Re: [libvirt] [Qemu-devel] [PATCH 2/2] qapi: deprecate implicit filters

Am 15.08.2019 um 18:07 hat John Snow geschrieben: > > > On 8/15/19 6:49 AM, Kevin Wolf wrote: > > Am 14.08.2019 um 21:27 hat John Snow geschrieben: > >> > >> > >> On 8/14/19 6:07 AM, Vladimir Sementsov-Ogievskiy wrote: > >>> To get rid of implicit filters related workarounds in future let's > >>> deprecate them now. > >>> > >>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov(a)virtuozzo.com&gt; > >>> --- > >>> qemu-deprecated.texi | 7 +++++++ > >>> qapi/block-core.json | 6 ++++-- > >>> include/block/block_int.h | 10 +++++++++- > >>> blockdev.c | 10 ++++++++++ > >>> 4 files changed, 30 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi > >>> index 2753fafd0b..8222440148 100644 > >>> --- a/qemu-deprecated.texi > >>> +++ b/qemu-deprecated.texi > >>> @@ -183,6 +183,13 @@ the 'wait' field, which is only applicable to sockets in server mode > >>> > >>> Use blockdev-mirror and blockdev-backup instead. > >>> > >>> +@subsection implicit filters (since 4.2) > >>> + > >>> +Mirror and commit jobs inserts filters, which becomes implicit if user > >>> +omitted filter-node-name parameter. So omitting it is deprecated, set it > >>> +always. Note, that drive-mirror don't have this parameter, so it will > >>> +create implicit filter anyway, but drive-mirror is deprecated itself too. > >>> + > >>> @section Human Monitor Protocol (HMP) commands > >>> > >>> @subsection The hub_id parameter of 'hostfwd_add' / 'hostfwd_remove' (since 3.1) > >>> diff --git a/qapi/block-core.json b/qapi/block-core.json > >>> index 4e35526634..0505ac9d8b 100644 > >>> --- a/qapi/block-core.json > >>> +++ b/qapi/block-core.json > >>> @@ -1596,7 +1596,8 @@ > >>> # @filter-node-name: the node name that should be assigned to the > >>> # filter driver that the commit job inserts into the graph > >>> # above @top. If this option is not given, a node name is > >>> -# autogenerated. (Since: 2.9) > >>> +# autogenerated. Omitting this option is deprecated, it will > >>> +# be required in future. (Since: 2.9) > >>> # > >>> # @auto-finalize: When false, this job will wait in a PENDING state after it has > >>> # finished its work, waiting for @block-job-finalize before > >>> @@ -2249,7 +2250,8 @@ > >>> # @filter-node-name: the node name that should be assigned to the > >>> # filter driver that the mirror job inserts into the graph > >>> # above @device. If this option is not given, a node name is > >>> -# autogenerated. (Since: 2.9) > >>> +# autogenerated. Omitting this option is deprecated, it will > >>> +# be required in future. (Since: 2.9) > >>> # > >>> # @copy-mode: when to copy data to the destination; defaults to 'background' > >>> # (Since: 3.0) > >>> diff --git a/include/block/block_int.h b/include/block/block_int.h > >>> index 3aa1e832a8..624da0b4a2 100644 > >>> --- a/include/block/block_int.h > >>> +++ b/include/block/block_int.h > >>> @@ -762,7 +762,15 @@ struct BlockDriverState { > >>> bool sg; /* if true, the device is a /dev/sg* */ > >>> bool probed; /* if true, format was probed rather than specified */ > >>> bool force_share; /* if true, always allow all shared permissions */ > >>> - bool implicit; /* if true, this filter node was automatically inserted */ > >>> + > >>> + /* > >>> + * @implicit field is deprecated, don't set it to true for new filters. > >>> + * If true, this filter node was automatically inserted and user don't > >>> + * know about it and unprepared for any effects of it. So, implicit > >>> + * filters are workarounded and skipped in many places of the block > >>> + * layer code. > >>> + */ > >>> + bool implicit; > >>> > >>> BlockDriver *drv; /* NULL means no media */ > >>> void *opaque; > >>> diff --git a/blockdev.c b/blockdev.c > >>> index 36e9368e01..b3cfaccce1 100644 > >>> --- a/blockdev.c > >>> +++ b/blockdev.c > >>> @@ -3292,6 +3292,11 @@ void qmp_block_commit(bool has_job_id, const char *job_id, const char *device, > >>> BlockdevOnError on_error = BLOCKDEV_ON_ERROR_REPORT; > >>> int job_flags = JOB_DEFAULT; > >>> > >>> + if (!has_filter_node_name) { > >>> + warn_report("Omitting filter-node-name parameter is deprecated, it " > >>> + "will be required in future"); > >>> + } > >>> + > >>> if (!has_speed) { > >>> speed = 0; > >>> } > >>> @@ -3990,6 +3995,11 @@ void qmp_blockdev_mirror(bool has_job_id, const char *job_id, > >>> Error *local_err = NULL; > >>> int ret; > >>> > >>> + if (!has_filter_node_name) { > >>> + warn_report("Omitting filter-node-name parameter is deprecated, it " > >>> + "will be required in future"); > >>> + } > >>> + > >>> bs = qmp_get_root_bs(device, errp); > >>> if (!bs) { > >>> return; > >>> > >> > >> This might be OK to do right away, though. > >> > >> I asked Markus this not too long ago; do we want to amend the QAPI > >> schema specification to allow commands to return with "Warning" strings, > >> or "Deprecated" stings to allow in-band deprecation notices for cases > >> like these? > >> > >> example: > >> > >> { "return": {}, > >> "deprecated": True, > >> "warning": "Omitting filter-node-name parameter is deprecated, it will > >> be required in the future" > >> } > >> > >> There's no "error" key, so this should be recognized as success by > >> compatible clients, but they'll definitely see the extra information. > >> > >> Part of my motivation is to facilitate a more aggressive deprecation of > >> legacy features by ensuring that we are able to rigorously notify users > >> through any means that they need to adjust their scripts. > > > > Who would read this, though? In the best case it ends up deep in a > > libvirt log that nobody will look at because there was no error. In the > > more common case, the debug level is configured so that QMP traffic > > isn't even logged. > > > > Kevin > > > > I believe you are right, but I also can't shake the feeling that this > attitude ensures that we'll never find a way to expose this information > to the end-user. Is this not too defeatist? I think the discussed approach that seemed most likely to me to succeed was adding a command line option that makes QEMU just crash if you use a deprecated feature, and enable that in libvirt test cases (or possibly even any non-release builds, though maybe it's a bit harsh there).

