Re: How to avoid data copies in a driver ?
From: Jeremy Fitzhardinge
Date: Fri May 16 2008 - 04:10:51 EST
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?
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