[igt-dev] [PATCH i-g-t] lib/sysfs: Avoid using FILE* temporary for igt_sysfs_[v]printf

[Chris Wilson]

Quoting Chris Wilson (2018-08-30 09:44:33)
> Currently we wrap our fd inside a FILE* stream to make use of vfprintf,
> but the man page leaves the question of errno and signal handling in
> doubt. It is documented as returning a negative value and setting
> ferror(), but we have been interpreting errno to handle signal
> restarting. As that is in doubt, reduce it to a sprintf and reuse our
> common interrupt handling write() that already returns -errno.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Katarzyna Dec <katarzyna.dec at intel.com>
> ---
>  lib/igt_sysfs.c | 37 ++++++++++++++++++++++++++-----------
>  1 file changed, 26 insertions(+), 11 deletions(-)
> 
> diff --git a/lib/igt_sysfs.c b/lib/igt_sysfs.c
> index 8efe889be..b39da4c2a 100644
> --- a/lib/igt_sysfs.c
> +++ b/lib/igt_sysfs.c
> @@ -387,22 +387,37 @@ int igt_sysfs_scanf(int dir, const char *attr, const char *fmt, ...)
>  
>  int igt_sysfs_vprintf(int dir, const char *attr, const char *fmt, va_list ap)
>  {
> -       FILE *file;
> -       int fd;
> -       int ret = -1;
> +       char stack[128], *buf = stack;
> +       va_list tmp;
> +       int ret, fd;
>  
>         fd = openat(dir, attr, O_WRONLY);
>         if (fd < 0)
> -               return -1;
> +               return -errno;
>  
> -       file = fdopen(fd, "w");
> -       if (file) {
> -               do {
> -                       ret = vfprintf(file, fmt, ap);
> -               } while (ret == -1 && errno == EINTR);
> -               fclose(file);
> +       va_copy(tmp, ap);
> +       ret = vsnprintf(buf, sizeof(stack), fmt, tmp);
> +       va_end(tmp);
> +       if (ret < 0)
> +               return -EINVAL;
> +
> +       if (ret > sizeof(stack)) {
> +               int len = ret + 1;
> +
> +               buf = malloc(len);
> +               if (!buf)
> +                       return -ENOMEM;
> +
> +               ret = vsnprintf(buf, ret, fmt, ap);
> +               if (ret > len) {
> +                       free(buf);
> +                       return -EINVAL;
> +               }
>         }
> -       close(fd);
> +
> +       ret = writeN(fd, buf, ret);
> +       if (buf != stack)
> +               free(buf);

+ close(fd);

>  
>         return ret;
>  }
> -- 
> 2.19.0.rc1
>