linux-kernel - Re: [PATCH v2 0/2] usbip: Implement SG support

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Date:   Sun, 21 Jul 2019 18:01:29 +0900
From:   Suwan Kim <suwan.kim027@...il.com>
To:     shuah <shuah@...nel.org>
Cc:     valentina.manea.m@...il.com, stern@...land.harvard.edu,
        gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] usbip: Implement SG support

On Fri, Jul 19, 2019 at 04:04:20PM -0600, shuah wrote:
> 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.
> > 
> > To support SG, vhci doesn't map and unmap URB for DMA to use native
> > SG list (urb->num_sgs). In DMA mapping function of vhci, it sets
> > URB_DMA_MAP_SG flag in urb->transfer_flags if URB has SG list and
> > this flag will tell the stub driver to use SG list.
> > 
> > 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.
> > 
> > Alan fixed vhci bug with the USB 3.0 storage device by modifying
> > USB storage driver.
> > ("usb-storage: Set virt_boundary_mask to avoid SG overflows")
> > But the fundamental solution of it is to add SG support to vhci.
> > 
> > This patch works well with the USB 3.0 storage devices without Alan's
> > patch, and we can revert Alan's patch if it causes some troubles.
> > 
> > Suwan Kim (2):
> >    usbip: Skip DMA mapping and unmapping for urb at vhci
> >    usbip: Implement SG support to vhci
> > 
> >   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     |  29 ++++-
> >   drivers/usb/usbip/vhci_tx.c      |  49 ++++++--
> >   7 files changed, 391 insertions(+), 121 deletions(-)
> > 
> 
> Hi Suwan,
> 
> I have been traveling and would like to test this series before I ask
> Greg to pick it up.
> 
> Just a quick note that I will get to this early next week.

Ok. Thank you for reviewing the patch, Shuah.
Please let me know if you have any problems reviewing the patch :)

Regards

Suwan Kim