Re: [PATCH 2/5] tracing_bprintk: don't increment @pos in t_start()

[Wang Liming]

Li Zefan wrote:
> Wang Liming wrote:
> > Hi,
> >
> > Li Zefan wrote:
> > > It's wrong to increment @pos in t_start(), otherwise we'll lose
> > > some entries when reading printk_formats, if the output is large
> > > than PAGE_SIZE.
> > >
> > > [ Impact: fix missing entries when reading printk_formats ]
> > >
> > > Reported-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
> > > Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
> > > ---
> > >  kernel/trace/trace_printk.c |   26 ++++++--------------------
> > >  1 files changed, 6 insertions(+), 20 deletions(-)
> > >
> > > diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
> > > index 9bece96..7b62781 100644
> > > --- a/kernel/trace/trace_printk.c
> > > +++ b/kernel/trace/trace_printk.c
> > > @@ -155,25 +155,19 @@ int __ftrace_vprintk(unsigned long ip, const
> > > char *fmt, va_list ap)
> > >  EXPORT_SYMBOL_GPL(__ftrace_vprintk);
> > >  
> > >  static void *
> > > -t_next(struct seq_file *m, void *v, loff_t *pos)
> > > +t_start(struct seq_file *m, loff_t *pos)
> > >  {
> > > -    const char **fmt = m->private;
> > > -    const char **next = fmt;
> > > -
> > > -    (*pos)++;
> > > +    const char **fmt = __start___trace_bprintk_fmt + *pos;
> > >  
> > >      if ((unsigned long)fmt >= (unsigned long)__stop___trace_bprintk_fmt)
> > >          return NULL;
> > > -
> > > -    next = fmt;
> > > -    m->private = ++next;
> > > -
> > >      return fmt;
> > >  }
> > >  
> > > -static void *t_start(struct seq_file *m, loff_t *pos)
> > > +static void *t_next(struct seq_file *m, void * v, loff_t *pos)
> > >  {
> > > -    return t_next(m, NULL, pos);
> > > +    (*pos)++;
> > > +    return t_start(m, pos);
> > >  }
> > >  
> > I prefer to .start to call .next, so I rewrite it to following:
>
> Thanks for the comment, but I don't think .next calls .start is bad,
> and I'm not the only one doing this. Grep c_start() to see some of
> them.
Yes, you are not the only one, but it's the only one in the tracing code. :)
I just think we should make the seq_* uniform so that we can understand them 
more clearly.

Liming Wang
>

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