Re: [PATCH] perf, tool, record: Fix the header generation for pipe

Jiri Olsa
2011-08-22T14:52:25Z

On Mon, Aug 22, 2011 at 04:38:33PM +0200, Eric Dumazet wrote:
> Le lundi 22 août 2011 à 16:23 +0200, Jiri Olsa a écrit :
> > The generation of the perf data file fails when using pipe
> > as the output file descriptor.
> >
> > When record command generates the data header, several files are put
> > inside and the file size is stored ahead of the file contents itself.
> >
> > The problem is that debugfs files cannot be stat-ed for size so we
> > need to read the whole file, count the size and update the file size
> > via seek&write (pwrite call).
> > This cannot be done for pipes, since it's not allowed to seek on it.
> >
> > The attached patch changes current behaviour for pipes to get the
> > file size first and write correct data within the first pass.
> > For other than pipe files, the current behaviour stands.
> >
> > This issue was caught when running the script command:
> >
> > # perf script syscall-counts ls
> >
> > since it connects record and report via pipe.
> >
> > Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> > ---
> > tools/perf/util/trace-event-info.c | 81 +++++++++++++++++++++++++++++++-----
> > 1 files changed, 70 insertions(+), 11 deletions(-)
> >
> > diff --git a/tools/perf/util/trace-event-info.c b/tools/perf/util/trace-event-info.c
> > index 3403f81..62ab9a2 100644
> > --- a/tools/perf/util/trace-event-info.c
> > +++ b/tools/perf/util/trace-event-info.c
> > @@ -59,6 +59,7 @@ unsigned int page_size;
> >
> > static const char *output_file = "trace.info";
> > static int output_fd;
> > +static int output_is_pipe;
> >
> > struct event_list {
> > struct event_list *next;
> > @@ -183,20 +184,59 @@ int bigendian(void)
> > return *ptr == 0x01020304;
> > }
> >
> > +static off_t get_file_size(int fd)
> > +{
> > + off_t size = 0;
> > + char buf[BUFSIZ];
> > + int r;
> > +
> > + do {
> > + r = read(fd, buf, BUFSIZ);
> > + if (r > 0)
> > + size += r;
> > + } while (r > 0);
> > +
> > + if (lseek(fd, 0, SEEK_SET))
> > + die("seek failed");
> > +
> > + return size;
> > +}
>
> This part makes no sense :
>
> If fd is a pipe, you'll call die("seek failed")
>
> If it's not a pipe, you can try lseek(fd, 0, SEEK_END)+lseek(fd, 0,
> SEEK_SET) or fstat(fd, &st) instead of the read() loop.

- fd is always file.. the descriptor, which might be pipe, is in output_fd variable
but, maybe the die call is not necessary.. this should not fail

- the record_file function is called only on debugfs or procfs files:
events/header_page
events/header_event
events/**/format
printk_formats
/proc/kallsyms

so I think I need to read the whole file as in current code.

thanks,
jirka