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Re: [PATCH] Add support for usbfs zerocopy.

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On Fri, 2016-01-08 at 01:45 -0800, Christoph Hellwig wrote:
> On Wed, Jan 06, 2016 at 10:35:05AM -0500, Alan Stern wrote:
> > Indeed, the I/O operations we are using with mmap here are not reads or 
> > writes; they are ioctls.  As far as I know, the kernel doesn't have any 
> > defined interface for zerocopy ioctls.
> 
> IF it was using mmap for I/O it would read in through the page fault
> handler an then mark the page dirty for writeback by the VM.  Thats
> clearly not the case.

That won't work because we need the ability to determine the chunk size
IO is done in. USB devices don't map to files, yet the memory they can
operate on depends on the device, so allocation in the kernel for
a specific device is a necessity.

	Regards
		Oliver

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Thread

Does vm_operations_struct require a .owner field? Alan Stern <stern@rowland.harvard.edu> - 2016-01-05 17:30 +0100
  Re: Does vm_operations_struct require a .owner field? "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-01-05 22:00 +0100
    Re: Does vm_operations_struct require a .owner field? Alan Stern <stern@rowland.harvard.edu> - 2016-01-05 22:40 +0100
      Re: Does vm_operations_struct require a .owner field? "Steinar H. Gunderson" <sesse@google.com> - 2016-01-06 01:00 +0100
      [PATCH] Add support for usbfs zerocopy. "Steinar H. Gunderson" <sesse@google.com> - 2016-01-06 01:00 +0100
        Re: [PATCH] Add support for usbfs zerocopy. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-01-06 01:20 +0100
          Re: [PATCH] Add support for usbfs zerocopy. "Steinar H. Gunderson" <sesse@google.com> - 2016-01-06 01:30 +0100
          [PATCH v2] Add support for usbfs zerocopy. "Steinar H. Gunderson" <sesse@google.com> - 2016-01-06 01:30 +0100
            Re: [PATCH v2] Add support for usbfs zerocopy. Lingzhu Xiang <lingzhu.xiang@mail.utoronto.ca> - 2016-01-07 03:40 +0100
              Re: [PATCH v2] Add support for usbfs zerocopy. Alan Stern <stern@rowland.harvard.edu> - 2016-01-07 16:50 +0100
                Re: [PATCH v2] Add support for usbfs zerocopy. Oliver Neukum <oneukum@suse.com> - 2016-01-11 12:20 +0100
                Re: [PATCH v2] Add support for usbfs zerocopy. Oliver Neukum <oneukum@suse.com> - 2016-01-12 11:10 +0100
            Re: [PATCH v2] Add support for usbfs zerocopy. Lingzhu Xiang <lingzhu.xiang@mail.utoronto.ca> - 2016-01-09 05:20 +0100
              Re: [PATCH v2] Add support for usbfs zerocopy. "Steinar H. Gunderson" <sesse@google.com> - 2016-01-09 12:00 +0100
        Re: [PATCH] Add support for usbfs zerocopy. Christoph Hellwig <hch@infradead.org> - 2016-01-06 07:50 +0100
          Re: [PATCH] Add support for usbfs zerocopy. "Steinar H. Gunderson" <sesse@google.com> - 2016-01-06 15:50 +0100
            Re: [PATCH] Add support for usbfs zerocopy. Peter Stuge <peter@stuge.se> - 2016-01-06 16:30 +0100
              Re: [PATCH] Add support for usbfs zerocopy. "Steinar H. Gunderson" <sesse@google.com> - 2016-01-06 16:40 +0100
              Re: [PATCH] Add support for usbfs zerocopy. Alan Stern <stern@rowland.harvard.edu> - 2016-01-06 16:40 +0100
            Re: [PATCH] Add support for usbfs zerocopy. Alan Stern <stern@rowland.harvard.edu> - 2016-01-06 16:40 +0100
              Re: [PATCH] Add support for usbfs zerocopy. Christoph Hellwig <hch@infradead.org> - 2016-01-08 10:50 +0100
                RE: [PATCH] Add support for usbfs zerocopy. David Laight <David.Laight@ACULAB.COM> - 2016-01-08 11:30 +0100
                Re: [PATCH] Add support for usbfs zerocopy. Oliver Neukum <oneukum@suse.com> - 2016-01-08 17:10 +0100
                Re: [PATCH] Add support for usbfs zerocopy. "Steinar H. Gunderson" <sesse@google.com> - 2016-01-12 22:30 +0100
                Re: [PATCH] Add support for usbfs zerocopy. Alan Stern <stern@rowland.harvard.edu> - 2016-01-12 23:10 +0100
                Re: [PATCH] Add support for usbfs zerocopy. Lingzhu Xiang <lingzhu.xiang@mail.utoronto.ca> - 2016-01-13 08:10 +0100
                Re: [PATCH] Add support for usbfs zerocopy. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-01-13 18:30 +0100
            Re: [PATCH] Add support for usbfs zerocopy. Christoph Hellwig <hch@infradead.org> - 2016-01-08 10:50 +0100

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