On Wed, Jun 07, 2017 at 11:07:02AM -0600, Jason Gunthorpe wrote: > On Wed, Jun 07, 2017 at 08:00:37PM +0300, Leon Romanovsky wrote: > > On Wed, Jun 07, 2017 at 10:47:50AM -0600, Jason Gunthorpe wrote: > > > On Wed, Jun 07, 2017 at 07:43:44PM +0300, Leon Romanovsky wrote: > > > > On Wed, Jun 7, 2017 at 7:37 PM, Jason Gunthorpe > > > > <jgunthorpe@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > On Wed, Jun 07, 2017 at 07:19:01PM +0300, Leon Romanovsky wrote: > > > > >> It makes me wonder if it is expected behavior for > > > > >> ibnl_rcv_reply_skb() to handle !NLM_F_REQUEST messages and do we > > > > >> really need it? What are the scenarios? In my use case, which is > > > > >> for sure different from yours, I'm always setting NLM_F_REQUEST > > > > >> while communicating with kernel. > > > > > > > > > > If I recall the user space SA code issues REQUESTS from the kernel to > > > > > userspace, so userspace returns with the response format. This is > > > > > abnormal for netlink hence the special function. > > > > > > > > In netlink semantics, kernel side is supposed to send netlink > > > > notification message and userspace is supposed to send REQUEST. > > > > > > That pattern is for async communications, the SA stuff needs a sync > > > protocol, unfortunately. > > > > There is special flag NLM_F_ACK for it and userspace will set > > NLM_F_REQUEST | NLM_F_ACK once synchronization is needed. > > AFAIK, that is different, that is acking and retriggering a single shot > notification, not completing a kernel initiated handshake. It is acking that message from user was received by kernel and now processing. The message from kernel to user are anyway unreliable [1], so I don't understand on which handshake you are talking. [1] "reliable transmissions from kernel to user are impossible in any case" https://linux.die.net/man/7/netlink > > Jason
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