possible (tcl) hanging fix on linux

[john heasley]

great!  i've reported this to the expect folks.  hopefully they will be
able to fix this properly.

Wed, Aug 15, 2001 at 08:32:36AM -0500, Mike Hyde:
> the hack is working great.  Have had no problems since putting this on.
> 
> 
> 
> -----Original Message-----
> From: owner-rancid-discuss at shrubbery.net
> [mailto:owner-rancid-discuss at shrubbery.net]On Behalf Of john heasley
> Sent: Tuesday, August 14, 2001 4:04 PM
> To: rancid-discuss at guelah.shrubbery.net
> Subject: possible (tcl) hanging fix on linux
> 
> 
> disclaimer: i am not at all sure that this is the proper way to fix
> this problem (where rancid's *logins hang while collecting info from
> devices on linux platforms with tcl8.3* and expect 5.32*) or if it
> will have adverse affects on other expect scripts.
> 
> what is happening (usually amid write term or show config, cisco-ism
> or juniper-ism) is the last chunk of data before the prompt has been
> read into the internal ("channel") buffer, expect asks for more data,
> but instead of tcl reading from the buffer or checking if the file
> descriptor is actually ready for reading, it just calls read() via
> expect's ExpInputProc() where it hangs with the router waiting for
> input (until the router's session-timeout expires).
> 
> i believe this is due to Tcl_WaitForEvent() not differentiating properly
> between timeout and "ready_for_read", but i did not unwrap the maze of
> callbacks within tcl and don't have time to right now.
> 
> the (inefficient) patch below makes sure the filedescriptor is
> set non-blocking, so the read will return immediately if the FD
> is not ready for reading and thus give the tcl timer functions the
> opportunity to timeout an operation (and apparently look at the internal
> buffer for more data).  i have no idea why this doesnt happen/affect netbsd.
> 
> it works for me with tcl8.3.b2 and expect 5.32.1 on the linux box i have
> freewill-access to, or at least do-diffs completed flawlessly 4 times,
> whereas before it barely even got out of the gate.  i think this is
> RedCrap 6.1 or so...uname says Linux 2.2.16-22, but i'm guessing that's
> just the kernel and i'm blissfully unaware of where all the other version
> info is hidden.
> 
> you'll have to apply this to your expect 5.32.1 source; cd expect-5.32;
> patch < patchfile; make install
> 
> - - - - - - - - - - - - - c u t  h e r e - - - - - - - - - - - - - -
> *** exp_chan.c.FCS	Tue Aug 14 16:55:54 2001
> --- exp_chan.c	Tue Aug 14 16:59:25 2001
> ***************
> *** 119,124 ****
> --- 119,125 ----
>        * nonblocking, the read will never block.
>        */
> 
> + fcntl(esPtr->fdin, F_SETFL, O_NONBLOCK);
>       bytesRead = read(esPtr->fdin, buf, (size_t) toRead);
>       /*printf("ExpInputProc: read(%d,,) = %d\r\n",esPtr->fdin,bytesRead);*/
>       if (bytesRead > -1) {