[PATCH 0/2] hfs/hfsplus: release preallocated blocks on truncate

[Viacheslav Dubeyko]

HFS and HFS+ extend a fork in whole clumps, and when an inode
is loaded the number of allocated blocks comes from the on-disk
physical size of the fork, while i_size and phys_size come from
the logical size. So the fork can hold more blocks than i_size
needs even when phys_size equals i_size.

hfs_file_truncate() and hfsplus_file_truncate() return early when
i_size equals phys_size, before comparing the required block
count with the allocated one. This logic has been added
to avoid dirtying an unchanged inode, but it also skips
releasing the extra blocks:

 - a file whose size is aligned on the block size keeps its clump
   preallocation after the last close;

 - the catalog delete path does not free the data fork and relies
   on truncating the inode to zero size, so a file with zero
   logical size but allocated blocks leaves those blocks marked
   as used in the bitmap after it has been deleted.

Make the early return happen only when neither the
size nor the allocation needs to be trimmed, which keeps the
original intent of not dirtying an unchanged inode.

Viacheslav Dubeyko (2):
  hfsplus: release preallocated blocks in hfsplus_file_truncate()
  hfs: release preallocated blocks in hfs_file_truncate()

 fs/hfs/extent.c      | 13 +++++++++++--
 fs/hfsplus/extents.c | 11 +++++++++--
 2 files changed, 20 insertions(+), 4 deletions(-)

-- 
2.43.0