Re: [PATCH 4/6] libmpathutil: silence compiler warning in vector_del_slot()

[Benjamin Marzinski <bmarzins@redhat.com>]

On Mon, May 05, 2025 at 06:29:56PM +0200, Martin Wilck wrote:
> Try to silence a gcc warning. Also, replace the wrong-looking
> VECTOR_DEFAULT_SIZE by 1 (after all, we've just deleted a single
> element).
> 
> Found by Fedora's static analysis [1].
> 
> [1] https://openscanhub.fedoraproject.org/task/51915/log/device-mapper-multipath-0.11.1-1.fc43/scan-results.html
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  libmpathutil/vector.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/libmpathutil/vector.c b/libmpathutil/vector.c
> index 7f763cb..3386651 100644
> --- a/libmpathutil/vector.c
> +++ b/libmpathutil/vector.c
> @@ -107,28 +107,28 @@ int find_slot(vector v, const void *addr)
>  void
>  vector_del_slot(vector v, int slot)
>  {
> -	int i;
> +	int i, allocated;
>  
>  	if (!v || !v->allocated || slot < 0 || slot >= VECTOR_SIZE(v))
>  		return;
>  
>  	for (i = slot + 1; i < VECTOR_SIZE(v); i++)
> -		v->slot[i-1] = v->slot[i];
> +		v->slot[i - 1] = v->slot[i];
>  
> -	v->allocated -= VECTOR_DEFAULT_SIZE;
> +	allocated = v->allocated - 1;
>  
> -	if (v->allocated <= 0) {
> +	if (allocated <= 0) {
>  		free(v->slot);
>  		v->slot = NULL;
>  		v->allocated = 0;
>  	} else {
>  		void *new_slot;
>  
> -		new_slot = realloc(v->slot, sizeof (void *) * v->allocated);
> -		if (!new_slot)
> -			v->allocated += VECTOR_DEFAULT_SIZE;
> -		else
> +		new_slot = realloc(v->slot, sizeof(void *) * allocated);
> +		if (new_slot) {
>  			v->slot = new_slot;
> +			v->allocated = allocated;
> +		}

Actually, now that I think about this a bit more, I don't think that
this was ever the right thing to do. If the realloc() fails, I see no
harm in keeping the smaller v->allocated value. Future realloc()s and
free()s will still work correctly. On the other hand, if we restore the
old, larger v->allocated value (or with your code, never reduce it in
the first place) there will be a duplicate value on the list, which I
can definitely see causing problems.

-Ben

>  	}
>  }
>  
> -- 
> 2.49.0