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

[Ian Rogers]

On Mon, Dec 11, 2023 at 3:25 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Wed, Dec 6, 2023 at 9:04 PM Ian Rogers <irogers@xxxxxxxxxx> 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);
>       |     ^~~~~~~~

Presumably there is a #define getdents64 getdents .. Could we stop
caring about this version of Alpine linux?

Thanks,
Ian

> Thanks,
> Namhyung
>
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> >  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
> >