arch/um/drivers/slip_common.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __UM_SLIP_COMMON_H
   3 #define __UM_SLIP_COMMON_H
   4
   5 #define BUF_SIZE 1500
   6  /* two bytes each for a (pathological) max packet of escaped chars +  *
   7   * terminating END char + initial END char                            */
   8 #define ENC_BUF_SIZE (2 * BUF_SIZE + 2)
   9
  10 /* SLIP protocol characters. */
  11 #define SLIP_END             0300       /* indicates end of frame       */
  12 #define SLIP_ESC             0333       /* indicates byte stuffing      */
  13 #define SLIP_ESC_END         0334       /* ESC ESC_END means END 'data' */
  14 #define SLIP_ESC_ESC         0335       /* ESC ESC_ESC means ESC 'data' */
  15
  16 static inline int slip_unesc(unsigned char c, unsigned char *buf, int *pos,
  17                              int *esc)
  18 {
  19         int ret;
  20
  21         switch(c){
  22         case SLIP_END:
  23                 *esc = 0;
  24                 ret=*pos;
  25                 *pos=0;
  26                 return(ret);
  27         case SLIP_ESC:
  28                 *esc = 1;
  29                 return(0);
  30         case SLIP_ESC_ESC:
  31                 if(*esc){
  32                         *esc = 0;
  33                         c = SLIP_ESC;
  34                 }
  35                 break;
  36         case SLIP_ESC_END:
  37                 if(*esc){
  38                         *esc = 0;
  39                         c = SLIP_END;
  40                 }
  41                 break;
  42         }
  43         buf[(*pos)++] = c;
  44         return(0);
  45 }
  46
  47 static inline int slip_esc(unsigned char *s, unsigned char *d, int len)
  48 {
  49         unsigned char *ptr = d;
  50         unsigned char c;
  51
  52         /*
  53          * Send an initial END character to flush out any
  54          * data that may have accumulated in the receiver
  55          * due to line noise.
  56          */
  57
  58         *ptr++ = SLIP_END;
  59
  60         /*
  61          * For each byte in the packet, send the appropriate
  62          * character sequence, according to the SLIP protocol.
  63          */
  64
  65         while (len-- > 0) {
  66                 switch(c = *s++) {
  67                 case SLIP_END:
  68                         *ptr++ = SLIP_ESC;
  69                         *ptr++ = SLIP_ESC_END;
  70                         break;
  71                 case SLIP_ESC:
  72                         *ptr++ = SLIP_ESC;
  73                         *ptr++ = SLIP_ESC_ESC;
  74                         break;
  75                 default:
  76                         *ptr++ = c;
  77                         break;
  78                 }
  79         }
  80         *ptr++ = SLIP_END;
  81         return (ptr - d);
  82 }
  83
  84 struct slip_proto {
  85         unsigned char ibuf[ENC_BUF_SIZE];
  86         unsigned char obuf[ENC_BUF_SIZE];
  87         int more; /* more data: do not read fd until ibuf has been drained */
  88         int pos;
  89         int esc;
  90 };
  91
  92 static inline void slip_proto_init(struct slip_proto * slip)
  93 {
  94         memset(slip->ibuf, 0, sizeof(slip->ibuf));
  95         memset(slip->obuf, 0, sizeof(slip->obuf));
  96         slip->more = 0;
  97         slip->pos = 0;
  98         slip->esc = 0;
  99 }
 100
 101 extern int slip_proto_read(int fd, void *buf, int len,
 102                            struct slip_proto *slip);
 103 extern int slip_proto_write(int fd, void *buf, int len,
 104                             struct slip_proto *slip);
 105
 106 #endif