[PATCH 3/4] cifs: Fix creating of SFU fifo special files

[Pali Rohár]

SFU-style fifo is empty file with system attribute set. This format is used
by old Microsoft POSIX subsystem and later also by OpenNT/Interix subsystem
(which replaced Microsoft POSIX subsystem and is part of Microsoft SFU).

This format of SFU-style fifos is recognized also by Windows NFS server
included in the latest version on Windows Server 2022.

Currently when sfu mount option is specified then CIFS creates new fifo
files with content LnxFIFO. This was introduced in commit 72bc63f5e23a
("smb3: fix creating FIFOs when mounting with "sfu" mount option").

It is important to note that LnxFIFO is not SFU-compatible and neither
Interix, SFU, SUA or Windows NFS server recognize file with content of
LnxFIFO as special fifo file.

So when sfu mount option is specified, fix this problem and create all fifo
special files compatible with SFU format, as it is expected by sfu mount
option. This allows interoperability with other SFU implementations and
also with Windows NFS server.

Fixes: 72bc63f5e23a ("smb3: fix creating FIFOs when mounting with "sfu" mount option")
Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
---
 fs/smb/client/smb2ops.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index dc56f7ba1a06..406f2399f0c5 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -5115,10 +5115,8 @@ int __cifs_sfu_make_node(unsigned int xid, struct inode *inode,
 		type[0] = '\0';
 		break;
 	case S_IFIFO:
-		type_len = 8;
-		strscpy(type, "LnxFIFO");
-		data = (u8 *)&pdev;
-		data_len = sizeof(pdev);
+		/* SFU fifo is system file which is empty */
+		type_len = 0;
 		break;
 	default:
 		rc = -EPERM;
-- 
2.20.1