Re: [PATCH bpf-next 2/5] bpf: add bpf_trace_vprintk helper

On Mon, Aug 23, 2021 at 9:50 PM Andrii Nakryiko
[off-list ref] wrote:

On Fri, Aug 20, 2021 at 7:59 PM Dave Marchevsky [off-list ref] wrote:

quoted

This helper is meant to be "bpf_trace_printk, but with proper vararg

We have bpf_snprintf() and bpf_seq_printf() names for other BPF
helpers using the same approach. How about we call this one simply
`bpf_printf`? It will be in line with other naming, it is logical BPF
equivalent of user-space printf (which outputs to stderr, which in BPF
land is /sys/kernel/debug/tracing/trace_pipe). And it will be logical
to have a nice and short BPF_PRINTF() convenience macro provided by
libbpf.

quoted

support". Follow bpf_snprintf's example and take a u64 pseudo-vararg
array. Write to dmesg using the same mechanism as bpf_trace_printk.

Are you sure about the dmesg part?... bpf_trace_printk is outputting
into /sys/kernel/debug/tracing/trace_pipe.

Actually I like bpf_trace_vprintk() name, since it makes it obvious that
it's a flavor of bpf_trace_printk() and its quirks that users learned
to deal with.
I would reserve bpf_printf() for the future. We might have standalone
bpf programs in the future (without user space component) and a better
equivalent
of stdin/stdout. clang -target bpf hello_world.c -o a.out; ./a.out
should print to a terminal. Such future hello world in bpf would be
using bpf_printf()
or bpf_dprintf().