Hi Michael et al, On 04/24/2014 09:42 AM, Michael Kerrisk (man-pages) wrote:
Willem, Daniel, Carsten, Neil, All of you have submitted patches in the recent past for packet.7, and are presumably somewhat knowledgeable. Could one or more of your Ack (or, if needed, improve) Stefan's proposed change?
Sorry for replying so late as I was just way to busy with other stuff. Yes, I agree with you and Carsten that the man-page still need more improvements, it's not perfect, and I'm glad that since a long time Willem chipped in to at least bring the man page a bit more up to date. I tried to update ... - http://lingrok.org/xref/linux-net-next/Documentation/networking/packet_mmap.txt - http://lingrok.org/xref/linux-net-next/Documentation/networking/filter.txt ... over time, both are somewhat tightly coupled as AF_PACKET users heavily deal with BPF filters as well; so that at least it's a bit more clear for other [kernel] developers as even the kernel documentation was very terse for many years and without examples. Now to your question. It can easily be seen from the if_packet.h header file http://lingrok.org/xref/linux-net-next/include/uapi/linux/if_packet.h#93 that TP_STATUS_* are individual bits that are set in tp_status field. TP_STATUS_USER simply means a frame was received in the ring and is ready for user space to be processed. If the field also indicates TP_STATUS_LOSING then this means that there were packet drops in the rx ring itself so a user knows it didn't get all traffic. This bit is being reset on getsockopt() when querying PACKET_STATISTICS, otherwise it stays. Drops occur when the ring buffer was not emptied fast enough by user space (so no free slot with TP_STATUS_KERNEL), e.g. due to high incoming traffic load. However, the current frame you're reading that has TP_STATUS_USER|TP_STATUS_LOSING is fine by itself. Hope that clarifies it? Thanks, Daniel
Thanks, Michael On Tue, Feb 25, 2014 at 10:24 PM, Stefan Puiu <stefan.puiu@xxxxxxxxx> wrote:[re-sending since the original message was bounced back, something about HTML subpart] Hi, I'm playing with the PACKET_RX_RING option to packet sockets and I noticed that the status field from the tpacket_hdr structures inside the mmaped buffer is actually a bit mask. I'm testing with 4Gbps traffic rates and sometimes I get status=5. I'm using Ubuntu 12.04 with a 3.8.0-29 kernel, and at least from the code (I got it using "sudo apt-get source linux-image-$(uname -r)") it seems the 5 means TP_STATUS_USER | TP_STATUS_LOSING. The 3.8.0 kernel code has this line in tpacket_rcv(): /* * LOSING will be reported till you read the stats, * because it's COR - Clear On Read. * Anyways, moving it for V1/V2 only as V3 doesn't need this * at packet level. */ if (po->stats.tp_drops) status |= TP_STATUS_LOSING; Also, in some source code example I found using google (http://www.google.ro/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&ved=0CEIQFjAE&url=http%3A%2F%2Fstuff.mit.edu%2Fafs%2Fsipb%2Fcontrib%2Flinux%2Ftools%2Ftesting%2Fselftests%2Fnet%2Fpsock_fanout.c&ei=lM8MU5yhB-iK7Aan7IGgAQ&usg=AFQjCNFtZBHSWgzHZkV3LNfLOSSTq0pV4Q&sig2=razCT0kUDv2-BIm_8gTE5g&bvm=bv.61725948,d.ZGU), the status is checked like this: while (header->tp_status & TP_STATUS_USER && count < RING_NUM_FRAMES) { [...] I haven't yet figured out how TP_STATUS_LOSING works, but I think it would be worthwhile to at least document that the status is a bit mask and not a value - that's what the patch at the end does. Michael, maybe you can Cc somebody more knowledgeable on this to confirm? IIRC there were some message exchanges on this on the list recently... diff --git a/man7/packet.7 b/man7/packet.7 index 1d3f222..6bac465 100644 --- a/man7/packet.7 +++ b/man7/packet.7 @@ -353,9 +353,9 @@ The packet socket owns all slots with status .BR TP_STATUS_KERNEL . After filling a slot, it changes the status of the slot to transfer ownership to the application. -During normal operation, the new status is -.BR TP_STATUS_USER , -to signal that a correctly received packet has been stored. +During normal operation, the new status has the +.BR TP_STATUS_USER +bit set to signal that a correctly received packet has been stored. When the application has finished processing a packet, it transfers ownership of the slot back to the socket by setting the status to -- 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
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