---
 libhfs/os/unix.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- a/libhfs/os/unix.c
+++ b/libhfs/os/unix.c
@@ -47,6 +47,13 @@ int fstat(int, struct stat *);
 # include "libhfs.h"
 # include "os.h"
 
+/* do not write to a block device if the partition is busy */
+static int path_is_blockdevice(const char *path)
+{
+	struct stat sb;
+	return (stat(path, &sb) == 0 && S_ISBLK(sb.st_mode));
+}
+
 /*
  * NAME:	os->open()
  * DESCRIPTION:	open and lock a new descriptor from the given path and mode
@@ -55,26 +62,29 @@ int os_open(void **priv, const char *pat
 {
   long int fd;
   struct flock lock;
+  int os_mode = 0;
 
   switch (mode)
     {
     case HFS_MODE_RDONLY:
-      mode = O_RDONLY;
+      os_mode |= O_RDONLY;
       break;
 
     case HFS_MODE_RDWR:
+      if (path_is_blockdevice(path))
+	      os_mode |= O_EXCL;
     default:
-      mode = O_RDWR;
+      os_mode |= O_RDWR;
       break;
     }
 
-  fd = open(path, mode);
+  fd = open(path, os_mode);
   if (fd == -1)
     ERROR(errno, "error opening medium");
 
   /* lock descriptor against concurrent access */
 
-  lock.l_type   = (mode == O_RDONLY) ? F_RDLCK : F_WRLCK;
+  lock.l_type   = (os_mode == O_RDONLY) ? F_RDLCK : F_WRLCK;
   lock.l_start  = 0;
   lock.l_whence = SEEK_SET;
   lock.l_len    = 0;