Re: Zero-copy CameraFile transfer?

On Wed, Mar 09, 2022 at 07:02:40PM -0800, Dave Taylor wrote:
> Hi, I've been looking through the libgphoto2 API for a way to
> implement zero-copy transfers such as through Linux's sendfile(2)
> system call, but it seems there isn't currently an exposed way to get
> at an open CameraFile's file descriptor to pull this off.
> 
> I do see that the CameraFile object has an fd member in it that
> gp_file_slurp() references, but the comments say that gp_file_slurp()
> is an internal function and that gp_file_open() is now deprecated.
> 
> Is there a cleaner way to do this?  Or should I not play with matches?  :)

If you create a CameraFile from a fd or a handler (gp_file_new_from_fd /
gp_file_new_from_handler), it will only use a small local buffer (currently 512kb)
to transfer data.

gp_file_new() itself would use in-memory storage for the full image.

I can take a look to avoid any kind of buffering, not sure if libusb1 allows this.

Ciao, Marcus