Re: [patch] packet.7: PACKET_LOSS has inverse meaning

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Daniel, Willem,


Daniel, your patch (dbb4f7516b) added the text on PACKET_LOSS. 
Could you comment on the patch below please?

Thanks,

Michael


On 04/22/2014 06:01 PM, Carsten Andrich wrote:
> Hey there,
> 
> I stumbled upon an error in packet.7 regarding the meaning of the
> PACKET_LOSS socket option. According to the current git version of
> linux-man setting PACKET_LOSS causes malformed packets to *not* be
> silently dropped.
> 
> However it is the other way round. If PACKET_LOSS is *not* set,
> malformed packets will be marked TP_STATUS_WRONG_FORMAT and the
> transmission process aborted, leaving untransmitted packets in the ring.
> If it *is* set, malformed packets will be silently skipped, their status
> set to TP_STATUS_AVAILABLE and the transmission process continued with
> the following packet.
> 
> This behaviour can be clearly seen in net/packet/af_packet.c:
> http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/net/packet/af_packet.c#n2300
> 
> The value accompanying TP_PACKET_LOSS translates into po->tp_loss:
> http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/net/packet/af_packet.c#n3304
> 
> I inverted the meaning of PACKET_LOSS and clarified the description in
> the attached patch.

diff --git a/man7/packet.7 b/man7/packet.7
index d8257f9..5085814 100644
--- a/man7/packet.7
+++ b/man7/packet.7
@@ -319,9 +319,15 @@ original fanout algorithm selects a backlogged socket, the packet
 rolls over to the next available one.
 .TP
 .BR PACKET_LOSS " (with " PACKET_TX_RING )
-If set, do not silently drop a packet on transmission error, but
-return it with status set to
-.BR TP_STATUS_WRONG_FORMAT .
+When a malformed packet is encountered on a transmit ring, the default is to
+set its status to
+.BR TP_STATUS_WRONG_FORMAT
+and abort the transmission immediately (it and following packets are left
+lingering on the ring). However if
+.BR PACKET_LOSS
+is set, malformed packets will be skipped, their status reset to
+.BR TP_STATUS_AVAILABLE
+and the transmission process continued.
 .TP
 .BR PACKET_RESERVE " (with " PACKET_RX_RING )
 By default, a packet receive ring writes packets immediately following the
@@ -419,7 +425,7 @@ or
 then that overrides the socket default.
 On successful transmission, the socket resets the slot to
 .BR TP_STATUS_AVAILABLE .
-It discards packets silently on error unless
+It immediately aborts the transmission on error unless
 .BR PACKET_LOSS
 is set.
 .TP


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html