Re: [PATCH v5 13/15] tools/testing/selftests/bpf: use TASK_COMM_LEN_16 instead of hard-coded 16

[Yafang Shao]

On Fri, Oct 22, 2021 at 6:44 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Wed, Oct 20, 2021 at 8:46 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> >
> > The hard-coded 16 is used in various bpf progs. These progs get task
> > comm either via bpf_get_current_comm() or prctl() or
> > bpf_core_read_str(), all of which can work well even if the task comm size
> > is changed.
> > Below is the detailed information,
> >
> > bpf_get_current_comm:
> >     progs/test_ringbuf.c
> >     progs/test_ringbuf_multi.c
> >
> > prctl:
> >     prog_tests/test_overhead.c
> >     prog_tests/trampoline_count.c
> >
> > bpf_core_read_str:
> >     progs/test_core_reloc_kernel.c
> >     progs/test_sk_storage_tracing.c
> >
> > We'd better replace the hard-coded 16 with TASK_COMM_LEN_16 to make it
> > more grepable.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: Petr Mladek <pmladek@xxxxxxxx>
> > ---
> >  tools/testing/selftests/bpf/Makefile                      | 2 +-
> >  tools/testing/selftests/bpf/prog_tests/ringbuf.c          | 3 ++-
> >  tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c    | 3 ++-
> >  .../testing/selftests/bpf/prog_tests/sk_storage_tracing.c | 3 ++-
> >  tools/testing/selftests/bpf/prog_tests/test_overhead.c    | 3 ++-
> >  tools/testing/selftests/bpf/prog_tests/trampoline_count.c | 3 ++-
> >  tools/testing/selftests/bpf/progs/profiler.h              | 7 ++++---
> >  tools/testing/selftests/bpf/progs/profiler.inc.h          | 8 ++++----
> >  tools/testing/selftests/bpf/progs/pyperf.h                | 4 ++--
> >  tools/testing/selftests/bpf/progs/strobemeta.h            | 6 +++---
> >  .../testing/selftests/bpf/progs/test_core_reloc_kernel.c  | 3 ++-
> >  tools/testing/selftests/bpf/progs/test_ringbuf.c          | 3 ++-
> >  tools/testing/selftests/bpf/progs/test_ringbuf_multi.c    | 3 ++-
> >  .../testing/selftests/bpf/progs/test_sk_storage_tracing.c | 5 +++--
> >  tools/testing/selftests/bpf/progs/test_skb_helpers.c      | 5 ++---
> >  tools/testing/selftests/bpf/progs/test_stacktrace_map.c   | 5 +++--
> >  tools/testing/selftests/bpf/progs/test_tracepoint.c       | 5 +++--
> >  17 files changed, 41 insertions(+), 30 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > index 799b88152e9e..5e72d783d3fe 100644
> > --- a/tools/testing/selftests/bpf/Makefile
> > +++ b/tools/testing/selftests/bpf/Makefile
> > @@ -279,7 +279,7 @@ MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
> >
> >  CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
> >  BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)                  \
> > -            -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)                   \
> > +            -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR) -I${TOOLSINCDIR}  \
>
> please don't add new include paths unnecessarily. See my comment on
> another patch, if you add those new constants as enums, they will be
> automatically available in vmlinux BTF and thus in auto-generated
> vmlinux.h header (for those programs using it).

Yes, after converting it to enum, the BPF programs can get it from the
generated vmlinux.h.

> For others, I'd just
> leave hard-coded 16 or re-defined TASK_COMM_LEN_16 where appropriate.
>

It seems not all the BPF programs can include the vmlinux.h.
What we really care about here is the copy of task comm should be with
a nul terminator, if we can assure it, then the size used by the BPF
is not important.
I have checked the copy of task comm in all these BPF programs one by
one, and replaced the unsafe bpf_probe_read_kernel() with
bpf_probe_read_kernel_str(), after that change, I think we can leave
hard-coded 16 for the progs which can't include vmlinux.h.

> >              -I$(abspath $(OUTPUT)/../usr/include)
> >
> >  CLANG_CFLAGS = $(CLANG_SYS_INCLUDES) \
> > diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > index 4706cee84360..ac82d57c09dc 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > @@ -12,6 +12,7 @@
> >  #include <sys/sysinfo.h>
> >  #include <linux/perf_event.h>
> >  #include <linux/ring_buffer.h>
> > +#include <linux/sched/task.h>
> >  #include "test_ringbuf.lskel.h"
> >
> >  #define EDONE 7777
> > @@ -22,7 +23,7 @@ struct sample {
> >         int pid;
> >         int seq;
> >         long value;
> > -       char comm[16];
> > +       char comm[TASK_COMM_LEN_16];
>
> how much value is in this "grep-ability", really? I'm not convinced
> all this code churn is justified.
>
> >  };
> >
> >  static int sample_cnt;
> > diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c b/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c
> > index 167cd8a2edfd..f0748305ffd6 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c
> > @@ -2,6 +2,7 @@
> >  #define _GNU_SOURCE
> >  #include <test_progs.h>
> >  #include <sys/epoll.h>
> > +#include <linux/sched/task.h>
> >  #include "test_ringbuf_multi.skel.h"
> >
> >  static int duration = 0;
>
> [...]


-- 
Thanks
Yafang