Added a --bits (-n) option to corrupt.

1 files changed, 84 insertions, 25 deletions

diff --git a/corrupt.c b/corrupt.c
index f8c5cd2..0d29453 100644
--- a/corrupt.c
+++ b/corrupt.c
@@ -17,6 +17,7 @@
 
 
 #define _LARGEFILE64_SOURCE
+#define _GNU_SOURCE
 
 #include <errno.h>
 #include <limits.h>
@@ -28,6 +29,11 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <getopt.h>
+
+
+/* Number of bits to corrupt. */
+static int num_bits = 1;
 
 
 /* Choose a random integer in [0..n-1]. */
@@ -47,33 +53,27 @@ static long choose(long n)
 }
 
 
-static int corrupt(const char *filename)
+static int seek(const char *filename, int fd, off_t offset)
 {
-    int fd;
-    struct stat st;
-    
-    fd = open(filename, O_RDWR | O_LARGEFILE);
-    if (fd == -1) {
-        fprintf(stderr, "Can't open %s: %s\n", filename, strerror(errno));
+    if (lseek(fd, offset, SEEK_SET) == (off_t) -1) {
+        fprintf(stderr, "Can't seek in %s: %s", filename, strerror(errno));
         return -1;
     }
+    return 0;
+}
 
-    if (fstat(fd, &st) == -1) {
-        fprintf(stderr, "Can't find length of %s: %s", filename, 
-                strerror(errno));
-        return -1;
-    }
 
-    long offset = choose(st.st_size);
-    long bit = choose(CHAR_BIT);
-    printf("%s: offset=%ld bit=%ld\n", filename, offset, bit);
+static int corrupt_one_bit(const char *filename, int fd, struct stat st)
+{
+    long offset;
+    long bit;
+    unsigned char byte;
+
+    offset = choose(st.st_size);
+    bit = choose(CHAR_BIT);
     
-    if (lseek(fd, offset, SEEK_SET) == (off_t) -1) {
-        fprintf(stderr, "Can't seek in %s: %s", filename, strerror(errno));
+    if (seek(filename, fd, offset) == -1)
         return -1;
-    }
-    
-    unsigned char byte;
     if (read(fd, &byte, 1) == -1) {
         fprintf(stderr, "Can't read %s: %s", filename, strerror(errno));
         return -1;
@@ -87,14 +87,37 @@ static int corrupt(const char *filename)
     byte = others | toggled;
     
     /* Now write it back. */
-    if (lseek(fd, offset, SEEK_SET) == (off_t) -1) {
-        fprintf(stderr, "Can't seek in %s: %s", filename, strerror(errno));
+    if (seek(filename, fd, offset) == -1)
         return -1;
-    }
     if (write(fd, &byte, 1) != 1) {
         fprintf(stderr, "Can't write %s: %s", filename, strerror(errno));
         return -1;
     }
+    
+    return 0;
+}
+
+
+static int corrupt(const char *filename)
+{
+    int fd;
+    struct stat st;
+    
+    fd = open(filename, O_RDWR | O_LARGEFILE);
+    if (fd == -1) {
+        fprintf(stderr, "Can't open %s: %s\n", filename, strerror(errno));
+        return -1;
+    }
+
+    if (fstat(fd, &st) == -1) {
+        fprintf(stderr, "Can't find length of %s: %s", filename, 
+                strerror(errno));
+        return -1;
+    }
+
+    for (int i = 0; i < num_bits; ++i)
+        if (corrupt_one_bit(filename, fd, st) == -1)
+            return -1;
 
     if (close(fd) == -1) {
         fprintf(stderr, "Can't close %s: %s", filename, strerror(errno));
@@ -105,13 +128,49 @@ static int corrupt(const char *filename)
 }
 
 
+static int parse_args(int argc, char **argv)
+{
+    const char optstring[] = "n:";
+    const struct option longopts[] = {
+        { "bits", required_argument, NULL, 'n' },
+        { 0 },
+    };
+    char *endptr;
+    
+    for (;;) {
+        int opt = getopt_long(argc, argv, optstring, longopts, NULL);
+        switch (opt) {
+        case -1:
+            return optind;
+
+        case 'n':
+            num_bits = strtol(optarg, &endptr, 10);
+            if (*endptr != '\0') {
+                fprintf(stderr, "Invalid number of bits: %s\n", optarg);
+                exit(1);
+            }
+            break;
+            
+        default:
+        case '?':
+            exit(1);
+        }
+    }
+}
+
+
 int main(int argc, char **argv)
 {
     int exit_code;
-    
+    int i;
+
+    i = parse_args(argc, argv);
+    if (i == -1)
+        return 1;
+
     srandom(time(NULL) + getpid());
     exit_code = 0;
-    for (int i = 1; i < argc; ++i)
+    for (; i < argc; ++i)
         if (corrupt(argv[i]) == -1)
             exit_code = 1;
     return exit_code;