Always use permissive mode

Right now, there is no way to check that the correct device was opened
in general without relying on udev.  Furthermore, this information is
not currently available in the case of qvm-block, which uses names under
/dev/ that can be reused.

not-script/not-script.c

@@ -88,7 +88,7 @@ static int setup_loop(struct loop_context *ctx,
 
 static void
 process_blk_dev(int fd, const char *path, bool writable, dev_t *dev,
-                uint64_t *diskseq, bool permissive, bool autoclear)
+                uint64_t *diskseq, bool autoclear)
 {
     struct stat statbuf;
     char buf[45];
@@ -97,12 +97,9 @@ process_blk_dev(int fd, const char *path, bool writable, dev_t *dev,
         err(1, "fstat");
 
     if (S_ISBLK(statbuf.st_mode)) {
-        if (permissive)
-            goto skip;
-
         /* block device */
-        if (strncmp(DEV_MAPPER, path, DEV_MAPPER_SIZE))
-            errx(1, "Only device-mapper block devices are supported (got %s)", path);
+        if (strncmp(DEV_MAPPER, path, DEV_MAPPER_SIZE) != 0)
+            goto skip;
 
         const char *const devname = path + DEV_MAPPER_SIZE;
         size_t const devname_len = strlen(devname);
@@ -345,7 +342,6 @@ int main(int argc, char **argv)
         ADD,
         REMOVE,
     } action;
-    bool permissive;
     redirect_stderr();
 #define XENBUS_PATH_PREFIX "XENBUS_PATH="
 #define BACKEND_VBD "backend/vbd/"
@@ -356,11 +352,6 @@ int main(int argc, char **argv)
     if (argc < 2 || argc > 3)
         errx(1, "Usage: [add|remove] [XENBUS_PATH=backend/vbd/REMOTE_DOMAIN/ID] (got %d arguments, expected 2 or 3)", argc);
 
-    const char *last_slash = strrchr(argv[0], '/');
-    last_slash = last_slash ? last_slash + 1 : argv[0];
-
-    permissive = strcmp(last_slash, "block") == 0;
-
     if (argc >= 3) {
         if (strncmp(argv[2], ARGV2_PREFIX, sizeof(ARGV2_PREFIX) - 1))
             errx(1, "Second argument must begin with XENBUS_PATH=backend/vbd/");
@@ -471,7 +462,7 @@ int main(int argc, char **argv)
         err(1, "open(%s)", data);
     char phys_dev[16 + 8 + 8 + 2 + 1];
 
-    process_blk_dev(fd, data, writable, &dev, &diskseq, permissive, autoclear);
+    process_blk_dev(fd, data, writable, &dev, &diskseq, autoclear);
     unsigned const int l =
         (unsigned)(autoclear ?
                    snprintf(phys_dev, sizeof phys_dev, "%" PRIx64 "@%lx:%lx",