SO_RERROR indicates that receive buffer overflows should be handled as errors.

Historically receive buffer overflows have been ignored and programs
could not tell if they missed messages or messages had been truncated
because of overflows. Since programs historically do not expect to get
receive overflow errors, this behavior is not the default.

This is really really important for programs that use route(4) to keep in sync
with the system. If we loose a message then we need to reload the full system
state, otherwise the behaviour from that point is undefined and can lead
to chasing bogus bug reports.

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/libc/sys/getsockopt.2 b/lib/libc/sys/getsockopt.2
index 1e4ed6827170..223eb3e8a28b 100644
--- a/lib/libc/sys/getsockopt.2
+++ b/lib/libc/sys/getsockopt.2
@@ -28,7 +28,7 @@
 .\"     @(#)getsockopt.2	8.4 (Berkeley) 5/2/95
 .\" $FreeBSD$
 .\"
-.Dd June 3, 2020
+.Dd Feb 07, 2020
 .Dt GETSOCKOPT 2
 .Os
 .Sh NAME
@@ -177,6 +177,7 @@ for the socket
 .It Dv SO_PROTOCOL Ta "get the protocol number for the socket (get only)"
 .It Dv SO_PROTOTYPE Ta "SunOS alias for the Linux SO_PROTOCOL (get only)"
 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
+.It Dv SO_RERROR Ta "enables receive error reporting"
 .It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
 .El
 .Pp
@@ -514,6 +515,13 @@ returns any pending error on the socket and clears
 the error status.
 It may be used to check for asynchronous errors on connected
 datagram sockets or for other asynchronous errors.
+.Dv SO_RERROR
+indicates that receive buffer overflows should be handled as errors.
+Historically receive buffer overflows have been ignored and programs
+could not tell if they missed messages or messages had been truncated
+because of overflows.
+Since programs historically do not expect to get receive overflow errors,
+this behavior is not the default.
 .Pp
 .Dv SO_LABEL
 returns the MAC label of the socket.