Re: [PATCH 1/3] util: validate whether O_DIRECT is supported after failure

[Philippe Mathieu-Daudé]

On 7/1/20 6:05 PM, Daniel P. Berrangé wrote:
> Currently we suggest that a filesystem may not support O_DIRECT after
> seeing an EINVAL. Other things can cause EINVAL though, so it is better
> to do an explicit check, and then report a definitive error message.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  util/osdep.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/util/osdep.c b/util/osdep.c
> index 4829c07ff6..4bdbe81cec 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -342,8 +342,17 @@ int qemu_open(const char *name, int flags, ...)
>  
>  #ifdef O_DIRECT
>      if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
> -        error_report("file system may not support O_DIRECT");
> -        errno = EINVAL; /* in case it was clobbered */
> +        int newflags = flags & ~O_DIRECT;
> +# ifdef O_CLOEXEC
> +        ret = open(name, newflags | O_CLOEXEC, mode);
> +# else
> +        ret = open(name, newflags, mode);
> +# endif

Can we use this simpler form (easier to set a breakpoint)?

   #ifdef O_CLOEXEC
           newflags |= O_CLOEXEC;
   #endif
           ret = open(name, newflags, mode);

Whichever you prefer:
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> +        if (ret != -1) {
> +            close(ret);
> +            error_report("file system does not support O_DIRECT");
> +            errno = EINVAL;
> +        }
>      }
>  #endif /* O_DIRECT */
>  
>