> I think deprecation notices in the QMP stream has two benefits: > > 1) Any direct usages via qmp-shell or manual JSON connection are likely > to see this message in development or testing. I feel the usage of QEMU > directly is more likely to increase with time as other stacks seek to > work around libvirt. > > [Whether or not they should is another question, but I believe the > current reality to be that people are trying to.] I don't know about other people, but as a human user, I don't care about deprecation notices. As long as something works, I use it, and once I get an error message back, I'll use something else. If I manually enter drive_mirror and get a warning back, that doesn't tell me that libvirt still does the same thing and needs to be fixed. It just tells me that in the future I might need to change the commands that I use manually. I guess this would still prevent adding new libvirt features that build on deprecated QEMU features because some manual testing will be involved there. But was this ever a problem?

> 2) Programmatic deprecation notices can't be presented to a user at all > if we don't send them; at least this way it becomes libvirt's problem > over what to do with them. Perhaps even just in testing and regression > suites libvirt can assert that it sees no deprecation warnings (or > whitelist certain ones it knows about.) > > In the case of libvirt, it's not even necessarily about making sure the > end user sees it, because it isn't even necessarily the user's fault -- > it's libvirt's. This is a sure-fire programmatic way to communicate > compatibility changes to libvirt. If libvirt uses this to make test cases fail, it could work.