On Thu, 2017-05-04 at 17:03 +0000, Ilya Lesokhin wrote:
> I don't understand the need for MSG_SENDPAGE_NOTLAST and I'm hoping
> someone can enlighten me.
>
> According to commit 35f9c09 ('tcp: tcp_sendpages() should call
> tcp_push() once'):
> "We need to call tcp_flush() at the end of the last page processed in
> tcp_sendpages(), or else transmits can be deferred and future sends
> stall."
>
> I don't understand why we need to differentiate between the user
> setting MSG_MORE
> and splice indicating that more data is going to be sent.
> if the user passed MSG_MORE and didn't push any extra data, isn't it
> the users fault?
> Do we need it because poorly written applications were broken when
> MSG_MORE was added to tcp_sendpage? Or is there a deeper reason?
>
The answer lies to how splice() is working.
User can issue one splice without MSG_MORE semantic, right ?
Still, we want an implicit MORE behavior for all individual pages, but
the last one.
> The reason I'm asking is that we are working on a kernel TLS
> implementation
> and I would like to know if we can coalesce multiple tls_sendpage
> calls with MSG_MORE into a single
> tls record or whether we must push out the record as soon as
> MSG_SENDPAGE_NOTLAST is cleared?
Make sure you handle partial writes (you want to coalesce 10 pages, but
stack will only take 5 of them)
