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SubjectRe: [PATCH v4 3/4] usb: ffs: check quirk to pad epout buf size when not aligned to maxpacketsize
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On Thu, Nov 07 2013, Alan Stern wrote:
> What happens if the userspace daemon writes to epfile but the host
> changes the config or altsetting before all the data can be sent? Does
> the remaining data get flushed?

Each read and write is mapped to a single request, so the usual.

> I'm still a little unclear on this. Disabling the function ought to
> have much the same effect as changing the config or altsetting: Writes
> to endpoint files should be flushed and reads should be terminated.
> Otherwise you would end up sending stale data to the host or reading
> data that the daemon isn't prepared for.

You may have a point here. I'll try to prepare a patch over the weekend.

> Given that, there doesn't seem to be any need for a loop. Copy the
> data; if the function was disabled in the meantime then throw away the
> data and return an appropriate error code.

Right.

> I don't see any reason why you should ever have to copy the same data
> from userspace multiple times.

That actually never happens. The data is copied at most once.

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