On Thursday, November 25, 2021 6:41 PM, Stefano Garzarella wrote:

On Thu, Nov 25, 2021 at 09:27:40AM +0000, Wang, Wei W wrote:

quoted

On Thursday, November 25, 2021 3:16 PM, Wang, Wei W wrote:

quoted

-	/* Update CID in case it has changed after a transport reset event */
-	vsk->local_addr.svm_cid = dst.svm_cid;
-
 	if (space_available)
 		sk->sk_write_space(sk);

Not sure if anybody knows how this affects the transport reset.

I believe the primary use case is when a guest is migrated.

After the migration, the transport gets a reset event from the hypervisor and
all connected sockets are closed. The ones in listen remain open though.

Also the guest's CID may have changed after migration. So if an application has
open listening sockets, bound to the old CID, this should ensure that the socket
continues to be usable.

OK, thanks for sharing the background.

The patch would then change this behavior.

So maybe to avoid problems, we could update the CID only if it is different
from VMADDR_CID_ANY:

	if (vsk->local_addr.svm_cid != VMADDR_CID_ANY)
		vsk->local_addr.svm_cid = dst.svm_cid;


When this code was written, a guest only supported a single transport, so it
could only have one CID assigned, so that wasn't a problem.
For that reason I'll add this Fixes tag:
Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")

Sounds good to me.

Thanks,
Wei
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