[dpdk-stable] [PATCH 16.11] vhost-user: fix false negative in handling user messages

[Ilya Maximets]

On 28.11.2018 19:20, Luca Boccassi wrote:
> vhost_user_msg_handler checks an accumulated return code before
> returning, and prints an error and returns -1 if it's non-zero.
> But some of the possible user messages cannot fail and thus do not
> set the variable, which might retain a previously set and unrelated
> value, causing unnecessary failures and error messages.
> 
> Reset the return code before use.
> 
> Fixes: 0ce9e73d1e8d ("vhost-user: drop connection on message handling failures")
> 
> Signed-off-by: Luca Boccassi <bluca at debian.org>
> ---
> Found this issue when testing with the Vyatta stuff, "ret" is set at
> the beginning of the function and never reset when the message is for example
> VHOST_USER_GET_FEATURES so there's a flurry of errors.

Hmm. Yes, current implementation in 16.11 branch doesn't work at all.
I think that it's a kind of an issue in the original patch 0d7853a4d.
But it uncovered only after backporting. On master we had additional
call 'ret = vhost_user_check_and_alloc_queue_pair()' before the main
handling switch and this function could only return 0 or -1. So, the
'ret' was always zero if we reached the handling switch.

LGTM,
Acked-by: Ilya Maximets <i.maximets at samsung.com>

> 
>  lib/librte_vhost/vhost_user.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index 00872c868..618d413fe 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -1087,6 +1087,7 @@ vhost_user_msg_handler(int vid, int fd)
>  
>  	}
>  
> +	ret = 0;
>  	switch (msg.request) {
>  	case VHOST_USER_GET_FEATURES:
>  		msg.payload.u64 = vhost_user_get_features();
>