2011/6/21 Michal Novotny <minovotn(a)redhat.com&gt;: > Hi, > as I've been working on libvirt-php I've been able to see that sometimes > the virConnectClose() API function is returning the undefined value, > like in this example: > > [2011-06-21 17:29:59 libvirt-php/core]: libvirt_domain_get_info: > virDomainGetInfo(0xb3184158) returned 0 > [2011-06-21 17:29:59 libvirt-php/core]: Freeing libvirt domain resource > at 0x3d9751b3184158 > [2011-06-21 17:29:59 libvirt-php/core]: free_resource: > virDomainFree(0xb3184158) completed successfully > [2011-06-21 17:29:59 libvirt-php/core]: php_libvirt_connection_dtor: > virConnectClose(0xb3382588) returned 1 ((null)) > [2011-06-21 17:29:59 libvirt-php/core]: check_resource_allocation: > libvirt domain resource (conn 0xb3184158) is not allocated > > In the API reference of libvirt there's an information that it returns 0 > or -1 ("0 in case of success or -1 in case of error" as can be seen at > [1]) however according to my libvirt-php tests with the debug log > enabled there's a return value of 1 with the error string (as caught by > libvirt error handler) undefined, i.e. NULL. > > Does anybody have an idea what may be wrong and why is libvirt sometimes > returning undefined value for this function? > > Thanks, > Michal > > [1] http://libvirt.org/html/libvirt-libvirt.html#virConnectClose > In contrast to the documentation virConnectClose returns the remaining reference count of the connection after unref'ing it. This means virConnectClose returns -1 on error and returns 0 when there is no reference left and the connection is really closed. When it returns > 0 then the connection isn't closed yet, but is kept open because there are still objects alive that depend on it. For example when you open a connection and get a virDomainPtr from it then the refcount of the connection is increased, because the domain object depends on it. When the domain object is freed then the refcount of the connection is decreased again. All objects in libvirt like connections, domains, networks etc are reference counted. But in contrast to virConnectClose other free functions like virDomainFree don't return the remaining reference count, they really just return -1 or 0. So the question is: do we change virConnectClose to really just return -1 or 0, or do we update the documentation, because someone might depend on virConnectClose allowing to detect via its return value whether the connection was really closed or not.

On 06/21/2011 09:53 AM, Matthias Bolte wrote: >> [1] http://libvirt.org/html/libvirt-libvirt.html#virConnectClose >> > > In contrast to the documentation virConnectClose returns the remaining > reference count of the connection after unref'ing it. This means > virConnectClose returns -1 on error and returns 0 when there is no > reference left and the connection is really closed. When it returns > > 0 then the connection isn't closed yet, but is kept open because there > are still objects alive that depend on it. For example when you open a > connection and get a virDomainPtr from it then the refcount of the > connection is increased, because the domain object depends on it. When > the domain object is freed then the refcount of the connection is > decreased again. > > All objects in libvirt like connections, domains, networks etc are > reference counted. But in contrast to virConnectClose other free > functions like virDomainFree don't return the remaining reference > count, they really just return -1 or 0. So the question is: do we > change virConnectClose to really just return -1 or 0, or do we update > the documentation, because someone might depend on virConnectClose > allowing to detect via its return value whether the connection was > really closed or not. At this point, I worry that changing return values might break existing code, so I would favor a documentation update, but I'd also like to hear an opinion from DV or danpb.

On Wed, Jun 22, 2011 at 04:48:31PM +0100, Daniel P. Berrange wrote: > On Wed, Jun 22, 2011 at 09:41:57AM -0600, Eric Blake wrote: >> On 06/21/2011 09:53 AM, Matthias Bolte wrote: >>>> [1] http://libvirt.org/html/libvirt-libvirt.html#virConnectClose >>>> >>> In contrast to the documentation virConnectClose returns the remaining >>> reference count of the connection after unref'ing it. This means >>> virConnectClose returns -1 on error and returns 0 when there is no >>> reference left and the connection is really closed. When it returns > >>> 0 then the connection isn't closed yet, but is kept open because there >>> are still objects alive that depend on it. For example when you open a >>> connection and get a virDomainPtr from it then the refcount of the >>> connection is increased, because the domain object depends on it. When >>> the domain object is freed then the refcount of the connection is >>> decreased again. >>> >>> All objects in libvirt like connections, domains, networks etc are >>> reference counted. But in contrast to virConnectClose other free >>> functions like virDomainFree don't return the remaining reference >>> count, they really just return -1 or 0. So the question is: do we >>> change virConnectClose to really just return -1 or 0, or do we update >>> the documentation, because someone might depend on virConnectClose >>> allowing to detect via its return value whether the connection was >>> really closed or not. >> At this point, I worry that changing return values might break existing >> code, so I would favor a documentation update, but I'd also like to hear >> an opinion from DV or danpb. > I think we shouldn't change the semantics. Just to clarify: The code is right. The docs are wrong. This is actually a good general rule for resolving any doubts :-) Daniel