On Tue, Apr 30, 2019 at 04:43:03PM +0300, Nir Soffer wrote:
> On Tue, Apr 30, 2019, 15:46 Richard W.M. Jones <rjones@redhat.com> wrote:
>
> > I believe there is no simple NBD client library. Am I wrong about
> > this? Let's assume I'm not for the sake of the rest of this email ...
> >
> > We do however have at least 4 places this could be consumed if it existed:
> >
> > - fio's proposed NBD engine
> > https://www.spinics.net/lists/fio/msg07831.html
> >
> > - nbdkit-nbd-plugin
> > https://github.com/libguestfs/nbdkit/tree/master/plugins/nbd
> >
> > - Martin K's forthcoming VMware liberation tool
> >
> > - qemu, maybe?
> > https://github.com/qemu/qemu/blob/master/block/nbd-client.c
>
>
> oVirt imageio, replacing pure python client, used to implement nbd-http
> proxy
> https://github.com/oVirt/ovirt-imageio/blob/master/common/ovirt_imageio_common/nbd.py
It looks like imageio is Python 2. I'm trying to write libnbd
bindings for Python now, but TBH supporting Python 2 is turning out to
be painful, because there are plenty of Python 3 features it would be
nice to use ("b" boolean conversions, proper bytes handling and
PyUnicode_FSConverter are three particular features). Do you really
need Python 2? What is the roadmap for using Python 3 with imageio?
Rich.
>
> > In this email I'm trying to assemble some requirements for such a
> > library, and I've also attempted to categorize them according to how
> > difficult they might be to implement. I guess everyone will have
> > their own opinions on which features are most "required" and which are
> > optional, but I've added mine below too.
> >
> > Did I miss out anything?
> >
> > 1 = easy to implement ... 5 = hard to implement
> > |
> > | R* = required, library could not be used without it
> > | R = required
> > | O+ = optional, but very useful for many users
> > | O = optional
> > | O- = optional, not likely to be useful for many users
> > | |
> > v v
> >
> > 1 R* Library which runs in userspace, callable from C programs
> >
> > 3 O+ Callable from other programming languages, eg Python etc.
> >
> > 1 R* Connect to Unix domain socket
> >
> > 1 R* Connect to TCP port
> >
> > 1 R Connect to TCP port over IPv6
> >
> > 1 O- Connect to arbitrary file descriptor [eg. for nbdkit -s]
> >
> > 2 R Synchronous support for easy initial use
> >
> > 5 O+ Non-blocking/asynch support, use with select/poll
> >
> > 4 O+ Integrates with external main loops, glib2, APR pollset, etc.
> >
> > 4 O TLS support using X.509 certs
> >
> > 4 O TLS-PSK support
> >
> > 5 O NBD MULTI_CONN
> >
> > 5 O NBD out of order requests on single socket
> >
> > 2 O- Old-style protocol
> >
> > 3 R NBD_OPT_INFO mode [required for qemu]
> >
> > 5 O NBD structured replies
> >
>
> Should be O+, this gives huge performance improvment when reading mostly
> empty range, even without block status.
>
> This is also not so hard to implement, maybe 3?
>
>
> > 3 O+ NBD block status querying
> >
>
> Should be able to query qemu meta context
>
>
> > ? ? NBD resize extension
> >
>
> Nir
--
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