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Re: [libvirt] [PATCH] [v2] API: Improve log for domain related APIs

On 01/05/2011 03:40 AM, Osier Yang wrote:
>> Then maybe the patch should be altered to output both name and UUID
>> (probably by introducing a helper function, which when given a
>> virDomainPtr outputs all three pieces of debug information rather than
>> the current %p).  I like the idea behind the patch, but only if we can
>> come up with the correct way of getting the extra information when
>> debugging is enabled, and without adding extra time when debugging is
>> off.  I'm not even sure what the right internal APIs for the job would
>> be, or if they even exist yet.
> Hi, Eric,
> I implemented a helper function like so in src/libvirt.c:
> static const char *
> virDomainNameUUID(virDomainPtr domain) {
>     char *entry = NULL;
>     const char *name = NULL;
>     char uuidstr[VIR_UUID_STRING_BUFLEN];
>     if (!VIR_IS_DOMAIN(domain)) {
>         entry = strdup("(VM: invalid domain)");

malloc'd return...

>         return entry;
>     }
>     name = domain->name;
>     virUUIDFormat(domain->uuid, uuidstr);
>     if(virAsprintf(&entry, "(VM: name=%s, uuid=%s)", name,
>                    uuidstr) < 0)
>          virReportOOMError();
>     return NULLSTR(entry);

and static return.  Ouch - that means the caller doesn't know whether to
call free or not.  You have to be consistent (the result is either NULL
or malloc'd; or the result is always static).

> }
> But how to avoid extra time when debugging is off? Following
> is not correct way definitely, as malloc'ed "entry" need to be
> freed.
> virConnectPtr
> virDomainGetConnect (virDomainPtr dom)
> {
>     DEBUG("dom=%p, %s", dom, virDomainNameUUID(dom));

When I envisioned a helper function, I'm thinking more like callers
using a simpler:


and a helper like:

DEBUG_DOMAIN (virDomainPtr dom)
    if !DEBUG then early exit
    gather data
    DEBUG("dom=%p, %s", dom, virDomainNameUUID(dom));
    free any gathered data if needed

That would mean that your new helper function would need to look at the
guts of DEBUG to mirror the same decision of whether DEBUG will result
in any output.

Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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