Write-Side Processing

Write side processing of the ldterm(7M) module is performed by the write-side put and service procedures.

The ldterm module supports the following ioctls:

TCSETA, TCSETAW, TCSETAF, TCSETS, TCSETSW, TCSETSF, TCGETA, TCGETS, TCXONC, TCFLSH, and TCSBRK.

All ioctl(2) not recognized by the ldterm(7M) module are passed downstream to the neighboring module or driver.

The following messages can be received on the write side:

M_DATA, M_DELAY, M_BREAK, M_FLUSH, M_STOP, M_START, M_STOP, M_START, M_READ, M_IOCDATA, M_CTL, and M_IOCTL.

On the write side, the ldterm module processes M_FLUSH, M_DATA, M_IOCTL, and M_READ messages, and all other messages are passed downstream unchanged.

An M_CTL message is generated by ldterm(7M) as a query to the driver for an intelligent peripheral and to decide on the functional split for termio(7I) processing. If all or part of termio(7I) processing is done by the intelligent peripheral, ldterm(7M) can turn off this processing to avoid computational overhead. This is done by sending an appropriate response to the M_CTL message, as follows:

• If all of the termio(7I) processing is done by the peripheral hardware, the driver sends an M_CTL message back to ldterm(7M) with ioc_cmd of the structure iocblk(9S) set to MC_NO_CANON. If ldterm(7M) is to handle all termio(7I) processing, the driver sends an M_CTL message with ioc_cmd set to MC_DO_CANON. The default is MC_DO_CANON.

• If the peripheral hardware handles only part of the termio(7I) processing, it informs ldterm(7M) in the following way:

  The driver for the peripheral device allocates an M_DATA message large enough to hold a termios(3) structure. The driver then turns on those c_iflag, c_oflag, and c_lflag fields of the termios(3) structure that are processed on the peripheral device by ORing the flag values. The M_DATA message is then attached to the b_cont field of the M_CTL message it received. The message is sent back to ldterm(7M) with ioc_cmd in the data buffer of the M_CTL message set to MC_PART_CANON.

One difference between AT&T STREAMS and SunOS 5 is that AT&T's line discipline module does not check if write side flow control is in effect before forwarding data downstream. It expects the downstream module or driver to add the messages to its queue until flow control is lifted. This is not true in SunOS 5.