[libnftnl PATCH] set: add helper to get the first set_elem

[libnftnl PATCH] set: add helper to get the first set_elem

[Arturo Borrero Gonzalez]

Add a helper that returns a pointer to the first set_elem in a given set.

This function is useful in situations where you know the set only have one
element (ie, event reporting from the kernel).

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
---
 include/libnftnl/set.h |    1 +
 src/libnftnl.map       |    1 +
 src/set.c              |   16 ++++++++++++++++
 3 files changed, 18 insertions(+)

diff --git a/include/libnftnl/set.h b/include/libnftnl/set.h
index a975f1c..739fa2a 100644
--- a/include/libnftnl/set.h
+++ b/include/libnftnl/set.h
@@ -89,6 +89,7 @@ struct nft_set_elem *nft_set_elem_alloc(void);
 void nft_set_elem_free(struct nft_set_elem *s);
 
 void nft_set_elem_add(struct nft_set *s, struct nft_set_elem *elem);
+struct nft_set_elem *nft_set_get_first_elem(struct nft_set *s);
 
 void nft_set_elem_attr_unset(struct nft_set_elem *s, uint16_t attr);
 void nft_set_elem_attr_set(struct nft_set_elem *s, uint16_t attr, const void *data, uint32_t data_len);
diff --git a/src/libnftnl.map b/src/libnftnl.map
index b11db67..b63c2d1 100644
--- a/src/libnftnl.map
+++ b/src/libnftnl.map
@@ -151,6 +151,7 @@ global:
   nft_set_elem_alloc;
   nft_set_elem_free;
   nft_set_elem_add;
+  nft_set_get_first_elem;
   nft_set_elem_foreach;
   nft_set_elem_attr_is_set;
   nft_set_elem_attr_unset;
diff --git a/src/set.c b/src/set.c
index 550c262..50107d3 100644
--- a/src/set.c
+++ b/src/set.c
@@ -737,6 +737,22 @@ void nft_set_elem_add(struct nft_set *s, struct nft_set_elem *elem)
 }
 EXPORT_SYMBOL(nft_set_elem_add);
 
+struct nft_set_elem *nft_set_get_first_elem(struct nft_set *s)
+{
+	struct nft_set_elems_iter *sei;
+	struct nft_set_elem *se;
+
+	sei = nft_set_elems_iter_create(nls);
+	if (sei == NULL)
+		return NULL;
+
+	se = nft_set_elems_iter_cur(sei);
+	nft_set_elems_iter_destroy(sei);
+
+	return se;
+}
+EXPORT_SYMBOL(nft_set_get_first_elem);
+
 struct nft_set_list {
 	struct list_head list;
 };

Re: [libnftnl PATCH] set: add helper to get the first set_elem

[Patrick McHardy]

On Tue, Apr 15, 2014 at 09:58:42AM +0200, Arturo Borrero Gonzalez wrote:
> Add a helper that returns a pointer to the first set_elem in a given set.
> 
> This function is useful in situations where you know the set only have one
> element (ie, event reporting from the kernel).

That doesn't seem right to me. As I said in my review of the notification
patch, userspace *must* be prepared for multiple elements being reported
at once since it is very likely that we will change the kernel side in
the future for efficiency reasons.

Re: [libnftnl PATCH] set: add helper to get the first set_elem

[Pablo Neira Ayuso]

On Tue, Apr 15, 2014 at 10:04:32AM +0200, Patrick McHardy wrote:
> On Tue, Apr 15, 2014 at 09:58:42AM +0200, Arturo Borrero Gonzalez wrote:
> > Add a helper that returns a pointer to the first set_elem in a given set.
> > 
> > This function is useful in situations where you know the set only have one
> > element (ie, event reporting from the kernel).
> 
> That doesn't seem right to me. As I said in my review of the notification
> patch, userspace *must* be prepared for multiple elements being reported
> at once since it is very likely that we will change the kernel side in
> the future for efficiency reasons.

I see. Arturo, you have to consider that the set may have more than
one element in the event from userspace, even if currently we only
have one single element. So use the set iterator to print all the
elements in the set instead.

Re: [libnftnl PATCH] set: add helper to get the first set_elem

[Arturo Borrero Gonzalez]

On 15 April 2014 10:11, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Tue, Apr 15, 2014 at 10:04:32AM +0200, Patrick McHardy wrote:
>> On Tue, Apr 15, 2014 at 09:58:42AM +0200, Arturo Borrero Gonzalez wrote:
>> > Add a helper that returns a pointer to the first set_elem in a given set.
>> >
>> > This function is useful in situations where you know the set only have one
>> > element (ie, event reporting from the kernel).
>>
>> That doesn't seem right to me. As I said in my review of the notification
>> patch, userspace *must* be prepared for multiple elements being reported
>> at once since it is very likely that we will change the kernel side in
>> the future for efficiency reasons.
>
> I see. Arturo, you have to consider that the set may have more than
> one element in the event from userspace, even if currently we only
> have one single element. So use the set iterator to print all the
> elements in the set instead.

ok!

regards.
-- 
Arturo Borrero González
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