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fs/ntfs3: add delayed-allocation (delalloc) support

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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>
This commit is contained in:
Konstantin Komarov 2026-02-16 17:10:26 +01:00
commit 10d7c95af0
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12 changed files with 886 additions and 344 deletions
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