Re: [PATCH net] datagram: When peeking datagrams with offset < 0 don't skip empty skbs

On Tue, 2017-08-15 at 12:45 -0400, Willem de Bruijn wrote:

On Tue, Aug 15, 2017 at 11:40 AM, Paolo Abeni [off-list ref] wrote:

quoted

For the record, I thought something like the following (uncomplete,
does not even compile):
---

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 8b13db5163cc..5085cf003b88 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h

@@ -286,6 +286,7 @@ struct ucred {
 #define MSG_SENDPAGE_NOTLAST 0x20000 /* sendpage() internal : not the last page */
 #define MSG_BATCH      0x40000 /* sendmmsg(): more messages coming */
 #define MSG_EOF         MSG_FIN
+#define MSG_PEEK_OFF   0x80000

Yes, that also works well.

I'm afraid about exhausting the MSG_* flag space here for a
feature that is not exposed to userspace. We don't have many flags
left. We could shadow an existing flag that is unused in this context.

That was my concern, too. Fortunately there are a bunch of flags
defined but apparently unused (MSG_FIN, MSG_SYN, MSG_RST) since long
time (if I'm not too low on coffee).

We can shadow one of them (and ev. drop the above define, if really
unused).

I think that the MSG_PEEK_OFF should be explicitly cleared in
sk_peek_offset() when the 'sk_peek_off' is negative, to avoid beeing
fooled by stray bits into the 'flags' argument.

I'll try to scatch-up something tomorrow.

Thanks,

Paolo