On Tue, Apr 22, 2014 at 2:23 PM, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > Hi Daniel, Willem, > > > Daniel, your patch (dbb4f7516b) added the text on PACKET_LOSS. > Could you comment on the patch below please? Carsten is correct. I made a mistake in that explanation, accidentally inverting the branch. My apologies and thanks for following up with a replacement text, Carsten. That looks good to me. > > 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
