add STATX_DIO_READ_ALIGN v2

[Christoph Hellwig <hch@lst.de>]

Hi all,

file systems that write out of place usually require different alignment
for direct I/O writes than what they can do for reads.  This series tries
to address this by adding yet another statx field.

Changes from v1:
 - improve the comment in xfs_report_dioalign based on a contribution
   from Darrick
 - improve man page wording and formatting
 - also report the larger alignment in XFS_IOC_DIOINFO

Changes from RFC:
 - add a cleanup patch for xfs_vn_getattr
 - use xfs_inode_alloc_unitsize in xfs_vn_getattr
 - improve a comment in XFS

Diffstat:
 fs/stat.c                 |    1 
 fs/xfs/xfs_ioctl.c        |   11 ++++-
 fs/xfs/xfs_iops.c         |   62 +++++++++++++++++-----------
 include/linux/stat.h      |    1 
 include/uapi/linux/stat.h |   99 ++++++++++++++++++++++++++++++++++------------
 5 files changed, 125 insertions(+), 49 deletions(-)