Re: [PATCH v5 06/50] tools lib api: Add io_dir an allocation free readdir alternative

[Ian Rogers]

On Thu, Nov 30, 2023 at 9:21 AM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
>
> Em Mon, Nov 27, 2023 at 02:08:18PM -0800, Ian Rogers escreveu:
> > 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.
>
> Now, on some systems:
>
>   CC      /tmp/build/perf/pmu-events/pmu-events.o
> In file included from util/machine.c:39:
> /tmp/build/perf/libapi/include/api/io_dir.h: In function ‘io_dir__readdir’:
> /tmp/build/perf/libapi/include/api/io_dir.h:46:16: error: implicit declaration of function ‘getdents64’; did you mean ‘getentropy’? [-Werror=implicit-function-declaration]
>    ssize_t rc = getdents64(iod->dirfd, iod->buff, sizeof(iod->buff));
>                 ^~~~~~~~~~
>                 getentropy
>   CC      /tmp/build/perf/tests/workloads/brstack.o
>   CC      /tmp/build/perf/tests/workloads/datasym.o
>   CC      /tmp/build/perf/util/maps.o


Sorry for that. Is it a _GNU_SOURCE issue? I thought we generally had
_GNU_SOURCE defined on the command line for reallocarray. Maybe we
shouldn't define this on the command line and do it immediately before
the relevant include with:

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

like in tools/perf/util/intel-pt-decoder/intel-pt-decoder.c

Thanks,
Ian

>
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> >  tools/lib/api/Makefile |  2 +-
> >  tools/lib/api/io_dir.h | 75 ++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 76 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..f3479006edb6
> > --- /dev/null
> > +++ b/tools/lib/api/io_dir.h
> > @@ -0,0 +1,75 @@
> > +/* 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>
> > +
> > +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
> > --
> > 2.43.0.rc1.413.gea7ed67945-goog
> >
>
> --
>
> - Arnaldo