hfsplus: fix potential Allocation File corruption after fsync

hfsplus: fix potential Allocation File corruption after fsync

The generic/348 test-case has revealed the issue of
HFS+ volume corruption after simulated power failure:

FSTYP -- hfsplus
PLATFORM -- Linux/x86_64 hfsplus-testing-0001 6.15.0-rc4+ #8 SMP PREEMPT_DYNAMIC Thu May 1 16:43:22 PDT 2025
MKFS_OPTIONS -- /dev/loop51
MOUNT_OPTIONS -- /dev/loop51 /mnt/scratch

generic/348 _check_generic_filesystem: filesystem on /dev/loop51 is inconsistent
(see xfstests-dev/results//generic/348.full for details)

The fsck tool complains about Allocation File (block bitmap)
corruption as a result of such event. The generic/348 creates
a symlink, fsync its parent directory, power fail and mount
again the filesystem. Currently, HFS+ logic has several flags
HFSPLUS_I_CAT_DIRTY, HFSPLUS_I_EXT_DIRTY, HFSPLUS_I_ATTR_DIRTY,
HFSPLUS_I_ALLOC_DIRTY. If inode operation modified the Catalog
File, Extents Overflow File, Attributes File, or Allocation
File, then inode is marked as dirty and one of the mentioned
flags has been set. When hfsplus_file_fsync() has been called,
then this set of flags is checked and dirty b-tree or/and
block bitmap is flushed. However, block bitmap can be modified
during file's content allocation. It means that if we call
hfsplus_file_fsync() for directory, then we never flush
the modified Allocation File in such case because such inode
cannot receive HFSPLUS_I_ALLOC_DIRTY flag. Moreover, this
inode-centric model is not good at all because Catalog File,
Extents Overflow File, Attributes File, and Allocation File
represent the whole state of file system metadata. This
inode-centric policy is the main reason of the issue.

This patch saves the whole approach of using HFSPLUS_I_CAT_DIRTY,
HFSPLUS_I_EXT_DIRTY, HFSPLUS_I_ATTR_DIRTY, and
HFSPLUS_I_ALLOC_DIRTY flags. But Catalog File, Extents Overflow
File, Attributes File, and Allocation File have associated
inodes. And namely these inodes become the mechanism of
checking the dirty state of metadata. The hfsplus_file_fsync()
method checks the dirtiness of file system metadata by
testing HFSPLUS_I_CAT_DIRTY, HFSPLUS_I_EXT_DIRTY,
HFSPLUS_I_ATTR_DIRTY, and HFSPLUS_I_ALLOC_DIRTY flags of
Catalog File's, Extents Overflow File's, Attributes File's, or
Allocation File's inodes. As a result, even if we call
hfsplus_file_fsync() for parent folder, then dirty Allocation File
will be flushed anyway.

Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
cc: Yangtao Li <frank.li@vivo.com>
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20260220220152.152721-1-slava@dubeyko.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>