The imsg_init(3) man page currently doesn't make it clear whether
this library can be used for remote communication.
The current text reads:
The imsg functions provide a simple mechanism for communication
between processes using sockets. Each transmitted message is
guaranteed to be presented to the receiving program whole. They
are commonly used in privilege separated processes, where
processes with different rights are required to cooperate.
It also mentions socketpair(2) later but does not specify whether
this would work over tcp(4) connections.
Looking at the libutil imsg code, it doesn't look like there's any
htonl(3) or byte order swapping when accessing the sizes, so this was
probably not intended for network use.
So my questions are:
(a) Am I correct in understanding imsg cannot be used to
communicate over networks in an architecture-independent way?
(b) Should the manual page be updated to reflect this reality,
so users can better compare possible IPC mechanisms?
(c) Should the library itself be updated to use network byte
order, so it could be used between different architectures
over an established TCP connection?
Simplest possible patch for (b) below.
Index: imsg_init.3
===================================================================
RCS file: /cvs/src/lib/libutil/imsg_init.3,v
retrieving revision 1.21
diff -u -p -u -r1.21 imsg_init.3
--- imsg_init.3 16 Feb 2018 07:42:07 -0000 1.21
+++ imsg_init.3 14 Sep 2018 20:53:10 -0000
@@ -106,7 +106,7 @@
.Sh DESCRIPTION
The
.Nm imsg
-functions provide a simple mechanism for communication between processes
+functions provide a simple mechanism for communication between local processes
using sockets.
Each transmitted message is guaranteed to be presented to the receiving program
whole.
