Am Freitag, den 25.04.2014, 07:02 -0400 schrieb Neil Horman:
> On Thu, Apr 24, 2014 at 06:14:17PM +0200, Carsten Andrich wrote:
> [...]
> > +When a malformed packet is encountered on a transmit ring, the default is
> > +to reset its
> > +.I tp_status
> > +to
> > +.BR TP_STATUS_WRONG_FORMAT
> > +and abort the transmission immediately (it and following packets are left
> > +lingering on the ring).
>
> I'm not sure this is 100% clear. Any of these error status flags leave the
> packet in memory on the ring. WRONG_FORMAT, doesn't do anything special here.
The RX-related flags simply denote additional information, which are not
essential for RX ring operation, i.e. it won't hurt you if you ignore
them.
TP_STATUS_WRONG_FORMAT is different. It's only set if the transmission
process is aborted by the kernel. If this occurs the sendto()-call will
return EINVAL. In this case you have to walk the ring backwards from the
current userspace frame pointer, look for a frame with tp_status ==
TP_STATUS_WRONG_FORMAT, fix it and set its tp_status =
TP_STATUS_SEND_REQUEST. I assume PACKET_LOSS was introduced to obviate
the need to do this.
This should qualify TP_STATUS_WRONG_FORMAT as special. This behaviour
probably deserves a little more detail in the man-page, but I'll defer
that until the general overhaul takes place.
I've hacked up a demonstration and attached it.
Sorry, I'm a freedom-fighter against the 80-character-oppression :)
I also updated my patch for merge-less application to current
git-master:
diff --git a/man2/getsockopt.2 b/man2/getsockopt.2
index 925fa90..151cd31 100644
--- a/man2/getsockopt.2
+++ b/man2/getsockopt.2
@@ -205,6 +205,7 @@ system.
.BR getprotoent (3),
.BR protocols (5),
.BR ip (7),
+.BR packet (7),
.BR socket (7),
.BR tcp (7),
.BR udp (7),
diff --git a/man7/packet.7 b/man7/packet.7
index 11bca48..667568a 100644
--- a/man7/packet.7
+++ b/man7/packet.7
@@ -319,14 +319,18 @@ original fanout algorithm selects a backlogged socket, the packet
rolls over to the next available one.
.TP
.BR PACKET_LOSS " (with " PACKET_TX_RING )
-When a malformed packet is encountered on a transmit ring, the default is to
-set its status to
+When a malformed packet is encountered on a transmit ring, the default is
+to reset its
+.I tp_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, any malformed packet will be skipped, its status reset to
+is set, any malformed packet will be skipped, its
+.I tp_status
+reset to
.BR TP_STATUS_AVAILABLE ,
and the transmission process continued.
.TP
@@ -360,15 +364,21 @@ Packet socket and application communicate the head and tail of the ring
through the
.I tp_status
field.
-The packet socket owns all slots with status
+The packet socket owns all slots with
+.I tp_status
+equal to
.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 has the
+During normal operation, the new
+.I tp_status
+value has at least the
.BR TP_STATUS_USER
bit set to signal that a 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
+ownership of the slot back to the socket by setting
+.I tp_status
+equal to
.BR TP_STATUS_KERNEL .
Packet sockets implement multiple variants of the packet ring.
The implementation details are described in
@@ -407,9 +417,13 @@ Create a memory-mapped ring buffer for packet transmission.
This option is similar to
.BR PACKET_RX_RING
and takes the same arguments.
-The application writes packets into slots with status
+The application writes packets into slots with
+.I tp_status
+equal to
.BR TP_STATUS_AVAILABLE
-and schedules them for transmission by changing the status to
+and schedules them for transmission by changing
+.I tp_status
+to
.BR TP_STATUS_SEND_REQUEST .
When packets are ready to be transmitted, the application calls
.BR send (2)
@@ -424,7 +438,9 @@ If an address is passed using
or
.BR sendmsg (2),
then that overrides the socket default.
-On successful transmission, the socket resets the slot to
+On successful transmission, the socket resets
+.I tp_status
+to
.BR TP_STATUS_AVAILABLE .
It immediately aborts the transmission on error unless
.BR PACKET_LOSS
@@ -633,6 +649,11 @@ The
.I <linux/if_ether.h>
include file for physical layer protocols.
-The example source file
+The Linux kernel source tree.
+.IR /Documentation/networking/filter.txt
+describes how to apply Berkeley Packet Filters to packet sockets.
.IR /tools/testing/selftests/net/psock_tpacket.c
-in the Linux kernel source tree.
+contains example source code for all available versions of
+.BR PACKET_RX_RING
+and
+.BR PACKET_TX_RING .
