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    SubjectRe: USBIP protocol documentation?

    matt mooney wrote:
    > On 22:25 Tue 24 May , Németh Márton wrote:
    >> Greg KH wrote:
    >>> 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.

    Could you please give some hints witch function names to look for and
    where to start "reading" the source code to see how the userspace protocol
    looks like?

    > On Tue, May 24, 2011 at 10:25:18PM +0200, Németh Márton wrote:
    >> 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?

    Greg KH wrote:
    > It might not work well on Windows, which the current code does today.
    >
    > I think that the TCP vs. SCTP is the least of the protocol issues at the
    > moment, there are lots of other things to work on :)

    matt mooney wrote:
    > 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!

    OK, I see your point. I tried to check the "source code" for a TODO list,
    but I think I failed at that point because I just found:

    | $ cat linux-2.6/drivers/staging/usbip/README
    | TODO:
    | - more discussion about the protocol
    | - testing
    | - review of the userspace interface
    |
    | Please send patches for this code to Greg Kroah-Hartman <greg@kroah.com>

    These are quite hard tasks to solve. More discussion about the protocol? I
    think the first problem is that it is difficult (at least for me) to see clearly
    the protocol because of lack of documentation.

    Testing: when you test something you compare the running code against something.
    If you compare the running code against the source code then you will not test
    the USBIP implementation/protocol, but the compiler itself, whether the compiler
    generated the same code which is available in source format.

    Review of the userspace interface: first I will need to understand how it looks
    like befor I can do anything on this point.

    Do you have a bit detailed TODO list somewhere written down or in your heads
    so beginners can also help? E.g. running "scripts/checkpatch.pl -f" and
    solving the errors/warnings helps at this point? Or compiling with "make W=1 C=1 ..."
    and solving those warnings helps?

    Regards,

    Márton Németh
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