Re: Zero-copy CameraFile transfer?

I'm familiar.  I don't see how to open a file descriptor to a file
sitting on the camera storage medium.  The gp_file_from_new_fd()
function presumes the file descriptor is already created.

Does the gp_file_open() call return a file descriptor to the file on
the camera storage medium?  The docs say it just returns an error
code.

        =-ddt->

On Fri, Mar 11, 2022 at 5:44 AM Alan Corey <[email protected]> wrote:
>
> Looks fun, see the sendfile man page.
>
> On Fri, Mar 11, 2022 at 3:10 AM Marcus Meissner <[email protected]> wrote:
>>
>> Hi,
>>
>> No, this works both ways.
>>
>> You can download files into a filedescriptor / handler or memory,
>> or upload.
>>
>> But both use some buffering. As far as I see libusb with its urb model
>> is not directly doing filedescriptor passing, so there will always be
>> a bit of buffers involved.
>>
>> Ciao, Marcus
>>
>> On Thu, Mar 10, 2022 at 09:36:09AM -0800, Dave Taylor wrote:
>> > That would work for transferring a file to the camera, right?  I'm
>> > more concerned about transferring a file from the camera.
>> >
>> >         =-ddt->
>> >
>> > On Wed, Mar 9, 2022 at 11:32 PM Marcus Meissner <[email protected]> wrote:
>> > >
>> > > 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
>> >
>> >
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