Re: [PATCH v1 2/6] tools lib api: Add io_dir an allocation free readdir alternative

[Namhyung Kim <namhyung@kernel.org>]

On Wed, Dec 6, 2023 at 9:04 PM Ian Rogers <irogers@google.com> wrote:
>
> 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.
>
> As getdents64 may be missing from libc, add support using syscall.

Unfortunately my alpine build has:

In file included from util/machine.c:2:
/build/libapi/include/api/io_dir.h:17:23: error: conflicting types for
'getdents'; have 'ssize_t(int,  void *, size_t)' {aka 'long int(int,
void *, long unsigned int)'}
   17 | static inline ssize_t getdents64(int fd, void *dirp, size_t count)
      |                       ^~~~~~~~~~
/usr/include/dirent.h:52:5: note: previous declaration of 'getdents'
with type 'int(int,  struct dirent *, size_t)' {aka 'int(int,  struct
dirent *, long unsigned int)'}
   52 | int getdents(int, struct dirent *, size_t);
      |     ^~~~~~~~

Thanks,
Namhyung

>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/lib/api/Makefile     |  2 +-
>  tools/lib/api/io_dir.h     | 84 ++++++++++++++++++++++++++++++++++++++
>  tools/perf/Makefile.config |  4 ++
>  3 files changed, 89 insertions(+), 1 deletion(-)
>  create mode 100644 tools/lib/api/io_dir.h
>
> diff --git a/tools/lib/api/Makefile b/tools/lib/api/Makefile
> index 044860ac1ed1..186aa407de8c 100644
> --- a/tools/lib/api/Makefile
> +++ b/tools/lib/api/Makefile
> @@ -99,7 +99,7 @@ install_lib: $(LIBFILE)
>                 $(call do_install_mkdir,$(libdir_SQ)); \
>                 cp -fpR $(LIBFILE) $(DESTDIR)$(libdir_SQ)
>
> -HDRS := cpu.h debug.h io.h
> +HDRS := cpu.h debug.h io.h io_dir.h
>  FD_HDRS := fd/array.h
>  FS_HDRS := fs/fs.h fs/tracing_path.h
>  INSTALL_HDRS_PFX := $(DESTDIR)$(prefix)/include/api
> diff --git a/tools/lib/api/io_dir.h b/tools/lib/api/io_dir.h
> new file mode 100644
> index 000000000000..9b702497e05c
> --- /dev/null
> +++ b/tools/lib/api/io_dir.h
> @@ -0,0 +1,84 @@
> +/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
> +/*
> + * Lightweight directory reading library.
> + */
> +#ifndef __API_IO_DIR__
> +#define __API_IO_DIR__
> +
> +#include <dirent.h>
> +#include <fcntl.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <sys/stat.h>
> +
> +#ifndef HAVE_GETDENTS64
> +#include <sys/syscall.h>
> +
> +static inline ssize_t getdents64(int fd, void *dirp, size_t count)
> +{
> +       return syscall(SYS_getdents64, fd, dirp, count);
> +}
> +#endif
> +
> +struct io_dirent64 {
> +       ino64_t        d_ino;    /* 64-bit inode number */
> +       off64_t        d_off;    /* 64-bit offset to next structure */
> +       unsigned short d_reclen; /* Size of this dirent */
> +       unsigned char  d_type;   /* File type */
> +       char           d_name[NAME_MAX + 1]; /* Filename (null-terminated) */
> +};
> +
> +struct io_dir {
> +       int dirfd;
> +       ssize_t available_bytes;
> +       struct io_dirent64 *next;
> +       struct io_dirent64 buff[4];
> +};
> +
> +static inline void io_dir__init(struct io_dir *iod, int dirfd)
> +{
> +       iod->dirfd = dirfd;
> +       iod->available_bytes = 0;
> +}
> +
> +static inline void io_dir__rewinddir(struct io_dir *iod)
> +{
> +       lseek(iod->dirfd, 0, SEEK_SET);
> +       iod->available_bytes = 0;
> +}
> +
> +static inline struct io_dirent64 *io_dir__readdir(struct io_dir *iod)
> +{
> +       struct io_dirent64 *entry;
> +
> +       if (iod->available_bytes <= 0) {
> +               ssize_t rc = getdents64(iod->dirfd, iod->buff, sizeof(iod->buff));
> +
> +               if (rc <= 0)
> +                       return NULL;
> +               iod->available_bytes = rc;
> +               iod->next = iod->buff;
> +       }
> +       entry = iod->next;
> +       iod->next = (struct io_dirent64 *)((char *)entry + entry->d_reclen);
> +       iod->available_bytes -= entry->d_reclen;
> +       return entry;
> +}
> +
> +static inline bool io_dir__is_dir(const struct io_dir *iod, struct io_dirent64 *dent)
> +{
> +       if (dent->d_type == DT_UNKNOWN) {
> +               struct stat st;
> +
> +               if (fstatat(iod->dirfd, dent->d_name, &st, /*flags=*/0))
> +                       return false;
> +
> +               if (S_ISDIR(st.st_mode)) {
> +                       dent->d_type = DT_DIR;
> +                       return true;
> +               }
> +       }
> +       return dent->d_type == DT_DIR;
> +}
> +
> +#endif
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index aa55850fbc21..1cef1ab4ddb7 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -357,6 +357,10 @@ ifeq ($(feature-stackprotector-all), 1)
>    CORE_CFLAGS += -fstack-protector-all
>  endif
>
> +ifeq ($(feature-getdents64), 1)
> +  CFLAGS += -DHAVE_GETDENTS64
> +endif
> +
>  ifeq ($(DEBUG),0)
>    ifeq ($(feature-fortify-source), 1)
>      CORE_CFLAGS += -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2
> --
> 2.43.0.rc2.451.g8631bc7472-goog
>