doc: packet: simplify tpacket example code

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>

1 files changed, 28 insertions, 105 deletions

diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
index 23dd80e82b8e..8572796b1eb6 100644
--- a/Documentation/networking/packet_mmap.txt
+++ b/Documentation/networking/packet_mmap.txt
@@ -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>
@@ -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
@@ -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;
 }
@@ -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) {
@@ -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));
@@ -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);
@@ -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);
@@ -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)
@@ -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;
 
@@ -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);