On Tue, Apr 14, 2015 at 03:16:22PM -0700, Andy Zhou wrote:
> On Tue, Apr 14, 2015 at 2:55 PM, Russell Bryant <rbry...@redhat.com> wrote:
> > On 04/14/2015 05:51 PM, Andy Zhou wrote:
> >> Gcc complains about:
> >> lib/perf-counter.c:43:13: error: ignoring return value of 'read',
> >> declared with attribute warn_unused_result [-Werror=unused-result]
> >> read(fd__, counter, sizeof(*counter));
> >>
> >> Signed-off-by: Andy Zhou <az...@nicira.com>
> >>
> >> ---
> >> v1->v2: Combine two 'if's into using only one.
> >> ---
> >> lib/perf-counter.c | 6 +++---
> >> 1 file changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/lib/perf-counter.c b/lib/perf-counter.c
> >> index 7bd7834..a6e63ac 100644
> >> --- a/lib/perf-counter.c
> >> +++ b/lib/perf-counter.c
> >> @@ -39,9 +39,9 @@ static int fd__ = 0;
> >> uint64_t
> >> perf_counter_read(uint64_t *counter)
> >> {
> >> - if (fd__ > 0) {
> >> - read(fd__, counter, sizeof(*counter));
> >> - } else {
> >> + int size = sizeof *counter;
> >
> > Minor nit ... this should be size_t instead of int.
> >
> Thanks, I wlll make the suggested changes.
I'm pretty sure that using size_t instead of int will actually bust
this. read returns ssize_t, a signed type, and C says that in an
expression like "ssize_t < size_t" the left-hand operand gets
converted to size_t. Thus, if "read" returns -1, it gets converted to
SIZE_MAX, which is not less than sizeof *counter.
If I'm correct, then size should be declared as int or ssize_t.
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