On Mon, May 28, 2018 at 01:04:28PM +0530, Sukrit Bhatnagar wrote:
On 25 May 2018 at 16:20, Pavel Hrdina <phrdina@redhat.com> wrote:
On Fri, May 25, 2018 at 12:06:50PM +0200, Andrea Bolognani wrote:
On Fri, 2018-05-25 at 10:04 +0200, Pavel Hrdina wrote:
On Fri, May 25, 2018 at 09:13:51AM +0200, Andrea Bolognani wrote:
However, I realize it might not be possible to register free functions for a native type without having to introduce something like
typedef char * virString;
thus causing massive churn. How does GLib deal with that?
If you would look into GLib documentation you would see that this design basically copies the one in GLib:
Sorry, I should have looked up the documentation and implementation before asking silly questions. Guess the morning coffee hadn't quite kicked in yet :/
GLib libvirt
g_autofree VIR_AUTOFREE g_autoptr VIR_AUTOPTR g_auto VIR_AUTOCLEAR
For what it's worth, I think VIR_AUTOCLEAR is a much better name than g_auto :)
In GLib you are using them like this:
g_autofree char *string = NULL; g_autoptr(virDomain) dom = NULL; g_auto(virDomain) dom = { 0 };
So yes it would require to introduce a lot of typedefs for basic types and that is not worth it.
I'm not sure we would need so many typedefs, but there would certainly be a lot of churn involved.
Personally, I'm not so sure it wouldn't be worth the effort, but it's definitely something that we can experiment with it at a later time instead of holding up what's already a pretty significant improvement.
In libvirt we would have:
VIR_AUTOFREE char *string = NULL; VIR_AUTOPTR(virDomainPtr) dom = NULL; VIR_AUTOCLEAR(virDomain) dom = { 0 };
If you notice the difference, in libvirt we can use virDomainPtr directly because we have these typedefs, in GLib macro G_DEFINE_AUTOPTR_CLEANUP_FUNC creates similar typedef.
While I'm not a fan of our *Ptr typedefs in general, I guess this time I'm glad we have them because VIR_AUTOPTR() doesn't hide the fact that what you're declaring is a pointer; that is, the macro argument is also exactly the type of the variable.
So let's make a summary of how it could look like:
VIR_AUTOFREE(char *) string = NULL; VIR_AUTOPTR(virDomainPtr) vm = NULL; VIR_AUTOCLEAR(virDomain) dom = { 0 };
VIR_DEFINE_AUTOFREE_FUNC(virDomainPtr, virDomainFree); VIR_DEFINE_AUTOCLEAR_FUNC(virDomain, virDomainClear);
Do we define new functions for freeing/clearing, because that is what VIR_DEFINE_AUTOFREE_FUNC seems to do.
This is what new macros will look like:
# define _VIR_TYPE_PTR(type) type##Ptr
# define _VIR_ATTR_AUTOFREE_PTR(type) __attribute__((cleanup(type##Free))) # define _VIR_ATTR_AUTOCLOSE_PTR(type) __attribute__((cleanup(type##Close))) # define _VIR_ATTR_AUTOCLEAN_PTR(type) __attribute__((cleanup(type##Clean)))
# define VIR_AUTOFREE_PTR(type) _VIR_ATTR_AUTOFREE_PTR(type) _VIR_TYPE_PTR(type)
The problem is that our vir*Free functions take on vir*Ptr as the parameter and not vir*Ptr * (pointer to it).
For example, instead of: void virArpTableFree(virArpTablePtr table);
we would need: void virArpTableFree(virArpTablePtr *table);
Hmm, so gcc claims the cleanup attribute to take a function which is required to take a pointer to the type which it already is, it's just typedef'd, I haven't tried this myself but do you get a compiler error if you try it with the existing function, i.e. the one which doesn't mention the explicit '*' to signal a pointer type? If so and we can't use the our typedef'd Ptr type directly, then we'll need to switch all the free callback signatures to a plain virSomeType *arg rather than trying to pass a double pointer which is just unnecessary and ugly.
if we declare something like: VIR_AUTOFREE_PTR(virArpTable) table = NULL;
Also, I tried to add a new function: void virArpTablePtrFree(virArpTablePtr *table) { size_t i;
if (!*table) return;
for (i = 0; i < (*table)->n; i++) { VIR_FREE((*table)->t[i].ipaddr); VIR_FREE((*table)->t[i].mac); } VIR_FREE((*table)->t); VIR_FREE((*table)); VIR_FREE(table);
My honest guess would be ^this you're trying to free the double pointer itself which you didn't and you're also not supposed to allocate. Erik