Re: [PATCH]fix VMX "xm console" issue

[Anthony Liguori <aliguori@us.ibm.com>]

Looking at the qemu code to create a PTY device, it's not quite optimal.

For instance, it's not suggested that you pass a name parameter to 
openpty() b/c it's unclear what's a safe size of the buffer.  Instead, 
ptsname() should be called on the slave fd.

I think the right fix is to tcsetattr() a cfmakeraw() on the slave PTY 
fd after openpty() is called in vl.c.  Otherwise, it's quite possible 
(and likely) to get strange buffering behavior depending on the terminal 
attributes that are inherited when ioemu is spawned.

Regards,

Anthony Liguori

Daniel Stekloff wrote:

>There's a problem with xm console and VMX guests, the handshaking isn't 
>exactly right. I can run xm console on the VMX guest in one window - seeing 
>the handshaking being off, run minicom on the /dev/pts/? in another window, 
>and see the original xm console window correct itself so it's usable. Before 
>minicom, you can't interact with the xm console - it doesn't seem to receive 
>the input. 
>
>I don't know about the patch here... but I've seen some odd things trying to 
>discover what's wrong. I see where xenconsoled sets the cfmakeraw() - but 
>it's like those settings aren't taking. I do an stty -f /dev/pts/? -a and the 
>settings don't match. 
>
>I've done a stty -f /dev/pts/? -a before and after minicom is invoked and seen 
>the differences. I've tried changing some of the terminos settings to match 
>minicom's in xenconsoled, but it doesn't seem to make a difference or even 
>seem to be set at all.
>
>I'm probably doing something wrong. 
>
>I'll look at this more this week. I started on it last week and was off for 
>the holiday. 
>
>Thanks,
>
>Dan
>
>
>
>On Tuesday 29 November 2005 06:10, Anthony Liguori wrote:
>  
>
>>I'm not sure what this patch does.  cfmakeraw() will already set all of
>>those flags.  You shouldn't have to set a baud rate on a PTY either.  Is
>>the real bug that somehow init_term() wasn't being called when it should
>>have been?
>>
>>What flag, in particular, did you need set that wasn't being set by
>>cfmakeraw()?  xenconsoled sets it's end of the PTY with cfmakeraw() so
>>if we modify the client to use different termios settings we probably
>>need to update the server too.
>>
>>Regards,
>>
>>Anthony Liguori
>>
>>Ian Pratt wrote:
>>    
>>
>>>>>Please expand upon what this issue with the console client is. Why
>>>>>hasn't the issue been seen with paravirtualized domains?
>>>>>          
>>>>>
>>>>"xm console" in VMX could not work well now, as we know. We
>>>>can see the output of the console, but it keeps scrolling
>>>>like hitting enter.
>>>>When I investigate this bug, I found that the serial
>>>>parameter has not been set anywhere, which might be the cause
>>>>of this issue.
>>>>        
>>>>
>>>I'd prefer to understand the issue a bit more first/
>>>
>>>      
>>>
>>>>The VMX console model for VMX is somewhat different with
>>>>domU's. When the serial port is redirect to pty, write the
>>>>allocated device to xenstore, then xm console can get it,
>>>>thus xenconsole is independent of xenconsoled in VMX.
>>>>        
>>>>
>>>But xenconsole is used by paravirt guests too. What effect does this
>>>patch have on them?
>>>
>>>Ian
>>>
>>>      
>>>
>>>>>What behaviour does the tcsetattr alter, and why not just set that
>>>>>particular bit?
>>>>>          
>>>>>
>>>>I found that Minicom can work well in "xm console" VMX, and
>>>>borrow minicom's behavior to set some parameter for "xen
>>>>console" and domU is working well too.
>>>>
>>>>        
>>>>
>>>>>Thanks,
>>>>>Ian
>>>>>
>>>>>          
>>>>>
>>>>>># HG changeset patch
>>>>>># User Ping Yu <ping.y.yu@intel.com>
>>>>>># Node ID 71111788840f0dd557d7cfc4e919beb511c0237c
>>>>>># Parent  8451c65671238604e2678a1f44c2f582ec6ebf96
>>>>>>Fix an issue for VMX console.
