similar to: Extending the nbdkit python plugin

As mentioned in my reviews, I wonder if we should make our python callbacks look a bit more Pythonic by having kwargs added for each new flag that we want to expose. The idea was first floated here: https://www.redhat.com/archives/libguestfs/2018-April/msg00108.html Note that with my proposal, there is no need for a python script to expose a global API_VERSION variable; new flags are added

On 11/22/19 3:20 PM, Nir Soffer wrote: >>> +# There are several variants of the API. nbdkit will call this >>> +# function first to determine which one you want to use. This is the >>> +# latest version at the time this example was written. >>> +def api_version(): >>> + return 2 >> >> Matches the C counterpart of #define

First out of our four language bindings to add FUA support (for reference, I added 'zero' support for python, perl, and ruby back in 1.1.13, then Rich had to add it for ocaml in 1.1.20). I tested this heavily under python 2, but for now only compile tested under python 3; I plan to do further testing there and make any tweaks if necessary. I wrote patch 5 early on, but then realized I

On 11/22/19 1:53 PM, Richard W.M. Jones wrote: > To avoid breaking existing plugins, Python plugins wishing to use > version 2 of the API must opt in by declaring: > > def api_version(): > return 2 > > (Plugins which do not do this are assumed to want API version 1). Could we also permit the python code to declare a global variable instead of a function? But a

On Thu, Nov 21, 2019 at 01:57:28PM +0000, Richard W.M. Jones wrote: > We have an nbdkit plugin that lets you write NBD servers in Python. > An example of an existing Python plugin is here: > > https://github.com/libguestfs/nbdkit/blob/master/plugins/python/example.py#L1 > > This morning I tried to modify the plugin to use the newer nbdkit API > (version 2). One of the

On Thu, Nov 21, 2019 at 02:17:43PM +0000, Daniel P. Berrangé wrote: > I would define a new 'api_version()' method for your python > plugins. > > Existing plugins don't implement that of course so when your > C code invokes that it'll get an exception, and can assume > the classic API contract for pwrite(). > > If the plugin implements

v1: https://www.redhat.com/archives/libguestfs/2019-November/msg00153.html v2: - Fix implementation of can_cache. - Add implementation of can_fua. - Add a very thorough test suite which tests every command + flag combination.

As suggested by Nir, here: https://www.redhat.com/archives/libguestfs/2019-November/thread.html#00220

And fill out most of the missing bits of the API. Rich.

v2 was here: https://www.redhat.com/archives/libguestfs/2019-November/msg00163.html I pushed patch 1 (with spelling fix), patch 4 and patch 5 since those were previously ACKed on the list. Differences in v3: - Add error checking to PyModule_AddIntConstant. - Use API_VERSION constant instead of function. - Add max API version supported to --dump-plugin output. - Print API_VERSION selected by

v3 was here: https://www.redhat.com/archives/libguestfs/2019-November/msg00209.html In v4: - Rebase on top of current master. Includes various fixes and updates required because of Nir's patches that went into master. - Fix api_version() -> API_VERSION in patch 2 noted previously on the mailing list. Rich.

On 11/22/19 3:14 PM, Richard W.M. Jones wrote: >>> @@ -54,20 +61,20 @@ def get_size(h): >>> return len(disk) >>> -def pread(h, count, offset): >>> +def pread(h, count, offset, flags): >>> global disk >>> return disk[offset:offset+count] >> >> Do we really want to be passing 'flags' as an integer that the

On 11/22/19 3:46 PM, Nir Soffer wrote: >>>> and for zero (once fast zero is supported later in the series), it could >>>> look like: >>>> >>>> def zero(h, count, offset, may_trim=False, fua=False, fast=False): >>> >>> This is nicer - but not extensible. >> >> Why not? Any future flag additions would still appear as new

On Wed, Apr 11, 2018 at 12:03:41AM -0500, Eric Blake wrote: > +=item C<can_fua> > + > +(Optional) > + > + def can_fua(h): > + # return a boolean > + > +Unlike the C counterpart, the Python callback does not need a > +tri-state return value, because Python introspection is sufficient to > +learn whether callbacks support FUA. Thus, this function only returns

In preparation for adding other optional flag arguments to the python bindings, start by making the existing 'may_trim' flag to 'zero' be optional. That is, the plugin need not define the parameter if it does not make any semantic difference (ie. if the plugin ignores the hint and never trims); while if the parameter exists, we now pass it as a keyword argument rather than as a

On Fri, Nov 22, 2019 at 9:55 PM Richard W.M. Jones <rjones@redhat.com> wrote: > > This tests the Python plugin thoroughly by issuing client commands > through libnbd and checking we get the expected results. > --- > tests/Makefile.am | 13 +-- > tests/test-python-plugin.py | 134 ++++++++++++++++++++++++++++ > tests/test-python.py | 172

This may be confusing at first but is not that difficult once you wrap your head around it. There are two types of arguments in Python: positional(*) and keyword(**). There is a rule that all positional arguments are defined before the keyword arguments. Also once an argument has a default value it is considered keyword (not positional). There are some nuances for which is best to reach to some

Begin the language binding followups to my new .zero callback, since Rich was indeed correct that we want them. I'm more familiar with python and perl (at least to the point that I was able to modify the appropriate example files and prove to myself that the bindings worked), so I've started with those. I'm less familiar with ruby and ocaml, so I've left those for tomorrow (it

On Fri, Nov 22, 2019 at 11:53 PM Nir Soffer <nsoffer@redhat.com> wrote: > > On Fri, Nov 22, 2019 at 11:35 PM Eric Blake <eblake@redhat.com> wrote: > > > > On 11/22/19 3:20 PM, Nir Soffer wrote: > > > > >>> +# There are several variants of the API. nbdkit will call this > > >>> +# function first to determine which one you want to

In the just-added nbdkit-sh-plugin.pod, you documented that unlike other plugins (where introspection or struct member population) can be used to determine which functionalities are supported, the shell plugin has to implement can_write and friends to return a special status 2 to document not supported, and 3 to indicate false, in part because you can't detect if a pwrite function is