[PATCH v4 3/7] smb/client: mark file sparse before emulating insert range

[Huiwen He <huiwen.he@linux.dev>]

From: Huiwen He <hehuiwen@kylinos.cn>

The SMB client emulates FALLOC_FL_INSERT_RANGE with SET_EOF, COPYCHUNK
and SET_ZERO_DATA.

SET_ZERO_DATA creates a hole only when the file is sparse. On a
non-sparse file, it clears the inserted range but leaves its blocks
allocated, causing the extent count check in xfstests generic/064 to
fail.

Fix this by marking the file sparse before modifying it.

This patch produces the expected sparse extents in xfstests generic/064
only when the server-reported block size is compatible with the server's
deallocation granularity.

For ksmbd, the reported block size follows the backing filesystem,
and the test passes. For Samba, the test passes with a block size
matching the backend granularity, for example, 4 KiB on Btrfs, but not
with the default 1 KiB value. For Windows Server 2022, 4 KiB inserts do
not generate holes, while aligned inserts of 64 KiB or larger do.

Fixes: 7fe6fe95b936 ("cifs: add FALLOC_FL_INSERT_RANGE support")
Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
---
 fs/smb/client/smb2ops.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index f823f9bc90eb..1eff607a1e74 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -4013,6 +4013,11 @@ static long smb3_insert_range(struct file *file, struct cifs_tcon *tcon,
 
 	count = old_eof - off;
 
+	/* SET_ZERO_DATA creates a hole only in a sparse file. */
+	rc = smb2_set_sparse(xid, tcon, cfile, inode, true);
+	if (rc)
+		goto out;
+
 	filemap_invalidate_lock(inode->i_mapping);
 	rc = filemap_write_and_wait_range(inode->i_mapping, off, new_eof - 1);
 	if (rc < 0)
-- 
2.43.0