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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Mon, 08 Feb 2016 18:43:55 +0000
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Subject: Re: [Qemu-devel] [PULL 05/13] trace: split trace_init_file out of
	trace_init_backends
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: "Denis V. Lunev" <den@openvz.org>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, Peter Maydell <peter.maydell@linaro.org>


Stefan Hajnoczi <stefanha@redhat.com> writes:

> From: Paolo Bonzini <pbonzini@redhat.com>
>
> This is cleaner, and improves error reporting with -daemonize.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Message-id: 1452174932-28657-4-git-send-email-den@openvz.org
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  qemu-io.c       |  2 +-
>  trace/control.c | 17 ++++++++++++-----
>  trace/control.h | 13 ++++++++++++-
>  trace/simple.c  |  6 ++----
>  trace/simple.h  |  4 ++--
>  vl.c            | 13 +++++++++----
>  6 files changed, 38 insertions(+), 17 deletions(-)
>
> diff --git a/qemu-io.c b/qemu-io.c
> index 1c11d57..83c48f4 100644
> --- a/qemu-io.c
> +++ b/qemu-io.c
> @@ -435,7 +435,7 @@ int main(int argc, char **argv)
>              }
>              break;
>          case 'T':
> -            if (!trace_init_backends(optarg)) {
> +            if (!trace_init_backends()) {
>                  exit(1); /* error message will have been printed */
>              }
>              break;
> diff --git a/trace/control.c b/trace/control.c
> index 931d64c..f5a497a 100644
> --- a/trace/control.c
> +++ b/trace/control.c
> @@ -145,17 +145,24 @@ void trace_init_events(const char *fname)
>      loc_pop(&loc);
>  }
>
> -bool trace_init_backends(const char *file)
> +void trace_init_file(const char *file)
>  {
>  #ifdef CONFIG_TRACE_SIMPLE
> -    if (!st_init(file)) {
> -        fprintf(stderr, "failed to initialize simple tracing backend.\n");
> -        return false;
> -    }
> +    st_set_trace_file(file);

This breaks "make check" as st_set_trace_file will attempt to flush the
file:

    /* Halt trace writeout */
    flush_trace_file(true);
    trace_writeout_enabled = false;
    flush_trace_file(true);

And this deadlocks waiting for trace_empty_cond to get tickled which
will never happen because:

<snip>
> diff --git a/vl.c b/vl.c
> index ff2a7d5..955f364 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2988,7 +2988,7 @@ int main(int argc, char **argv, char **envp)
>      bool userconfig = true;
>      const char *log_mask = NULL;
>      const char *log_file = NULL;
> -    const char *trace_file = NULL;
> +    char *trace_file = NULL;
>      ram_addr_t maxram_size;
>      uint64_t ram_slots = 0;
>      FILE *vmstate_dump_file = NULL;
> @@ -3905,7 +3905,10 @@ int main(int argc, char **argv, char **envp)
>                      exit(1);
>                  }
>                  trace_init_events(qemu_opt_get(opts, "events"));
> -                trace_file = qemu_opt_get(opts, "file");
> +                if (trace_file) {
> +                    g_free(trace_file);
> +                }
> +                trace_file = g_strdup(qemu_opt_get(opts, "file"));
>                  qemu_opts_del(opts);
>                  break;
>              }
> @@ -4089,6 +4092,8 @@ int main(int argc, char **argv, char **envp)
>          exit(0);
>      }
>
> +    trace_init_file(trace_file);
> +

This happens before:

>       */
>      if (log_file) {
> @@ -4106,7 +4111,7 @@ int main(int argc, char **argv, char **envp)
>      }
>
>      if (!is_daemonized()) {
> -        if (!trace_init_backends(trace_file)) {
> +        if (!trace_init_backends()) {
>              exit(1);
>          }
>      }
> @@ -4653,7 +4658,7 @@ int main(int argc, char **argv, char **envp)
>      os_setup_post();
>
>      if (is_daemonized()) {
> -        if (!trace_init_backends(trace_file)) {
> +        if (!trace_init_backends()) {

This which creates the thread.

>              exit(1);
>          }
>      }


--
Alex Bennée