On Tue, Apr 22, 2014 at 2:55 PM, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > On 04/22/2014 08:36 PM, Willem de Bruijn wrote: >> 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. > > @Willem: thanks for the quick response. That helps so much. > > @Carsten: I've applied your patch, but I have a question. You wrote: > > [[ > However if > .BR PACKET_LOSS > is set, malformed packets will be skipped, their status reset to > .BR TP_STATUS_AVAILABLE > ]] > > What does "their" in "their status" refer to? I interpreted this as the tp_status field of the malformed packets. To make clear that it does not refer to the "following packets", it could be revised to "is set, transmission continues, skipping over any malformed packets. The status of the malformed packets is reset to TP_STATUS_AVAILABLE." > > Cheers, > > 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/ >> > > > -- > 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
