Hi Damien,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[cannot apply to v5.3-rc5 next-20190820]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Damien-Le-Moal/fs-New-zonefs-file-system/20190820-232131
config: x86_64-allyesconfig (attached as .config)
compiler: gcc-7 (Debian 7.4.0-10) 7.4.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All error/warnings (new ones prefixed by >>):

>> fs/zonefs/super.c:83:37: warning: 'struct iomap_writepage_ctx' declared inside parameter list will not be visible outside of this definition or declaration
    static int zonefs_map_blocks(struct iomap_writepage_ctx *wpc,
                                        ^~~~~~~~~~~~~~~~~~~
   fs/zonefs/super.c: In function 'zonefs_map_blocks':
>> fs/zonefs/super.c:86:19: error: dereferencing pointer to incomplete type 'struct iomap_writepage_ctx'
     if (offset >= wpc->iomap.offset &&
                      ^~
   fs/zonefs/super.c: At top level:
>> fs/zonefs/super.c:95:21: error: variable 'zonefs_writeback_ops' has initializer but incomplete type
    static const struct iomap_writeback_ops zonefs_writeback_ops = {
                        ^~~~~~~~~~~~~~~~~~~
>> fs/zonefs/super.c:96:3: error: 'const struct iomap_writeback_ops' has no member named 'map_blocks'
     .map_blocks  = zonefs_map_blocks,
      ^~~~~~~~~~
>> fs/zonefs/super.c:96:17: warning: excess elements in struct initializer
     .map_blocks  = zonefs_map_blocks,
                    ^~~~~~~~~~~~~~~~~
   fs/zonefs/super.c:96:17: note: (near initialization for 'zonefs_writeback_ops')
   fs/zonefs/super.c: In function 'zonefs_writepage':
>> fs/zonefs/super.c:101:9: error: variable 'wpc' has initializer but incomplete type
     struct iomap_writepage_ctx wpc = { };
            ^~~~~~~~~~~~~~~~~~~
>> fs/zonefs/super.c:101:29: error: storage size of 'wpc' isn't known
     struct iomap_writepage_ctx wpc = { };
                                ^~~
>> fs/zonefs/super.c:103:9: error: implicit declaration of function 'iomap_writepage'; did you mean 'iomap_readpage'? [-Werror=implicit-function-declaration]
     return iomap_writepage(page, wbc, &wpc, &zonefs_writeback_ops);
            ^~~~~~~~~~~~~~~
            iomap_readpage
   fs/zonefs/super.c:101:29: warning: unused variable 'wpc' [-Wunused-variable]
     struct iomap_writepage_ctx wpc = { };
                                ^~~
   fs/zonefs/super.c: In function 'zonefs_writepages':
   fs/zonefs/super.c:109:9: error: variable 'wpc' has initializer but incomplete type
     struct iomap_writepage_ctx wpc = { };
            ^~~~~~~~~~~~~~~~~~~
   fs/zonefs/super.c:109:29: error: storage size of 'wpc' isn't known
     struct iomap_writepage_ctx wpc = { };
                                ^~~
>> fs/zonefs/super.c:111:9: error: implicit declaration of function 'iomap_writepages'; did you mean 'do_writepages'? [-Werror=implicit-function-declaration]
     return iomap_writepages(mapping, wbc, &wpc, &zonefs_writeback_ops);
            ^~~~~~~~~~~~~~~~
            do_writepages
   fs/zonefs/super.c:109:29: warning: unused variable 'wpc' [-Wunused-variable]
     struct iomap_writepage_ctx wpc = { };
                                ^~~
   fs/zonefs/super.c: At top level:
>> fs/zonefs/super.c:95:41: error: storage size of 'zonefs_writeback_ops' isn't known
    static const struct iomap_writeback_ops zonefs_writeback_ops = {
                                            ^~~~~~~~~~~~~~~~~~~~
   fs/zonefs/super.c: In function 'zonefs_writepages':
>> fs/zonefs/super.c:112:1: warning: control reaches end of non-void function [-Wreturn-type]
    }
    ^
   fs/zonefs/super.c: In function 'zonefs_writepage':
   fs/zonefs/super.c:104:1: warning: control reaches end of non-void function [-Wreturn-type]
    }
    ^
   cc1: some warnings being treated as errors

vim +86 fs/zonefs/super.c

    82	
  > 83	static int zonefs_map_blocks(struct iomap_writepage_ctx *wpc,
    84				     struct inode *inode, loff_t offset)
    85	{
  > 86		if (offset >= wpc->iomap.offset &&
    87		    offset < wpc->iomap.offset + wpc->iomap.length)
    88			return 0;
    89	
    90		memset(&wpc->iomap, 0, sizeof(wpc->iomap));
    91		return zonefs_iomap_begin(inode, offset, zonefs_file_max_size(inode),
    92					  0, &wpc->iomap);
    93	}
    94	
  > 95	static const struct iomap_writeback_ops zonefs_writeback_ops = {
  > 96		.map_blocks		= zonefs_map_blocks,
    97	};
    98	
    99	static int zonefs_writepage(struct page *page, struct writeback_control *wbc)
   100	{
 > 101		struct iomap_writepage_ctx wpc = { };
   102	
 > 103		return iomap_writepage(page, wbc, &wpc, &zonefs_writeback_ops);
   104	}
   105	
   106	static int zonefs_writepages(struct address_space *mapping,
   107				     struct writeback_control *wbc)
   108	{
 > 109		struct iomap_writepage_ctx wpc = { };
   110	
 > 111		return iomap_writepages(mapping, wbc, &wpc, &zonefs_writeback_ops);
 > 112	}
   113	

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