fs: Move metadata bh tracking from address_space

Hello,

here is a next revision of the patchset cleaning up buffer head metadata
tracking and use of address_space's private_list and private_lock. Functionally
this should be identical to v2, most of the changes were in improving
changelogs, patch ordering, function names, etc. The patches have survived some
testing with fstests and ltp however I didn't test AFFS and KVM guest_memfd
changes so a help with testing those would be very welcome.  Thanks.

Changes since v2:
* Added Reviewed-by tags from Christoph
* Dropped the patch unifying fsync implementation in fs/libfs.c and fs/buffer.c
* Put fsync locking change into a separate commit
* Reordered series to place all fsync path modifications close together
* Improved some changelogs
* Renamed some functions based on Christoph's feedback

Changes since v1:
* Fixed hugetlbfs handling of root directory
* Reworked mapping_metadata_bhs handling functions to get the tracking
  structure as an argument so we now don't need iops method to fetch the struct
  from the inode
* Reordered patches into more sensible order
* Added patch to merge two mostly duplicate generic fsync implementations
* Added Reviewed-by tags
* Couple more minor changes that were requested during review

Original cover letter:

this patch series cleans up the mess that has accumulated over the years in
metadata buffer_head tracking for inodes, moves the tracking into dedicated
structure in filesystem-private part of the inode (so that we don't use
private_list, private_data, and private_lock in struct address_space), and also
moves couple other users of private_data and private_list so these are removed
from struct address_space saving 3 longs in struct inode for 99% of inodes.  I
would like to get rid of private_lock in struct address_space as well however
the locking changes for buffer_heads are non-trivial there and the patch series
is long enough as is. So let's leave that for another time.

 block/bdev.c                |    1 
 fs/affs/affs.h              |    2 
 fs/affs/dir.c               |    1 
 fs/affs/file.c              |    1 
 fs/affs/inode.c             |    2 
 fs/affs/super.c             |    6 
 fs/affs/symlink.c           |    1 
 fs/aio.c                    |   78 +++++++-
 fs/bfs/bfs.h                |    2 
 fs/bfs/dir.c                |    1 
 fs/bfs/file.c               |    4 
 fs/bfs/inode.c              |    9 +
 fs/buffer.c                 |  387 +++++++++++++++++---------------------------
 fs/ext2/ext2.h              |    2 
 fs/ext2/file.c              |    1 
 fs/ext2/inode.c             |    3 
 fs/ext2/namei.c             |    2 
 fs/ext2/super.c             |    6 
 fs/ext2/symlink.c           |    2 
 fs/ext4/ext4.h              |    4 
 fs/ext4/file.c              |    1 
 fs/ext4/inode.c             |    9 -
 fs/ext4/namei.c             |    2 
 fs/ext4/super.c             |    9 -
 fs/ext4/symlink.c           |    3 
 fs/fat/fat.h                |    2 
 fs/fat/file.c               |    1 
 fs/fat/inode.c              |   16 +
 fs/fat/namei_msdos.c        |    1 
 fs/fat/namei_vfat.c         |    1 
 fs/gfs2/glock.c             |    1 
 fs/hugetlbfs/inode.c        |   10 -
 fs/inode.c                  |   24 +-
 fs/minix/file.c             |    1 
 fs/minix/inode.c            |   10 +
 fs/minix/minix.h            |    2 
 fs/minix/namei.c            |    1 
 fs/ntfs3/file.c             |    3 
 fs/ocfs2/dlmglue.c          |    1 
 fs/ocfs2/namei.c            |    3 
 fs/udf/file.c               |    1 
 fs/udf/inode.c              |    2 
 fs/udf/namei.c              |    1 
 fs/udf/super.c              |    6 
 fs/udf/symlink.c            |    1 
 fs/udf/udf_i.h              |    1 
 fs/udf/udfdecl.h            |    1 
 include/linux/buffer_head.h |    6 
 include/linux/fs.h          |   11 -
 include/linux/hugetlb.h     |    1 
 mm/hugetlb.c                |   10 -
 virt/kvm/guest_memfd.c      |   12 -
 52 files changed, 360 insertions(+), 309 deletions(-)

								Honza

Previous versions:
Link: http://lore.kernel.org/r/20260303101717.27224-1-jack@suse.cz # v1
Link: http://lore.kernel.org/r/20260320131728.6449-1-jack@suse.cz # v2