LDP
/
man-pages
mirror of https://github.com/mkerrisk/man-pages
0
1
Fork 0
Code Releases Activity

packet.7: PACKET_LOSS has inverse meaning 

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.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Carsten Andrich 2014-04-22 18:01:59 +02:00 committed by Michael Kerrisk
parent d63ff76e2a
commit 8c26e99bce
1 changed files with 10 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
man7/packet.7
View File

@ -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