netdev - Re: [PATCH RFC iproute2-next 1/2] rdma: add 'link add/delete' commands

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Date:   Wed, 28 Nov 2018 13:34:14 -0600
From:   Steve Wise <swise@...ngridcomputing.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     dsahern@...il.com, stephen@...workplumber.org,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        BMT@...ich.ibm.com
Subject: Re: [PATCH RFC iproute2-next 1/2] rdma: add 'link add/delete'
 commands

...

>>> +	rd_prepare_msg(rd, RDMA_NLDEV_CMD_NEWLINK, &seq,
>>> +		       (NLM_F_REQUEST | NLM_F_ACK));
>>> +	mnl_attr_put_strz(rd->nlh, RDMA_NLDEV_ATTR_DEV_NAME, name);
>>> +	mnl_attr_put_strz(rd->nlh, RDMA_NLDEV_ATTR_LINK_TYPE, type);
>>> +	mnl_attr_put_strz(rd->nlh, RDMA_NLDEV_ATTR_NDEV_NAME, dev);
>>> +	ret = rd_send_msg(rd);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	ret = rd_recv_msg(rd, link_add_parse_cb, rd, seq);
>>> +	if (ret)
>>> +		perror(NULL);
>> Why do you need rd_recv_msg()? I think that it is not needed, at least
>> for rename, I didn't need it.
>> https://git.kernel.org/pub/scm/network/iproute2/iproute2-next.git/tree/rdma/dev.c#n244
> To get the response of if it was successfully added.  It provides the
> errno value.
If I don't do the rd_recv_msg, then adding the same name twice fails
without any error notification.  Ditto for deleting a non-existent
link.  So the rd_recv_msg() allows getting the failure reason (and
detecting the failure).