tty,vcs removing con_buf/conf_buf_mtx

seems there's no longer need for using con_buf/conf_buf_mtx
as vcs_read/vcs_write buffer for user's data.

The do_con_write function, that was the other user of this,
is currently using its own kmalloc-ed buffer.

Not sure when this got changed, as I was able to find this code
in 2.6.9, but it's already gone as far as current git history
goes - 2.6.12-rc2.

AFAICS there's a behaviour change with the current change.
The lseek is not completely mutually exclusive with the
vcs_read/vcs_write - the file->f_pos might get updated
via lseek callback during the vcs_read/vcs_write processing.

I tried to find out if the prefered behaviour is to keep
this in sync within read/write/lseek functions, but I did
not find any pattern on different places.

I guess if user end up calling write/lseek from different
threads she should know what she's doing. If needed we
could use dedicated fd mutex/buffer.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/tty/vt/vt.c

@@ -2068,18 +2068,6 @@ static void do_con_trol(struct tty_struct *tty, struct vc_data *vc, int c)
 	}
 }
 
-/* This is a temporary buffer used to prepare a tty console write
- * so that we can easily avoid touching user space while holding the
- * console spinlock.  It is allocated in con_init and is shared by
- * this code and the vc_screen read/write tty calls.
- *
- * We have to allocate this statically in the kernel data section
- * since console_init (and thus con_init) are called before any
- * kernel memory allocation is available.
- */
-char con_buf[CON_BUF_SIZE];
-DEFINE_MUTEX(con_buf_mtx);
-
 /* is_double_width() is based on the wcwidth() implementation by
  * Markus Kuhn -- 2007-05-26 (Unicode 5.0)
  * Latest version: http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c