Messages in this thread | | | Subject | Re: Doing a zero-copy move of data from a kernel buffer to hard disk | From | Miklos Szeredi <> | Date | Wed, 22 Sep 2010 10:54:49 +0200 |
| |
On Mon, 20 Sep 2010, Neeraj Kumar wrote: > I am trying to move data from a buffer in kernel space into the hard > disk without having to incur any additional copies from kernel buffer to > user buffers or any other kernel buffers. Any ideas/suggestions would be > most helpful. > > The use case is basically a demux driver which collects data into a > demux buffer in kernel space and this buffer has to be emptied > periodically by copying the contents into a FUSE-based partition on the > disk. As the buffer gets full, a user process is signalled which then > determines the sector numbers on the disk the contents need to be copied > to. > > I was hoping to mmap the above demux kernel buffer into user address > space and issue a write system call to the raw partition device. But > from what I can see, the this data is being cached by the kernel on its > way to the Hard Disk driver. And so I am assuming that involves > additional copies by the linux kernel.
Isn't this functionality already served by relayfs?
> At this point I am wondering if there is any other mechansim to do this > without involving additional copies by the kernel. I realize this is an > unsual usage scenario for non-embedded environments, but I would > appreciate any feedback on possible options. > > BTW - I have tried using O_DIRECT when opening the raw partition, but > the subsequent write call fails if the buffer being passed is the > mmapped buffer.
The other zero-copy mechanism is splice(2).
Thanks, Miklos
| |