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committed 361bf8a9d88 printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);// SPDX-License-Identifier: GPL-1.0+/* generic HDLC line discipline for Linux * * Written by Paul Fulghum paulkf@microgate.com * for Microgate Corporation * * Microgate and SyncLink are registered trademarks of Microgate Corporation * * Adapted from ppp.c, written by Michael Callahan <callahan@maths.ox.ac.uk>, * Al Longyear <longyear@netcom.com>, * Paul Mackerras <Paul.Mackerras@cs.anu.edu.au> * * Original release 01/11/99 * * This module implements the tty line discipline N_HDLC for use with * tty device drivers that support bit-synchronous HDLC communications. * * All HDLC data is frame oriented which means: * * 1. tty write calls represent one complete transmit frame of data * The device driver should accept the complete frame or none of * the frame (busy) in the write method. Each write call should have * a byte count in the range of 2-65535 bytes (2 is min HDLC frame * with 1 addr byte and 1 ctrl byte). The max byte count of 65535 * should include any crc bytes required. For example, when using * CCITT CRC32, 4 crc bytes are required, so the maximum size frame * the application may transmit is limited to 65531 bytes. For CCITT * CRC16, the maximum application frame size would be 65533. * * * 2. receive callbacks from the device driver represents * one received frame. The device driver should bypass * the tty flip buffer and call the line discipline receive * callback directly to avoid fragmenting or concatenating * multiple frames into a single receive callback. * * The HDLC line discipline queues the receive frames in separate * buffers so complete receive frames can be returned by the * tty read calls. * * 3. tty read calls returns an entire frame of data or nothing. * * 4. all send and receive data is considered raw. No processing * or translation is performed by the line discipline, regardless * of the tty flags * * 5. When line discipline is queried for the amount of receive * data available (FIOC), 0 is returned if no data available, * otherwise the count of the next available frame is returned. * (instead of the sum of all received frame counts). * * These conventions allow the standard tty programming interface * to be used for synchronous HDLC applications when used with * this line discipline (or another line discipline that is frame * oriented such as N_PPP). * * The SyncLink driver (synclink.c) implements both asynchronous * (using standard line discipline N_TTY) and synchronous HDLC * (using N_HDLC) communications, with the latter using the above * conventions. * * This implementation is very basic and does not maintain * any statistics. The main point is to enforce the raw data