Re: [PATCH 2/4] perf tools: Add cgroup_is_v2() helper

[Namhyung Kim <namhyung@kernel.org>]

Hi Ian,

On Tue, Jun 29, 2021 at 8:51 AM Ian Rogers <irogers@google.com> wrote:
>
> On Fri, Jun 25, 2021 at 12:18 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > The cgroup_is_v2() is to check if the given subsystem is mounted on
> > cgroup v2 or not.  It'll be used by BPF cgroup code later.
> >
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> >  tools/perf/util/cgroup.c | 19 +++++++++++++++++++
> >  tools/perf/util/cgroup.h |  2 ++
> >  2 files changed, 21 insertions(+)
> >
> > diff --git a/tools/perf/util/cgroup.c b/tools/perf/util/cgroup.c
> > index ef18c988c681..e819a4f30fc2 100644
> > --- a/tools/perf/util/cgroup.c
> > +++ b/tools/perf/util/cgroup.c
> > @@ -9,6 +9,7 @@
> >  #include <linux/zalloc.h>
> >  #include <sys/types.h>
> >  #include <sys/stat.h>
> > +#include <sys/statfs.h>
> >  #include <fcntl.h>
> >  #include <stdlib.h>
> >  #include <string.h>
> > @@ -70,6 +71,24 @@ int read_cgroup_id(struct cgroup *cgrp)
> >  }
> >  #endif  /* HAVE_FILE_HANDLE */
> >
> > +#ifndef CGROUP2_SUPER_MAGIC
> > +#define CGROUP2_SUPER_MAGIC  0x63677270
> > +#endif
> > +
> > +int cgroup_is_v2(const char *subsys)
> > +{
> > +       char mnt[PATH_MAX + 1];
> > +       struct statfs stbuf;
> > +
> > +       if (cgroupfs_find_mountpoint(mnt, PATH_MAX + 1, subsys))
> > +               return -1;
> > +
> > +       if (statfs(mnt, &stbuf) < 0)
> > +               return -1;
> > +
> > +       return (stbuf.f_type == CGROUP2_SUPER_MAGIC);
> > +}
> > +
> >  static struct cgroup *evlist__find_cgroup(struct evlist *evlist, const char *str)
> >  {
> >         struct evsel *counter;
> > diff --git a/tools/perf/util/cgroup.h b/tools/perf/util/cgroup.h
> > index 707adbe25123..1549ec2fd348 100644
> > --- a/tools/perf/util/cgroup.h
> > +++ b/tools/perf/util/cgroup.h
> > @@ -47,4 +47,6 @@ int read_cgroup_id(struct cgroup *cgrp)
> >  }
> >  #endif  /* HAVE_FILE_HANDLE */
> >
> > +int cgroup_is_v2(const char *subsys);
> > +
>
> I think this is okay. It may make sense to have this in
> tools/lib/api/fs/fs.h, for example fs__valid_mount is already checking
> magic numbers. Perhaps we can avoid a statfs call, but it'd need some
> reorganization of the fs.h code.
>
> Acked-by: Ian Rogers <irogers@google.com>

Thanks for your review!

Actually I'm ok with moving it to tools/lib.  Will do it in the next spin,
if it needs one. :)

Thanks,
Namhyung