1From: "Doug Graham" <dgraham@nortel.com> 2Date: 2009-01-22 07:20 3 4Hello, 5 6Busybox's telnetd does not disable local (client-side) flow control 7properly. It does not put the pty into packet mode and then notify the 8client whenever flow control is disabled by an application running under 9its control. The result is that ^S/^Q are not passed through to the 10application, which is painful when the application is an emacs variant. 11 12I suppose that support for this might be considered bloat, but the 13included patch only adds about 200 bytes of text to x86 busybox and 300 14bytes to mipsel busybox. Please consider applying. 15 16============================= 17 18NB: the patch doesn't work as-is because we now have iac_safe_write() 19which quotes IACs on output. 20 21============================= 22Docs: 23 24The following ioctl(2) calls apply only to pseudo terminals: 25 26TIOCSTOP Stops output to a terminal (e.g. like typing ^S). Takes no parameter. 27 28TIOCSTART Restarts output (stopped by TIOCSTOP or by typing ^S). Takes no parameter. 29 30TIOCPKT Enable/disable packet mode. When applied to the master side of a pseudo terminal, each 31subsequent read(2) from the terminal will return data written on the slave part of the pseudo terminal preceded by a 32zero byte (symbolically defined as TIOCPKT_DATA), or a single byte reflecting control status information. 33In the latter case, the byte is an inclusive-or of zero or more of the bits: 34 35TIOCPKT_FLUSHREAD whenever the read queue for the terminal is flushed. 36TIOCPKT_FLUSHWRITE whenever the write queue for the terminal is flushed. 37TIOCPKT_STOP whenever output to the terminal is stopped a la ^S. 38TIOCPKT_START whenever output to the terminal is restarted. 39TIOCPKT_DOSTOP whenever t_stopc is ^S and t_startc is ^Q. 40TIOCPKT_NOSTOP whenever the start and stop characters are not ^S/^Q. 41 42While this mode is in use, the presence of control status information to be read from the master side may be detected 43by a select(2) for exceptional conditions. 44 45This mode is used by rlogin(1) and rlogind(8) to implement a remote-echoed, locally ^S/^Q flow-controlled remote login 46with proper back-flushing of output; it can be used by other similar programs. 47 48TIOCUCNTL Enable/disable a mode that allows a small number of simple user ioctl(2) commands to be passed through 49the pseudo-terminal, using a protocol similar to that of TIOCPKT. The TIOCUCNTL and TIOCPKT modes are mutually 50exclusive. This mode is enabled from the master side of a pseudo terminal. Each subsequent read(2) from the master side 51will return data written on the slave part of the pseudo terminal preceded by a zero byte, or a single byte reflecting a 52user control operation on the slave side. A user control command consists of a special ioctl(2) operation with no data; 53the command is given as UIOCCMD (n), where n is a number in the range 1-255. The operation value n will be received as 54a single byte on the next read(2) from the master side. The ioctl(2) UIOCCMD (0) is a no-op that may be used to probe 55for the existence of this facility. As with TIOCPKT mode, command operations may be detected with a select(2) for 56exceptional conditions. 