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    SubjectRe: How to avoid data copies in a driver ?
    Francis Moreau wrote:
    > 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 ?
    >

    It's fairly rare to have an application which requires moving data to
    file with absolutely no processing; normally there's at least a bit of
    massaging/parsing/etc. If that's really what you want to do, maybe you
    can do it with splice? I haven't looked at it at all, but the intention
    is that you can splice file descriptors together, so you can splice your
    device fd to a file fd and have it all just work...

    Alternatively you could read() from your device into a mmaped file.
    That's a single copy from device to file, which is about the best you
    can do without going to heroic lengths.

    Also, it really depends on your application. Is it a high-bandwidth
    thing in which the copy is a huge cost? Or do you want to eliminate the
    copies because it seems like a nice thing to do?


    J


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