On Thu, 5 Mar 2020, David Laight wrote:

From: Jere Leppanen

quoted

Sent: 04 March 2020 17:13
On Wed, 4 Mar 2020, Xin Long wrote:

quoted

On Wed, Mar 4, 2020 at 2:38 AM Leppanen, Jere (Nokia - FI/Espoo)
[off-list ref] wrote:

quoted

On Mon, 2 Mar 2020, Xin Long wrote:

quoted

As it says in rfc6458#section-9.2:

  The application uses the sctp_peeloff() call to branch off an
  association into a separate socket.  (Note that the semantics are
  somewhat changed from the traditional one-to-one style accept()
  call.)  Note also that the new socket is a one-to-one style socket.
  Thus, it will be confined to operations allowed for a one-to-one
  style socket.

Prior to this patch, sctp_peeloff() returned a one-to-many type socket,
on which some operations are not allowed, like shutdown, as Jere
reported.

This patch is to change it to return a one-to-one type socket instead.

Thanks for looking into this. I like the patch, and it fixes my simple
test case.

But with this patch, peeled-off sockets are created by copying from a
one-to-many socket to a one-to-one socket. Are you sure that that's
not going to cause any problems? Is it possible that there was a
reason why peeloff wasn't implemented this way in the first place?

I'm not sure, it's been there since very beginning, and I couldn't find
any changelog about it.

I guess it was trying to differentiate peeled-off socket from TCP style
sockets.

Well, that's probably the reason for UDP_HIGH_BANDWIDTH style. And maybe
there is legitimate need for that differentiation in some cases, but I
think inventing a special socket style is not the best way to handle it.

But actually I meant why is a peeled-off socket created as SOCK_SEQPACKET
instead of SOCK_STREAM. It could be to avoid copying from SOCK_SEQPACKET
to SOCK_STREAM, but why would we need to avoid that?

Because you don't want all the acks and retransmissions??

I don't follow. The socket type and style have virtually no effect on the 
protocol side of things, I think.

	David

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