linux-kernel - Re: [Patch v3] block: introduce block_rq

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Date:   Tue, 25 Jan 2022 09:38:46 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>, linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [Patch v3] block: introduce block_rq_error tracepoint

On Tue, 25 Jan 2022 09:37:02 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> > > +TRACE_EVENT(block_rq_error,
> > > +
> > > +       TP_PROTO(struct request *rq, int error, unsigned int nr_bytes),
> > > +
> > > +       TP_ARGS(rq, error, nr_bytes),
> > > +
> > > +       TP_STRUCT__entry(
> > > +               __field(  dev_t,        dev                     )
> > > +               __string( name,         rq->rq_disk ? rq->rq_disk->disk_name : "?")
> > > +               __field(  sector_t,     sector                  )
> > > +               __field(  unsigned int, nr_sector               )
> > > +               __field(  int,          error                   )
> > > +               __array(  char,         rwbs,   RWBS_LEN        )  
> 
> Why is the above not "__string" ?
> 
> > > +       ),
> > > +
> > > +       TP_fast_assign(
> > > +               __entry->dev       = rq->rq_disk ? disk_devt(rq->rq_disk) : 0;
> > > +               __assign_str(name,   rq->rq_disk ? rq->rq_disk->disk_name : "?");  
> 
> __assign_str() will not work on an __array() type. It only works here
> because you added it at the end, but it's just shear luck that it didn't
> crash.

Never mind :-p  I see the above is for name which is __string, and the
array is for rwbs which is filled below. I need to finish my first cup of
coffee before reviewing patches.

-- Steve

> 
> 
> > > +               __entry->sector    = blk_rq_pos(rq);
> > > +               __entry->nr_sector = nr_bytes >> 9;
> > > +               __entry->error     = error;
> > > +
> > > +               blk_fill_rwbs(__entry->rwbs, rq->cmd_flags, nr_bytes);
> > > +       ),
> > > +
> > > +       TP_printk("%d,%d %s %s %llu + %u [%d]",
> > > +                 MAJOR(__entry->dev), MINOR(__entry->dev),
> > > +                 __get_str(name), __entry->rwbs,
> > > +                 (unsigned long long)__entry->sector,
> > > +                 __entry->nr_sector, __entry->error)
> > > +);
> > > +