drivers/md/md-ctl.c:47:26: error: call to undeclared library function 'isdigit' with type 'int (int)'; ISO C99 and later do not support implicit function declarations

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

tree:   https://github.com/intel-lab-lkp/linux/commits/Abd-Alrhman-Masalkhi/md-make-mddev-lookup-and-ioctl-helpers-non-static/20260928-201223
head:   6b0c58a68cb9e72a888a76dac60d49a88d347118
commit: 6b0c58a68cb9e72a888a76dac60d49a88d347118 md: add a control device for array management
date:   31 hours ago
config: s390-randconfig-2000-20260930 (https://download.01.org/0day-ci/archive/20260930/202609300507.5HFYs9aS-lkp@intel.com/config)
compiler: clang version 24.0.0git (https://github.com/llvm/llvm-project 7615da10b75c57286a4032eac8bb43c1b8d2ba46)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260930/202609300507.5HFYs9aS-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/202609300507.5HFYs9aS-lkp@intel.com/

All errors (new ones prefixed by >>):

>> drivers/md/md-ctl.c:47:26: error: call to undeclared library function 'isdigit' with type 'int (int)'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
      47 |         if (name[2] != '_' && (!isdigit(name[2]) ||
         |                                 ^
   drivers/md/md-ctl.c:47:26: note: include the header <ctype.h> or explicitly provide a declaration for 'isdigit'
   1 error generated.


vim +47 drivers/md/md-ctl.c

    38	
    39	static struct mddev *get_mddev_name(const char *name)
    40	{
    41		unsigned long minor;
    42		struct mddev *mddev, *ret = NULL;
    43	
    44		if (strncmp(name, "md", 2))
    45			return ERR_PTR(-EINVAL);
    46	
  > 47		if (name[2] != '_' && (!isdigit(name[2]) ||
    48				       kstrtoul(&name[2], 10, &minor) ||
    49				       minor > MINORMASK))
    50			return ERR_PTR(-EINVAL);
    51	
    52		spin_lock(&all_mddevs_lock);
    53		list_for_each_entry(mddev, &all_mddevs, all_mddevs) {
    54			if (mddev->gendisk &&
    55			    strcmp(mddev->gendisk->disk_name, name) == 0) {
    56				ret = mddev_get(mddev);
    57				break;
    58			}
    59		}
    60		spin_unlock(&all_mddevs_lock);
    61	
    62		return ret ? ret : ERR_PTR(-ENODEV);
    63	}
    64	

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