Re: [PATCH net-next v10 12/12] libeth: xdp: access ->pp through netmem_desc instead of page

[kernel test robot]

Hi Byungchul,

kernel test robot noticed the following build warnings:

[auto build test WARNING on c65d34296b2252897e37835d6007bbd01b255742]

url:    https://github.com/intel-lab-lkp/linux/commits/Byungchul-Park/netmem-introduce-struct-netmem_desc-mirroring-struct-page/20250714-200214
base:   c65d34296b2252897e37835d6007bbd01b255742
patch link:    https://lore.kernel.org/r/20250714120047.35901-13-byungchul%40sk.com
patch subject: [PATCH net-next v10 12/12] libeth: xdp: access ->pp through netmem_desc instead of page
config: m68k-allmodconfig (https://download.01.org/0day-ci/archive/20250715/202507150748.9sVeInO8-lkp@xxxxxxxxx/config)
compiler: m68k-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250715/202507150748.9sVeInO8-lkp@xxxxxxxxx/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202507150748.9sVeInO8-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

   In file included from drivers/net/ethernet/intel/libeth/tx.c:6:
   include/net/libeth/xdp.h: In function 'libeth_xdp_prepare_buff':
>> include/net/libeth/xdp.h:1295:44: warning: passing argument 1 of 'pp_page_to_nmdesc' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
    1295 |                          pp_page_to_nmdesc(page)->pp->p.offset, len, true);
         |                                            ^~~~
   In file included from include/linux/skbuff.h:41,
                    from include/net/net_namespace.h:43,
                    from include/linux/netdevice.h:38,
                    from include/trace/events/xdp.h:8,
                    from include/linux/bpf_trace.h:5,
                    from include/net/libeth/xdp.h:7:
   include/net/netmem.h:270:66: note: expected 'struct page *' but argument is of type 'const struct page *'
     270 | static inline struct netmem_desc *pp_page_to_nmdesc(struct page *page)
         |                                                     ~~~~~~~~~~~~~^~~~


vim +1295 include/net/libeth/xdp.h

  1263	
  1264	bool libeth_xdp_buff_add_frag(struct libeth_xdp_buff *xdp,
  1265				      const struct libeth_fqe *fqe,
  1266				      u32 len);
  1267	
  1268	/**
  1269	 * libeth_xdp_prepare_buff - fill &libeth_xdp_buff with head FQE data
  1270	 * @xdp: XDP buffer to attach the head to
  1271	 * @fqe: FQE containing the head buffer
  1272	 * @len: buffer len passed from HW
  1273	 *
  1274	 * Internal, use libeth_xdp_process_buff() instead. Initializes XDP buffer
  1275	 * head with the Rx buffer data: data pointer, length, headroom, and
  1276	 * truesize/tailroom. Zeroes the flags.
  1277	 * Uses faster single u64 write instead of per-field access.
  1278	 */
  1279	static inline void libeth_xdp_prepare_buff(struct libeth_xdp_buff *xdp,
  1280						   const struct libeth_fqe *fqe,
  1281						   u32 len)
  1282	{
  1283		const struct page *page = __netmem_to_page(fqe->netmem);
  1284	
  1285	#ifdef __LIBETH_WORD_ACCESS
  1286		static_assert(offsetofend(typeof(xdp->base), flags) -
  1287			      offsetof(typeof(xdp->base), frame_sz) ==
  1288			      sizeof(u64));
  1289	
  1290		*(u64 *)&xdp->base.frame_sz = fqe->truesize;
  1291	#else
  1292		xdp_init_buff(&xdp->base, fqe->truesize, xdp->base.rxq);
  1293	#endif
  1294		xdp_prepare_buff(&xdp->base, page_address(page) + fqe->offset,
> 1295				 pp_page_to_nmdesc(page)->pp->p.offset, len, true);
  1296	}
  1297	

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