[Libguestfs] pread(into) (was: Re: [PATCH nbdkit v2 10/10] tests: Test the Python plugin thoroughly.)

> On Sat, Nov 23, 2019 at 06:11:47PM +0200, Nir Soffer wrote: > > There is performance implication for v1 plugins like rhv-upload-plugin > that > > need to copy the bytes from imageio server on python side: > > > > r = http.getresponse() > > ... > > return bytearray(r.read()) > > > > This is sad because on the C side we mempcpy the data again. So with > this patch > > we avoid one copy of the two. > > > > To avoid all unneeded copies, we need to change pread() to: > > > > def pread(h, buf, offset): > > > > So the python side we can do: > > > > f.readinto(buf) > > > > Or: > > > > sock.recv_info(buf) > > > > It does not work for HTTPResponse, so in this case we have to do: > > > > buf[:] = r.read() > > > > Since we work on v2 now, I think we should consider this change. > > Right, we can consider this for v2, while leaving v1 callers alone. > > > An uglier alternative is: > > > > def preadinto(h, buf, offset): > > > > Matching python read() and readinto() interface.