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Date: Sun, 04 Feb 2007 16:52:35 -0800 (PST) From: David Miller <davem@...emloft.net> To: dkabs@...otix.com Cc: linux-kernel@...r.kernel.org Subject: Re: Problem with unix sockets: SOCK_DGRAM ignores MSG_TRUNC From: Daniel Kabs <dkabs@...otix.com> Date: Mon, 29 Jan 2007 12:59:49 +0100 > I use unix domain datagram sockets for IPC, e.g. I receive messages by > calling recv(). > > "man 2 recv" tells me about the flags argument to a recv() call, namely: > > MSG_TRUNC > Return the real length of the packet, even when it was longer > than the passed buffer. Only valid for packet sockets. > > Thus I used recv() with flags MSG_TRUNC|MSG_PEEK in order to detect > message truncation due to insufficient buffer size. What part of "Only valid for packet sockets" from the manual page escapes you? :-)) It's a feature which only was meant to be valid for AF_PACKET sockets. What UDP is doing is different, it's returning the full packet length when the packet is larger then the given buffer size, but it does this irregardless of whether you set MSG_TRUNC in the recvmsg() passed-in flags. UDP itself sets the MSG_TRUNC flag when it detects this situation. I checked the history and our AF_UNIX sockets have always behaved like this. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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