[lttng-dev] [PATCH lttng-tools] Fix: unchecked return value

[jeremie.galarneau@efficios.com (Jérémie Galarneau)]

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On Tue, May 17, 2016 at 12:17 PM, Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
> Found by Coverity:
>
> CID 1019971 (#1 of 1): Unchecked return value from library
> (CHECKED_RETURN)2. check_return: Calling posix_fadvise(outfd,
> orig_offset - stream->max_sb_size, stream->max_sb_size, 4) without
> checking return value. This library function may fail and return an
> error code.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
>  src/common/consumer/consumer.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/src/common/consumer/consumer.c b/src/common/consumer/consumer.c
> index cb05a1e..e22de4d 100644
> --- a/src/common/consumer/consumer.c
> +++ b/src/common/consumer/consumer.c
> @@ -1262,8 +1262,10 @@ void lttng_consumer_sync_trace_file(struct lttng_consumer_stream *stream,
>          * defined. So it can be expected to lead to lower throughput in
>          * streaming.
>          */
> -       posix_fadvise(outfd, orig_offset - stream->max_sb_size,
> -                       stream->max_sb_size, POSIX_FADV_DONTNEED);
> +       if (posix_fadvise(outfd, orig_offset - stream->max_sb_size,
> +                       stream->max_sb_size, POSIX_FADV_DONTNEED)) {
> +               DBG("Ignoring posix_fadvise() error: %s.", strerror(errno));

posix_fadvise() does not set errno on error, it returns the error code directly.
I have merged an alternative fix as:

commit c7a78aabfa0491974d4ffc188d72eb1e67c7344e
Author: Jérémie Galarneau <jeremie.galarneau at gmail.com>
Date:   Tue May 17 12:17:05 2016 -0400

    Fix: unchecked posix_fadvise() return value

    Found by Coverity:

    CID 1019971 (#1 of 1): Unchecked return value from library
    (CHECKED_RETURN)2. check_return: Calling posix_fadvise(outfd,
    orig_offset - stream->max_sb_size, stream->max_sb_size, 4) without
    checking return value. This library function may fail and return an
    error code.

    Signed-off-by: Jérémie Galarneau <jeremie.galarneau at efficios.com>


I also set this to WARN() since we'd probably want to know if we're
misusing posix_fadvise or passing a bad FD, etc.


Thanks!
Jérémie


> +       }
>  }
>
>  /*
> --
> 2.1.4
>



-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com