xfs: only grab shared inode locks for source file during reflink

Reflink and dedupe operations remap blocks from a source file into a
destination file.  The destination file needs exclusive locks on all
levels because we're updating its block map, but the source file isn't
undergoing any block map changes so we can use a shared lock.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7f8d96d68f34..5cbeab8a63ca 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -748,6 +748,11 @@ static inline void inode_lock_nested(struct inode *inode, unsigned subclass)
 	down_write_nested(&inode->i_rwsem, subclass);
 }
 
+static inline void inode_lock_shared_nested(struct inode *inode, unsigned subclass)
+{
+	down_read_nested(&inode->i_rwsem, subclass);
+}
+
 void lock_two_nondirectories(struct inode *, struct inode*);
 void unlock_two_nondirectories(struct inode *, struct inode*);