cp -af fails on special files

[Ian Jackson]

If you cp -af a special file, it doesn't cope if the destination
exists.  After mknod fails with EEXIST, it should call unlink and then
retry the mknod again.  The patch below, against coreutils 5.96, does
this.

Thanks,
Ian.

address@hidden:d> ls
address@hidden:d> cp -a /dev/null a
address@hidden:d> cp -a /dev/null a
cp: cannot create special file `a': File exists
address@hidden:d> cp -af /dev/null a
cp: cannot create special file `a': File exists
address@hidden:d> cp -a --remove-destination /dev/null a
address@hidden:d>

--- coreutils-5.93/src/copy.c~  2006-07-03 17:23:18.000000000 +0100
+++ coreutils-5.96/src/copy.c   2006-07-03 18:05:25.000000000 +0100
@@ -1593,26 +1593,46 @@
        goto un_backup;
     }
   else
+#define CALL_PERHAPS_UNLINK(call,errormsg) do{                          \
+      if (call)                                                                
 \
+       {                                                                \
+         if (errno != EEXIST || !x->unlink_dest_after_failed_open)      \
+           {                                                            \
+             errormsg                                                   \
+             goto un_backup;                                            \
+           }                                                            \
+         if (unlink (dst_name) != 0)                                    \
+           {                                                            \
+             error (0, errno, _("cannot remove %s"), quote (dst_name)); \
+             goto un_backup;                                            \
+           }                                                            \
+         if (call)                                                      \
+           {                                                            \
+             errormsg                                                   \
+             goto un_backup;                                            \
+           }                                                            \
+       }                                                                \
+  }while(0)
 #ifdef S_ISFIFO
   if (S_ISFIFO (src_mode))
     {
-      if (mkfifo (dst_name, src_mode))
-       {
+      CALL_PERHAPS_UNLINK
+       (
+         mkfifo (dst_name, src_mode),
          error (0, errno, _("cannot create fifo %s"), quote (dst_name));
-         goto un_backup;
-       }
+       );
     }
   else
 #endif
     if (S_ISBLK (src_mode) || S_ISCHR (src_mode)
        || S_ISSOCK (src_mode))
     {
-      if (mknod (dst_name, src_mode, src_sb.st_rdev))
-       {
+      CALL_PERHAPS_UNLINK
+       (
+         mknod (dst_name, src_mode, src_sb.st_rdev),
          error (0, errno, _("cannot create special file %s"),
                 quote (dst_name));
-         goto un_backup;
-       }
+       );
     }
   else
 #ifdef S_ISLNK