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Re: passfd on more platforms

From: Bastien ROUCARIES
Subject: Re: passfd on more platforms
Date: Mon, 14 Mar 2011 15:02:26 +0100

On Mon, Mar 14, 2011 at 2:45 PM, Paolo Bonzini <address@hidden> wrote:
> On 03/14/2011 02:36 PM, Bastien ROUCARIES wrote:
>> Or you could ask throught the socket, the process id of the receiving
>> process than send the handle.
>> Remember:
>> It is assumed that the two sides have coordinated and agreed to
>> transfer a file descriptor already, so that the sendfd is met with a
>> recvfd instead of an ordinary read.
> No, you cannot unfortunately.  Say that process 1 will do this:
>    send "getfd\n"
>    sendfd
> then the following will work on Unix in process 2:
>    recv(socket, buf, 512) => return 6, buf = "getfd\n"
>    parse getfd
>    recvfd
> If the recvfd info is sent on the normal channel (i.e. not out-of-band),
> process 2 is going to fail like this:
>    recv(socket, buf, 512) => return 17, buf = "getfd\n0x12345678\0"
>    parse getfd
>    recvfd fails, or even worse it blocks (possibly forever)
>    even if recvfd doesn't block, parsing 0x12345678\0 fails

Why ? It is like sending and receiving data throught a protocol. i
will emulate AF_UNIX by tcp socket over localhost with TCP_NODELAY

And we already send data using unix fd passing

> Paolo

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