Re: [PATCH 2/8] trace-cmd: Create API tracecmd_read_pre_headers()

[Tzvetomir Stoyanov <tz.stoyanov@gmail.com>]

Hi Steven,

On Mon, Mar 1, 2021 at 4:38 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
>
> The trace-cmd restore operation can create a partial header to read the
> trace event formats and kallsyms and other data into a stand alone header
> before it has access to the cpu data. Then it will also read this header to
> put together a broken trace, and it reads the header that does not have the
> cpu data attached to it.
>
> In order to handle this case, it needs a way to read the headers but stop
> short of reading the CPU information. That requires breaking up
> tracecmd_read_headers() with just stopping short of adding the cpu data.

While looking at these changes, I think it could be more flexible instead of
introducing a new API, to enhance the existing tracecmd_read_headers().
We can add an additional (optional) parameter to point out what headers
to be read, i.e. the desired new state of reading the file. Something like that:
   int tracecmd_read_headers(struct tracecmd_input *handle, int state);
It will read the file from its current file_state to the desired state.
The API could be called multiple times, to progress the reading of the
file, header by header if needed, or a bunch of headers.



>
> A new API is added called tracecmd_read_pre_headers() that does exactly that.
>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
>  .../include/private/trace-cmd-private.h       |  1 +
>  lib/trace-cmd/trace-input.c                   | 25 ++++++++++++++++---
>  tracecmd/trace-restore.c                      |  2 +-
>  3 files changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/lib/trace-cmd/include/private/trace-cmd-private.h b/lib/trace-cmd/include/private/trace-cmd-private.h
> index fc968cc9efe1..c7ef3af7c8f7 100644
> --- a/lib/trace-cmd/include/private/trace-cmd-private.h
> +++ b/lib/trace-cmd/include/private/trace-cmd-private.h
> @@ -153,6 +153,7 @@ typedef void (*tracecmd_handle_init_func)(struct tracecmd_input *handle,
>  struct tracecmd_input *tracecmd_alloc(const char *file, int flags);
>  struct tracecmd_input *tracecmd_alloc_fd(int fd, int flags);
>  void tracecmd_ref(struct tracecmd_input *handle);
> +int tracecmd_read_pre_headers(struct tracecmd_input *handle);
>  int tracecmd_read_headers(struct tracecmd_input *handle);
>  int tracecmd_get_parsing_failures(struct tracecmd_input *handle);
>  int tracecmd_long_size(struct tracecmd_input *handle);
> diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
> index 9ef7b9f16951..9e1a44540201 100644
> --- a/lib/trace-cmd/trace-input.c
> +++ b/lib/trace-cmd/trace-input.c
> @@ -772,14 +772,17 @@ static int read_cpus(struct tracecmd_input *handle)
>  }
>
>  /**
> - * tracecmd_read_headers - read the header information from trace.dat
> + * tracecmd_read_pre_headers - read the header information from trace.dat
>   * @handle: input handle for the trace.dat file
>   *
>   * This reads the trace.dat file for various information. Like the
>   * format of the ring buffer, event formats, ftrace formats, kallsyms
> - * and printk.
> + * and printk, but stops before reading cpu and options.
> + *
> + * This is needed by the restore operation where the header does not
> + * have the CPU information yet.
>   */
> -int tracecmd_read_headers(struct tracecmd_input *handle)
> +int tracecmd_read_pre_headers(struct tracecmd_input *handle)
>  {
>         int ret;
>
> @@ -815,6 +818,22 @@ int tracecmd_read_headers(struct tracecmd_input *handle)
>                 return -1;
>         handle->file_state = TRACECMD_FILE_CMD_LINES;
>
> +       return 0;
> +}
> +
> +/**
> + * tracecmd_read_headers - read the header information from trace.dat
> + * @handle: input handle for the trace.dat file
> + *
> + * This reads the trace.dat file for various information. Like the
> + * format of the ring buffer, event formats, ftrace formats, kallsyms
> + * and printk.
> + */
> +int tracecmd_read_headers(struct tracecmd_input *handle)
> +{
> +       if (tracecmd_read_pre_headers(handle))
> +               return -1;
> +
>         if (read_cpus(handle) < 0)
>                 return -1;
>         handle->file_state = TRACECMD_FILE_CPU_COUNT;
> diff --git a/tracecmd/trace-restore.c b/tracecmd/trace-restore.c
> index 13f803053582..bf6940991178 100644
> --- a/tracecmd/trace-restore.c
> +++ b/tracecmd/trace-restore.c
> @@ -122,7 +122,7 @@ void trace_restore (int argc, char **argv)
>                 if (!ihandle)
>                         die("error reading file %s", input);
>                 /* make sure headers are ok */
> -               if (tracecmd_read_headers(ihandle) < 0)
> +               if (tracecmd_read_pre_headers(ihandle) < 0)
>                         die("error reading file %s headers", input);
>
>                 handle = tracecmd_copy(ihandle, output);
> --
> 2.30.0
>
>


--
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center