Re: [Xen-devel] [PATCH v1 2/7] tools/livepatch: Set stdout and stderr unbuffered

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 12/12/2016 05:02 PM, Wei Liu wrote:
> On Mon, Dec 12, 2016 at 04:18:05PM +0000, Ross Lagerwall wrote:
> > Using both stdout and stderr interleaved without newlines can result in
> > strange output when using line buffered mode (e.g. a terminal) or when
> > fully buffered (e.g. redirected to a file). Set both to unbuffered mode
> > to fix this.
> >
> > Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> > ---
> >  tools/misc/xen-livepatch.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/misc/xen-livepatch.c b/tools/misc/xen-livepatch.c
> > index f6c7c8a..2f6721b 100644
> > --- a/tools/misc/xen-livepatch.c
> > +++ b/tools/misc/xen-livepatch.c
> > @@ -330,7 +330,6 @@ int action_func(int argc, char *argv[], unsigned int idx)
> >          }
> >
> >          printf(".");
> > -        fflush(stdout);
> >          usleep(DELAY);
> >      } while ( ++retry < RETRIES );
> >
> > @@ -416,6 +415,13 @@ int main(int argc, char *argv[])
> >  {
> >      int i, j = 0, ret;
> >
> > +    /*
> > +     * Set stdout and stderr to be unbuffered to avoid having to fflush
> > +     * when printing without a newline.
> > +     */
> > +    setvbuf(stdout, NULL, _IONBF, 0);
> > +    setvbuf(stderr, NULL, _IONBF, 0);
> > +
> OOI why would you need to set stderr? It is unbuffered by default.
>
> There is no harm in setting it though.
Good point. I'll drop it since it is unnecessary.

> And perhaps you should check the return value of setvbuf?
I don't think there's anything that can be done if it fails, so there's 
not much point in checking the return value.
--
Ross Lagerwall

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