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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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.

> ---
> 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;



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