Re: [PATCH] loop: prohibit the use of sysfs as a backing file

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

Hi Edward,

kernel test robot noticed the following build errors:

[auto build test ERROR on axboe/for-next]
[also build test ERROR on linus/master v7.3 next-20261030]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Edward-Adam-Davis/loop-prohibit-the-use-of-sysfs-as-a-backing-file/20261102-183354
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git for-next
patch link:    https://lore.kernel.org/r/20261102103354.427722-1-eadavis%40sina.com
patch subject: [PATCH] loop: prohibit the use of sysfs as a backing file
config: nios2-defconfig (https://download.01.org/0day-ci/archive/20261103/202611030239.QMvbuUI3-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 11.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261103/202611030239.QMvbuUI3-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/202611030239.QMvbuUI3-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/block/loop.c: In function 'loop_check_backing_file':
>> drivers/block/loop.c:537:48: error: 'SYSFS_MAGIC' undeclared (first use in this function)
     537 |         if (file_inode(file)->i_sb->s_magic == SYSFS_MAGIC)
         |                                                ^~~~~~~~~~~
   drivers/block/loop.c:537:48: note: each undeclared identifier is reported only once for each function it appears in


vim +/SYSFS_MAGIC +537 drivers/block/loop.c

   528	
   529	static int loop_check_backing_file(struct file *file)
   530	{
   531		if (!file->f_op->read_iter)
   532			return -EINVAL;
   533	
   534		if ((file->f_mode & FMODE_WRITE) && !file->f_op->write_iter)
   535			return -EINVAL;
   536	
 > 537		if (file_inode(file)->i_sb->s_magic == SYSFS_MAGIC)
   538			return -EINVAL;
   539	
   540		return 0;
   541	}
   542	

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