Re: [PATCH bpf-next 1/3] bpf: implement relay map basis

[kernel test robot <lkp@intel.com>]

Hi Philo,

kernel test robot noticed the following build warnings:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Philo-Lu/bpf-implement-relay-map-basis/20231222-204545
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link:    https://lore.kernel.org/r/20231222122146.65519-2-lulie%40linux.alibaba.com
patch subject: [PATCH bpf-next 1/3] bpf: implement relay map basis
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20231223/202312230850.NQeIZXj6-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231223/202312230850.NQeIZXj6-lkp@intel.com/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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202312230850.NQeIZXj6-lkp@intel.com/

All warnings (new ones prefixed by >>):

   kernel/bpf/relaymap.c: In function 'relay_map_alloc':
>> kernel/bpf/relaymap.c:79:13: warning: the comparison will always evaluate as 'true' for the address of 'map_name' will never be NULL [-Waddress]
      79 |         if (!attr->map_name || strlen(attr->map_name) == 0)
         |             ^
   In file included from include/linux/bpf.h:7,
                    from include/linux/filter.h:9,
                    from kernel/bpf/relaymap.c:3:
   include/uapi/linux/bpf.h:1394:25: note: 'map_name' declared here
    1394 |                 char    map_name[BPF_OBJ_NAME_LEN];
         |                         ^~~~~~~~


vim +79 kernel/bpf/relaymap.c

    43	
    44	/* bpf_attr is used as follows:
    45	 * - key size: must be 0
    46	 * - value size: value will be used as directory name by map_update_elem
    47	 *   (to create relay files). If passed as 0, it will be set to NAME_MAX as
    48	 *   default
    49	 *
    50	 * - max_entries: subbuf size
    51	 * - map_extra: subbuf num, default as 8
    52	 *
    53	 * When alloc, we do not set up relay files considering dir_name conflicts.
    54	 * Instead we use relay_late_setup_files() in map_update_elem(), and thus the
    55	 * value is used as dir_name, and map->name is used as base_filename.
    56	 */
    57	static struct bpf_map *relay_map_alloc(union bpf_attr *attr)
    58	{
    59		struct bpf_relay_map *rmap;
    60	
    61		if (unlikely(attr->map_flags & ~RELAY_CREATE_FLAG_MASK))
    62			return ERR_PTR(-EINVAL);
    63	
    64		/* key size must be 0 in relay map */
    65		if (unlikely(attr->key_size))
    66			return ERR_PTR(-EINVAL);
    67	
    68		if (unlikely(attr->value_size > NAME_MAX)) {
    69			pr_warn("value_size should be no more than %d\n", NAME_MAX);
    70			return ERR_PTR(-EINVAL);
    71		} else if (attr->value_size == 0)
    72			attr->value_size = NAME_MAX;
    73	
    74		/* set default subbuf num */
    75		attr->map_extra = attr->map_extra & UINT_MAX;
    76		if (!attr->map_extra)
    77			attr->map_extra = 8;
    78	
  > 79		if (!attr->map_name || strlen(attr->map_name) == 0)
    80			return ERR_PTR(-EINVAL);
    81	
    82		rmap = bpf_map_area_alloc(sizeof(*rmap), NUMA_NO_NODE);
    83		if (!rmap)
    84			return ERR_PTR(-ENOMEM);
    85	
    86		bpf_map_init_from_attr(&rmap->map, attr);
    87	
    88		rmap->relay_cb.create_buf_file = create_buf_file_handler;
    89		rmap->relay_cb.remove_buf_file = remove_buf_file_handler;
    90		if (attr->map_flags & BPF_F_OVERWRITE)
    91			rmap->relay_cb.subbuf_start = subbuf_start_overwrite;
    92	
    93		rmap->relay_chan = relay_open(NULL, NULL,
    94								attr->max_entries, attr->map_extra,
    95								&rmap->relay_cb, NULL);
    96		if (!rmap->relay_chan)
    97			return ERR_PTR(-EINVAL);
    98	
    99		return &rmap->map;
   100	}
   101	

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