Am 15.08.2019 um 21:24 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@xxxxxxxxxx> writes:
>
> > 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@xxxxxxxxxxxxx>
> >> >>> ---
> >> >>> 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).
>
> Yup. BoF minutes: "The one way to get people read log files is crashing
> their application."
>
> >> 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?
>
> You're right in that relying on *humans* to read the machine-readable
> deprecation notice probaly won't work for old client code trying to use
> newly deprecated QMP. It should work for new client code trying to use
> already deprecated QMP.
>
> >> 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.
>
> Yes.
>
> However, ensuring tests fail whenever libvirt receives a deprecation
> notice via QMP seems harder than having them pass --future to QEMU to
> make it crash instead of sending such a notice.
>
> Let's assume all libvirt ever does with deprecation notices is logging
> them. Would that solve the problem of reliably alerting libvirt
> developers to deprecation issues? Nope. But it could help
> occasionally.
I'm not saying that deprecation notices would hurt, just that they
probably won't solve problem alone.
Crashing if --future is given and logging otherwise seems reasonable
enough to me. Whether we need to wire up a new deprecation mechanism in
QMP for the logging or if we can just keep printing to stderr is
debatable. stderr already ends up in a log file, a QMP extension would
require new libvirt code. If libvirt would log deprecation notices more
prominently, or use the information for tainting or any other kind of
processing, a dedicated QMP mechanism could be justified.
Kevin
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