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Make the packet-dump code work with a FIFO.

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mkfifo /tmp/dnsmasq.pipe
dnsmasq --dumpfile=/tmp/dnsmasq.pipe ....
wireshark -i /tmp/dnsmasq.pipe

gives real-time display of network traffic in Wireshark.
This commit is contained in:
Simon Kelley
2024-11-27 16:03:13 +00:00
parent c6bc22adc7
commit 41d2ae3203
2 changed files with 17 additions and 9 deletions
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2
man/dnsmasq.8
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@@ -781,7 +781,7 @@ The address range can be of the form
must fall in the same /64 network, or prefix-length must be greater than or equal to 64 except that shorter prefix lengths than 64 are allowed only if non-sequential names are in use.
.TP
.B --dumpfile=<path/to/file>
Specify the location of a pcap-format file which dnsmasq uses to dump copies of network packets for debugging purposes. If the file exists when dnsmasq starts, it is not deleted; new packets are added to the end.
Specify the location of a pcap-format file which dnsmasq uses to dump copies of network packets for debugging purposes. If the file exists when dnsmasq starts, it is not deleted; new packets are added to the end. The file may be a named-pipe which Wireshark is listening to.
.TP
.B --dumpmask=<mask>
Specify which types of packets should be added to the dumpfile. The argument should be the OR of the bitmasks for each type of packet to be dumped: it can be specified in hex by preceding the number with 0x in the normal way. Each time a packet is written to the dumpfile, dnsmasq logs the packet sequence and the mask

24
src/dump.c
View File

@@ -51,22 +51,30 @@ void dump_init(void)
packet_count = 0;
header.magic_number = 0xa1b2c3d4;
header.version_major = 2;
header.version_minor = 4;
header.thiszone = 0;
header.sigfigs = 0;
header.snaplen = daemon->edns_pktsz + 200; /* slop for IP/UDP headers */
header.network = 101; /* DLT_RAW http://www.tcpdump.org/linktypes.html */
if (stat(daemon->dump_file, &buf) == -1)
{
/* doesn't exist, create and add header */
header.magic_number = 0xa1b2c3d4;
header.version_major = 2;
header.version_minor = 4;
header.thiszone = 0;
header.sigfigs = 0;
header.snaplen = daemon->edns_pktsz + 200; /* slop for IP/UDP headers */
header.network = 101; /* DLT_RAW http://www.tcpdump.org/linktypes.html */
if (errno != ENOENT ||
(daemon->dumpfd = creat(daemon->dump_file, S_IRUSR | S_IWUSR)) == -1 ||
!read_write(daemon->dumpfd, (void *)&header, sizeof(header), RW_WRITE))
die(_("cannot create %s: %s"), daemon->dump_file, EC_FILE);
}
else if (S_ISFIFO(buf.st_mode))
{
/* File is named pipe (with wireshark on the other end, probably.)
Send header. */
if ((daemon->dumpfd = open(daemon->dump_file, O_APPEND | O_RDWR)) == -1 ||
!read_write(daemon->dumpfd, (void *)&header, sizeof(header), RW_WRITE))
die(_("cannot open pipe %s: %s"), daemon->dump_file, EC_FILE);
}
else if ((daemon->dumpfd = open(daemon->dump_file, O_APPEND | O_RDWR)) == -1 ||
!read_write(daemon->dumpfd, (void *)&header, sizeof(header), RW_READ))
die(_("cannot access %s: %s"), daemon->dump_file, EC_FILE);