Re: [PATCH 6/9] perf record: Support synthesizing cgroup events

[Namhyung Kim]

Hi Arnaldo,

On Tue, Mar 31, 2020 at 1:43 AM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
>
> Em Mon, Mar 30, 2020 at 01:30:58PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Wed, Mar 25, 2020 at 09:45:33PM +0900, Namhyung Kim escreveu:
> > > Synthesize cgroup events by iterating cgroup filesystem directories.
> > > The cgroup event only saves the portion of cgroup path after the mount
> > > point and the cgroup id (which actually is a file handle).
> >
> > Breaks the build on alpine linux (musl libc):
> >
> >   CC       /tmp/build/perf/util/srccode.o
> >   CC       /tmp/build/perf/util/synthetic-events.o
> > util/synthetic-events.c: In function 'perf_event__synthesize_cgroup':
> > util/synthetic-events.c:427:22: error: field 'fh' has incomplete type
> >    struct file_handle fh;
> >                       ^
> > util/synthetic-events.c:441:6: error: implicit declaration of function 'name_to_handle_at' [-Werror=implicit-function-declaration]
> >   if (name_to_handle_at(AT_FDCWD, path, &handle.fh, &mount_id, 0) < 0) {
> >       ^
> > util/synthetic-events.c:441:2: error: nested extern declaration of 'name_to_handle_at' [-Werror=nested-externs]
> >   if (name_to_handle_at(AT_FDCWD, path, &handle.fh, &mount_id, 0) < 0) {
> >   ^
> >   CC       /tmp/build/perf/util/data.o
> > cc1: all warnings being treated as errors
> > mv: can't rename '/tmp/build/perf/util/.synthetic-events.o.tmp': No such file or directory
> >
> >
> > I'm trying to fix
>
> musl libc up to 1.2.21 (IIRC) lacks name_to_handle_at and its structs,
> then from the one that is in alpine linux 3.10 the error changes to:
>
>   CC       /tmp/build/perf/util/cloexec.o
> util/synthetic-events.c:427:22: error: field 'fh' with variable sized type 'struct file_handle' not at the end of a struct or class is a GNU
>       extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
>                 struct file_handle fh;
>                                    ^
> 1 error generated.
> mv: can't rename '/tmp/build/perf/util/.synthetic-events.o.tmp': No such file or directory
> make[4]: *** [/git/linux/tools/build/Makefile.build:97: /tmp/build/perf/util/synthetic-events.o] Error 1
> make[4]: *** Waiting for unfinished jobs....
> make[3]: *** [/git/linux/tools/build/Makefile.build:139: util] Error 2
> make[2]: *** [Makefile.perf:617: /tmp/build/perf/perf-in.o] Error 2
> make[1]: *** [Makefile.perf:225: sub-make] Error 2
> make: *** [Makefile:70: all] Error 2
> make: Leaving directory '/git/linux/tools/perf'
> + exit 1
> [root@quaco ~]#
>
> So probably we'll need a feature test to catch this and do some
> workaround or disable the feature on such systems, providing some
> warning.
>
> I left the container build tests running to see if some other system has
> problems with this, perhaps the ones with uCLibc or some older glibc,
> we'll see.
>
> So far all the alpine versions failed with the above problems and ALT
> Linux p8 and p9 built without problems.

Hmm.. right, the CONFIG_FHANDLE can be turned off or old systems
lack support.  I'll send a patch for the feature test soon.

Thanks
Namhyung