- Remove redundant 'busy' flag, use ctlfd > -1 to check busy state
- Remove 'sid' field from file_context, use tty->sid directly
- Fix fd comparison to use > -1 instead of > 0 for consistency
- Simplify file_context_reset by removing unnecessary busy flag reset
This reduces memory usage and
Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>