Re: [Libguestfs] [PATCH libnbd v4] Add Go language bindings (golang) (RHBZ#1814538).

On Wed, Mar 25, 2020 at 10:14:30AM +0000, Daniel P. Berrangé wrote: > On Wed, Mar 25, 2020 at 10:01:02AM +0000, Richard W.M. Jones wrote: > > On Wed, Mar 25, 2020 at 09:48:02AM +0000, Daniel P. Berrangé wrote: > > > On Wed, Mar 25, 2020 at 09:42:19AM +0000, Richard W.M. Jones wrote: > > > > Now runs a complete set of tests, notably including the AIO test. > > > > > > > > File descriptors are passed in and out as plain ints (instead of > > > > *os.File) for a couple of reasons: (1) We have to pass the plain int > > > > to syscall.Select. (2) Turning an fd into an os.File causes golang to > > > > set the blocking flag which is deeply unhelpful. > > > > > > FWIW, using non-blocking FDs and syscall.Select is not normal best > > > practice for Go, where the expected model would be to use goroutines > > > with the file in blocking mode. > > > > Right, however I couldn't find any documentation about how to > > integrate a C library with that mechanism. Does libvirt-go do > > anything like this? > > What's the intended usage of the FD ? I was thinking it was just for > doing plain read/write I/O from Go, but now I'm thinking this was wrong > interpretation http://libguestfs.org/libnbd.3.html#Socket-and-direction For example here's how it's integrated with glib: https://github.com/libguestfs/libnbd/blob/master/examples/glib-main-loop.c Integration with poll(2): https://github.com/libguestfs/libnbd/blob/a5fe64ab5323d649d348e61c9126ef7... It currently works from golang too, but it seems likely that synchronous calls like nbd_pread are blocking the golang main loop (because we make our own call to poll(2)). The asynch stuff also works (see libnbd_590_aio_copy_test.go in the attached patch) but it's rather awkward.