Re: [libvirt] [GSoC] Code design for scalar and external types

On Mon, 2018-06-11 at 12:12 +0200, Pavel Hrdina wrote: > Another issue that we need to take into account is that the external > free functions might not be 'NULL' safe which we need to somehow ensure > if they will be used with attribute cleanup. > > The original design is probably wrong and was heavily counting on the > existing libvirt implementation. We might need to update the design > to make it the similar as GLib: > > #define VIR_AUTOPTR_FUNC_NAME(type) virAutoPtr##type > #define VIR_AUTOPTR_TYPE_NAME(type) ##typeAutoPtr > > #define VIR_AUTOPTR(type) \ > __attribute__((cleanup(VIR_AUTOPTR_FUNC_NAME(type)))) VIR_AUTOPTR_TYPE_NAME(type) > > #define VIR_DEFINE_AUTOPTR_FUNC(type, func) \ > typedef type *VIR_AUTOPTR_TYPE_NAME(type); \ > static inline void VIR_AUTOPTR_FUNC_NAME(type)(type **_ptr) \ > { \ > if (*_ptr) \ > (func)(*_ptr); \ > } > > The usage would like this: > > VIR_DEFINE_AUTOPTR_FUNC(virAuthConfig, virAuthConfigFree) > > VIR_AUTOPTR(virAuthConfig) authConfig = NULL; > > > That way we can use any existing free function regardless whether it > checks if the variable is NULL or not and without the need to manually > define new type. > > The only exception would be the virStringList where we would have to use > the different type. As danpb (CC'd) mentioned in [1], having the vir*Free() function take a double pointer is good because it allows it to also set it to NULL. I will add that any vir*Free() function that doesn't deal gracefully with being passed a NULL pointer is already buggy and should be fixed.

[1] https://www.redhat.com/archives/libvir-list/2018-June/msg00033.html