Re: [PATCH 6/8] trace-cmd output: Set file_state of output handle after copy of headers

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

On Tue, Mar 2, 2021 at 4:19 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Tue, 2 Mar 2021 10:10:24 +0200
> Tzvetomir Stoyanov <tz.stoyanov@gmail.com> wrote:
>
> > On Mon, Mar 1, 2021 at 4:38 PM Steven Rostedt <rostedt@goodmis.org> wrote:
> > >
> > > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> > >
> > > Now that the input and output handles know the state they are at in reading
> > > or writing, the tracecmd_copy() has to set the state of the output handle it
> > > creates.
> > >
> > > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > > ---
> > >  lib/trace-cmd/trace-output.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/lib/trace-cmd/trace-output.c b/lib/trace-cmd/trace-output.c
> > > index 6d504cbaf133..1156899a85d3 100644
> > > --- a/lib/trace-cmd/trace-output.c
> > > +++ b/lib/trace-cmd/trace-output.c
> > > @@ -1656,6 +1656,8 @@ struct tracecmd_output *tracecmd_copy(struct tracecmd_input *ihandle,
> > >         if (tracecmd_copy_headers(ihandle, handle->fd) < 0)
> > >                 goto out_free;
> > >
> > > +       handle->file_state = TRACECMD_FILE_CMD_LINES;
> >
> > Why is the state overwritten here, isn't it more logical to be set in
> > tracecmd_copy_headers(), by each function that copies a header to set
>
> That's because the handle is not passed into tracecmd_copy_headers.
>
> And because the handle is a struct tracecmd_output, the
> tracecmd_copy_headers() which is in trace-input.c doesn't have access to
> this structure, and I prefer to keep it that way.
>
> That said, we could modify tracecmd_copy_header() to return the state that
> it copied up to, or negative on error.
>
>         state = tracecmd_copy_headers(ihandle, handle->fd);
>         if (state < 0)
>                 goto out_free;
>
>         handle->file_state = state;

The output handle should have the same state as the input handle,
so we can just have:

      handle->file_state = tracecmd_get_file_state(ihandle);

There is exactly the same use case in tracecmd_get_output_handle_fd(),
where the out handle is built on a partially written file.

>
> That would be more robust!
>
> -- Steve
>
>
> > the relevant state. The last call in tracecmd_copy_headers()
> > is copy_command_lines(), which should set state to
> > TRACECMD_FILE_CMD_LINES in case of success.
> > The state is already TRACECMD_FILE_CMD_LINES
> > in tracecmd_copy_headers(), but right before its exit it
> > is overwritten to the old file state. And here again it is
> > overwritten back to TRACECMD_FILE_CMD_LINES.
> > May be I miss something here, cannot understand the logic.
> >
> > > +
> > >         /* The file is all ready to have cpu data attached */
> > >         return handle;
> > >
> > > --
> > > 2.30.0
> > >
> > >
> >
> >
>


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