Date: Tue, 22 Jan 2002 13:26:21 -0500 (EST) From: sandeepj@research.bell-labs.com (Sandeep Joshi) To: freebsd-net@freebsd.org Subject: soreceive error handling question Message-ID: <200201221826.NAA15250@aura.research.bell-labs.com>
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I am seeing some unexplained behaviour while calling
TCP "soreceive" directly within some kernel code.
Can someone (or someone else..) tell me if this is
a bug/feature.
(This is seen on 4.3REL & 4.4 REL)
The (abbreviated) code does as follows:
---------------------------- (Fig 1)
do {
/* SS_NBIO is not set, rcv_timeo is non-zero */
err = soreceive(so, 0, &uio, 0, 0, MSG_WAITALL);
..process uio data appropriate..
} while (err == 0);
----------------------------
This works fine... until the thing at the other end
of the socket goes down and sends us a FIN. At
this point, the above code fragment hangs in an
infinite loop, since soreceive keeps returning a
zero error code but no data.
so->so_state has changed to 0x34, which is SS_CANTRCVMORE
and SS_ISCONNECTED. This is due to tcp_input() calling
socantrcvmore() on TH_FIN. And there is no read data
pending (so_rcv.sb_mb) in the socket.
I suspect that soreceive() enters the code path below
and returns from "release:" without having the error set.
----------------------------(Fig 2)
> if (so->so_state & SS_CANTRCVMORE) {
> if (m)
> goto dontblock;
> else
> goto release;
> }
----------------------------
The code calling soreceive (Fig 1) was enhanced to break
if (so_state & SS_CANTRCVMORE). This prevented the
infinite loop.
Is this extra check required OR is there a problem in
soreceive ? I am unable to determine why read(socket_fd)
(i.e. soo_read) does not exhibit similar error behaviour.
Any clarifications welcome..
Thanks
-Sandeep
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