> On Thu, Dec 21, 2017 at 10:08:44AM -0800, kan.li...@intel.com wrote:
>
> SNIP
>
> > +/*
> > + * Report the start and end of the available data in ringbuffer
> > + */
> > +int perf_mmap__read_init(struct perf_mmap *map, bool overwrite,
> > + u64 *start, u64 *end)
> > {
> > - u64 head = perf_mmap__read_head(md);
> > - u64 old = md->prev;
> > - u64 end = head, start = old;
> > - unsigned char *data = md->base + page_size;
> > + u64 head = perf_mmap__read_head(map);
> > + u64 old = map->prev;
> > + unsigned char *data = map->base + page_size;
> > unsigned long size;
> > - void *buf;
> > - int rc = 0;
> >
> > - start = overwrite ? head : old;
> > - end = overwrite ? old : head;
> > + /*
> > + * Check if event was unmapped due to a POLLHUP/POLLERR.
> > + */
> > + if (!refcount_read(&map->refcnt))
> > + return -EINVAL;
> >
> > - if (start == end)
> > - return 0;
> > + *start = overwrite ? head : old;
> > + *end = overwrite ? old : head;
> >
> > - size = end - start;
> > - if (size > (unsigned long)(md->mask) + 1) {
> > + if (*start == *end)
> > + return -EAGAIN;
> > +
> > + size = *end - *start;
> > + if (size > (unsigned long)(map->mask) + 1) {
> > if (!overwrite) {
> > WARN_ONCE(1, "failed to keep up with mmap data.
> (warn only once)\n");
> >
>
> I know you did not change this, but is this leg even possible
> in !overwrite mode? I think kernel will throw away the data,
> keep the head and wait for tail to be read by user..
Right, it should not happen in !overwrite mode. I guess it's just
sanity check.
It should not bring any problems.
I think I will still keep it for V4 if no objection?
Thanks,
Kan
>
> jirka
>
> > - md->prev = head;
> > - perf_mmap__consume(md, overwrite);
> > - return 0;
> > + map->prev = head;
> > + perf_mmap__consume(map, overwrite);
> > + return -EAGAIN;
>
> SNIP
