--- /dev/null
+# can_socket_blocking.txt
+#
+# The purpose of this experiment is to show:
+# 1) "Nonblocking behaviour" (return value of -ENOBUFS) of write() call to
+# CAN socket (with default settings set to BLOCKING).
+# This can be caused by:
+# -- Amount of data sent to a device is much higher than
+# the device is capable of sending (i.e. frames are dropped by the
+# device driver).
+# -- Amount of data sent to a qdisc (default pfifo gets its size from
+# txqueuelen parameter of a device) is much higher than the qdisc
+# can handle -- this leads to packet drop.
+#
+# 2) Possibility of blocking behaviour of write() call when internal socket
+# buffer (SO_SNDBUF option) is smaller than qdiscs buffer. (3rd part of
+# the experiment tries to show that write is "really blocked" -- that this
+# desired behaviour is not caused only in the manner that none ot the
+# buffers overruns).
+################################################################################
+
+# Set the same for all parts of the experiment
+$ sudo ip link set can0 txqueuelen 50
+
+################################################################################
+##### Default cangen #####
+################################################################################
+
+$ ip link show dev can0
+3: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UNKNOWN qlen 50
+ link/can
+
+$ ./cangen -g 0 can0 -I i -L 1 -D i -v -v
+ can0 0 [1] 00
+ can0 1 [1] 01
+ can0 2 [1] 02
+ can0 3 [1] 03
+ can0 4 [1] 04
+ can0 5 [1] 05
+ can0 6 [1] 06
+ can0 7 [1] 07
+ can0 8 [1] 08
+ can0 9 [1] 09
+ can0 A [1] 0A
+ can0 B [1] 0B
+ can0 C [1] 0C
+ can0 D [1] 0D
+ can0 E [1] 0E
+ can0 F [1] 0F
+ can0 10 [1] 10
+ can0 11 [1] 11
+ can0 12 [1] 12
+ can0 13 [1] 13
+ can0 14 [1] 14
+ can0 15 [1] 15
+ can0 16 [1] 16
+ can0 17 [1] 17
+ can0 18 [1] 18
+ can0 19 [1] 19
+ can0 1A [1] 1A
+ can0 1B [1] 1B
+ can0 1C [1] 1C
+ can0 1D [1] 1D
+ can0 1E [1] 1E
+ can0 1F [1] 1F
+ can0 20 [1] 20
+ can0 21 [1] 21
+ can0 22 [1] 22
+ can0 23 [1] 23
+ can0 24 [1] 24
+ can0 25 [1] 25
+ can0 26 [1] 26
+ can0 27 [1] 27
+ can0 28 [1] 28
+ can0 29 [1] 29
+ can0 2A [1] 2A
+ can0 2B [1] 2B
+ can0 2C [1] 2C
+ can0 2D [1] 2D
+ can0 2E [1] 2E
+ can0 2F [1] 2F
+ can0 30 [1] 30
+ can0 31 [1] 31
+ can0 32 [1] 32
+ can0 33 [1] 33
+ can0 34 [1] 34
+ can0 35 [1] 35
+ can0 36 [1] 36
+ can0 37 [1] 37
+ can0 38 [1] 38
+ can0 39 [1] 39
+write: No buffer space available
+
+$ strace -o cangen.strace -r ./cangen -g 0 can0 -I 125 -L 1 -D i
+write: No buffer space available
+
+$ cat cangen.strace | tail -30
+ 0.000082 write(3, "%\1\0\0\1\0\0\0\27\6\0\0\0\0\0\0", 16) = 16
+ 0.000091 write(3, "%\1\0\0\1\0\0\0\30\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0\31\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0\32\6\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0\33\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0\34\6\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0\35\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0\36\6\0\0\0\0\0\0", 16) = 16
+ 0.000050 write(3, "%\1\0\0\1\0\0\0\37\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0 \6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0!\6\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0\"\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0#\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0$\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0%\6\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0&\6\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0'\6\0\0\0\0\0\0", 16) = 16
+ 0.000080 write(3, "%\1\0\0\1\0\0\0(\6\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0)\6\0\0\0\0\0\0", 16) = -1 ENOBUFS (No buffer space available)
+ 0.000110 dup(2) = 4
+ 0.000076 fcntl64(4, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)
+ 0.000177 brk(0) = 0x804e000
+ 0.000067 brk(0x806f000) = 0x806f000
+ 0.000092 fstat64(4, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
+ 0.000151 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7840000
+ 0.000079 _llseek(4, 0, 0xbff26d08, SEEK_CUR) = -1 ESPIPE (Illegal seek)
+ 0.000107 write(4, "write: No buffer space available"..., 33) = 33
+ 0.000095 close(4) = 0
+ 0.000066 munmap(0xb7840000, 4096) = 0
+ 0.000100 exit_group(1) = ?