>>>>>>Add a function to set serial parameter, thus make "xm
>>>>>>            
>>>>>>
>>>>console" work
>>>>
>>>>        
>>>>
>>>>>>well both in domU and VMX
>>>>>>
>>>>>>Signed-off-by: Ping Yu <ping.y.yu@intel.com>
>>>>>>
>>>>>>diff -r 8451c6567123 -r 71111788840f tools/console/client/main.c
>>>>>>--- a/tools/console/client/main.c       Wed Nov 23 19:37:33 2005
>>>>>>+++ b/tools/console/client/main.c       Mon Nov 28 15:53:17 2005
>>>>>>@@ -87,6 +87,92 @@
>>>>>>	tcsetattr(fd, TCSAFLUSH, &new_term);  }
>>>>>>
>>>>>>+/* Code borrowed from Minicom
>>>>>>+ * Set baudrate, parity and number of bits  */ static void
>>>>>>+set_serial_argument(int fd, char *baudr, char *par,
>>>>>>+		char *bits, char *stopb, int hwf, int swf) {
>>>>>>+	int spd = -1;
>>>>>>+	int newbaud;
>>>>>>+	int bit = bits[0];
>>>>>>+
>>>>>>+	struct termios tty;
>>>>>>+
>>>>>>+	tcgetattr(fd, &tty);
>>>>>>+
>>>>>>+	  /* We generate mark and space parity ourself. */
>>>>>>+	if (bit == '7' && (par[0] == 'M' || par[0] == 'S'))
>>>>>>+		bit = '8';
>>>>>>+
>>>>>>+	 /* Check if 'baudr' is really a number */
>>>>>>+	if ((newbaud = (atol(baudr) / 100)) == 0 && baudr[0] != '0')
>>>>>>+		newbaud = -1;
>>>>>>+
>>>>>>+	switch(newbaud) {
>>>>>>+	case 0:
>>>>>>+	case 3:         spd = B300;     break;
>>>>>>+	case 6:         spd = B600;     break;
>>>>>>+	case 12:        spd = B1200;    break;
>>>>>>+	case 24:        spd = B2400;    break;
>>>>>>+	case 48:        spd = B4800;    break;
>>>>>>+	case 96:        spd = B9600;    break;
>>>>>>+	case 192:       spd = B19200;   break;
>>>>>>+	case 384:       spd = B38400;   break;
>>>>>>+	case 576:       spd = B57600;   break;
>>>>>>+	case 1152:      spd = B115200;  break;
>>>>>>+	case 2304:      spd = B230400;  break;
>>>>>>+	}
>>>>>>+
>>>>>>+	if (spd != -1) {
>>>>>>+		cfsetospeed(&tty, (speed_t)spd);
>>>>>>+		cfsetispeed(&tty, (speed_t)spd);
>>>>>>+	}
>>>>>>+
>>>>>>+	switch (bit) {
>>>>>>+	case '5':
>>>>>>+		tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS5;
>>>>>>+		break;
>>>>>>+	case '6':
>>>>>>+		tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS6;
>>>>>>+		break;
>>>>>>+	case '7':
>>>>>>+		tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS7;
>>>>>>+		break;
>>>>>>+	case '8':
>>>>>>+	default:
>>>>>>+		tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;
>>>>>>+		break;
>>>>>>+	}
>>>>>>+
>>>>>>+	  /* Set into raw, no echo mode */
>>>>>>+	tty.c_iflag =  IGNBRK;
>>>>>>+	tty.c_lflag = 0;
>>>>>>+	tty.c_oflag = 0;
>>>>>>+	tty.c_cflag |= CLOCAL | CREAD;
>>>>>>+	tty.c_cc[VMIN] = 1;
>>>>>>+	tty.c_cc[VTIME] = 5;
>>>>>>+
>>>>>>+	if (swf)
>>>>>>+		tty.c_iflag |= IXON | IXOFF;
>>>>>>+	else
>>>>>>+		tty.c_iflag &= ~(IXON|IXOFF|IXANY);
>>>>>>+
>>>>>>+	tty.c_cflag &= ~(PARENB | PARODD);
>>>>>>+	if (par[0] == 'E')
>>>>>>+		tty.c_cflag |= PARENB;
>>>>>>+	else if (par[0] == 'O')
>>>>>>+		tty.c_cflag |= (PARENB | PARODD);
>>>>>>+
>>>>>>+	if (stopb[0] == '2')
>>>>>>+		tty.c_cflag |= CSTOPB;
>>>>>>+	else
>>>>>>+		tty.c_cflag &= ~CSTOPB;
>>>>>>+
>>>>>>+	tcsetattr(fd, TCSANOW, &tty);
>>>>>>+
>>>>>>+}
>>>>>>+
>>>>>>static void restore_term(int fd, struct termios *old)  {
>>>>>>	tcsetattr(fd, TCSAFLUSH, old);
>>>>>>@@ -260,6 +346,7 @@
>>>>>>	free(path);
>>>>>>
>>>>>>	init_term(STDIN_FILENO, &attr);
>>>>>>+	set_serial_argument(spty, "115200", "N", "8", "1", 1, 0);
>>>>>>	console_loop(xc_handle, domid, spty);
>>>>>>	restore_term(STDIN_FILENO, &attr);
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>Sincerely Yours
>>>>>>
>>>>>>Yu Ping
>>>>>>            
>>>>>>
>>>_______________________________________________
>>>Xen-devel mailing list
>>>Xen-devel@lists.xensource.com
>>>http://lists.xensource.com/xen-devel
>>>      
>>>
>>_______________________________________________
>>Xen-devel mailing list
>>Xen-devel@lists.xensource.com
>>http://lists.xensource.com/xen-devel
>>    
>>
>
>  
>