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    SubjectRe: How to avoid data copies in a driver ?
    On Thu, May 15, 2008 at 1:50 PM, Arnd Hannemann <arnd@arndnet.de> wrote:
    > Francis Moreau wrote:
    >> Hello,
    >>
    >> On Wed, May 14, 2008 at 11:23 PM, linux-os (Dick Johnson)
    >> <linux-os@analogic.com> wrote:
    >>> You memory-map the data. Impliment mmap() in your driver.
    >>> You can also impliment poll() { select() } so your
    >>> application knows when new data are available.
    >>>
    >>> You cannot use a user-mode file-descriptor in the kernel.
    >>>
    >>
    >> Why not ?
    >
    > http://kernelnewbies.org/FAQ/WhyWritingFilesFromKernelIsBad
    >

    ok, relayfs might be what I need, thanks.

    >>
    >> I'm suprised because what I need doens't seem so uncommon, usually
    >> devices send or
    >> receive data to/from files. So a helper (system call ?) to achieve
    >> that other than the basic
    >> read/write seems needed, no ?
    >
    > Usually devices send or receive just data, and they shouldn't care about
    > file format, filesystems, permissions and all this stuff...
    >

    The fact is that the data usually ends into a file.

    thanks
    --
    Francis


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