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Re: [Qemu-block] [Qemu-devel] [PATCH v14 12/21] option: allow qemu_opts_
Re: [Qemu-block] [Qemu-devel] [PATCH v14 12/21] option: allow qemu_opts_to_qdict to merge repeated options
Wed, 12 Oct 2016 19:46:00 +0200
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)
"Daniel P. Berrange" <address@hidden> writes:
> If given an option string such as
> the qemu_opts_to_qdict() method will currently overwrite
> the values for repeated option keys, so only the last
> value is in the returned dict:
> With this change the caller can optionally ask for all
> the repeated values to be stored in a QList. In the
> above example that would result in 'nodes' being a
> QList, so the returned dict would contain
> Note that the conversion has no way of knowing whether
> any given key is expected to be a list upfront - it can
> only figure that out when seeing the first duplicated
> key. Thus the caller has to be prepared to deal with the
> fact that if a key 'foo' is a list, then the returned
> qdict may contain either a QString or a QList for the
> key 'foo'.
> In a third mode, it is possible to ask for repeated
> options to be reported as an error, rather than silently
> dropping all but the last one.
To serve as a replacement for the options visitor, this needs to be able
to behave exactly the same together with a suitably hacked up QObject
input visitor. Before I dive into the actual patch, let me summarize
QemuOpts and options visitor behavior.
Warning, this is going to get ugly.
QemuOpts faithfully represents a key=value,... string as a list of
QemuOpt. Each QemuOpt represents one key=value. They are in the same
order. If key occurs multiple times in the string, it occurs just the
same in the list.
*Except* key "id" is special: it's stored outside the list, and all but
the first one are silently ignored.
Most users only ever get the last value of a key. Any non-last
key=value are silently ignored.
We actually exploit this behavior to do defaults, by *prepending* them
to the list. See the use of qemu_opts_set_defaults() in main().
A few users get all values of keys (other than key "id"):
* -device, in qdev_device_add() with callback set_property().
We first get "driver" and "bus" normally (silently ignoring non-last
values, as usual). All other keys are device properties. To set
them, we get all (key, value), ignore keys "driver" and "bus", and set
the rest. If a key occurs multiple times, it gets set multiple times.
This effectively ignores all but the last one, silently.
* -semihosting-config, in main() with callback add_semihosting_arg().
We first get a bunch of keys normally. Key "arg" is special: it may
be repeated to build a list. To implement that, we get all (key,
value), ignore keys other than "arg", and accumulate the values.
* -machine & friends, in main() with callback machine_set_property()
Similar to -device, only for machines, with "type" instead of "driver"
* -spice, in qemu_spice_init() with callback add_channel()
Keys "tls-channel" and "plaintext-channel" may be used repeated to
specify multiple channels. To implement that, we get all (key,
value), ignore keys other than "tls-channel" and "plaintext-channel",
and set up a channel for each of the others.
* -writeconfig, in config_write_opts() with callback config_write_opt()
We write out all keys in order.
* The options visitor, in opts_start_struct()
We convert the list of (key, value) to a hash table of (key, list of
values). Most of the time, the list of values has exactly one
When the visitor's user asks for a scalar, we return the last element
of the list of values, in lookup_scalar().
When the user asks for list elements, we return the elements of the
list of values in order, in opts_next_list(), or if there are none,
the empty list in opts_start_list().
Unlike the options visitor, this patch (judging from your description)
makes a list only when keys are repeated. The QObject visitor will have
to cope with finding both scalars and lists. When it finds a scalar,
but needs a list, it'll have to wrap it in a list (PATCH 09, I think).
When it finds a list, but needs a scalar, it'll have to fish it out of
the list (where is that?).
> All existing callers are all converted to explicitly
> request the historical behaviour of only reporting the
> last key. Later patches will make use of the new modes.
> Signed-off-by: Daniel P. Berrange <address@hidden>
Out of steam for today.
- Re: [Qemu-block] [Qemu-devel] [PATCH v14 12/21] option: allow qemu_opts_to_qdict to merge repeated options,
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