Re: [PATCH net-next] net: sched: cls_api: improve the error message for ID allocation failure

[Simon Horman <horms@kernel.org>]

On Thu, Sep 12, 2024 at 02:53:06PM -0700, Jakub Kicinski wrote:
> We run into an exhaustion problem with the kernel-allocated filter IDs.
> Our allocation problem can be fixed on the user space side,
> but the error message in this case was quite misleading:
> 
>   "Filter with specified priority/protocol not found" (EINVAL)
> 
> Specifically when we can't allocate a _new_ ID because filter with
> lowest ID already _exists_, saying "filter not found", is confusing.
> 
> Kernel allocates IDs in range of 0xc0000 -> 0x8000, giving out ID one
> lower than lowest existing in that range. The error message makes sense
> when tcf_chain_tp_find() gets called for GET and DEL but for NEW we
> need to provide more specific error messages for all three cases:
> 
>  - user wants the ID to be auto-allocated but filter with ID 0x8000
>    already exists
> 
>  - filter already exists and can be replaced, but user asked
>    for a protocol change
> 
>  - filter doesn't exist
> 
> Caller of tcf_chain_tp_insert_unique() doesn't set extack today,
> so don't bother plumbing it in.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Simon Horman <horms@kernel.org>