Re: passfd on more platforms

[Paolo Bonzini]

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

Paolo