Re: Does anyone still care about BSD ptys?

["H. Peter Anvin" <hpa@zytor.com>]

Albert Cahalan wrote:
> 
> The BSD-style ptys are used all the time for
> serial port emulation. The SysV-style ones are
> useless for this, since they don't have a fixed
> mapping from master to slave. You might make a
> symlink from /dev/testbox to /dev/ptyp0, then
> configure gdb to use /dev/testbox for remote
> debugging. Then you start a remserial process
> to connect /dev/ttyp0 with port 7455 on some
> terminal server, and on the terminal server you
> have remserial connect port 7455 to /dev/C7.
> Now, whenever you run gdb, you're debugging
> a test box over a serial line connected to the
> terminal server. With SysV-style ttys, you
> can't set up your config as nicely. The above
> would likely have a few extra symlinks BTW.
> 

Eh?!  Have your server process create the appropriate symlinks... 
problem solved.

> In your use of the larger dev_t, please keep
> the first 2047 or 2048 ptys as they are today.
> Let the last major use the full 20-bit minor,
> while restricting the first 7 minors to 8 bits.
> This avoids breaking userspace software.

No bloody way in hell.  However, unless I have a strong reason to the 
contrary I'll keep them on major 136, so your little formula should 
still woprk.

> For example, due to the lack of /proc/*/tty links,
> procps uses min+(maj-136)*256 to guess the number
> of a SysV-style pty. A 32-bit dev_t will be handled
> correctly by procps 3.2 if you extend the pty usage
> as explained above.


> Adding /proc/*/tty links solves the problem as
> well, subject to a linux-2.7.0 version check.

Presumably it should be: subject to an existence check.

	-hpa