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doc: packet: simplify tpacket example code
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This patch simplifies the tpacket_v3 example code a bit by getting rid
of unecessary macro wrappers, removing some debugging code so that it is
more to the point, and also adds a header comment. Now this example code
is the very minimum one needs to start from when dealing with tpacket_v3
and ~100 lines smaller than before.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Daniel Borkmann authored and David S. Miller committed Jun 7, 2013
1 parent 93a306a commit d70a3f8
Showing 1 changed file with 28 additions and 105 deletions.
133 changes: 28 additions & 105 deletions Documentation/networking/packet_mmap.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -704,6 +704,12 @@ So it seems to be a good candidate to be used with packet fanout.
Minimal example code by Daniel Borkmann based on Chetan Loke's lolpcap (compile
it with gcc -Wall -O2 blob.c, and try things like "./a.out eth0", etc.):

/* Written from scratch, but kernel-to-user space API usage
* dissected from lolpcap:
* Copyright 2011, Chetan Loke <loke.chetan@gmail.com>
* License: GPL, version 2.0
*/

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
Expand All @@ -722,27 +728,6 @@ it with gcc -Wall -O2 blob.c, and try things like "./a.out eth0", etc.):
#include <linux/if_ether.h>
#include <linux/ip.h>

#define BLOCK_SIZE (1 << 22)
#define FRAME_SIZE 2048

#define NUM_BLOCKS 64
#define NUM_FRAMES ((BLOCK_SIZE * NUM_BLOCKS) / FRAME_SIZE)

#define BLOCK_RETIRE_TOV_IN_MS 64
#define BLOCK_PRIV_AREA_SZ 13

#define ALIGN_8(x) (((x) + 8 - 1) & ~(8 - 1))

#define BLOCK_STATUS(x) ((x)->h1.block_status)
#define BLOCK_NUM_PKTS(x) ((x)->h1.num_pkts)
#define BLOCK_O2FP(x) ((x)->h1.offset_to_first_pkt)
#define BLOCK_LEN(x) ((x)->h1.blk_len)
#define BLOCK_SNUM(x) ((x)->h1.seq_num)
#define BLOCK_O2PRIV(x) ((x)->offset_to_priv)
#define BLOCK_PRIV(x) ((void *) ((uint8_t *) (x) + BLOCK_O2PRIV(x)))
#define BLOCK_HDR_LEN (ALIGN_8(sizeof(struct block_desc)))
#define BLOCK_PLUS_PRIV(sz_pri) (BLOCK_HDR_LEN + ALIGN_8((sz_pri)))

#ifndef likely
# define likely(x) __builtin_expect(!!(x), 1)
#endif
Expand All @@ -765,7 +750,7 @@ struct ring {
static unsigned long packets_total = 0, bytes_total = 0;
static sig_atomic_t sigint = 0;

void sighandler(int num)
static void sighandler(int num)
{
sigint = 1;
}
Expand All @@ -774,6 +759,8 @@ static int setup_socket(struct ring *ring, char *netdev)
{
int err, i, fd, v = TPACKET_V3;
struct sockaddr_ll ll;
unsigned int blocksiz = 1 << 22, framesiz = 1 << 11;
unsigned int blocknum = 64;

fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
if (fd < 0) {
Expand All @@ -788,13 +775,12 @@ static int setup_socket(struct ring *ring, char *netdev)
}

memset(&ring->req, 0, sizeof(ring->req));
ring->req.tp_block_size = BLOCK_SIZE;
ring->req.tp_frame_size = FRAME_SIZE;
ring->req.tp_block_nr = NUM_BLOCKS;
ring->req.tp_frame_nr = NUM_FRAMES;
ring->req.tp_retire_blk_tov = BLOCK_RETIRE_TOV_IN_MS;
ring->req.tp_sizeof_priv = BLOCK_PRIV_AREA_SZ;
ring->req.tp_feature_req_word |= TP_FT_REQ_FILL_RXHASH;
ring->req.tp_block_size = blocksiz;
ring->req.tp_frame_size = framesiz;
ring->req.tp_block_nr = blocknum;
ring->req.tp_frame_nr = (blocksiz * blocknum) / framesiz;
ring->req.tp_retire_blk_tov = 60;
ring->req.tp_feature_req_word = TP_FT_REQ_FILL_RXHASH;

err = setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &ring->req,
sizeof(ring->req));
Expand All @@ -804,8 +790,7 @@ static int setup_socket(struct ring *ring, char *netdev)
}

ring->map = mmap(NULL, ring->req.tp_block_size * ring->req.tp_block_nr,
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED,
fd, 0);
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0);
if (ring->map == MAP_FAILED) {
perror("mmap");
exit(1);
Expand Down Expand Up @@ -835,58 +820,6 @@ static int setup_socket(struct ring *ring, char *netdev)
return fd;
}

