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Re: passfd on more platforms

From: Paolo Bonzini
Subject: Re: passfd on more platforms
Date: Mon, 14 Mar 2011 16:05:04 +0100
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On 03/14/2011 03:44 PM, Eric Blake wrote:
>  No, that's exactly the_wrong_  reason for TCP_NODELAY.  You simply
>  cannot expect message boundaries to be respected when using SOCK_STREAM.
>  So, either sendfd/recvfd must be documented to work only on SOCK_DGRAM
>  sockets, or they have to be rethought (if possible at all).

Note that just last week libvirt found an issue with SOCK_STREAM hanging
forever on recvfd when the sendfd side was skipped, but SOCK_DGRAM was
able to reliably detect when the sending side of the socket is closed.
I'm perfectly fine with documenting that sendfd/recvfd must be used on

But that was a different problem.  That was not related to sendfd/recvfd.

However, there are cases in which you want to send a file descriptor as out-of-band messages on a stream socket, and libvirt also has one of those.

From a quick experiment, BTW, on a SOCK_DGRAM Unix socket you don't need to send fake data at the same time, but I may be wrong and/or that may not be portable.


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