Re: [Libguestfs] [libnbd PATCH v3 5/5] python: Slice structured read callback buffer from original

On Thu, Jun 09, 2022 at 08:34:47AM -0500, Eric Blake wrote: > The Py_BuildValue "y#" format copies data; this is because Python > assumes our C memory can go out of scope, while the user's python > callback can stash off whatever bytearray object it got. But this > copying is inefficient. Now that we already have a Python buffer-like > object in scope for the duration of all structured reads > (pread_structured since commit f8c76c01, aio_pread_structured since > commit 4f15d0e9), we know that the C memory parameter to our > chunk_callback is already (a portion of) the underlying contiguous > memory of an original Python object. If we pass the Python callback a > memoryview object over the correct slice of that memory, then Python > will correctly handle the intricacies of what happens if the callback > saves our memoryview object for later use, all without any data > copying overhead, making use of the pread_structured form much faster. >

Acked-by: Richard W.M. Jones <rjones(a)redhat.com&gt;