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From: Anthony Liguori <anthony@codemonkey.ws>
To: Cam Macdonell <cam@cs.ualberta.ca>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] Passing fds through a qemu char device
Date: Fri, 22 May 2009 21:10:41 -0500	[thread overview]
Message-ID: <4A175B21.6010306@codemonkey.ws> (raw)
In-Reply-To: <4A172800.8080406@cs.ualberta.ca>

Cam Macdonell wrote:
>
> Hi,
>
> I'm trying to pass eventfds between qemu processes and I'm trying to 
> use a qemu char device to do this.  AFAICT with a qemu_chr_device the 
> polling handler only has support to call read()/write(), not 
> send/recvmsg() which are necessary to send and receive fds with 
> SCM_RIGHTS through the socket.  Is this true or is there support in 
> Qemu for recvmsg() that I'm not seeing?

The TCP/Unix implementations for CharDriverState use send/recv.  You can 
convert the recv path to always use recvmsg() and introduce an 
qemu_chr_ioctl() to pass/recv fds.

You can be smart about storing the recv'd fd in the char driver state 
and that would allow qemu_chr_ioctl(CHR_IOCTL_GET_FD) to not block.  
qemu_chr_ioctl(CHR_IOCTL_SET_FD) would set the fd to be sent for the 
next qemu_chr_write() operation.

Just a thought, other interfaces could also work.

Regards,

Anthony Liguori

  reply	other threads:[~2009-05-23  2:10 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-05-22 22:32 [Qemu-devel] Passing fds through a qemu char device Cam Macdonell
2009-05-23  2:10 ` Anthony Liguori [this message]
2009-05-26 17:47   ` Cam Macdonell

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