Date:   Fri, 2 Aug 2019 07:33:59 -0600
From:   shuah <shuah@...nel.org>
To:     Suwan Kim <suwan.kim027@...il.com>
Cc:     stern@...land.harvard.edu, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        shuah <shuah@...nel.org>
Subject: Re: [PATCH v2 2/2] usbip: Implement SG support to vhci

On 8/2/19 1:41 AM, Suwan Kim wrote:
> On Thu, Aug 01, 2019 at 08:03:59AM -0600, shuah wrote:
>> 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@...il.com>
>>>>>>> ---
>>>>>>>      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'm confused about the test case. Do I add the test case for each
> SG support status of vhci_hcd and usbip_host in usbip_test.sh?
> Or, do I implement the test logic in vhci_hcd code that asks if
> usbip_host supports SG when attaching a remote device?
> I'm sorry but I don't know what exactly you want to add.
> 

What I am asking you do is:

1. test with mismatched host and client.
2. run usbip_test.sh

These two are separate tests. I am not asking you to add any tests.
If you want to add it, I am not going say no :)

How close are you sending the patch?

thanks,
-- Shuah

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