Re: [PATCH v3 1/2] usb: gadget: loopback: fix: Don't share qlen and buflen between instances

[Felipe Balbi <balbi@ti.com>]

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On Thu, Sep 24, 2015 at 07:10:53PM +0200, Krzysztof Opasiak wrote:
> 
> 
> On 09/24/2015 06:51 PM, Felipe Balbi wrote:
> >On Thu, Sep 24, 2015 at 05:19:12PM +0200, Robert Baldyga wrote:
> >>On 09/22/2015 08:40 PM, Krzysztof Opasiak wrote:
> >>>Each instance of loopback function may have different qlen
> >>>and buflen attributes values. When linking function to
> >>>configuration those values had been assigned to global
> >>>variables. Linking other instance to config overwrites those
> >>>values.
> >>>
> >>>This commit moves those values to f_loopback structure
> >>>to avoid overwriting. Now each function has its own instance
> >>>of those values.
> >>>
> >>>Cc: <stable@vger.kernel.org> # 3.10+
> >>>Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
> >>
> >>Reviewed-by: Robert Baldyga <r.baldyga@samsung.com>
> >
> >doesn't seem to fit stable IMO. Care to explain why you think we need
> >to backport this to v3.10+ ?
> >
> 
> Let's consider following set of commands:
> 
> cd $CFS_ROOT/usb_gadget
> mkdir g1
> cd g1
> mkdir functions/SourceSink.1
> mkdir functions/SourceSink.2
> echo 1024 > functions/SourceSink.1/buflen
> echo 512 > functions/SourceSink.2/buflen
> mkdir configs/c.1
> ln -s functions/SourceSink.1 configs/c.1/
> ln -s functions/SourceSink.2 configs/c.1/
> echo $UDC > UDC
> 
> You assume that after executing this script you will get two instances of
> SourceSink functions and one of them will alloc requests buffers which has
> 1024 and second one which has only 512.
> 
> Unfortunately due to using global variables both of them are going to alloc
> only 512 bytes for each request. The same situation is with qlen. All
> instances are going to use attributes values from the last one in the
> system, even if they are in multiple gadgets.

that's all fine and dandy, but it's still a new requirement. It fits easily
into "has never worked before" category. If it was something which really
regressed, IOW we used to support it but some other commit broke it, then
I'd agree.

> In my opinion second patch in this series is much more important as it makes
> loopback function working again after almost year of being only /dev/null
> and /dev/zero. But that one should to go only to 3.18.

ok

-- 
balbi

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