Re: [PATCH v4 5/6] util: give a specific error message when O_DIRECT doesn't work

[Markus Armbruster <armbru@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> writes:

> A common error scenario is to tell QEMU to use O_DIRECT in combination
> with a filesystem that doesn't support it. To aid users to diagnosing
> their mistake we want to provide a clear error message when this happens.
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  util/osdep.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/util/osdep.c b/util/osdep.c
> index a4956fbf6b..6c24985f7a 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -345,6 +345,19 @@ qemu_open_internal(const char *name, int flags, mode_t mode, Error **errp)
>  
>      if (ret == -1) {
>          const char *action = flags & O_CREAT ? "create" : "open";
> +#ifdef O_DIRECT
> +        if (errno == EINVAL && (flags & O_DIRECT)) {
> +            ret = open(name, flags & ~O_DIRECT, mode);
> +            if (ret != -1) {
> +                close(ret);
> +                error_setg(errp, "Could not %s '%s' flags 0x%x: "
> +                           "filesystem does not support O_DIRECT",
> +                           action, name, flags);
> +                errno = EINVAL; /* close() clobbered earlier errno */

More precise: close() may have clobbered

Sure open() can only fail with EINVAL here?

> +                return -1;
> +            }
> +        }
> +#endif /* O_DIRECT */
>          error_setg_errno(errp, errno, "Could not %s '%s' flags 0x%x",
>                           action, name, flags);
>      }

There is no qemu_set_cloexec().  Intentional?