[libvirt] [PATCH v2 4/4] util: alloc: Note that VIR_AUTOPTR/VIR_AUTOCLEAN must not be used with vectors

[Peter Krempa]

On Wed, Feb 27, 2019 at 15:05:18 +0100, Erik Skultety wrote:
> On Tue, Feb 26, 2019 at 04:48:26PM +0100, Peter Krempa wrote:
> > We'd free only the first element of the vector leaking the rest.
> >
> > Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> > ---
> >  src/util/viralloc.h | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/src/util/viralloc.h b/src/util/viralloc.h
> > index 15451d4673..572b7d1c1c 100644
> > --- a/src/util/viralloc.h
> > +++ b/src/util/viralloc.h
> > @@ -650,6 +650,9 @@ void virAllocTestHook(void (*func)(int, void*), void *data);
> >   * the variable declared with it by calling the function
> >   * defined by VIR_DEFINE_AUTOPTR_FUNC when the variable
> >   * goes out of scope.
> > + *
> > + * Note that this macro must NOT be used with vectors! The cleaning function
> > + * will not free any elements beyond the first.
> 
> s/cleaning/freeing/
> 
> I understand, but if you have happen to have a dedicated list type, then you'd
> have a dedicated destructor, so both of these would be okay with vectors. On

Note that the function registered via __attribute(cleanup ... gets only
the pointer to the stack'd variable as an argument. This means that you
can do only 'value-terminated' (NULL, -1, ... ) lists.

Anything requiring count of elements will need to be encapsulated in a
struct which makes it a container. Thus the comment does not apply.

> the other hand I'm not sure whether we have such a thing at the moment, so I
> guess it's meaningful to document in the meantime.

I don't think we'll get much value terminated lists because the usage is
quite cumbersome and error-prone (e.g. if you forget your terminator).

In such case we can always do a rather simple macro for them.
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