AIO operation and CMSG

AIO operation and CMSG

[Stephan Müller]

Hi,

I am working on the user space library providing a wrapper to the AF_ALG user 
space interface [1]. The AF_ALG interface supports asynchronous operation 
which is utilized with the io_* system calls, including io_submit. All works 
as expected.

The syscall io_submit sends data to the kernel and invokes the respective 
handler function in the kernel such as the recvmsg handler. What I am 
wondering is whether there is a way to send CMSG data along with the io_submit 
syscall? If not, is CMSG handling with the AIO syscalls possible at all?

Thank you very much.

[1] http://www.chronox.de/libkcapi.html

Ciao
Stephan

Re: AIO operation and CMSG

[Christoph Hellwig]

On Sun, Jan 14, 2018 at 09:01:00AM +0100, Stephan Müller wrote:
> The syscall io_submit sends data to the kernel and invokes the respective 
> handler function in the kernel such as the recvmsg handler. What I am 
> wondering is whether there is a way to send CMSG data along with the io_submit 
> syscall? If not, is CMSG handling with the AIO syscalls possible at all?

Not as-is, but it could be easily added by repurposing unused fields
in the iocb.  The big question is if it should be done to the existing
IOCB_CMD_PREADV/IOCB_CMD_PWRITEV types, or if new SENDMSG/RECVMSG ones
should be added instead.

Also you really want to Cc the relevant lists, I've only accidentally
seen this on linux-kernel.

> 
> Thank you very much.
> 
> [1] http://www.chronox.de/libkcapi.html
> 
> Ciao
> Stephan
> 
> 
---end quoted text---

Re: AIO operation and CMSG

[Stephan Mueller]

Am Mittwoch, 17. Januar 2018, 20:22:13 CET schrieb Christoph Hellwig:

Hi Christoph,

> On Sun, Jan 14, 2018 at 09:01:00AM +0100, Stephan Müller wrote:
> > The syscall io_submit sends data to the kernel and invokes the respective
> > handler function in the kernel such as the recvmsg handler. What I am
> > wondering is whether there is a way to send CMSG data along with the
> > io_submit syscall? If not, is CMSG handling with the AIO syscalls
> > possible at all?
> Not as-is, but it could be easily added by repurposing unused fields
> in the iocb.  The big question is if it should be done to the existing
> IOCB_CMD_PREADV/IOCB_CMD_PWRITEV types, or if new SENDMSG/RECVMSG ones
> should be added instead.

Thank you for the clarification. I think for the moment we have found another 
solution that we are discussing at linux-crypto. Therefore, I would currently 
not see the need for an additional support of CMSG in AIO.

Ciao
Stephan