57 58--- busybox-1.13.2/networking/telnetd.c 2009/01/21 20:02:39 1.1 59+++ busybox-1.13.2/networking/telnetd.c 2009/01/22 00:35:28 60@@ -38,6 +38,9 @@ 61 int sockfd_read, sockfd_write, ptyfd; 62 int shell_pid; 63 64+#ifdef TIOCPKT 65+ int flowstate; 66+#endif 67 /* two circular buffers */ 68 /*char *buf1, *buf2;*/ 69 /*#define TS_BUF1 ts->buf1*/ 70@@ -170,6 +173,9 @@ 71 int fd, pid; 72 char tty_name[GETPTY_BUFSIZE]; 73 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2); 74+#ifdef TIOCPKT 75+ int on = 1; 76+#endif 77 78 /*ts->buf1 = (char *)(ts + 1);*/ 79 /*ts->buf2 = ts->buf1 + BUFSIZE;*/ 80@@ -180,6 +186,10 @@ 81 maxfd = fd; 82 ts->ptyfd = fd; 83 ndelay_on(fd); 84+#ifdef TIOCPKT 85+ ioctl(fd, TIOCPKT, &on); 86+ ts->flowstate = TIOCPKT_DOSTOP; 87+#endif 88 #if ENABLE_FEATURE_TELNETD_STANDALONE 89 ts->sockfd_read = sock; 90 /* SO_KEEPALIVE by popular demand */ 91@@ -385,6 +395,16 @@ 92 portnbr = 23, 93 }; 94 #endif 95+#ifdef TIOCPKT 96+ int control; 97+ static const char lflow_on[] ALIGN1 = 98+ {IAC, SB, TELOPT_LFLOW, LFLOW_ON, IAC, SE}; 99+ static const char lflow_off[] ALIGN1 = 100+ {IAC, SB, TELOPT_LFLOW, LFLOW_OFF, IAC, SE}; 101+# define RESERVED sizeof(lflow_on) 102+#else 103+# define RESERVED 0 104+#endif 105 /* Even if !STANDALONE, we accept (and ignore) -i, thus people 106 * don't need to guess whether it's ok to pass -i to us */ 107 opt = getopt32(argv, "f:l:Ki" IF_FEATURE_TELNETD_STANDALONE("p:b:F"), 108@@ -475,7 +495,7 @@ 109 FD_SET(ts->sockfd_read, &rdfdset); 110 if (ts->size2 > 0) /* can write to socket */ 111 FD_SET(ts->sockfd_write, &wrfdset); 112- if (ts->size2 < BUFSIZE) /* can read from pty */ 113+ if (ts->size2 < (BUFSIZE - RESERVED)) /* can read from pty */ 114 FD_SET(ts->ptyfd, &rdfdset); 115 } 116 ts = next; 117@@ -593,6 +613,52 @@ 118 goto skip4; 119 goto kill_session; 120 } 121+#ifdef TIOCPKT 122+ control = TS_BUF2[ts->rdidx2]; 123+ if (--count > 0 && control == TIOCPKT_DATA) { 124+ /* 125+ * If we are in packet mode, and we have 126+ * just read a chunk of actual data from 127+ * the pty, then there is the TIOCPKT_DATA 128+ * byte (zero) that we have got to remove 129+ * somehow. If there were no chars in 130+ * TS_BUF2 before we did this read, then 131+ * we can optimize by just advancing wridx2. 132+ * Otherwise we have to copy the new data down 133+ * to close the gap (Could use readv() instead). 134+ */ 135+ if (ts->size2 == 0) 136+ ts->wridx2++; 137+ else { 138+ memmove(TS_BUF2 + ts->rdidx2, 139+ TS_BUF2 + ts->rdidx2 + 1, count); 140+ } 141+ } 142+ 143+ /* 144+ * If the flow control state changed, notify 145+ * the client. If "control" is not TIOCPKT_DATA, 146+ * then there are no data bytes to worry about. 147+ */ 148+ if ((control & (TIOCPKT_DOSTOP|TIOCPKT_NOSTOP)) != 0 149+ && ts->flowstate != (control & TIOCPKT_DOSTOP)) { 150+ const char *p = ts->flowstate ? lflow_off : lflow_on; 151+ 152+ /* 153+ * We know we have enough free slots available 154+ * (see RESERVED) but they are not necessarily 155+ * contiguous; we may have to wrap. 156+ */ 157+ for (count = sizeof(lflow_on); count > 0; count--) { 158+ TS_BUF2[ts->rdidx2++] = *p++; 159+ if (ts->rdidx2 >= BUFSIZE) 160+ ts->rdidx2 = 0; 161+ ts->size2++; 162+ } 163+ 164+ ts->flowstate = control & TIOCPKT_DOSTOP; 165+ } 166+#endif /* TIOCPKT */ 167 ts->size2 += count; 168 ts->rdidx2 += count; 169 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */ 170 171--Doug 172_______________________________________________ 173busybox mailing list 174busybox@busybox.net 175http://lists.busybox.net/mailman/listinfo/busybox 176