* Markus Armbruster (arm...@redhat.com) wrote: > Stefan Hajnoczi <stefa...@gmail.com> writes: > > 4. Go and Rust bindings would also be useful. There is > > https://github.com/intel/govmm but I think it makes sense to keep it > > in qemu.git and provide an interface similar to our Python modules. > > Mapping QAPI/QMP commands and events to function signatures isn't hard > (the QAPI code generator does). Two problems (at least): > > 1. Leads to some pretty ridiculous functions. Here's one: > > void qmp_blockdev_mirror(bool has_job_id, const char *job_id, > const char *device, > const char *target, > bool has_replaces, const char *replaces, > MirrorSyncMode sync, > bool has_speed, int64_t speed, > bool has_granularity, uint32_t granularity, > bool has_buf_size, int64_t buf_size, > bool has_on_source_error, > BlockdevOnError on_source_error, > bool has_on_target_error, BlockdevOnError > on_target_error, > bool has_filter_node_name, const char > *filter_node_name, > bool has_copy_mode, MirrorCopyMode copy_mode, > bool has_auto_finalize, bool auto_finalize, > bool has_auto_dismiss, bool auto_dismiss, > Error **errp);
Those might not be as bad when mapped to other languages, all the bool/value pairs would become Option<...> so that removes that doubling. The Error ** mechanism should somehow map onto functions returning a normal Rust Result<> type. Dave > We commonly use 'boxed': true for such beasts, which results in > functions like this one: > > void qmp_blockdev_add(BlockdevOptions *arg, Error **errp); > > 2. Many schema changes that are nicely backward compatible in QMP are > anything but in such an "obvious" C API. Adding optional arguments, > for instance, or changing integer type width. The former is less of > an issue with 'boxed': true. > > Perhaps less of an issue with dynamic languages. > > I figure a static language would need much more expressive oomph than C > to be a good target. No idea how well Go or Rust bindings can work. > > > 5. A jailer is needed to isolate the QEMU process and vhost-user > > device backends using seccomp, Linux namespaces, and maybe > > SELinux/AppArmor. We used to be able to rely on libvirt for QEMU > > security, but it's becoming a common task for any device backend and > > IMO should be its own launcher tool. > > Perhaps the libvirt refactoring effort can give us one. > > > 6. A configuration file format is sorely needed so that guest > > configuration can be persisted and easily launched. Today you have to > > create a shell script that executes a QEMU command-line, but this is > > suboptimal because sharing executable scripts is dangerous from a > > security perspective and is hard to parse or modify programmatically. > > No argument. There is -readconfig, but it falls way short. > > With command line QAPIfication, a real configuration file will be quite > feasible. > > The main reason for the lack of progress there is our dedication to > backward compatibility. A functional replacement of our CLI is a huge > task already. Throwing in backward compatibility makes it a daunting > one. Not least because nobody fully understands all the quirks. > > > In many of these areas we already have a partial solution. It just > > needs more work. I think it would be worth the effort and the mental > > shift to really providing APIs that are easy to use by applications. > > > > What do you think? > > > > Have I missed things that are needed? > > > > Have I included things that are unnecessary? > > I feel we need to make up our minds what kind of interface(s) we want to > provide. > > We provide a low-level interface for management applications. I feel we > need to nail this one. Its QMP part is okay, I think, the CLI part is > not. > > We also try to provide friendlier interfaces for human users. Not only > do we suck at it, we're also prone to create liabilities for later: much > of the compatibility woes that have been holding us back are rooted in > "convenience" features. And don't get me started on the folly of us > dabbling in GUI. > > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
