Re: [Xen-devel] [PATCH v3] libvchan: tidy up usages of fcntl in select-type sample application

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 11/01/2013 09:28 AM, Ian Campbell wrote:
> On Fri, 2013-11-01 at 13:33 +1300, Matthew Daley wrote:
> > Namely, don't overwrite all the other flags when twiddling O_NONBLOCK,
> > and add basic error handling.
> >
> > Coverity-ID: 1055041
> > Signed-off-by: Matthew Daley <mattjd@xxxxxxxxx>
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>
> I'll give Daniel a chance to comment before applying.
Looks good to me.

Reviewed-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>

> > ---
> > v2: Adjust other fcntl usage further down as well. Use F_GETFL to modify
> > only the O_NONBLOCK flag. Both suggested by Daniel De Graaf.
> > Improve commit message.
> >
> > v3: Make a new function, set_nonblocking, to do the twiddling
> >
> >   tools/libvchan/node-select.c |   27 ++++++++++++++++++++++++---
> >   1 file changed, 24 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/libvchan/node-select.c b/tools/libvchan/node-select.c
> > index 6c6c19e..13c5822 100644
> > --- a/tools/libvchan/node-select.c
> > +++ b/tools/libvchan/node-select.c
> > @@ -80,6 +80,22 @@ void stdout_wr() {
> >         }
> >   }
> >
> > +static int set_nonblocking(int fd, int nonblocking) {
> > +       int flags = fcntl(fd, F_GETFL);
> > +       if (flags == -1)
> > +               return -1;
> > +
> > +       if (nonblocking)
> > +               flags |= O_NONBLOCK;
> > +       else
> > +               flags &= ~O_NONBLOCK;
> > +
> > +       if (fcntl(fd, F_SETFL, flags) == -1)
> > +               return -1;
> > +
> > +       return 0;
> > +}
> > +
> >   /**
> >       Simple libxenvchan application, both client and server.
> >         Both sides may write and read, both from the libxenvchan and from
> > @@ -105,8 +121,10 @@ int main(int argc, char **argv)
> >                 exit(1);
> >         }
> >
> > -       fcntl(0, F_SETFL, O_NONBLOCK);
> > -       fcntl(1, F_SETFL, O_NONBLOCK);
> > +       if (set_nonblocking(0, 1) || set_nonblocking(1, 1)) {
> > +               perror("set_nonblocking");
> > +               exit(1);
> > +       }
> >
> >         libxenvchan_fd = libxenvchan_fd_for_select(ctrl);
> >         for (;;) {
> > @@ -153,7 +171,10 @@ int main(int argc, char **argv)
> >                         stdout_wr();
> >                 }
> >                 if (!libxenvchan_is_open(ctrl)) {
> > -                       fcntl(1, F_SETFL, 0);
> > +                       if (set_nonblocking(1, 0)) {
> > +                               perror("set_nonblocking");
> > +                               exit(1);
> > +                       }
> >                         while (outsiz)
> >                                 stdout_wr();
> >                         return 0;

--
Daniel De Graaf
National Security Agency

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