linux-kernel - Re: USBIP protocol documentation?

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Date:	Tue, 24 May 2011 20:12:22 -0700
From:	matt mooney <mfm@...eddisk.com>
To:	N??meth M??rton <nm127@...email.hu>
Cc:	Greg KH <greg@...ah.com>, Matthew Wilcox <matthew@....cx>,
	linux-usb@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	usbip-devel@...ts.sourceforge.net
Subject: Re: USBIP protocol documentation?

On 22:25 Tue 24 May     , N??meth M??rton wrote:
> Greg KH wrote:
> > On Tue, May 24, 2011 at 08:28:13PM +0200, N??meth M??rton wrote:
> >> Hi,
> >>
> >> I'm looking for the USBIP protocol documentation. I found that
> >> there was already a discussion about the USBIP protocol and
> >> there is some draft about it:
> >>
> >>   * http://marc.info/?l=linux-kernel&m=122001863119269&w=2
> >>   * http://www.kernel.org/pub/linux/kernel/people/willy/usbip/usbip-protocol-draft-1
> >>
> >> Unfortunately I couldn't found any detailed protocol documentation
> >> on the project homepage:
> >>
> >>   * http://usbip.sourceforge.net/#documentation
> >>
> >> Do you know any follow-up on the USBIP protocol documentation?
> > 
> > I think the code is the "real" documentation.

I concur!
 
> If it is, then I need to read it in the right way, through it is not an easy task.
> I tried to find the points in the USBIP kernel code where opening, sending,
> receiving and closing of the TCP connection takes place. I took all function names
> from linux/net.h and I found the following places so far:
> 
> $ grep -n -E
> 'sock_wake_async|sock_register|sock_unregister|sock_create|sock_create_kern|sock_create_lite|sock_release|sock_sendmsg|sock_recvmsg|sock_map_fd|sockfd_lookup|sockfd_put|net_ratelimit|kernel_sendmsg|kernel_recvmsg|kernel_bind|kernel_listen|kernel_accept|kernel_connect|kernel_getsockname|kernel_getpeername|kernel_getsockopt|kernel_setsockopt|kernel_sendpage|kernel_sock_ioctl|kernel_sock_shutdown|SHUT_'
> linux-2.6/drivers/staging/usbip/*
> 
> linux-2.6/drivers/staging/usbip/stub_dev.c:201:         kernel_sock_shutdown(ud->tcp_socket, SHUT_RDWR);
> linux-2.6/drivers/staging/usbip/stub_dev.c:216:         sock_release(ud->tcp_socket);
> linux-2.6/drivers/staging/usbip/stub_tx.c:263:          ret = kernel_sendmsg(sdev->ud.tcp_socket, &msg,
> linux-2.6/drivers/staging/usbip/stub_tx.c:338:          ret = kernel_sendmsg(sdev->ud.tcp_socket, &msg, iov,
> linux-2.6/drivers/staging/usbip/usbip_common.c:382:                     result = kernel_sendmsg(sock, &msg, &iov, 1, size);
> linux-2.6/drivers/staging/usbip/usbip_common.c:384:                     result = kernel_recvmsg(sock, &msg, &iov, 1, size,
> linux-2.6/drivers/staging/usbip/vhci_hcd.c:845:         kernel_sock_shutdown(ud->tcp_socket, SHUT_RDWR);
> linux-2.6/drivers/staging/usbip/vhci_hcd.c:858:         sock_release(vdev->ud.tcp_socket);
> linux-2.6/drivers/staging/usbip/vhci_tx.c:119:          ret = kernel_sendmsg(vdev->ud.tcp_socket, &msg, iov, 3, txsize);
> linux-2.6/drivers/staging/usbip/vhci_tx.c:189:          ret = kernel_sendmsg(vdev->ud.tcp_socket, &msg, iov, 1, txsize);
> 
> I guess this is not all, there is also a protocol defined to the user-space world.

Very true, and part of what is taking place is a unification of the userspace
and kernel protocols. Then there will be some degree of documentation. Mainly in
the form of packet diagrams to show on-wire communication.
 
> > Note a number of developers are actively working on changing the protocol
> > and fixing it up based on Matthew's previous comments.  Look at the
> > thread on the usbip project's mailing list for a few details.  More will
> > be in the patches produced by the developers.
> 
> I had a look at the usbip-devel mailing list archive at
> http://sourceforge.net/mailarchive/forum.php?forum_name=usbip-devel and found
> a thread where I could find some protocol description also:
> 
>  * http://sourceforge.net/mailarchive/message.php?msg_id=27240940
> 
> The current protocol implementation is based on top of TCP. In the message
> at http://marc.info/?l=linux-kernel&m=122001883519653&w=2 the SCTP is mentioned.
> Have anybody worked on finding out what benefits the SCTP could give to USBIP
> and what would be the drawbacks?

I think sctp would be interesting, but as greg said, and I tend to agree, this
is the least of usbip's problems.

(Maybe eliminating the need to interact w/ windows would be a good project ;)
jk!

-matt
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