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From the bpftrace tutorial, I would have expected the one-liner

    bpftrace -e 'tracepoint:syscalls:sys_enter_open { printf("%d %s\n", pid, str(args->filename)); }'

to show me all open calls as they happen. I would have expected to see an open when I cat a file, for example. But trying the one-liner, I only see a few opens of files in /proc.

Can anyone explain what's happening?

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It actually turns out most of the calls are `openat(2)`. I had the same question initially.

(don't have access to a linux box I can test this on at the moment, so sorry for the stupid question)

In DTrace, you can specify a probe like

  syscall::*open*:entry / / { }

to grab open(2), openat(2), etc. Does eBPF allow wildcards in probe specifications?

You can do

    bpftrace -e 'tracepoint:syscalls:sys_enter_open* { printf("%d\n", pid); }'

but then you can't access the arguments of the different probes uniformly, i.e.

    bpftrace -e 'tracepoint:syscalls:sys_enter_open* { printf("%d %s\n", pid, str(args->filename)); }'

does not work.

You can do it like this:

    bpftrace -e 'tracepoint:syscalls:sys_enter_open { printf("%d %s\n", pid, str(args->filename)); } tracepoint:syscalls:sys_enter_openat { printf("%d %s\n", pid, str(args->filename)); }'

This is a bit awkward, but it seems that this will be fixed: https://github.com/iovisor/bpftrace/issues/132

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