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Re: [Qemu-devel] [RFC v4 02/13] qapi: qobject_compare() helper
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC v4 02/13] qapi: qobject_compare() helper |
Date: |
Tue, 15 Aug 2017 11:16:57 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 08/14/2017 04:57 PM, Eduardo Habkost wrote:
> The helper function will be useful when writing support code to
> deal with device slot information.
>
> TODO: documentation is incomplete and unclear, needs to be
> improved.
>
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---
> include/qapi/util.h | 39 +++++++++++++++++++++++++++++
> qapi/qapi-util.c | 66
> ++++++++++++++++++++++++++++++++++++++++++++++++++
> tests/test-qapi-util.c | 53 ++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 158 insertions(+)
>
> +/**
> + * qobject_compare:
> + *
> + * Compare the value of @a and @b.
> + *
> + * If @a and @b have the same type and the same value (see list
> + * of supported types below), return 0.
> + *
> + * If @a and @b are both strings, return strcmp(a, b).
> + *
> + * If @a and @b are numbers, return a negative value if a < b,
> + * and a positive value if a > b.
> + *
> + * Otherwise (if @a and @b are not the same, have different types,
> + * are of an unsupported type, or are different), return a non-zero value.
Is this number going to be commutative and distributive, in order to
provide stable qsort()ing? That is, if comparing a and b gives a
positive number, then comparing b and a should give a negative number;
and if comparing a and b then b and c results in two positive numbers,
then comparing a and c should also give a positive number. It is
unclear from the documentation whether you are able to make this
guarantee; and without it, it is unsafe to use this comparator in places
that require stability.
> + *
> + * Note that this function doesn't support some types, and may
> + * return false if the types are unsupported, or if the types don't
> + * match exactly.
How is a return of false (== 0, which also means equivalent) correct?
> + *
> + * Supported types:
> + * - QTYPE_QNULL
> + * - QTYPE_QSTRING
> + * - QTYPE_QBOOL
> + * - QTYPE_QNUM (integers only)
> + * - QTYPE_QLIST
> + *
> + * Unsupported (always return false):
> + * - QTYPE_QNUM (non-integer values)
> + * - QTYPE_QDICT
> + *
> + * TODO: rewrite documentation to be clearer.
> + * TODO: support non-integer QTYPE_NUM values and QTYPE_QDICT.
There's another patch series pending for qobject_is_equal(); should
these two patches share approaches or even code?
https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg01134.html
https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg02459.html
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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- [Qemu-devel] [RFC v4 00/13] qmp: query-device-slots command, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 01/13] qmp: Define query-device-slots command, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 02/13] qapi: qobject_compare() helper, Eduardo Habkost, 2017/08/14
- Re: [Qemu-devel] [RFC v4 02/13] qapi: qobject_compare() helper,
Eric Blake <=
- [Qemu-devel] [RFC v4 03/13] qdev: Add BusClass::device_type field, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 04/13] qdev: Slot info helpers, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 05/13] query-device-slots: Collapse similar entries, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 06/13] qdev core: generic enumerate_slots implementation, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 07/13] qdev: Enumerate CPU slots on query-device-slots, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 09/13] pci: pci_bus_has_pcie_upstream_port() function, Eduardo Habkost, 2017/08/14
- [Qemu-devel] [RFC v4 08/13] ide: enumerate_slots implementation, Eduardo Habkost, 2017/08/14