The following commit:
commit 56f3bae706
Author: Jim Cromie <jim.cromie@gmail.com>
Date: Wed Sep 7 17:14:00 2011 -0600
perf stat: Add --log-fd <N> option to redirect stderr elsewhere
introduced a bug in the way perf stat outputs the results by default,
i.e., without the --log-fd or --output option. It would default to
writing to file descriptor 0, i.e., stdin. Writing to stdin is allowed
and is equivalent to writing to stdout. However, there is a major
difference for any script that was already capturing the output of perf
stat via redirection:
perf stat >/tmp/log .... or perf stat 2>/tmp/log ....
They would not capture anything anymore. They would have to do:
perf stat 0>/tmp/log ...
This breaks compatibility with existing scripts and does not look very
natural.
This patch fixes the problem by looking at output_fd only when it was
modified by user (> 0). It also checks that the value if positive.
Passing --log-fd 0 is ignored.
I would also argue that defaulting to stderr for the results is not the
right thing to do, though this patch does not address this specific
issue.
Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jim Cromie <jim.cromie@gmail.com>
Link: http://lkml.kernel.org/r/20120515111111.GA9870@quad
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
fc3e4d077d