Re: [RFC][PATCH 03/12 v3] tracing: Create seq_buf layer in trace_seq

Steven Rostedt
2014-11-05T21:21:52Z

On Wed, 5 Nov 2014 16:17:20 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 5 Nov 2014 15:00:07 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > On Wed, 5 Nov 2014 13:41:47 -0500
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > >
> > > > > + */
> > > > > +int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
> > > > > + int nmaskbits)
> > > > > +{
> > > > > + unsigned int len = SEQ_BUF_LEFT(s);
> > > > >
> > > > > + int ret;
> > > > > +
> > > > > + WARN_ON(s->size == 0);
> > > > > +
> > > > > + if (s->len < s->size) {
> > > > > + ret = bitmap_scnprintf(s->buffer, len, maskp, nmaskbits);
> > > >
> > > > It writes to the beginning of the buffer. It should be
> > > >
> > > > ret = bitmap_scnprintf(s->buffer + s->len, len,
> > > > maskp, nmaskbits);
> > > >
> > >
> > > Yep thanks. Luckily its only user didn't care.
> > >
> > > Will fix.
> > >
> > > >
> > > > > + if (s->len + ret < s->size) {
> > > >
> > > > This will always happen because bitmap_scnprintf() is limited by SEQ_BUF_LEFT(s)
> > > > and it currently returns the remaining size - len - 1.
> > >
> > > Hmm, that's correct, as bitmap_scnprintf() returns the amount written
> > > instead of the amount that it would write like snprintf() would.
> > >
> > >
> > > >
> > > > You might want to use "s->size - s->len" instead of SEQ_BUF_LEFT(s).
> > >
> > > That wont help when we make overflow len > size.
> > >
> > > Probably should see if ret == the amount of bits required for the
> > > bitmask.
> >
> > Here's the new version:
> >
>
> Take 2:
>
> int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
> int nmaskbits)
> {
> unsigned int len = seq_buf_buffer_left(s);

Bah, I need to make this: len = s->size - s->len.

As this would work for both cases of what a overflowed buffer is.

-- Steve

> int ret;
>
> WARN_ON(s->size == 0);
>
> if (s->len < s->size) {
> ret = bitmap_scnprintf(s->buffer, len, maskp, nmaskbits);
> /*
> * Note, because bitmap_scnprintf() only returns the
> * number of bytes written and not the number that
> * would be written, we use the last byte of the buffer
> * to let us know if we overflowed. There's a small
> * chance that the bitmap could have fit exactly inside
> * the buffer, but it's not that critical if that does
> * happen.
> */
> if (s->len + ret < s->size) {
> s->len += ret;
> return 0;
> }
> }
> seq_buf_set_overflow(s);
> return -1;
> }
>
> -- Steve