linux-kernel - Re: [PATCH v1 1/2] tools api: Add simple timeout to io read

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Date:   Wed, 14 Jun 2023 10:36:47 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     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>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v1 1/2] tools api: Add simple timeout to io read

On Wed, Jun 7, 2023 at 11:20 PM Ian Rogers <irogers@...gle.com> wrote:
>
> In situations like reading from a pipe it can be useful to have a
> timeout so that the caller doesn't block indefinitely. Implement a
> simple one based on poll.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

There is overlap in what these patches aim to fix with the 2 submitted
patches making addr2line more robust:
https://lore.kernel.org/all/20230613034817.1356114-2-irogers@google.com/

I think it could be pragmatic to take both of them. Be robust but
timeout if addr2line doesn't respond for 1s. What do you think?

Thanks,
Ian

> ---
>  tools/lib/api/io.h | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
> index d5e8cf0dada0..9fc429d2852d 100644
> --- a/tools/lib/api/io.h
> +++ b/tools/lib/api/io.h
> @@ -8,6 +8,7 @@
>  #define __API_IO__
>
>  #include <errno.h>
> +#include <poll.h>
>  #include <stdlib.h>
>  #include <string.h>
>  #include <unistd.h>
> @@ -23,6 +24,8 @@ struct io {
>         char *end;
>         /* Currently accessed data pointer. */
>         char *data;
> +       /* Read timeout, 0 implies no timeout. */
> +       int timeout_ms;
>         /* Set true on when the end of file on read error. */
>         bool eof;
>  };
> @@ -35,6 +38,7 @@ static inline void io__init(struct io *io, int fd,
>         io->buf = buf;
>         io->end = buf;
>         io->data = buf;
> +       io->timeout_ms = 0;
>         io->eof = false;
>  }
>
> @@ -47,7 +51,29 @@ static inline int io__get_char(struct io *io)
>                 return -1;
>
>         if (ptr == io->end) {
> -               ssize_t n = read(io->fd, io->buf, io->buf_len);
> +               ssize_t n;
> +
> +               if (io->timeout_ms != 0) {
> +                       struct pollfd pfds[] = {
> +                               {
> +                                       .fd = io->fd,
> +                                       .events = POLLIN,
> +                               },
> +                       };
> +
> +                       n = poll(pfds, 1, io->timeout_ms);
> +                       if (n == 0)
> +                               errno = ETIMEDOUT;
> +                       if (n > 0 && !(pfds[0].revents & POLLIN)) {
> +                               errno = EIO;
> +                               n = -1;
> +                       }
> +                       if (n <= 0) {
> +                               io->eof = true;
> +                               return -1;
> +                       }
> +               }
> +               n = read(io->fd, io->buf, io->buf_len);
>
>                 if (n <= 0) {
>                         io->eof = true;
> --
> 2.41.0.rc0.172.g3f132b7071-goog
>