On Sat, Jun 12, 2021 at 11:54:58PM -0700, Greg Steuck wrote:
> I started with a failing test for Haskell network package on 6.9-current amd64
> (cabal get network-3.1.2.1 && cabal v2-test)
>
> network-3.1.2.1/build/spec/spec --match
> "/Network.Socket.ByteString/recvMsg/works well/"
>
> tests/Network/Socket/ByteStringSpec.hs:209:21:
> 1) Network.Socket.ByteString.recvMsg works well
> expected: MsgFlag {fromMsgFlag = 0}
> but got: MsgFlag {fromMsgFlag = 128}
>
> ktrace says:
>
> 47649 spec CALL sendto(14,0x8a2126e838c,0x16,0,0x8a4a3622df0,0x10)
> 47649 spec STRU struct sockaddr { AF_INET, 127.0.0.1:9486 }
> 47649 spec GIO fd 14 wrote 22 bytes
> "This is a test message"
> 47649 spec RET sendto 22/0x16
> 47649 spec CALL
> futex(0x8a4aef6f930,0x81<FUTEX_WAIT|FUTEX_PRIVATE_FLAG>,1,0,0)
> 47649 spec STRU struct kevent { ident=13, filter=EVFILT_READ,
> flags=0x11<EV_ADD|EV_ONESHOT>, fflags=0<>, data=38, udata=0x0 }
> 47649 spec RET kevent 1
> 47649 spec CALL recvmsg(13,0x8a4a3622c50,0)
> 47649 spec GIO fd 13 read 22 bytes
> "This is a test message"
> 47649 spec STRU struct sockaddr { AF_INET, 127.0.0.1:12293 }
> 47649 spec STRU struct msghdr { name=0x8a4a3622b70, namelen=16,
> iov=0x8a4a3622c30, iovlen=1, control=0x8a4a3622c10, controllen=0,
> flags=0x80<MSG_DONTWAIT> }
> 47649 spec STRU struct iovec { base=0x8a4a3622666, len=1002 }
> 47649 spec RET recvmsg 22/0x16
>
> This seems to contradict recvmsg(2) which doesn't list MSG_DONTWAIT as a
> possible value of the flags. Would this be useful as a C regress test?
Looks like this was missed in sys/kern/uipc_syscalls.c revision 1.178
date: 2018/07/30 12:22:14; author: mpi; state: Exp; lines: +10 -18;
commitid: K43aQe66cQkEOSbc;
Use FNONBLOCK instead of SS_NBIO to check/indicate that the I/O mode
for sockets is non-blocking.
This allows us to G/C SS_NBIO. Having to keep the two flags in sync
in a mp-safe way is complicated.
This change introduce a behavior change in sosplice(), it can now
always block. However this should not matter much due to the socket
lock being taken beforhand.
bluhm@, benno@, visa@
Wording taken from mpi's commit message which is exactly what recvit()
does in one place, i.e.
if (fp->f_flag & FNONBLOCK)
mp->msg_flags |= MSG_DONTWAIT;
Here's the documentation bits for it?
Feedback? Objections? OK?
Index: lib/libc/sys/recv.2
===================================================================
RCS file: /cvs/src/lib/libc/sys/recv.2,v
retrieving revision 1.47
diff -u -p -r1.47 recv.2
--- lib/libc/sys/recv.2 11 Jan 2019 06:10:13 -0000 1.47
+++ lib/libc/sys/recv.2 27 Jun 2021 13:30:33 -0000
@@ -248,6 +248,8 @@ for ancillary data.
Indicates that the packet was received as broadcast.
.It Dv MSG_MCAST
Indicates that the packet was received as multicast.
+.It Dv MSG_DONTWAIT
+Indicates that the I/O mode for the socket is non-blocking.
.El
.Sh RETURN VALUES
These calls return the number of bytes received, or \-1 if an error occurred.