#ifdef __checked
static uint64_t prev_block_seq_num = 0;

void assert_block_seq_num(struct block_desc *pbd)
{
if (unlikely(prev_block_seq_num + 1 != BLOCK_SNUM(pbd))) {
printf("prev_block_seq_num:%"PRIu64", expected seq:%"PRIu64" != "
"actual seq:%"PRIu64"\n", prev_block_seq_num,
prev_block_seq_num + 1, (uint64_t) BLOCK_SNUM(pbd));
exit(1);
}

prev_block_seq_num = BLOCK_SNUM(pbd);
}

static void assert_block_len(struct block_desc *pbd, uint32_t bytes, int block_num)
{
if (BLOCK_NUM_PKTS(pbd)) {
if (unlikely(bytes != BLOCK_LEN(pbd))) {
printf("block:%u with %upackets, expected len:%u != actual len:%u\n",
block_num, BLOCK_NUM_PKTS(pbd), bytes, BLOCK_LEN(pbd));
exit(1);
}
} else {
if (unlikely(BLOCK_LEN(pbd) != BLOCK_PLUS_PRIV(BLOCK_PRIV_AREA_SZ))) {
printf("block:%u, expected len:%lu != actual len:%u\n",
block_num, BLOCK_HDR_LEN, BLOCK_LEN(pbd));
exit(1);
}
}
}

static void assert_block_header(struct block_desc *pbd, const int block_num)
{
uint32_t block_status = BLOCK_STATUS(pbd);

if (unlikely((block_status & TP_STATUS_USER) == 0)) {
printf("block:%u, not in TP_STATUS_USER\n", block_num);
exit(1);
}

assert_block_seq_num(pbd);
}
#else
static inline void assert_block_header(struct block_desc *pbd, const int block_num)
{
}
static void assert_block_len(struct block_desc *pbd, uint32_t bytes, int block_num)
{
}
#endif

static void display(struct tpacket3_hdr *ppd)
{
struct ethhdr *eth = (struct ethhdr *) ((uint8_t *) ppd + ppd->tp_mac);
Expand Down Expand Up @@ -916,37 +849,27 @@ static void display(struct tpacket3_hdr *ppd)

static void walk_block(struct block_desc *pbd, const int block_num)
{
int num_pkts = BLOCK_NUM_PKTS(pbd), i;
int num_pkts = pbd->h1.num_pkts, i;
unsigned long bytes = 0;
unsigned long bytes_with_padding = BLOCK_PLUS_PRIV(BLOCK_PRIV_AREA_SZ);
struct tpacket3_hdr *ppd;

assert_block_header(pbd, block_num);

ppd = (struct tpacket3_hdr *) ((uint8_t *) pbd + BLOCK_O2FP(pbd));
ppd = (struct tpacket3_hdr *) ((uint8_t *) pbd +
pbd->h1.offset_to_first_pkt);
for (i = 0; i < num_pkts; ++i) {
bytes += ppd->tp_snaplen;
if (ppd->tp_next_offset)
bytes_with_padding += ppd->tp_next_offset;
else
bytes_with_padding += ALIGN_8(ppd->tp_snaplen + ppd->tp_mac);

display(ppd);

ppd = (struct tpacket3_hdr *) ((uint8_t *) ppd + ppd->tp_next_offset);
__sync_synchronize();
ppd = (struct tpacket3_hdr *) ((uint8_t *) ppd +
ppd->tp_next_offset);
}

assert_block_len(pbd, bytes_with_padding, block_num);

packets_total += num_pkts;
bytes_total += bytes;
}

void flush_block(struct block_desc *pbd)
static void flush_block(struct block_desc *pbd)
{
BLOCK_STATUS(pbd) = TP_STATUS_KERNEL;
__sync_synchronize();
pbd->h1.block_status = TP_STATUS_KERNEL;
}

static void teardown_socket(struct ring *ring, int fd)
Expand All @@ -962,7 +885,7 @@ int main(int argc, char **argp)
socklen_t len;
struct ring ring;
struct pollfd pfd;
unsigned int block_num = 0;
unsigned int block_num = 0, blocks = 64;
struct block_desc *pbd;
struct tpacket_stats_v3 stats;

Expand All @@ -984,15 +907,15 @@ int main(int argc, char **argp)

while (likely(!sigint)) {
pbd = (struct block_desc *) ring.rd[block_num].iov_base;
retry_block:
if ((BLOCK_STATUS(pbd) & TP_STATUS_USER) == 0) {

if ((pbd->h1.block_status & TP_STATUS_USER) == 0) {
poll(&pfd, 1, -1);
goto retry_block;
continue;
}

walk_block(pbd, block_num);
flush_block(pbd);
block_num = (block_num + 1) % NUM_BLOCKS;
block_num = (block_num + 1) % blocks;
}

len = sizeof(stats);
Expand Down

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