Messages in this thread | | | Date | Thu, 6 Nov 2014 17:33:54 +0100 | From | Petr Mladek <> | Subject | Re: [RFC][PATCH 03/12 v3] tracing: Create seq_buf layer in trace_seq |
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On Wed 2014-11-05 16:21:46, Steven Rostedt wrote: > 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.
Hmm, this would produce -1 (UNIT_MAX) when the overflow is (s->len = s->size + 1). I would keep seq_buf_buffer_left(s);
> > int ret; > > > > WARN_ON(s->size == 0); > > > > if (s->len < s->size) {
It does not make sense to try if there is only one byte left. I would do:
if (len > 1)
together with the change below.
> > 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. > > */
This is great explanation. You might want to move it above the "if (len > 1)" if you agree with it.
> > if (s->len + ret < s->size) {
This should work with both variants of the overflow if "len" is really the space left.
if (ret < len)
I mean that we fail if we wrote the buffer until the last possible byte.
> > s->len += ret; > > return 0; > > } > > } > > seq_buf_set_overflow(s); > > return -1; > > }
Best Regards, Petr
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