RawNetworkInterfaceDriver/labgrid-raw-interface Fixes #1745
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Bastian-Krause
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## master #1745 +/- ##
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- Coverage 45.3% 45.3% -0.1%
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Files 172 172
Lines 13517 13530 +13
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Hits 6131 6131
- Misses 7386 7399 +13
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Emantor
approved these changes
Sep 25, 2025
The current tcpdump timeout handling does not work. This is supposed to exit after 5 seconds: tcpdump --interface=eth0 -w - -G 5 -W 1 But that does not work if no packets are received. So in order to make the timeout actually work, prefix tcpdump with coreutils' timeout command instead: timeout --signal=INT --preserve-status <timeout> <tcpdump command> By sending SIGINT (`--signal=INT`), tcpdump exits gracefully and finishes writing received packets. Combined with `--preserve-status`, tcpdump's actual exit status is preserved, being 0 even on SIGINT if nothing else went wrong. An alternative would be to use subprocess, but that would prevent us from using `os.execvp()`, replacing the process. So the timeout command is the better approach here. Signed-off-by: Bastian Krause <[email protected]>
…ptional The intention of labgrid-raw-interface was to have an optional "count" argument, allowing for packet capture on an interface until a timeout is reached, no matter how many packets are received. This is used when calling: RawNetworkInterfaceDriver.start_record(filename, timeout=10) However, the missing `nargs="?"` kwarg when adding the argument actually required the argument to be given: usage: labgrid-raw-interface tcpdump [-h] [--timeout TIMEOUT] ifname count labgrid-raw-interface tcpdump: error: the following arguments are required: count The original commit introducing the option actually included it [1]. Fix that by re-adding `nargs="?"`. [1] 90cf941 ("helpers: add labgrid-raw-interface helper") Fixes: c1aec37 ("helpers/labgrid-raw-interface: introduce subparsers per program, pass options") Signed-off-by: Bastian Krause <[email protected]>
…ture started The expectation of RawNetworkInterfaceDriver.start_record() is that it returns once the packet capturing is running, so later code can start right away generating packets that are received on the interface. This does not work reliably currently because the labgrid-raw-interface helper (wrapping tcpdump) is started via subprocess.Popen(), but that does not mean the capture is actually running just yet. To fix this, wait until the subprocess emits "tcpdump: listening on", which is tcpdump's way of telling that it's now actually capturing. Signed-off-by: Bastian Krause <[email protected]>
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Description
Fixes:
RawNetworkInterfaceDriver.record(..., timeout=<timeout>)/start_record(..., timeout=<timeout>)never stopping tcpdump if no packets were received.RawNetworkInterfaceDriver.record(..., count=None)/start_record(..., count=None)calling labgrid-raw-interface leading to an error.RawNetworkInterfaceDriver.record(...)/start_record(...)returning before the actual capture started, leading to missed packetsChecklist
Fixes #1157
Fixes #1320
/cc @JoshuaWatt @nick-potenski