This fixe does page cache invalidation after DIO and async DIO writes for
both O_DIRECT and FOPEN_DIRECT_IO cases.

Commit b359af8275a9 ("fuse: Invalidate the page cache after FOPEN_DIRECT_IO
write") fixed xfstests generic/209 for DIO writes in the FOPEN_DIRECT_IO
path. DIO writes without FOPEN_DIRECT_IO are already handled by
generic_file_direct_write().
However, async DIO writes (xfstests generic/451) remain unhandled.

After this fix:
- Async write with FUSE_ASYNC_DIO:
    invalidate in fuse_aio_invalidate_worker()

- Otherwise (Sync or async write without FUSE_ASYNC_DIO):
    - With FOPEN_DIRECT_IO:
        invalidate in fuse_direct_write_iter()
    - Without FOPEN_DIRECT_IO:
        invalidate in generic_file_direct_write()

Workqueue is required for async write invalidation to prevent deadlock:
calling it directly in the I/O end routine (which is in fuse worker thread
context) can block on a folio lock held by a buffered I/O thread waiting
for the same fuse worker thread.

Co-developed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Cheng Ding <cding@ddn.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Pull superblock lock guard updates from Christian Brauner:
 "This starts the work of introducing guards for superblock related
  locks.

  Introduce super_write_guard for scoped superblock write protection.

  This provides a guard-based alternative to the manual sb_start_write()
  and sb_end_write() pattern, allowing the compiler to automatically
  handle the cleanup"

* tag 'vfs-6.19-rc1.guards' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  xfs: use super write guard in xfs_file_ioctl()
  open: use super write guard in do_ftruncate()
  btrfs: use super write guard in relocating_repair_kthread()
  ext4: use super write guard in write_mmp_block()
  btrfs: use super write guard in sb_start_write()
  btrfs: use super write guard btrfs_run_defrag_inode()
  btrfs: use super write guard in btrfs_reclaim_bgs_work()
  fs: add super_write_guard

Pull fs header updates from Christian Brauner:
 "This contains initial work to start splitting up fs.h.

  Begin the long-overdue work of splitting up the monolithic fs.h
  header. The header has grown to over 3000 lines and includes types and
  functions for many different subsystems, making it difficult to
  navigate and causing excessive compilation dependencies.

  This series introduces new focused headers for superblock-related
  code:

   - Rename fs_types.h to fs_dirent.h to better reflect its actual
     content (directory entry types)

   - Add fs/super_types.h containing superblock type definitions

   - Add fs/super.h containing superblock function declarations

  This is the first step in a longer effort to modularize the VFS
  headers.

  Cleanups:

   - Inode Field Layout Optimization (Mateusz Guzik)

     Move inode fields used during fast path lookup closer together to
     improve cache locality during path resolution.

   - current_umask() Optimization (Mateusz Guzik)

     Inline current_umask() and move it to fs_struct.h. This improves
     performance by avoiding function call overhead for this
     frequently-used function, and places it in a more appropriate
     header since it operates on fs_struct"

* tag 'vfs-6.19-rc1.fs_header' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  fs: move inode fields used during fast path lookup closer together
  fs: inline current_umask() and move it to fs_struct.h
  fs: add fs/super.h header
  fs: add fs/super_types.h header
  fs: rename fs_types.h to fs_dirent.h

Link: https://patch.msgid.link/20251104-work-guards-v1-1-5108ac78a171@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Split out super block associated functions into a separate header.

Link: https://patch.msgid.link/20251104-work-fs-header-v1-3-fb39a2efe39e@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>