04f41f6b70e43fff87959ecf819388064c Mon Sep 17 00:00:00 2001
From: Peter Wu <peter@lekensteyn.nl>
Date: Thu, 26 Jun 2014 21:55:31 +0200
Subject: wipe-sectors: wipe sectors which are non-zero

---
 wipe-sectors.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 wipe-sectors.c

diff --git a/wipe-sectors.c b/wipe-sectors.c
new file mode 100644
index 0000000..cac0028
--- /dev/null
+++ b/wipe-sectors.c
@@ -0,0 +1,98 @@
+/* Reads a block device and wipe a block if non-zero.
+ * Author: Peter Wu <peter@lekensteyn.nl>
+ * Date: 2014-06-26
+ */
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <err.h>
+#include <stdlib.h>
+
+#define BUFSIZE (1024 * 1024 * 2)
+
+static char zeroes[BUFSIZE];
+
+static void wipe(int fd, size_t len) {
+    off_t pos;
+    ssize_t r;
+
+    pos = lseek(fd, -len, SEEK_CUR);
+    if (pos == (off_t) -1)
+        err(1, "failed to seek before write");
+
+    r = write(fd, zeroes, len);
+    if (r < 0)
+        err(1, "failed to write zeroes");
+    if ((size_t) r != len)
+        errx(1, "could only write %zu instead of %zu bytes", r, len);
+}
+
+static void read_and_wipe(int fd) {
+    ssize_t r;
+    off_t endpos, pos;
+    char *buf = malloc(BUFSIZE);
+    unsigned iteration = 0, rounds;
+    if (buf == NULL)
+        err(1, "malloc");
+
+    endpos = lseek(fd, 0, SEEK_END);
+    if (endpos == (off_t) -1)
+        err(1, "failed to seek end");
+    if (endpos == 0) {
+        warnx("file is empty");
+        return;
+    }
+
+    pos = lseek(fd, 0, SEEK_SET);
+    if (pos == (off_t) -1)
+        err(1, "failed to seek to begin");
+
+    rounds = endpos / BUFSIZE;
+    if (rounds * BUFSIZE < endpos)
+        ++rounds;
+
+    do {
+        r = read(fd, buf, BUFSIZE);
+        printf("\r%u/%u -- %u%% (%llu/%llu)",
+            iteration, rounds,
+            (unsigned) (100 * pos / endpos),
+            (long long) pos, (long long) endpos);
+        if (r < 0) {
+            warn("read failed");
+        } else if (r > 0) {
+            char val = 0;
+            int i;
+            for (i = 0; i < r; i++) {
+                val |= buf[i];
+            }
+            pos += r;
+            /* if there are any non-zero bytes, act accordingly */
+            if (val != 0) {
+                printf(" WIPE ME!\n");
+                wipe(fd, r);
+            }
+        }
+        fflush(stdout);
+        ++iteration;
+    } while (r > 0);
+    putchar('\n');
+
+    free(buf);
+}
+
+int main(int argc, char **argv) {
+    int fd;
+
+    if (argc < 2)
+        errx(1, "Missing device argument");
+
+    fd = open(argv[1], O_RDWR);
+    if (fd < 0)
+        err(1, "failed to open file");
+
+    read_and_wipe(fd);
+
+    close(fd);
+
+    return 0;
+}
-- 
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