+
+
+################################################################################
+##### Cangen with setting of SO_SNDBUF option #####
+################################################################################
+
+$ git diff -U0
+diff --git a/can-utils/cangen.c b/can-utils/cangen.c
+index 95dfa46..db3fde2 100644
+--- a/can-utils/cangen.c
++++ b/can-utils/cangen.c
+@@ -105 +105,3 @@ void print_usage(char *prg)
+- "printing sent CAN frames)\n\n");
++ "printing sent CAN frames)\n");
++ fprintf(stderr, " -b (set SO_SNDBUF value of a buffer "
++ "-- the kernel doubles this value)\n\n");
+@@ -144,0 +147 @@ int main(int argc, char **argv)
++ int snd_buf = 0;
+@@ -168 +171 @@ int main(int argc, char **argv)
+- while ((opt = getopt(argc, argv, "ig:eI:L:D:xp:n:vh?")) != -1) {
++ while ((opt = getopt(argc, argv, "ig:eI:L:D:xp:n:vb:h?")) != -1) {
+@@ -226,0 +230,4 @@ int main(int argc, char **argv)
++ case 'b':
++ snd_buf = atoi(optarg);
++ break;
++
+@@ -301,0 +309,8 @@ int main(int argc, char **argv)
++ if (snd_buf > 0)
++ setsockopt(s, SOL_SOCKET, SO_SNDBUF, &snd_buf, sizeof(snd_buf));
++/* {
++ socklen_t len;
++ getsockopt(s, SOL_SOCKET, SO_SNDBUF, &snd_buf, &len);
++ printf("SO_SNDBUF: %d\n", snd_buf);
++ }
++*/
+
+$ ip link show dev can0
+3: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UNKNOWN qlen 50
+ link/can
+
+# There is no ENOBUFS error
+$ ./cangen -b 1024 -g 0 can0 -I 123 -L 1 -D i -v -v | head -10000 | wc -l
+10000
+
+
+################################################################################
+##### Throttling of outgoing traffic with TBF #####
+################################################################################
+
+# Default qdisc
+$ sudo tc qdisc del dev can0 root
+
+$ strace -o cangen.strace -r ./cangen -b 1024 -g 0 can0 -I 125 -L 1 -D i
+
+$ cat cangen.strace | tail -30
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\276.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\277.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\300.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\301.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\302.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\303.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\304.\0\0\0\0\0\0", 16) = 16
+ 0.000077 write(3, "%\1\0\0\1\0\0\0\305.\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\306.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\307.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\310.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\311.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\312.\0\0\0\0\0\0", 16) = 16
+ 0.000341 write(3, "%\1\0\0\1\0\0\0\313.\0\0\0\0\0\0", 16) = 16
+ 0.000077 write(3, "%\1\0\0\1\0\0\0\314.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\315.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\316.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\317.\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\320.\0\0\0\0\0\0", 16) = 16
+ 0.000080 write(3, "%\1\0\0\1\0\0\0\321.\0\0\0\0\0\0", 16) = 16
+ 0.000352 write(3, "%\1\0\0\1\0\0\0\322.\0\0\0\0\0\0", 16) = 16
+ 0.000087 write(3, "%\1\0\0\1\0\0\0\323.\0\0\0\0\0\0", 16) = 16
+ 0.000080 write(3, "%\1\0\0\1\0\0\0\324.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\325.\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\326.\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\327.\0\0\0\0\0\0", 16) = 16
+ 0.000114 --- SIGINT (Interrupt) @ 0 (0) ---
+ 0.000072 sigreturn() = ? (mask now [])
+ 0.000096 close(3) = 0
+ 0.000102 exit_group(0) = ?
