[PATCH 4.4 083/115] target/file: Do not return error for UNMAP if length is zero

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiang Yi <jiangyilism@xxxxxxxxx>


[ Upstream commit 594e25e73440863981032d76c9b1e33409ceff6e ]

The function fd_execute_unmap() in target_core_file.c calles

ret = file->f_op->fallocate(file, mode, pos, len);

Some filesystems implement fallocate() to return error if
length is zero (e.g. btrfs) but according to SCSI Block
Commands spec UNMAP should return success for zero length.

Signed-off-by: Jiang Yi <jiangyilism@xxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/target/target_core_file.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -466,6 +466,10 @@ fd_execute_unmap(struct se_cmd *cmd, sec
 	struct inode *inode = file->f_mapping->host;
 	int ret;
 
+	if (!nolb) {
+		return 0;
+	}
+
 	if (cmd->se_dev->dev_attrib.pi_prot_type) {
 		ret = fd_do_prot_unmap(cmd, lba, nolb);
 		if (ret)