Re: passfd on more platforms

[Paolo Bonzini]

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
> SOCK_DGRAM only.

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.

Paolo