linux-kernel - Re: [PATCH v5 05/50] tools api fs: Avoid reading whole file for a 1 byte bool

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Date:   Wed, 29 Nov 2023 17:42:46 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Nick Terrell <terrelln@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        "Steinar H. Gunderson" <sesse@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Colin Ian King <colin.i.king@...il.com>,
        Dmitrii Dolgov <9erthalion6@...il.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Ming Wang <wangming01@...ngson.cn>,
        James Clark <james.clark@....com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Leo Yan <leo.yan@...aro.org>,
        Ravi Bangoria <ravi.bangoria@....com>,
        German Gomez <german.gomez@....com>,
        Changbin Du <changbin.du@...wei.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Li Dong <lidong@...o.com>,
        Sandipan Das <sandipan.das@....com>,
        liuwenyu <liuwenyu7@...wei.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Guilherme Amadio <amadio@...too.org>
Subject: Re: [PATCH v5 05/50] tools api fs: Avoid reading whole file for a 1
 byte bool

On Mon, Nov 27, 2023 at 2:09 PM Ian Rogers <irogers@...gle.com> wrote:
>
> sysfs__read_bool used the first byte from a fully read file into a
> string. It then looked at the first byte's value. Avoid doing this and
> just read the first byte.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung

> ---
>  tools/lib/api/fs/fs.c | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/tools/lib/api/fs/fs.c b/tools/lib/api/fs/fs.c
> index 004f2af5504b..337fde770e45 100644
> --- a/tools/lib/api/fs/fs.c
> +++ b/tools/lib/api/fs/fs.c
> @@ -447,15 +447,22 @@ int sysfs__read_str(const char *entry, char **buf, size_t *sizep)
>
>  int sysfs__read_bool(const char *entry, bool *value)
>  {
> -       char *buf;
> -       size_t size;
> -       int ret;
> +       struct io io;
> +       char bf[16];
> +       int ret = 0;
> +       char path[PATH_MAX];
> +       const char *sysfs = sysfs__mountpoint();
> +
> +       if (!sysfs)
> +               return -1;
>
> -       ret = sysfs__read_str(entry, &buf, &size);
> -       if (ret < 0)
> -               return ret;
> +       snprintf(path, sizeof(path), "%s/%s", sysfs, entry);
> +       io.fd = open(path, O_RDONLY);
> +       if (io.fd < 0)
> +               return -errno;
>
> -       switch (buf[0]) {
> +       io__init(&io, io.fd, bf, sizeof(bf));
> +       switch (io__get_char(&io)) {
>         case '1':
>         case 'y':
>         case 'Y':
> @@ -469,8 +476,7 @@ int sysfs__read_bool(const char *entry, bool *value)
>         default:
>                 ret = -1;
>         }
> -
> -       free(buf);
> +       close(io.fd);
>
>         return ret;
>  }
> --
> 2.43.0.rc1.413.gea7ed67945-goog
>