Messages in this thread | | | Date | Sun, 7 Sep 2008 17:11:43 +0300 | From | Pekka Paalanen <> | Subject | Re: [Patch] Tracing/ftrace: Adds a marker to allow user comments |
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Steven,
is there a logic behind trace_seq_print_cont() printing the terminating newline only, when there actually is no TRACE_CONT entry?
Hmm, wait a minute, I don't understand how this thing works at all.
Let's take for instance print_lat_fmt() which is the first user of trace_seq_print_cont(). Now, print_lat_fmt() does
struct trace_entry *entry = iter->ent;
and uses 'entry'. Let's assume it is of type TRACE_PRINT. It does
case TRACE_PRINT: seq_print_ip_sym(s, field->print.ip, sym_flags); trace_seq_printf(s, ": %s", field->print.buf); if (field->flags & TRACE_FLAG_CONT) trace_seq_print_cont(s, iter); break;
Ok, it prints the beginning of the message, and if there should be continuation blocks, it calls trace_seq_print_cont(), defined as follows:
static void trace_seq_print_cont(struct trace_seq *s, struct trace_iterator *iter) { struct trace_array *tr = iter->tr; struct trace_array_cpu *data = tr->data[iter->cpu]; struct trace_entry *ent;
ent = trace_entry_idx(tr, data, iter, iter->cpu); if (!ent || ent->type != TRACE_CONT) { trace_seq_putc(s, '\n'); return; }
do { trace_seq_printf(s, "%s", ent->cont.buf); __trace_iterator_increment(iter, iter->cpu); ent = trace_entry_idx(tr, data, iter, iter->cpu); } while (ent && ent->type == TRACE_CONT); }
Here it uses trace_entry_idx() to get 'ent'. What's the difference to iter->ent? I don't understand how trace_entry_idx() works, but looking at how it is used, it must return the pointer to the *next* entry in the ring buffer. So I don't understand the name of the function, and I don't see a call to __trace_iterator_increment(), which is confusing.
If contrary to the assumption, 'ent' is not a continuation, it prints the terminating newline. This is an exceptional case, as the original entry was marked as having continuation entries.
The normal case then is to execute the do-while, until it hits a non-continuation entry. Here it does *not* print the terminating newline.
Steven, could you explain what is going on here?
Thanks.
On Thu, 4 Sep 2008 20:30:58 +0300 Pekka Paalanen <pq@iki.fi> wrote:
> b) have a customisable trace_seq_print_cont() > > I think I'd favour b). When I tried to use trace_seq_print_cont(), > I found it difficult to control the printing of \n at the end of > message. So I would implement my own routine to handle also what > trace_seq_print_cont() does, filtering the text while copying it > to struct trace_seq. I'm not sure where this function should live. > It could be useful to all tracers, that want "one line per marker > entry" style output, so it could live in trace.c.
-- Pekka Paalanen http://www.iki.fi/pq/
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