+
+
+
+
+# TBF
+$ sudo tc qdisc add dev can0 root tbf rate 1kbit burst 1kbit latency 50ms
+
+$ strace -o cangen.strace -r ./cangen -b 1024 -g 0 can0 -I 125 -L 1 -D i
+
+# Each 5th write blocks for a while
+$ cat cangen.strace | tail -30
+ 0.000048 write(3, "%\1\0\0\1\0\0\0\16\0\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\17\0\0\0\0\0\0\0", 16) = 16
+ 0.511054 write(3, "%\1\0\0\1\0\0\0\20\0\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0\21\0\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\22\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0\23\0\0\0\0\0\0\0", 16) = 16
+ 0.511835 write(3, "%\1\0\0\1\0\0\0\24\0\0\0\0\0\0\0", 16) = 16
+ 0.000104 write(3, "%\1\0\0\1\0\0\0\25\0\0\0\0\0\0\0", 16) = 16
+ 0.000050 write(3, "%\1\0\0\1\0\0\0\26\0\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\27\0\0\0\0\0\0\0", 16) = 16
+ 0.511787 write(3, "%\1\0\0\1\0\0\0\30\0\0\0\0\0\0\0", 16) = 16
+ 0.000078 write(3, "%\1\0\0\1\0\0\0\31\0\0\0\0\0\0\0", 16) = 16
+ 0.000049 write(3, "%\1\0\0\1\0\0\0\32\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0\33\0\0\0\0\0\0\0", 16) = 16
+ 0.511823 write(3, "%\1\0\0\1\0\0\0\34\0\0\0\0\0\0\0", 16) = 16
+ 0.000080 write(3, "%\1\0\0\1\0\0\0\35\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0\36\0\0\0\0\0\0\0", 16) = 16
+ 0.000049 write(3, "%\1\0\0\1\0\0\0\37\0\0\0\0\0\0\0", 16) = 16
+ 0.511859 write(3, "%\1\0\0\1\0\0\0 \0\0\0\0\0\0\0", 16) = 16
+ 0.000057 write(3, "%\1\0\0\1\0\0\0!\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0\"\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0#\0\0\0\0\0\0\0", 16) = 16
+ 0.511819 write(3, "%\1\0\0\1\0\0\0$\0\0\0\0\0\0\0", 16) = 16
+ 0.000085 write(3, "%\1\0\0\1\0\0\0%\0\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0&\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0'\0\0\0\0\0\0\0", 16) = 16
+ 0.234341 --- SIGINT (Interrupt) @ 0 (0) ---
+ 0.000036 sigreturn() = ? (mask now [])
+ 0.000064 close(3) = 0
+ 0.000069 exit_group(0) = ?
+
+
+# Setting socket as O_NONBLOCK
+# Observing behaviour with throttled outgoing traffic
+
+$ git diff -U0
+diff --git a/can-utils/cangen.c b/can-utils/cangen.c
+index 69b6323..0295f75 100644
+--- a/can-utils/cangen.c
++++ b/can-utils/cangen.c
+@@ -58,0 +59 @@
++#include <fcntl.h>
+@@ -311,0 +313,2 @@ int main(int argc, char **argv)
++ fcntl(s, F_SETFL, O_NONBLOCK);
++
+
+$ strace -o cangen.strace -r ./cangen -b 1024 -g 0 can0 -I 125 -L 1 -D i
+write: Resource temporarily unavailable
+
+$ cat cangen.strace | tail -30
+ 0.000043 setsockopt(3, SOL_SOCKET, SO_SNDBUF, [1024], 4) = 0
+ 0.000043 fcntl64(3, F_SETFL, O_RDONLY|O_NONBLOCK) = 0
+ 0.000042 bind(3, {sa_family=0x1d /* AF_??? */, sa_data="\0\0\3\0\0\0\1\0\0\0\3708z\267"}, 16) = 0
+ 0.000058 write(3, "%\1\0\0\1\0\0\0\0\0\0\0\0\0\0\0", 16) = 16
+ 0.000065 write(3, "%\1\0\0\1\0\0\0\1\0\0\0\0\0\0\0", 16) = 16
+ 0.000092 write(3, "%\1\0\0\1\0\0\0\2\0\0\0\0\0\0\0", 16) = 16
+ 0.000083 write(3, "%\1\0\0\1\0\0\0\3\0\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0\4\0\0\0\0\0\0\0", 16) = 16
+ 0.000082 write(3, "%\1\0\0\1\0\0\0\5\0\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0\6\0\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0\7\0\0\0\0\0\0\0", 16) = 16
+ 0.000081 write(3, "%\1\0\0\1\0\0\0\10\0\0\0\0\0\0\0", 16) = 16
+ 0.000079 write(3, "%\1\0\0\1\0\0\0\t\0\0\0\0\0\0\0", 16) = 16
+ 0.000050 write(3, "%\1\0\0\1\0\0\0\n\0\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\v\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0\f\0\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\r\0\0\0\0\0\0\0", 16) = 16
+ 0.000047 write(3, "%\1\0\0\1\0\0\0\16\0\0\0\0\0\0\0", 16) = 16
+ 0.000048 write(3, "%\1\0\0\1\0\0\0\17\0\0\0\0\0\0\0", 16) = -1 EAGAIN (Resource temporarily unavailable)
+ 0.000064 dup(2) = 4
+ 0.000040 fcntl64(4, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)
+ 0.000101 brk(0) = 0x804e000
+ 0.000035 brk(0x806f000) = 0x806f000
+ 0.000059 fstat64(4, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 4), ...}) = 0
+ 0.000079 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7784000
+ 0.000047 _llseek(4, 0, 0xbfbb37f8, SEEK_CUR) = -1 ESPIPE (Illegal seek)
+ 0.000079 write(4, "write: Resource temporarily unav"..., 40) = 40
+ 0.000059 close(4) = 0
+ 0.000036 munmap(0xb7784000, 4096) = 0
+ 0.000061 exit_group(1) = ?
+
+
projects / lisovros / iproute2_canprio.git / commitdiff