39 /* Simple minded read-ahead/write-behind subroutines for tftp user and
43    Todo:  add some sort of final error check so when the write-buffer
44    is finally flushed, the caller can detect if the disk filled up
67 #define BF_ALLOC -3             /* alloc'd but not yet filled */
68 #define BF_FREE  -2             /* free */
69 /* [-1 .. SEGSIZE] = size of data in the data buffer */
75 int newline = 0;        /* fillbuf: in middle of newline expansion */  variable
76 int prevchar = -1;      /* putbuf: previous char (cr check) */
80 struct tftphdr *w_init() { return rw_init(0); }         /* write-behind */  in w_init()
81 struct tftphdr *r_init() { return rw_init(1); }         /* read-ahead */  in r_init()
83 /* init for either read-ahead or write-behind */
84 /* x is zero for write-behind, one for read-head */
87 	newline = 0;            /* init crlf flag */  in rw_init()
88 	prevchar = -1;  in rw_init()
108 	if (b->counter == BF_FREE)      /* if it's empty */  in readit()
111 	assert(b->counter != BF_FREE);  /* check */  in readit()
113 	*dpp = (struct tftphdr *)b->buf;        /* set caller's ptr */  in readit()
114 	return b->counter;  in readit()
119  * conversions are  lf -> cr,lf  and cr -> cr, nul
130 	if (b->counter != BF_FREE)      /* nop if not free */  in read_ahead()
134 	dp = (struct tftphdr *)b->buf;  in read_ahead()
137 		b->counter = read(fileno(file), dp->th_data, SEGSIZE);  in read_ahead()
141 	p = dp->th_data;  in read_ahead()
143 		if (newline) {  in read_ahead()
147 			newline = 0;  in read_ahead()
155 				newline = 1;  in read_ahead()
160 	b->counter = (int)(p - dp->th_data);  in read_ahead()
180  * CR,NUL -> CR  and CR,LF => LF.
195 	if (b->counter < -1)            /* anything to flush? */  in write_behind()
198 	count = b->counter;             /* remember byte count */  in write_behind()
199 	b->counter = BF_FREE;           /* reset flag */  in write_behind()
200 	dp = (struct tftphdr *)b->buf;  in write_behind()
202 	buf = dp->th_data;  in write_behind()
204 	if (count <= 0) return -1;      /* nak logic? */  in write_behind()
211 	while (ct--) {                  /* loop over the buffer */  in write_behind()
215 		   fseek(file, -1, 1);  /* smash lf on top of the cr */  in write_behind()
231  * response to packet N is really their response to packet N-1.