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Re: [virt-tools-list] [libosinfo 3/3] Utility function to retrieve device by property



On Thu, Jan 19, 2012 at 5:42 PM, Zeeshan Ali (Khattak)
<zeeshanak gnome org> wrote:
> On Thu, Jan 19, 2012 at 5:28 PM, Christophe Fergeau <cfergeau redhat com> wrote:
>> On Thu, Jan 19, 2012 at 05:22:20PM +0200, Zeeshan Ali (Khattak) wrote:
>>> On Thu, Jan 19, 2012 at 11:51 AM, Christophe Fergeau
>>> <cfergeau redhat com> wrote:
>>> > On Thu, Jan 19, 2012 at 02:37:07AM +0200, Zeeshan Ali (Khattak) wrote:
>>> >> From: "Zeeshan Ali (Khattak)" <zeeshanak gnome org>
>>> >>
>>> >> ---
>>> >>  osinfo/libosinfo.syms |    1 +
>>> >>  osinfo/osinfo_os.c    |   41 +++++++++++++++++++++++++++++++++++++++++
>>> >>  osinfo/osinfo_os.h    |    4 ++++
>>> >>  3 files changed, 46 insertions(+), 0 deletions(-)
>>> >>
>>> >> diff --git a/osinfo/libosinfo.syms b/osinfo/libosinfo.syms
>>> >> index de1ff18..8e2d929 100644
>>> >> --- a/osinfo/libosinfo.syms
>>> >> +++ b/osinfo/libosinfo.syms
>>> >> @@ -109,6 +109,7 @@ LIBOSINFO_0.0.6 {
>>> >>       osinfo_os_new;
>>> >>       osinfo_os_get_devices;
>>> >>       osinfo_os_get_all_devices;
>>> >> +     osinfo_os_get_device_by_property;
>>> >>       osinfo_os_get_device_links;
>>> >>       osinfo_os_add_device;
>>> >>       osinfo_os_get_family;
>>> >> diff --git a/osinfo/osinfo_os.c b/osinfo/osinfo_os.c
>>> >> index 0facb08..ec7886a 100644
>>> >> --- a/osinfo/osinfo_os.c
>>> >> +++ b/osinfo/osinfo_os.c
>>> >> @@ -238,6 +238,47 @@ OsinfoDeviceList *osinfo_os_get_all_devices(OsinfoOs *os, OsinfoFilter *filter)
>>> >>  }
>>> >>
>>> >>  /**
>>> >> + * osinfo_os_get_device_by_property:
>>> >> + * @os: an operating system
>>> >> + * @property: the property of interest
>>> >> + * @value: the required value of property @property
>>> >> + * @inherited: Should devices from inherited and cloned OSs be included in the
>>> >> + * search.
>>> >> + *
>>> >> + * A utility function that gets the first device found from the list of devices
>>> >> + * @os supports, for which the value of @property is @value.
>>> >> + *
>>> >> + * Returns: (transfer full): The found device or NULL
>>> >> + */
>>> >> +OsinfoDevice *osinfo_os_get_device_by_property(OsinfoOs *os,
>>> >> +                                               const gchar *property,
>>> >> +                                               const gchar *value,
>>> >> +                                               gboolean inherited)
>>> >> +{
>>> >> +    OsinfoDevice *ret;
>>> >> +    OsinfoDeviceList *devices;
>>> >> +    OsinfoFilter *filter;
>>> >> +
>>> >> +    filter = osinfo_filter_new();
>>> >> +    osinfo_filter_add_constraint(filter, property, value);
>>> >> +
>>> >> +    if (inherited)
>>> >> +        devices = osinfo_os_get_all_devices(os, filter);
>>> >> +    else
>>> >> +        devices = osinfo_os_get_devices(os, filter);
>>> >> +    g_object_unref (filter);
>>> >
>>> > Don't you get a warning if you don't do g_object_unref(G_OBJECT(filter)); ?
>>> > (same comment for the g_object_unref(devices) below)
>>>
>>> Nope, should I be?
>>
>> It probably depends on your CFLAGS, but I'm quite sure I got warnings
>> in some occasions without the casts.
>>
>>>
>>> >> +
>>> >> +    if (osinfo_list_get_length(OSINFO_LIST(devices)) > 0)
>>> >> +        ret = OSINFO_DEVICE (osinfo_list_get_nth(OSINFO_LIST(devices), 0));
>>> >
>>> > I think it would be better to return the full list and let the app decide whether
>>> > it wants the first item in the list or more than that.
>>>
>>> I guess, we can provide another function 'get_devices_by_property'  as well..
>>
>> What kind of properties do we get? Does it really make sense to only return
>> the first one and ignore the other results? I don't know what kind of
>> results this function returns, so hardcoding in the library this kind of
>> "arbitrarily pick one result, drop the rest" makes me uncomfortable.
>
> https://bugzilla.gnome.org/show_bug.cgi?id=668229

To help you avoid reading Vala code, the usecase is of creating a new
VM for a paritcular OS. The sensible thing to do would be to add only
devices supported by that OS. It also would usually make sense to add
only one device of a particular class/type not all. So IMHO there is
good chances that this function will be useful to other apps as well.

-- 
Regards,

Zeeshan Ali (Khattak)
FSF member#5124


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