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RE: [PATCH] Add support for usbfs zerocopy.

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From: Christoph Hellwig
> Sent: 08 January 2016 09:46
> 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.

Indeed, and never is the case when mmap() is processed by a
driver rather than a filesystem.

> Instead it's using mmap on a file as a pecial purpose anonymous
> memory allocator, bypassing the VM and VM policies, including
> allowing to pin kernel memory that way.

Opening a driver often allocates kernel memory, not a big deal.

	David

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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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