[PATCH V17 16/18] Btrfs: btrfs_clone: Flush dirty blocks of a page that do not map the clone range

[Chandan Rajendra <chandan@linux.vnet.ibm.com>]

After cloning the required extents, we truncate all the pages that map
the file range being cloned. In subpage-blocksize scenario, we could
have dirty blocks before and/or after the clone range in the
leading/trailing pages. Truncating these pages would lead to data
loss. Hence this commit forces such dirty blocks to be flushed to disk
before performing the clone operation.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
---
 fs/btrfs/ioctl.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 4ff7cf8..7d39cba 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3849,6 +3849,7 @@ static noinline int btrfs_clone_files(struct file *file, struct file *file_src,
 	int ret;
 	u64 len = olen;
 	u64 bs = root->fs_info->sb->s_blocksize;
+	u64 dest_end;
 	int same_inode = src == inode;
 
 	/*
@@ -3909,6 +3910,21 @@ static noinline int btrfs_clone_files(struct file *file, struct file *file_src,
 			goto out_unlock;
 	}
 
+	if ((round_down(destoff, PAGE_SIZE) < inode->i_size) &&
+		!IS_ALIGNED(destoff, PAGE_SIZE)) {
+		ret = filemap_write_and_wait_range(inode->i_mapping,
+					round_down(destoff, PAGE_SIZE),
+					destoff - 1);
+	}
+
+	dest_end = destoff + len - 1;
+	if ((dest_end < inode->i_size) &&
+		!IS_ALIGNED(dest_end + 1, PAGE_SIZE)) {
+		ret = filemap_write_and_wait_range(inode->i_mapping,
+					dest_end + 1,
+					round_up(dest_end, PAGE_SIZE));
+	}
+
 	if (destoff > inode->i_size) {
 		ret = btrfs_cont_expand(inode, inode->i_size, destoff);
 		if (ret)
-- 
2.1.0