Re: Multiple call to pcap_open_live

[Michal Sekletar <msekleta () redhat com>]

On Mon, Nov 18, 2013 at 12:38:24AM -0500, Benjamin Vanheuverzwijn wrote:
> Hi,

Hi Benjamin,

> libpcap version: 1.4.0 (on archlinux)

I am running Fedora 19 (libpcap-1.4.0). 

> Is it possible to have multiple call to "pcap_open_live()" followed by
> pcap_close() ?

It shouldn't be a problem.

> It seems like pcap_close() doesn't cleanly close opened resources, if you
> strace the following program, you will see file descriptors growing up.

I am unable to reproduce the issue. In strace output I see only descriptor 3
which is acquired and closed on every iteration. Tried with two NICs, wired and
wireless.

> Am i doing it wrong? How it should be done?

> From output you have provided I have a suspicion that your problem is somehow
caused by calling open() on those /sys/bus/usb/* files. I don't have those in my
strace output, probably because interface you have used is hotplugged wireless
usb dongle, I guess (judging by interface name from udev).

I might be able to try again with wireless USB dongle tomorrow. Will keep you
posted on my findings.

> Thanks,

Cheers,

Michal
> To reproduce:
> // Compile with gcc -o openlive openlive.c -l pcap
> #include <pcap.h>
>
> int main(int argc, char *argv[]) {
>     int i=0;
>     for (i = 0; i != 2000; ++i) {
>         char errbuf[256];
>         pcap_t *pcap = pcap_open_live("wls3", 1024, 1, 0, errbuf);
>         pcap_close(pcap);
>     }
>     return 0;
> }
>
> $ strace ./openlive
> [...]
> open("/sys/bus/usb/devices/4-2/devnum", O_RDONLY) = 16
> fstat(16, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> 0x7f5e040f0000
> read(16, "8\n", 4096)                   = 2
> [...]
> open("/sys/bus/usb/devices/usb4/speed", O_RDONLY) = 91
> fstat(91, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> 0x7fc006371000
> read(91, "480\n", 4096)                 = 4
>
>
> -- 
> Benjamin Vanheuverzwijn
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