/*
* Copyright (c) 2014 Carsten Andrich <carsten.andrich@xxxxxxxxxxxxx>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include <arpa/inet.h>
#include <err.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <net/if.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <unistd.h>
#define ERR_DEFAULT 1
#define FRAME_SIZE 2048
#define FRAME_COUNT 16
#define RING_SIZE (FRAME_COUNT * FRAME_SIZE)
#define IFNAME "p2p1"
#define FRAME_DATA "\xFF\xFF\xFF\xFF\xFF\xFF\x00\x00\x00\x00\x00\x00\xDE\xAD"
union frame {
struct tpacket2_hdr tphdr;
uint8_t _reserved[FRAME_SIZE];
};
static int sockfd;
static void *init_socket(void)
{
if ((sockfd = socket(AF_PACKET, SOCK_RAW, 0)) == -1)
err(ERR_DEFAULT, "socket() error");
static struct sockaddr_ll bindaddr;
bindaddr.sll_family = AF_PACKET;
bindaddr.sll_protocol = 0;
bindaddr.sll_ifindex = if_nametoindex(IFNAME);
if (bind(sockfd, (struct sockaddr *) &bindaddr, (socklen_t) sizeof(bindaddr)) == -1)
err(ERR_DEFAULT, "bind() error");
static const int version = TPACKET_V2;
if (setsockopt(sockfd, SOL_PACKET, PACKET_VERSION, &version, sizeof(version)) == -1)
err(ERR_DEFAULT, "setsockopt() error");
static const struct tpacket_req ringbuf_alloc = {
.tp_block_size = RING_SIZE,
.tp_frame_size = FRAME_SIZE,
.tp_block_nr = 1,
.tp_frame_nr = FRAME_COUNT
};
if (setsockopt(sockfd, SOL_PACKET, PACKET_TX_RING, (void *) &ringbuf_alloc, sizeof(ringbuf_alloc)) == -1)
err(ERR_DEFAULT, "setsockopt() error");
void *addr;
if ((addr = mmap(NULL, RING_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, sockfd, 0)) == MAP_FAILED)
err(ERR_DEFAULT, "mmap() error");
return addr;
}
static union frame *frame_first, *frame_cur;
static char *status2name(uint32_t status)
{
switch (status) {
case TP_STATUS_AVAILABLE:
return "AVAILABLE";
case TP_STATUS_SEND_REQUEST:
return "SEND_REQUEST";
case TP_STATUS_SENDING:
return "SENDING";
case TP_STATUS_WRONG_FORMAT:
return "WRONG_FORMAT";
default:
return "UNKNOWN";
}
}
static void dump_frames(void)
{
for (int i = 0; i < FRAME_COUNT; i += 8) {
printf("%2d: %-16s %-16s %-16s %-16s\n", i,
status2name((frame_first + i + 0)->tphdr.tp_status),
status2name((frame_first + i + 1)->tphdr.tp_status),
status2name((frame_first + i + 2)->tphdr.tp_status),
status2name((frame_first + i + 3)->tphdr.tp_status)
);
}
printf("\n");
}
static void enqueue_frame(void *data, size_t size)
{
uint8_t *frame_payload = (uint8_t *) &frame_cur->tphdr + TPACKET2_HDRLEN - sizeof(struct sockaddr_ll);
memcpy(frame_payload, data, size);
frame_cur->tphdr.tp_len = size;
frame_cur->tphdr.tp_status = TP_STATUS_SEND_REQUEST;
if (frame_cur++ == frame_first + FRAME_COUNT)
frame_cur = frame_first;
}
int main()
{
frame_first = frame_cur = init_socket();
uint8_t data[64];
memset(data, 0, sizeof(data));
memcpy(data, FRAME_DATA, sizeof(FRAME_DATA));
// enqueue a few frames with different data
data[59] = '0';
enqueue_frame(data, 60);
data[59] = '1';
enqueue_frame(data, 60);
data[59] = '2';
enqueue_frame(data, 60);
data[59] = '3';
enqueue_frame(data, 60);
data[59] = '4';
enqueue_frame(data, 60);
// corrupt frame #2 to trigger kernel TX error
(frame_first + 2)->tphdr.tp_len = -1;
dump_frames();
sleep(1);
// sendto() fails due to malformed frame #2
if (sendto(sockfd, NULL, 0, MSG_DONTWAIT, NULL, 0) == -1)
warn("sendto() error");
// sendto() succeeds (but does nothing), since kernel aborted at frame #2
// and its tp_status != TP_STATUS_SEND_REQUEST
if (sendto(sockfd, NULL, 0, MSG_DONTWAIT, NULL, 0) == -1)
warn("sendto() error");
dump_frames();
sleep(1);
// repair frame #2 (its behind(!) frame_cur: frame_first+2 == frame_cur-3)
(frame_first + 2)->tphdr.tp_len = 60;
(frame_first + 2)->tphdr.tp_status = TP_STATUS_SEND_REQUEST;
// sendto() succeeds and sends remaing frames
if (sendto(sockfd, NULL, 0, MSG_DONTWAIT, NULL, 0) == -1)
warn("sendto() error");
dump_frames();
close(sockfd);
return 0;
}
