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>

include/linux/vt_kern.h

@@ -142,14 +142,6 @@ static inline bool vt_force_oops_output(struct vc_data *vc)
 	return false;
 }
 
-/*
- * vc_screen.c shares this temporary buffer with the console write code so that
- * we can easily avoid touching user space while holding the console spinlock.
- */
-
-#define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)
-extern char con_buf[CON_BUF_SIZE];
-extern struct mutex con_buf_mtx;
 extern char vt_dont_switch;
 extern int default_utf8;
 extern int global_cursor_default;