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Subject[PATCH 18/25] NTFS: Make ntfs_write_block() not instantiate sparse blocks if they are zero.
[PATCH 18/25] NTFS: Make ntfs_write_block() not instantiate sparse blocks if they are zero.

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>

---
fs/ntfs/ChangeLog | 2 ++
fs/ntfs/aops.c | 21 +++++++++++++++++++++
2 files changed, 23 insertions(+), 0 deletions(-)
8dcdebafb848415eae25924b00c4f0b9ec907da0
diff --git a/fs/ntfs/ChangeLog b/fs/ntfs/ChangeLog
--- a/fs/ntfs/ChangeLog
+++ b/fs/ntfs/ChangeLog
@@ -77,6 +77,8 @@ ToDo/Notes:
updating the times in the inode in ntfs_setattr().
- Fixup handling of sparse, compressed, and encrypted attributes in
fs/ntfs/inode.c::ntfs_read_locked_{,attr_,index_}inode().
+ - Make ntfs_write_block() not instantiate sparse blocks if they contain
+ only zeroes.

2.1.23 - Implement extension of resident files and make writing safe as well as
many bug fixes, cleanups, and enhancements...
diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
--- a/fs/ntfs/aops.c
+++ b/fs/ntfs/aops.c
@@ -670,6 +670,27 @@ lock_retry_remap:
}
/* It is a hole, need to instantiate it. */
if (lcn == LCN_HOLE) {
+ u8 *kaddr;
+ unsigned long *bpos, *bend;
+
+ /* Check if the buffer is zero. */
+ kaddr = kmap_atomic(page, KM_USER0);
+ bpos = (unsigned long *)(kaddr + bh_offset(bh));
+ bend = (unsigned long *)((u8*)bpos + blocksize);
+ do {
+ if (unlikely(*bpos))
+ break;
+ } while (likely(++bpos < bend));
+ kunmap_atomic(kaddr, KM_USER0);
+ if (bpos == bend) {
+ /*
+ * Buffer is zero and sparse, no need to write
+ * it.
+ */
+ bh->b_blocknr = -1;
+ clear_buffer_dirty(bh);
+ continue;
+ }
// TODO: Instantiate the hole.
// clear_buffer_new(bh);
// unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
-
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