Date: Sat, 2 Apr 2016 11:22:14 +0200 From: Hans Petter Selasky <hps@selasky.org> To: "Lundberg, Johannes" <johannes@brilliantservice.co.jp>, Luigi Rizzo <rizzo@iet.unipi.it> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: Zero copy data transfer from Linuxulator to FreeBSD? Message-ID: <56FF8F46.3040301@selasky.org> In-Reply-To: <CAASDrV=x8NrnXJFf%2BXEMH8ikO6c1ANbpvzb-2qVnOMuHpqyjkA@mail.gmail.com> References: <CAASDrVncEFU1tXxjEf3PuNSb8uLMbj_dZw9CbH1_79hk79TDDQ@mail.gmail.com> <56FE2E87.9090806@selasky.org> <CAASDrVmwqdp5nFixwuyozbUbPZ7XbK2MvEvNAtZ5e3AjdCK=kg@mail.gmail.com> <CA%2BhQ2%2Bh2VMVFm-wCECt2VUdZFYaAvBVYTmM89zGLsRVeO-=qnA@mail.gmail.com> <CAASDrV=x8NrnXJFf%2BXEMH8ikO6c1ANbpvzb-2qVnOMuHpqyjkA@mail.gmail.com>
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On 04/01/16 17:18, Lundberg, Johannes wrote: > Hi Luigi > > Since this is an embedded device running on battery every bit counts. > However, this is kind of a temporary solution so I'm considering accepting > it.. > > At any rate, I am generally curious what mechanism there are for > transferring data between Linux and native process in FreeBSD.. > Hi, libusb has only one copy to/from userspace. libusb v1.0 and v0.1 has some allocation during operation, while libusb v2.0 API doesn't. There was an optimisation done recently about IOCTLs allocating memory for the data argument. Maybe that is what is causing the problem you saw? Refer to SYS_IOCTL_SMALL_SIZE in sys/kern/ . --HPS
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