Hi,
in today's linux-next the build failed in my x86 system with the attached config.
The errors are as follows:
fs/btrfs/inode.c:8050:2: error: implicit declaration of function ‘iov_iter_alignment’ [-Werror=implicit-function-declaration]
 if (iov_iter_alignment(iter) & blocksize_mask)
 ^
fs/btrfs/inode.c:8061:26: error: dereferencing pointer to incomplete type
 for (seg = 0; seg < iter->nr_segs; seg++) {
                         ^
fs/btrfs/inode.c:8062:29: error: dereferencing pointer to incomplete type
 for (i = seg + 1; i < iter->nr_segs; i++) {
                           ^
fs/btrfs/inode.c:8063:12: error: dereferencing pointer to incomplete type
 if (iter->iov[seg].iov_base == iter->iov[i].iov_base)
          ^
fs/btrfs/inode.c:8063:39: error: dereferencing pointer to incomplete type
 if (iter->iov[seg].iov_base == iter->iov[i].iov_base)
                                     ^
fs/btrfs/inode.c: In function ‘btrfs_direct_IO’:
fs/btrfs/inode.c:8095:2: error: implicit declaration of function ‘iov_iter_count’ [-Werror=implicit-function-declaration]
 count = iov_iter_count(iter);
 ^

just to make sure i have done make distclean and checked one more time also.

regards
sudip