glibc's opendir allocates a minimum of 32kb, when called recursively
for a directory tree the memory consumption can add up - nearly 300kb
during perf start-up when processing modules. Add a stack allocated
variant of readdir sized a little more than 1kb

This was previously part of the memory saving change set:
https://lore.kernel.org/lkml/20231127220902.1315692-1-irogers@google.com/
It is separated here and a feature check and syscall workaround for
missing getdents64 added.

Ian Rogers (6):
  tools build: Add a feature test for getdents64
  tools lib api: Add io_dir an allocation free readdir alternative
  perf maps: Switch modules tree walk to io_dir__readdir
  perf pmu: Switch to io_dir__readdir
  perf header: Switch mem topology to io_dir__readdir
  perf events: Remove scandir in thread synthesis

 tools/build/Makefile.feature          |  1 +
 tools/build/feature/Makefile          |  4 ++
 tools/build/feature/test-all.c        |  5 ++
 tools/build/feature/test-getdents64.c | 12 ++++
 tools/lib/api/Makefile                |  2 +-
 tools/lib/api/io_dir.h                | 84 +++++++++++++++++++++++++++
 tools/perf/Makefile.config            |  4 ++
 tools/perf/util/header.c              | 31 +++++-----
 tools/perf/util/machine.c             | 19 +++---
 tools/perf/util/pmu.c                 | 48 ++++++---------
 tools/perf/util/pmus.c                | 30 ++++------
 tools/perf/util/synthetic-events.c    | 22 +++----
 12 files changed, 177 insertions(+), 85 deletions(-)
 create mode 100644 tools/build/feature/test-getdents64.c
 create mode 100644 tools/lib/api/io_dir.h

-- 
2.43.0.rc2.451.g8631bc7472-goog