Re: [PATCH iproute2] devlink: Ignore unknown attributes

On Fri, 19 Jan 2018 14:27:06 -0800
David Ahern [off-list ref] wrote:

On 1/19/18 2:02 PM, Stephen Hemminger wrote:

quoted

On Thu, 18 Jan 2018 20:42:44 -0800
David Ahern [off-list ref] wrote:
  

quoted

On 1/17/18 5:28 AM, Arkadi Sharshevsky wrote:  

quoted

In case of extending the UAPI old packages would break.

Signed-off-by: Arkadi Sharshevsky <redacted>
---
 devlink/devlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/devlink/devlink.c b/devlink/devlink.c
index 39cda06..c9d1838 100644
--- a/devlink/devlink.c
+++ b/devlink/devlink.c

@@ -343,7 +343,7 @@ static int attr_cb(const struct nlattr *attr, void *data)
 	int type;
 
 	if (mnl_attr_type_valid(attr, DEVLINK_ATTR_MAX) < 0)
-		return MNL_CB_ERROR;
+		return MNL_CB_OK;
 
 	type = mnl_attr_get_type(attr);
 	if (mnl_attr_validate(attr, devlink_policy[type]) < 0)
    

What's the point of calling mnl_attr_type_valid if you disregard a
failure? you might as well not call mnl_attr_type_valid at all.  

The way mnl handles attributes, you have to have a callback and it is up
to the callback to copy the values it wants.  The idea is that old code
running against a newer kernel will have a smaller array of attributes
it wants, and only copy those.
  

mnl_attr_type_valid calls mnl_attr_get_type which does attr->nla_type &
NLA_TYPE_MASK. Since you are no longer acknowledging the return code of
mnl_attr_type_valid, you don't care about its checks so you might as
well not call it. I don't see anything in libmnl that checks that
mnl_attr_type_valid is invoked on an attr, so hence my question -- given
the change above why call it all?

 The part that matters is:

static int attr_cb(const struct nlattr *attr, void *data)
{
	const struct nlattr **tb = data;
	int type;

	if (mnl_attr_type_valid(attr, DEVLINK_ATTR_MAX) < 0)         << makes sure that type < DEVLINK_ATTR_MAX
		return MNL_CB_OK;

	type = mnl_attr_get_type(attr);
	if (mnl_attr_validate(attr, devlink_policy[type]) < 0)        << this part doesn't matter really
		return MNL_CB_ERROR;

	tb[type] = attr;					<< necessary so that tb[] is filled in.
	return MNL_CB_OK;
}