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



On Thu, Jan 19, 2012 at 06:09:15PM +0200, Zeeshan Ali (Khattak) wrote:
> 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.

I'm not questioning the usefulness of the function you want to add (or a
variation on it), what I'm questioning is hardcoding the "let's only
keep the first device in the list" in the library, it feels cleaner to
return a list and let the application pick only the first device if it
wants to.

Christophe

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