Re: [PATCH v2 2/2] usbip: Implement SG support to vhci

[shuah]

On 8/1/19 12:38 AM, Suwan Kim wrote:
> On Mon, Jul 29, 2019 at 10:32:31AM -0600, shuah wrote:
> > On 7/29/19 8:52 AM, Suwan Kim wrote:
> > > Hi Shuah,
> > >
> > > On Tue, Jul 23, 2019 at 06:21:53PM -0600, shuah wrote:
> > > > Hi Suwan,
> > > >
> > > > On 7/5/19 10:43 AM, Suwan Kim wrote:
> > > > > There are bugs on vhci with usb 3.0 storage device. Originally, vhci
> > > > > doesn't supported SG, so USB storage driver on vhci breaks SG list
> > > > > into multiple URBs and it causes error that a transfer got terminated
> > > > > too early because the transfer length for one of the URBs was not
> > > > > divisible by the maxpacket size.
> > > > >
> > > > > In this patch, vhci basically support SG and it sends each SG list
> > > > > entry to the stub driver. Then, the 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 the stub driver receives
> > > > > completed URB, it again sends each SG list entry to vhci.
> > > > >
> > > > > If HCD of the server doesn't support SG, the stub driver breaks a
> > > > > single SG reqeust into several URBs and submit them to the server's
> > > > > HCD. When all the split URBs are completed, the stub driver
> > > > > reassembles the URBs into a single return command and sends it to
> > > > > vhci.
> > > > >
> > > > > Signed-off-by: Suwan Kim <suwan.kim027@xxxxxxxxx>
> > > > > ---
> > > > >     drivers/usb/usbip/stub.h         |   7 +-
> > > > >     drivers/usb/usbip/stub_main.c    |  52 +++++---
> > > > >     drivers/usb/usbip/stub_rx.c      | 207 ++++++++++++++++++++++---------
> > > > >     drivers/usb/usbip/stub_tx.c      | 108 +++++++++++-----
> > > > >     drivers/usb/usbip/usbip_common.c |  60 +++++++-- >   drivers/usb/usbip/vhci_hcd.c     |  10 +-
> > > > >     drivers/usb/usbip/vhci_tx.c      |  49 ++++++--
> > > > >     7 files changed, 372 insertions(+), 121 deletions(-)
> > > >
> > > > While you are working on v3 to fix chekpatch and other issues
> > > > I pointed out, I have more for you.
> > > >
> > > > What happens when you have mismatched server and client side?
> > > > i.e stub does and vhci doesn't and vice versa.
> > > >
> > > > Make sure to run checkpatch. Also check spelling errors in
> > > > comments and your commit log.
> > > >
> > > > I am not sure if your eeror paths are correct. Run usbip_test.sh
> > > >
> > > > tools/testing/selftests/drivers/usb/usbip
> > >
> > > I don't know what mismatch you mentioned. Are you saying
> > > "match busid table" at the end of usbip_test.sh?
> > > How does it relate to SG support of this patch?
> > > Could you tell me more about the problem situation?
> >
> > What happens when usbip_host is running a kernel without the sg
> > support and vhci_hcd does? Just make sure this works with the
> > checks for sg support status as a one of your tests for this
> > sg feature.
>
> Now I understand. Thanks for the details!
> As a result of testing, in the situation where vhci supports SG,
> but stub does not, or vice versa, usbip works normally. Moreover,
> 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 doesn't, because vhci sends
> only the total length of the buffer to stub as it did before the
> patch applied, stub only needs to allocate the required length of
> buffers regardless of whether vhci supports SG or not.
>
> If stub needs to send data buffer to vhci because of IN pipe, stub
> also sends only total length of buffer as metadata and then send real
> data as vhci does. Then vhci receive data from stub and store it to
> the corresponding buffer of SG list entry.
>
> In the case of stub that supports SG, if SG buffer is requested by
> vhci, buffer is allocated by sgl_alloc(). However, stub that does
> not support SG allocates buffer using only kmalloc(). Therefore, if
> vhci supports SG and stub doesn't, stub 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 big overhead in buffer
> allocation.
>
> And for the case of stub supports SG and vhci doesn't, since the
> USB storage driver checks that vhci doesn't support SG and sends
> the request to stub by splitting the SG list into multiple URBs,
> stub allocates a buffer with kmalloc() as it did before this patch.
>
> Therefore, everything works normally in a mismatch situation.

Looking for you add a test case for that. Please include this
in the commit log.

> I will send the v3 soon.

Please send it soon. It would be nice to have this done as soon
as possible.

thanks,
-- Shuah