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Patch for SOCAT correcting a bug when changing default speed of a serial asynchronous line, that occurs on some systems like FreeBSD.


With SOCAT (at least up to version on systems where b0 to b4000000 options are not available, like FreeBSD, setting the speed of a TERMIOS terminal is done using the ispeed and ospeed options.

But when using simultaneously ispeed and ospeed parameters with SOCAT, the speed values are set within two distinct ioctl requests, so changing the speed of terminals or devices that need matching input and output returns an Invalid argument error (the TIOCSETA/TIOCSETAW/TIOCSETAF ioctl returns -1 and sets errno to EINVAL).

This is especially the case On FreeBSD, where many tty device drivers need matching input and output speeds:
  • - those that depend on ucom(4): uark(4), ubsa(4), ubser(4), uftdi(4), umcs(4), uplcom(4), uslcom(4), uvscom(4)
  • - some others, even not depending on ucom(4): uart(4), sio(4), digi(4), rp(4)
But some don't: tty(4)

With those drivers, the input and output speeds must match and be set inside a single ioctl request (TIOCSETA, TIOCSETAW or TIOCSETAF). The only exception to this rule is when the input baud rate is zero because, according to POSIX, in that case, the input baud rate is set equal to the output baud rate.

For instance, this call to SOCAT on FreeBSD 10.1 terminates immediately with an EINVAL error:
# socat -d /dev/cuaU2,ispeed=57600,ospeed=57600,echo=0,raw TCP-LISTEN:9000,reuseaddr
2015/03/09 00:43:33 socat[20723] E tcsetattr(3, TCSADRAIN, 0x7fffffffe148): Invalid argument

The status of the bug report on FreeBSD: Bug 198441


- change directory to the SOCAT port directory:
# cd /usr/ports/net/socat
- download the patch: patch.diff
# fetch
- add the patch file to the port:
# mv patch.diff files/patch-xioopts.c
- compile and install the port:
# make
# make install


- download the SOCAT patched port: socat-port-patched.tar.gz
# fetch
- compile and install the port:
# tar zxf socat-port-patched.tar.gz
# cd socat
# make
# make install

Note: you can also download the compiled patched port (compiled for amd64 on 10.1-RELEASE).


- download the SOCAT patched package: socat-
# fetch
- install the package:
# pkg install socat-


- download the sources: socat-
# fetch
# tar zxf socat-

- download the patch: patch.diff
# fetch
- patch the sources:
# cd socat-
# patch < ../patch.diff
- compile and install SOCAT:
# autoconf
# ./configure
# make
# make install


- download the patched source tree: socat-
# fetch
# tar zxf socat-
- compile and install SOCAT:
# cd socat-
# autoconf
# ./configure
# make
# make install

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