This patch implements delayed allocation (delalloc) in ntfs3 driver.
It introduces an in-memory delayed-runlist (run_da) and the helpers to
track, reserve and later convert those delayed reservations into real
clusters at writeback time. The change keeps on-disk formats untouched and
focuses on pagecache integration, correctness and safe interaction with
fallocate, truncate, and dio/iomap paths.
Key points:
- add run_da (delay-allocated run tree) and bookkeeping for delayed clusters.
- mark ranges as delalloc (DELALLOC_LCN) instead of immediately allocating.
Actual allocation performed later (writeback / attr_set_size_ex / explicit
flush paths).
- direct i/o / iomap paths updated to avoid dio collisions with
delalloc: dio falls back or forces allocation of delayed blocks before
proceeding.
- punch/collapse/truncate/fallocate check and cancel delay-alloc reservations.
Sparse/compressed files handled specially.
- free-space checks updated (ntfs_check_free_space) to account for reserved
delalloc clusters and MFT record budgeting.
- delayed allocations are committed on last writer (file release) and on
explicit allocation flush paths.
Tested-by: syzbot@syzkaller.appspotmail.com
Reported-by: syzbot+2bd8e813c7f767aa9bb1@syzkaller.appspotmail.com
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
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