daemon: Make 'random_name' into a utility function.

This is mostly code motion, although the precise contract of this
function changes slightly to make it more generally useful

3 files changed, 51 insertions, 30 deletions

diff --git a/daemon/daemon.h b/daemon/daemon.h
index b4790788..85eec455 100644
--- a/daemon/daemon.h
+++ b/daemon/daemon.h
@@ -112,6 +112,8 @@ extern int prog_exists (const char *prog);
 
 extern void udev_settle (void);
 
+extern int random_name (char *template);
+
 /* This just stops gcc from giving a warning about our custom printf
  * formatters %Q and %R.  See guestfs(3)/EXTENDING LIBGUESTFS for more
  * info about these.
diff --git a/daemon/guestfsd.c b/daemon/guestfsd.c
index b09f74e1..2b0acf96 100644
--- a/daemon/guestfsd.c
+++ b/daemon/guestfsd.c
@@ -1190,6 +1190,52 @@ prog_exists (const char *prog)
   return 0;
 }
 
+/* Pass a template such as "/sysroot/XXXXXXXX.XXX".  This updates the
+ * template to contain a randomly named file.  Any 'X' characters
+ * after the final '/' are replaced with random characters.
+ *
+ * Notes: You should probably use an 8.3 path, so it's compatible with
+ * all filesystems including basic FAT.  Also this only substitutes
+ * lowercase ASCII letters and numbers, again for compatibility with
+ * lowest common denominator filesystems.
+ *
+ * This doesn't create a file or check whether or not the file exists
+ * (it would be extremely unlikely to exist as long as the RNG is
+ * working).
+ *
+ * If there is an error, -1 is returned.
+ */
+int
+random_name (char *template)
+{
+  int fd;
+  unsigned char c;
+  char *p;
+
+  fd = open ("/dev/urandom", O_RDONLY|O_CLOEXEC);
+  if (fd == -1)
+    return -1;
+
+  p = strrchr (template, '/');
+  if (p == NULL)
+    abort ();                   /* internal error - bad template */
+
+  while (*p) {
+    if (*p == 'X') {
+      if (read (fd, &c, 1) != 1) {
+        close (fd);
+        return -1;
+      }
+      *p = "0123456789abcdefghijklmnopqrstuvwxyz"[c % 36];
+    }
+
+    p++;
+  }
+
+  close (fd);
+  return 0;
+}
+
 /* LVM and other commands aren't synchronous, especially when udev is
  * involved.  eg. You can create or remove some device, but the /dev
  * device node won't appear until some time later.  This means that
diff --git a/daemon/zero.c b/daemon/zero.c
index 3076a602..14aef75d 100644
--- a/daemon/zero.c
+++ b/daemon/zero.c
@@ -228,35 +228,6 @@ do_is_zero_device (const char *device)
   return 1;
 }
 
-static int
-random_name (char *p)
-{
-  int fd;
-  unsigned char c;
-
-  fd = open ("/dev/urandom", O_RDONLY|O_CLOEXEC);
-  if (fd == -1) {
-    reply_with_perror ("/dev/urandom");
-    return -1;
-  }
-
-  while (*p) {
-    if (*p == 'X') {
-      if (read (fd, &c, 1) != 1) {
-        reply_with_perror ("read: /dev/urandom");
-        close (fd);
-        return -1;
-      }
-      *p = "0123456789abcdefghijklmnopqrstuvwxyz"[c % 36];
-    }
-
-    p++;
-  }
-
-  close (fd);
-  return 0;
-}
-
 /* Current implementation is to create a file of all zeroes, then
  * delete it.  The description of this function is left open in order
  * to allow better implementations in future, including
@@ -277,8 +248,10 @@ do_zero_free_space (const char *dir)
    * compatible with any filesystem type inc. FAT.
    */
   snprintf (filename, sysroot_len+len+14, "%s%s/XXXXXXXX.XXX", sysroot, dir);
-  if (random_name (&filename[sysroot_len+len]) == -1)
+  if (random_name (filename) == -1) {
+    reply_with_perror ("random_name");
     return -1;
+  }
 
   if (verbose)
     printf ("random filename: %s\n", filename);