• Suwan Kim's avatar
    usbip: Implement SG support to vhci-hcd and stub driver · ea44d190
    Suwan Kim authored
    There are bugs on vhci with usb 3.0 storage device. In USB, each SG
    list entry buffer should be divisible by the bulk max packet size.
    But with native SG support, this problem doesn't matter because the
    SG buffer is treated as contiguous buffer. But without native SG
    support, USB storage driver breaks SG list into several URBs and the
    error occurs because of a buffer size of URB that cannot be divided
    by the bulk max packet size. The error situation is as follows.
    
    When USB Storage driver requests 31.5 KB data and has SG list which
    has 3584 bytes buffer followed by 7 4096 bytes buffer for some
    reason. USB Storage driver splits this SG list into several URBs
    because VHCI doesn't support SG and sends them separately. So the
    first URB buffer size is 3584 bytes. When receiving data from device,
    USB 3.0 device sends data packet of 1024 bytes size because the max
    packet size of BULK pipe is 1024 bytes. So device sends 4096 bytes.
    But the first URB buffer has only 3584 bytes buffer size. So host
    controller terminates the transfer even though there is more data to
    receive. So, vhci needs to support SG transfer to prevent this error.
    
    In this patch, vhci supports SG regardless of whether the server's
    host controller supports SG or not, because stub driver splits SG
    list into several URBs if the server's host controller doesn't
    support SG.
    
    To support SG, vhci sets URB_DMA_MAP_SG flag in urb->transfer_flags
    if URB has SG list and this flag will tell stub driver to use SG
    list. After receiving urb from stub driver, vhci clear URB_DMA_MAP_SG
    flag to avoid unnecessary DMA unmapping in HCD.
    
    vhci sends each SG list entry to stub driver. Then, stub driver sees
    the total length of the buffer and allocates SG table and pages
    according to the total buffer length calling sgl_alloc(). After stub
    driver receives completed URB, it again sends each SG list entry to
    vhci.
    
    If the server's host controller doesn't support SG, stub driver
    breaks a single SG request into several URBs and submits them to
    the server's host controller. When all the split URBs are completed,
    stub driver reassembles the URBs into a single return command and
    sends it to vhci.
    
    Moreover, in the situation where vhci supports SG, but stub driver
    does not, or vice versa, usbip works normally. Because there is no
    protocol modification, there is no problem in communication between
    server and client even if the one has a kernel without SG support.
    
    In the case of vhci supports SG and stub driver doesn't, because
    vhci sends only the total length of the buffer to stub driver as
    it did before the patch applied, stub driver only needs to allocate
    the required length of buffers using only kmalloc() regardless of
    whether vhci supports SG or not. But stub driver has to allocate
    buffer with kmalloc() as much as the total length of SG buffer which
    is quite huge when vhci sends SG request, so it has overhead in
    buffer allocation in this situation.
    
    If stub driver needs to send data buffer to vhci because of IN pipe,
    stub driver also sends only total length of buffer as metadata and
    then sends real data as vhci does. Then vhci receive data from stub
    driver and store it to the corresponding buffer of SG list entry.
    
    And for the case of stub driver supports SG and vhci doesn't, since
    the USB storage driver checks that vhci doesn't support SG and sends
    the request to stub driver by splitting the SG list into multiple
    URBs, stub driver allocates a buffer for each URB with kmalloc() as
    it did before this patch.
    
    * Test environment
    
    Test uses two difference machines and two different kernel version
    to make mismatch situation between the client and the server where
    vhci supports SG, but stub driver does not, or vice versa. All tests
    are conducted in both full SG support that both vhci and stub support
    SG and half SG support that is the mismatch situation. Test kernel
    version is 5.3-rc6 with commit "usb: add a HCD_DMA flag instead of
    guestimating DMA capabilities" to avoid unnecessary DMA mapping and
    unmapping.
    
     - Test kernel version
        - 5.3-rc6 with SG support
        - 5.1.20-200.fc29.x86_64 without SG support
    
    * SG support test
    
     - Test devices
        - Super-speed storage device - SanDisk Ultra USB 3.0
        - High-speed storage device - SMI corporation USB 2.0 flash drive
    
     - Test description
    
    Test read and write operation of mass storage device that uses the
    BULK transfer. In test, the client reads and writes files whose size
    is over 1G and it works normally.
    
    * Regression test
    
     - Test devices
        - Super-speed device - Logitech Brio webcam
        - High-speed device  - Logitech C920 HD Pro webcam
        - Full-speed device  - Logitech bluetooth mouse
                             - Britz BR-Orion speaker
        - Low-speed device   - Logitech wired mouse
    
     - Test description
    
    Moving and click test for mouse. To test the webcam, use gnome-cheese.
    To test the speaker, play music and video on the client. All works
    normally.
    
    * VUDC compatibility test
    
    VUDC also works well with this patch. Tests are done with two USB
    gadget created by CONFIGFS USB gadget. Both use the BULK pipe.
    
            1. Serial gadget
            2. Mass storage gadget
    
     - Serial gadget test
    
    Serial gadget on the host sends and receives data using cat command
    on the /dev/ttyGS<N>. The client uses minicom to communicate with
    the serial gadget.
    
     - Mass storage gadget test
    
    After connecting the gadget with vhci, use "dd" to test read and
    write operation on the client side.
    
    Read  - dd if=/dev/sd<N> iflag=direct of=/dev/null bs=1G count=1
    Write - dd if=<my file path> iflag=direct of=/dev/sd<N> bs=1G count=1
    Signed-off-by: default avatarSuwan Kim <suwan.kim027@gmail.com>
    Acked-by: default avatarShuah khan <skhan@linuxfoundation.org>
    Link: https://lore.kernel.org/r/20190828032741.12234-1-suwan.kim027@gmail.comSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    ea44d190
vhci_tx.c 5.84 KB