Re: SIGINFO on Windows

[Guy Harris <guy () alum mit edu>]

On Jan 7, 2004, at 3:21 AM, Gisle Vanem wrote:

> I'm trying to support the requestinfo() functionality in Windump,
> but failed to find much info on SIGINFO. How often is this signal 
> handler
> called (on Linux/BSD)?

On Linux, not at all - it's not available on Linux (unless they picked 
it up for 2.6).

On BSD, it's generated when you type control-T on a terminal or in a 
terminal window in which tcpdump is running in the foreground; 
control-T generates SIGINFO.  It's not delivered automatically on some 
time schedule.

To quote the TERMIOS(4) man page on Mac OS X (which is pretty much a 
standard BSD TERMIOS(4) man page):

   Special Characters
     Certain characters have special functions on input or output or 
both.
     These functions are summarized as follows:

     INTR    Special character on input and is recognized if the ISIG 
flag
             (see the Local Modes section) is enabled.  Generates a 
SIGINT
             signal which is sent to all processes in the foreground 
process
             group for which the terminal is the controlling terminal.  
If
             ISIG is set, the INTR character is discarded when 
processed.

                ...

     The following special characters are extensions defined by this 
system
     and are not a part of 1003.1 termios.

                ...

     STATUS  Special character on input and is recognized if the ICANON 
flag
             is set.  Receipt of this character causes a SIGINFO signal 
to be
             sent to the foreground process group of the terminal.  
Also, if
             the NOKERNINFO flag is not set, it causes the kernel to 
write a
             status message to the terminal that displays the current 
load
             average, the name of the command in the foreground, its 
process
             ID, the symbolic wait channel, the number of user and 
system sec-
             onds used, the percentage of cpu the process is getting, 
and the
             resident set size of the process.

                ...

   Local Modes
     Values of the c_lflag field describe the control of various 
functions,
     and are composed of the following masks.

                ...

     If NOKERNINFO is set, the kernel does not produce a status message 
when
     processing STATUS characters (see STATUS).

   Special Control Characters
     The special control characters values are defined by the array 
c_cc.
     This table lists the array index, the corresponding special 
character,
     and the system default value.  For an accurate list of the system
     defaults, consult the header file <ttydefaults.h>.

           Index Name    Special Character    Default Value

                ...

           VINTR         INTR                 ^C

                ...

           VSTATUS       STATUS               ^T

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