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

Steven Rostedt
2014-11-05T21:17:26Z

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);
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